LED UNIT FOR ONE DISPLAY

Description

[Technical Field]

[0001] Exemplary implementations of the invention relate generally to a display apparatus and, more particularly, to a display apparatus having a light emitting diode (LED) unit pixel, a light emitting device for a display and a display apparatus, and to a light emitting device for a display with stacked structure of a plurality of LEDs and a display apparatus having the same.[Background Art]

[0002] A light emitting diode has been used as an inorganic light source in various fields such as display apparatuses, automotive lamps, and general lighting. With advantages of long lifespan, low power consumption, and high response speed, the light emitting diode has been rapidly replacing a conventional light source.

[0003] Meanwhile, a light emitting diode of the related art has been mainly used as a backlight light source in a display apparatus. However, a micro LED display has been recently developed as a next-generation display that directly implements an image using the light emitting diode.

[0004] In general, the display apparatus implements various colors by using mixed colors of blue, green, and red. The display apparatus includes a plurality of pixels to implement an image with various colors, and each of pixels includes sub-pixels of blue, green, and red. The color of a specific pixel is determined by the color of the sub-pixels, and the image is implemented by the combination of these pixels.

[0005] In the case of a micro LED display, the micro LEDs corresponding to each sub-pixel are arranged on a two-dimensional plane. Therefore, a large number of micro LEDs are required to be disposed on one substrate. However, the micro LED has a very small size having a surface area of 10,000 square ?m or less, and thus, there are various problems due to this small size. Particularly, it is difficult to handle a light emitting diode having a small size, and it is not easy to mount the light emitting diode on a display panel, especially over hundreds of thousands or millions, and to replace a defective LED of mounted micro LEDs with a good LED.

[0006] In addition, since sub-pixels are arranged on a two-dimensional plane, the area occupied by one pixel including the sub-pixels of blue, green, and red is relatively increased. Therefore, in order to arrange the sub-pixels within a limited area, it is required to reduce the area of each sub-pixel, thereby causing deterioration in brightness through reduction in luminous area.

[0007] Patent application US 2017 / 0288093 A1 discloses an LED light source module including a light emitting stacked body wherein electrical connection is established employing through electrode structures passing through a portion of the light emitting stacked body.

[0008] Publication US 2008 / 251799 A1 describes a light emitting device including three LED elements stacked one on another and optical filters being disposed between two adjacent ones of the LED elements.

[0009] The above information disclosed in this Background section is only for understanding of the background of the inventive concepts, and, therefore, it may contain information that does not constitute prior art.[Disclosure][Technical Problem]

[0010] Light emitting diodes constructed according to the principles and some exemplary implementations of the invention and displays using the same are capable of increasing a light emitting area of each sub-pixel without increasing the pixel area.

[0011] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention provide high reliability due to a stable LED structure and simplified manufacturing process in which a single via may be connected to one or more of semiconductor layers of each of the LED stacks.

[0012] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention provide pixels that can be simultaneously manufactured to obviate the cumbersome process of individually mounting the pixels.

[0013] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention are capable of being driven in an active matrix manner.

[0014] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention are capable of shortening a mounting process time.

[0015] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention are capable of preventing light interference between LED stacks by arranging first, second, and third LED stacks one over another to emit light with decreasing wavelengths of light. For example, the first, second, and third LED stacks may emit red light, green light, and blue light, respectively.

[0016] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention are capable of suppressing generation of secondary light between the LED stacks without arrangement of the color filters therebetween, which are generally formed between the LED stacks to prevent generation of secondary light by light emitted from adjacent LED stacks.

[0017] Additional features of the inventive concepts will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the inventive concepts.[Technical Solution]

[0018] A display apparatus not forming part of the invention includes a thin film transistor (TFT) substrate, a first LED sub-unit disposed on the TFT substrate, a second LED sub-unit disposed on the first LED sub-unit, a third LED sub-unit disposed on the second LED sub-unit, electrode pads disposed between the TFT substrate and the first LED sub-unit, and connectors connecting the first, second, and third LED sub-units to a respective one of the electrode pads, in which the first LED sub-unit, the second LED sub-unit, and the third LED sub-unit are configured to be independently driven, light generated from the first LED sub-unit is configured to be emitted to the outside of the display apparatus by passing through the second LED sub-unit and the third LED sub-unit, and light generated from the second LED sub-unit is configured to be emitted to the outside of the display apparatus by passing through the third LED sub-unit.

[0019] The first, second, and third LED sub-units may include a first LED stack, a second LED stack, and a third LED stack, respectively, and the first, second, and third LED stacks may be configured to emit red light, green light, and blue light, respectively.

[0020] The display apparatus may include a first reflective electrode disposed between the TFT substrate and the first LED sub-unit and in contact with a lower surface of the first LED sub-unit, in which the connectors may include a first lower connector connecting the first reflective electrode to a first one of the electrode pads.

[0021] The connectors may further include a first upper connector connecting an upper surface of the first LED sub-unit to a second one of the electrode pads.

[0022] The display apparatus may further include a second transparent electrode interposed between the first LED sub-unit and the second LED sub-unit and in ohmic contact with a lower surface of the second LED sub-unit, and a third transparent electrode interposed between the second LED sub-unit and the third LED sub-unit and in ohmic contact with a lower surface of the third LED sub-unit, in which the connectors may further include a second lower connector connecting the second transparent electrode to the first one of the electrode pads, a second upper connector connecting an upper surface of the second LED sub-unit to a third one of the electrode pads, a third lower connector connecting the third transparent electrode to the first one of the electrode pads, and a third upper connector connecting an upper surface of the third LED sub-unit to a fourth one of the electrode pads.

[0023] The first lower connector may be connected to an upper surface of the first reflective electrode, the second lower connector may be connected to an upper surface of the second transparent electrode, and the third lower connector may be connected to an upper surface of the third transparent electrode.

[0024] The first upper connector may be connected to the upper surface of the first LED sub-unit, the second upper connector may be connected to the upper surface of the second LED sub-unit, the third upper connector may be connected to the upper surface of the third LED sub-unit, and at least one the upper connectors may be substantially annular in shape.

[0025] The connectors may further include intermediate connectors connecting the second upper connector and the third upper connector to the third one and the fourth one of the electrode pads, respectively.

[0026] Each of the connectors may pass through at least one of the first, second, and third LED sub-units.

[0027] The first lower connector, the second lower connector, and the third lower connector may be connected to the first one of the electrode pads, and the first upper connector, the second upper connector, and the third upper connector may be connected to different ones of the electrode pads, respectively.

[0028] The first lower connector, the second lower connector, and the third lower connector may be stacked over each other in a vertical direction, and the first upper connector, the second upper connector, and the third upper connector may be spaced apart from each other in the vertical direction and in a lateral direction.

[0029] The display apparatus may further include a second transparent electrode interposed between the first LED sub-unit and the second LED sub-unit and in ohmic contact with a lower surface of the second LED sub-unit, and a third transparent electrode interposed between the second LED sub-unit and the third LED sub-unit and in ohmic contact with a lower surface of the third LED sub-unit, in which the connectors may further include a second lower connector connecting the second transparent electrode to a third one of the electrode pads, a second upper connector connecting an upper surface of the second LED sub-unit to the second one of the electrode pads, a third lower connector connecting the third transparent electrode to a fourth one of the electrode pads, and a third upper connector connecting an upper surface of the third LED sub-unit to the second one of the electrode pads, and the first lower connector, the second lower connector, and the third lower connector may be separated from each other and are connected to the first, third, and fourth ones of the electrode pads, respectively, and the first upper connector, the second upper connector, and the third upper connector may be electrically connected to the second one of the electrode pads.

[0030] The first lower connector, the second lower connector, and the third lower connector may be spaced apart from each other in a vertical direction and in a lateral direction, and the first upper connector, the second upper connector, and the third upper connector may be stacked in the vertical direction.

[0031] The display apparatus may further include a first color filter interposed between the first LED sub-unit and the second LED sub-unit, and configured to transmit light generated from the first LED sub-unit and reflect light generated from the second LED sub-unit, and a second color filter interposed between the second LED sub-unit and the third LED sub-unit, and configured to transmit light generated from the first and second LED sub-units and reflect light generated from the third LED sub-unit.

[0032] The display apparatus may further include a first bonding layer interposed between the TFT substrate and the first LED sub-unit, a second bonding layer interposed between the first LED sub-unit and the second LED sub-unit, and a third bonding layer interposed between the second LED sub-unit and the third LED sub-unit, in which the second bonding layer is configured to transmit light generated from the first LED sub-unit, and the third bonding layer is configured to transmit light generated from the first and second LED sub-units.

[0033] The display apparatus may be configured to be driven in an active matrix manner.

[0034] The third lower connector and the third upper connector may be exposed by the third LED sub-unit in plan view.

[0035] The first reflective electrode may be disposed between the first LED sub-unit and the electrode pads.

[0036] The first, second and third LED subunits may include a micro LED having a surface area less than about 10,000 square µm.

[0037] The first LED sub-unit may be configured to emit one of red, green, and blue light, the second LED sub-unit may be configured to emit a different one of red, green, and blue light from the first LED sub-unit, and the third LED sub-unit may be configured to emit a different one of red, green, and blue light from the first and second LED sub-units.

[0038] A light emitting device according to an exemplary embodiment includes a first LED sub-unit, a second LED sub-unit disposed adjacent to the first LED sub-unit, a third LED sub-unit disposed adjacent to the second LED sub-unit, and electrode pads disposed on the first LED sub-unit and electrically connected to the first, second, and third LED sub-units, the electrode pads including a common electrode pad electrically connected to each of the first, second, and third LED sub-units, and first, second, and third electrode pads connected to a respective one of the first, second, and third LED sub-units, in which the common electrode pad, the second electrode pad, and the third electrode pad are electrically connected to the second LED sub-unit and the third LED sub-unit through holes that pass through the first LED sub-unit, the first LED sub-unit, the second LED sub-unit, and the third LED sub-unit are configured to be independently driven, light generated in the first LED sub-unit is configured to be emitted to the outside of the light emitting device through the second LED sub-unit and the third LED sub-unit, and light generated in the second LED sub-unit is configured to be emitted to the outside of the light emitting device through the third LED sub-unit.

[0039] The first, second, and third LED sub-units may include a first LED stack, a second, LED stack, and a third LED stack, respectively, and the first, second, and third LED stacks may be configured to emit red light, green light, and blue light, respectively.

[0040] The light emitting device further includes a first reflective electrode disposed between the electrode pads and the first LED sub-unit and in ohmic contact with the first LED sub-unit, in which the common electrode pad is connected to the first reflective electrode.

[0041] The first reflective electrode includes an ohmic contact layer in ohmic contact with an upper surface of the first LED sub-unit and a reflective layer that covers the ohmic contact layer.

[0042] The first reflective electrode may have a hollow portion defined by a substantially annular-shaped member, and the common electrode pad may pass through the hollow portion of the substantially annular-shaped member.

[0043] The light emitting device further includes a second transparent electrode interposed between the second LED sub-unit and the third LED sub-unit and in ohmic contact with a lower surface of the second LED sub-unit, and a third transparent electrode in ohmic contact with an upper surface of the third LED sub-unit, in which the common electrode pad is electrically connected to the second transparent electrode and the third transparent electrode.

[0044] The common electrode pad may be connected to an upper surface of the second transparent electrode and an upper surface of the third transparent electrode.

[0045] Each of the first LED sub-unit and the third LED sub-unit may include a first conductivity type semiconductor layer and a second conductivity type semiconductor layer disposed on a partial region of the first conductivity type semiconductor layer, and the first electrode pad and the third electrode pad may be electrically connected to the first conductivity type semiconductor layer of the first LED sub-unit and the third LED sub-unit, respectively.

[0046] The light emitting device may further include a first ohmic electrode disposed on the first conductivity type semiconductor layer of the first LED sub-unit, in which the first electrode pad is connected to the first ohmic electrode.

[0047] The third electrode pad may be directly connected to the first conductivity type semiconductor layer of the third LED sub-unit.

[0048] The light emitting device may further include a first color filter disposed between the third transparent electrode and the second LED sub-unit, and a second color filter disposed between the first and second LED sub-units.

[0049] The first color filter and the second color filter may include insulating layers having different refractive indices.

[0050] The common electrode pad and the third electrode pad may be electrically connected to the third LED sub-unit through holes that pass through the second LED sub-unit.

[0051] The light emitting device may further include a substrate on which the third LED sub-unit is disposed.

[0052] The substrate may include a sapphire substrate or a gallium nitride substrate.

[0053] The light emitting device may further include an insulating layer disposed between the first LED sub-unit and the electrode pads, in which the electrode pads are electrically connected to the first, second, and third LED sub-units through the insulating layer.

[0054] The insulating layer may include at least one of a distributed Bragg reflector and a light blocking material.

[0055] A display apparatus may include a circuit board, and a plurality of light emitting devices arranged on the circuit board, at least some of the light emitting devices may include the light emitting device according to an exemplary embodiment, in which the electrode pads may be electrically connected to the circuit board.

[0056] Each of the light emitting devices may include a substrate coupled to the third LED sub-unit, and the substrates of the light emitting devices may be spaced apart from each other.

[0057] A light emitting device not forming part of the invention includes a substrate, a first LED sub-unit disposed on the substrate, a second LED sub-unit disposed on the first LED sub-unit, a third LED sub-unit disposed on the second LED sub-unit, and electrode pads electrically connected to the first, second, and third LED sub-units, the electrode pads including a common electrode pad electrically connected to each of the first, second, and third LED sub-units by a single through-hole via, and first, second, and third electrode pads connected to a respective one of the first, second, and third LED sub-units.

[0058] The electrode pads may be disposed between the substrate and the first LED sub-unit, the through-hole via may include a plurality of connectors connected to each of the first, second, and third LED sub-units, and the connectors may include a first portion having a width greater than a width of the through-hole via.

[0059] The first LED sub-unit may include a reflective electrode disposed on a lower surface thereof, and the reflective electrode may contact the first portion of the corresponding connector.

[0060] The first, second, and third LED sub-units may be disposed between the electrode pads and the substrate, and the through-hole via may have a width that narrows in a direction from the electrode pads to the substrate.

[0061] The third LED sub-unit may include a reflective electrode disposed on an upper surface thereof, and the common electrode pad may directly contact the reflective electrode.

[0062] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.[Advantageous Effects]

[0063] Light emitting diodes constructed according to the principles and some exemplary implementations of the invention and displays using the same are capable of increasing a light emitting area of each sub-pixel without increasing the pixel area.

[0064] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention provide high reliability due to a stable LED structure and simplified manufacturing process in which a single via may be connected to one or more of semiconductor layers of each of the LED stacks.

[0065] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention provide pixels that can be simultaneously manufactured to obviate the cumbersome process of individually mounting the pixels.

[0066] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention are capable of being driven in an active matrix manner.

[0067] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention are capable of shortening a mounting process time.

[0068] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention are capable of preventing light interference between LED stacks by arranging first, second, and third LED stacks one over another to emit light with decreasing wavelengths of light. For example, the first, second, and third LED stacks may emit red light, green light, and blue light, respectively.

[0069] Light emitting diodes and display using the light emitting diodes, e.g., micro LEDs, constructed according to the principles and some exemplary implementations of the invention are capable of suppressing generation of secondary light between the LED stacks without arrangement of the color filters therebetween, which are generally formed between the LED stacks to prevent generation of secondary light by light emitted from adjacent LED stacks.[Description of Drawings]

[0070] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention, and together with the description serve to explain the inventive concepts. FIG. 1 is a schematic plan view of a display apparatus not forming part of the invention. FIG. 2 is a schematic cross-sectional view taken along line A-A of FIG. 1. FIGS. 3A, 3B, 4A, 4B, 5A, 5B, 6A, 6B, 7A, 7B, 8A, 8B, 9A, 9B, 10A, 10B, 11A, 11B, 12A, 12B, 13A, 13B, 14A, 14B, 15A, 15B, 16A, and 16B are schematic plan views and schematic cross-sectional views illustrating a method of manufacturing a display apparatus not forming part of the invention. FIG. 17 is a schematic plan view of a display apparatus not forming part of the invention. FIG. 18 is a schematic cross-sectional view taken along line B-B of FIG. 17. FIG. 19 is a schematic circuit diagram of a display apparatus according to an exemplary embodiment. FIG. 20 is a schematic plan view of a display apparatus according to an exemplary embodiment. FIG. 21A is a schematic plan view of a light emitting device according to an exemplary embodiment. FIG. 21B is a schematic cross-sectional view taken along line A-A of FIG. 21A. FIGS. 22, 23, 24, 25, 26A, 26B, 27A, 27B, 28A, 28B, 29, 30A, 30B, 31A, 31B, 32A, 32B, 33A, 33B, 34A, 34B, 35A, and 35B are schematic plan views and cross-sectional views illustrating a method of manufacturing a light emitting device according to an exemplary embodiment. FIG. 36 is a schematic cross-sectional view of a light emitting diode stack for a display not forming part of the invention. FIGS. 37A, 37B, 37C, 37D, and 37E are schematic cross-sectional views illustrating a method of manufacturing a light emitting diode stack for a display not forming part of the invention. FIG. 38 is a schematic circuit diagram of a display apparatus not forming part of the invention. FIG. 39 is a schematic plan view of a display apparatus not forming part of the inventiont. FIG. 40 is an enlarged plan view of one pixel of the display apparatus of FIG. 39. FIG. 41 is a schematic cross-sectional view taken along line A-A of FIG. 40. FIG. 42 is a schematic cross-sectional view taken along line B-B of FIG. 40. FIGS. 43A, 43B, 43C, 43D, 43E, 43F, 43G, 43H, 43I, 43J, and 43K are schematic cross-sectional views illustrating a method of manufacturing a display apparatus not forming part of the invention. FIG. 44 is a schematic circuit diagram of a display apparatus not forming part of the invention. FIG. 45 is a schematic plan view of a display apparatus not forming part of the invention. FIG. 46 is a schematic cross-sectional view of a light emitting diode stack for a display not forming part of the invention. FIGS. 47A, 47B, 47C, 47D, and 47E are schematic cross-sectional views illustrating a method of manufacturing a light emitting diode stack for a display not forming part of the invention. FIG. 48 is a schematic circuit diagram of a display apparatus not forming part of the invention. *92FIG. 49 is a schematic plan view of the display apparatus not forming part of the invention. FIG. 50 is an enlarged plan view of one pixel of the display apparatus of FIG. 49. FIG. 51 is a schematic cross-sectional view taken along line A-A of FIG. 50. FIG. 52 is a schematic cross-sectional view taken along line B-B of FIG. 50. FIGS. 53A, 53B, 53C, 53D, 53E, 53F, 53G, 53H, 53I, 53J, and 53K are schematic cross-sectional views illustrating a method of manufacturing a display apparatus not forming part of the invention. FIG. 54 is a schematic circuit diagram of a display apparatus not forming part of the invention. FIG. 55 is a schematic plan view of a display apparatus not forming part of the invention. FIG. 56 is a schematic plan view of a display apparatus not forming part of the invention. FIG. 57 is a schematic cross-sectional view of a light emitting diode pixel for a display not forming part of the invention. FIG. 58 is a schematic circuit diagram of a display apparatus not forming part of the invention. FIG. 59A and FIG. 59B are a top view and a bottom view of one pixel of a display apparatus not forming part of the invention. FIG. 60A is a schematic cross-sectional view taken along line A-A of FIG. 59A. FIG. 60B is a schematic cross-sectional view taken along line B-B of FIG. 59A. FIG. 60C is a schematic cross-sectional view taken along line C-C of FIG. 59A. FIG. 60D is a schematic cross-sectional view taken along line D-D of FIG. 59A. FIGS. 61A, 61B, 62A, 62B, 63A, 63B, 64A, 64B, 65A, 65B, 66A, 66B, 67A, 67B, 68A, and 68B are schematic plan views and schematic cross-sectional view illustrating a method of manufacturing a display apparatus not forming part of the invention. FIG. 69 is a schematic cross-sectional view of a light emitting diode pixel for a display not forming part of the invention. FIG. 70 is an enlarged top view of one pixel of a display apparatus not forming part of the invention. FIG. 71A and FIG. 71B are cross-sectional views taken along lines G-G and H-H in FIG. 70, respectively. FIG. 72 is a schematic cross-sectional view of a light emitting diode (LED) stack for a display not forming part of the invention. FIGS. 73A, 73B, 73C, 73D, 73E, and 73F are schematic cross-sectional views illustrating a method for manufacturing a light emitting diode stack for a display not forming part of the invention. FIG. 74 is a schematic circuit diagram of a display apparatus not forming part of the invention. FIG. 75 is a schematic plan view of a display apparatus not forming part of the invention. FIG. 76 is an enlarged plan view of one pixel of the display apparatus of FIG. 75. FIG. 77 is a schematic cross-sectional view taken along line A-A of FIG. 76. FIG. 78 is a schematic cross-sectional view taken along line B-B of FIG. 76. FIGS. 79A, 79B, 79C, 79D, 79E, 79F, 79G, and 79H are schematic plan views illustrating a method for manufacturing a display apparatus not forming part of the invention. FIG. 80 is a schematic cross-sectional view of a light emitting stacked structure not forming part of the invention. FIGS. 81A and 81B are cross-sectional views of a light emitting stacked structure not forming part of the invention. FIG. 82 is a cross-sectional view of a light emitting stacked structure including a wiring part not forming part of the invention. FIG. 83 is a cross-section view of a light emitting stacked structure not forming part of the invention. FIG. 84 is a plan view of a display device not forming part of the invention. FIG. 85 is an enlarged plan view of portion P1 of FIG. 84. FIG. 86 is a structural diagram of a display device not forming part of the invention. FIG. 87 is a circuit diagram of one pixel of a passive type display device. FIG. 88 is a circuit diagram of one pixel of an active type display device. FIG. 89 is a plan view of a pixel not forming part of the invention. FIGS. 90A and 90B are cross-sectional views taken along lines I-I' and II-II' of FIG. 89, respectively. FIGS. 91A, 91B, and 91C are cross-sectional views taken along line I-I' in FIG. 89, illustrating a process of stacking first to third epitaxial stacks on a substrate not forming part of the invention. FIGS. 92, 94, 96, 98, 100, 102, 104 are plan views sequentially illustrating a method of manufacturing a pixel on a substrate. FIGS. 93A, 95A, 97A, 99A, 101A, 103A, and 105A are cross-sectional views taken along line I-I' of FIGS. 92, 94, 96, 98, 100, 102, 104, respectively. FIGS. 93B, 95B, 97B, 99B, 101B, 103B, and 105B are cross-sectional views taken along line II-II' of FIGS. 92, 94, 96, 98, 100, 102, 104, respectively. FIG. 106 is a schematic plan view of a display apparatus not forming part of the invention. FIG. 107A is a cross-sectional view of the display apparatus of FIG. 106. FIG. 107B is a schematic circuit diagram of a display apparatus not forming part of the invention. FIGS. 108A, 108B, 108C, 108D, 108E, 109A, 109B, 109C, 109D, 109E, 110A, 110B, 110C, 110D, 111A, 111B, 111C, 111D, 112A, 112B, 112C, 112D, 113A, 113B, and 114 are schematic plan views and cross-sectional views illustrating a manufacturing method of a display apparatus not forming part of the invention. FIGS. 115A, 115B, and 115C are schematic cross-sectional views of a metal bonding material according to exemplary embodiments not forming part of the invention. [Mode for Invention]

[0071] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of various exemplary embodiments or implementations of the invention. As used herein "embodiments" and "implementations" are interchangeable words that are non-limiting examples of devices or methods employing one or more of the inventive concepts disclosed herein. It is apparent, however, that various exemplary embodiments may be practiced without these specific details or with one or more equivalent arrangements. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring various exemplary embodiments. Further, various exemplary embodiments may be different, but do not have to be exclusive. For example, specific shapes, configurations, and characteristics of an exemplary embodiment may be used or implemented in another exemplary embodiment without departing from the inventive concepts.

[0072] Unless otherwise specified, the illustrated exemplary embodiments are to be understood as providing exemplary features of varying detail of some ways in which the inventive concepts may be implemented in practice. Therefore, unless otherwise specified, the features, components, modules, layers, films, panels, regions, and / or aspects, etc. (hereinafter individually or collectively referred to as "elements"), of the various embodiments may be otherwise combined, separated, interchanged, and / or rearranged without departing from the inventive concepts.

[0073] The use of cross-hatching and / or shading in the accompanying drawings is generally provided to clarify boundaries between adjacent elements. As such, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, dimensions, proportions, commonalities between illustrated elements, and / or any other characteristic, attribute, property, etc., of the elements, unless specified. Further, in the accompanying drawings, the size and relative sizes of elements may be exaggerated for clarity and / or descriptive purposes. When an exemplary embodiment may be implemented differently, a specific process order may be performed differently from the described order. For example, two consecutively described processes may be performed substantially at the same time or performed in an order opposite to the described order. Also, like reference numerals denote like elements.

[0074] When an element, such as a layer, is referred to as being "on," "connected to," or "coupled to" another element or layer, it may be directly on, connected to, or coupled to the other element or layer or intervening elements or layers may be present. When, however, an element or layer is referred to as being "directly on," "directly connected to," or "directly coupled to" another element or layer, there are no intervening elements or layers present. To this end, the term "connected" may refer to physical, electrical, and / or fluid connection, with or without intervening elements. Further, the D1-axis, the D2-axis, and the D3-axis are not limited to three axes of a rectangular coordinate system, such as the x, y, and z ? axes, and may be interpreted in a broader sense. For example, the D1-axis, the D2-axis, and the D3-axis may be perpendicular to one another, or may represent different directions that are not perpendicular to one another. For the purposes of this disclosure, "at least one of X, Y, and Z" and "at least one selected from the group consisting of X, Y, and Z" may be construed as X only, Y only, Z only, or any combination of two or more of X, Y, and Z, such as, for instance, XYZ, XYY, YZ, and ZZ. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0075] Although the terms "first," "second," etc. may be used herein to describe various types of elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another element. Thus, a first element discussed below could be termed a second element without departing from the teachings of the disclosure.

[0076] Spatially relative terms, such as "beneath," "below," "under," "lower," "above, " "upper, " "over, " "higher," "side" (e.g., as in "sidewall"), and the like, may be used herein for descriptive purposes, and, thereby, to describe one elements relationship to another element(s) as illustrated in the drawings. Spatially relative terms are intended to encompass different orientations of an apparatus in use, operation, and / or manufacture in addition to the orientation depicted in the drawings. For example, if the apparatus in the drawings is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. Furthermore, the apparatus may be otherwise oriented (e.g., rotated 90 degrees or at other orientations), and, as such, the spatially relative descriptors used herein interpreted accordingly.

[0077] The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting. As used herein, the singular forms, "a," "an, " and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Moreover, the terms "comprises," "comprising," "includes," and / or "including," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It is also noted that, as used herein, the terms "substantially," "about," and other similar terms, are used as terms of approximation and not as terms of degree, and, as such, are utilized to account for inherent deviations in measured, calculated, and / or provided values that would be recognized by one of ordinary skill in the art.

[0078] Various exemplary embodiments are described herein with reference to sectional and / or exploded illustrations that are schematic illustrations of idealized exemplary embodiments and / or intermediate structures. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and / or tolerances, are to be expected. Thus, exemplary embodiments disclosed herein should not necessarily be construed as limited to the particular illustrated shapes of regions, but are to include deviations in shapes that result from, for instance, manufacturing. In this manner, regions illustrated in the drawings may be schematic in nature and the shapes of these regions may not reflect actual shapes of regions of a device and, as such, are not necessarily intended to be limiting.

[0079] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure is a part. Terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense, unless expressly so defined herein.

[0080] As used herein, a light emitting device or a light emitting diode according to exemplary embodiments may include a micro LED, which has a surface area less than about 10,000 square µm as known in the art. In other exemplary embodiments, the micro LED's may have a surface area of less than about 4,000 square µm, or less than about 2,500 square µm, depending upon the particular application.

[0081] FIG. 1 is a schematic plan view of a display apparatus not forming part of the invention. FIG. 2 is a schematic cross-sectional view taken along line A-A of FIG. 1.

[0082] Referring to FIGS. 1 and 2, the display apparatus may include a substrate 51, electrode pads 53a, 53b, 53c, and 53d, a first LED stack 23, a second LED stack 33, a third LED stack 43, a first reflective electrode 25, a second transparent electrode 35, a third transparent electrode 45, a first color filter 37, a second color filter 47, a first bonding layer 55, a second bonding layer 65, and a third bonding layer 75. In addition, the display apparatus may include a plurality of connectors 59a, 59b, 59c, 59d, 69b, 69c, 69d, 79c, and 79d and insulating layers 57, 67, and 77. As used herein, a connector may be any type of structure, including through holes, vias, wires, lines, conductive material, and the like, that serves to electrically and / or mechanically connect two elements, such as layers.

[0083] The substrate 51 supports the LED stacks 23, 33, and 43. In addition, the substrate 51 may have an internal circuit. For example, the substrate 51 may be a silicon substrate in which thin film transistors are formed. TFT substrates have been widely used in display fields, such as LCD display fields, for driving a display apparatus in an active matrix manner. Since TFT substrates are well known in the art, detailed descriptions of a structure of a TFT substrate will be omitted.

[0084] Although FIGS. 1 and 2 show one unit pixel disposed on the substrate 51, a plurality of the unit pixels may be arranged on the substrate 51, and the plurality of the unit pixels may be driven in an active matrix manner.

[0085] The electrode pads 53a, 53b, 53c, and 53d are exposed on the substrate 51. Each of the electrode pads 53a, 53b, 53c, and 53d are connected to one of the subpixels of the unit pixel disposed on the substrate 51, but the electrode pad 53d is connected to each of the three subpixels. Each of the electrode pads 53a, 53b, 53c, and 53d may be connected to the internal circuit of the substrate 51.

[0086] The first LED stack 23, the second LED stack 33, and the third LED stack 43 each include an n-type semiconductor layer, a p-type semiconductor layer, and an active layer interposed therebetween. The active layer may have a multi-quantum well structure.

[0087] The closer to the substrate 51, the longer wavelength light may be emitted from the LED stacks. For example, the first LED stack 23 may be an inorganic light emitting diode configured to emit red light, the second LED stack 33 may be an inorganic light emitting diode configured to emit green light, and the third LED stack 43 may be an inorganic light emitting diode configured to emit blue light. The first LED stack 23 may include a GaInP-based well layer and the second LED stack 33 and the third LED stack 43 may include a GaInN-based well layer. However, the inventive concepts are not limited thereto, and when the pixel includes a micro LED, the first LED stack 23 may emit any one of red, green, and blue light, and the second and third LED stacks 33 and 43 may emit different one of red, green, and blue light, without adversely affection operation due to small form factor of a micro LED.

[0088] The surfaces of each of the LED stacks 23, 33, and 43 may be an n-type semiconductor layer and a p-type semiconductor layer, respectively. Hereinafter, an upper surface and a lower surface of each of the first to third LED stacks 23, 33, and 43 will be described as an n-type and a p-type, respectively. However, the inventive concepts are not limited thereto, and the type of the upper surface and the lower surface of each of the LED stacks may be reversed or variously modified.

[0089] When the upper surface of the third LED stack 43 is an n-type, the upper surface of the third LED stack 43 may be surface textured by chemical etching or the like to form a roughened surface. The upper surfaces of the first LED stack 23 and the second LED stack 33 may also be subjected to surface texturing. However, when the second LED stack 33 emits green light, since green light has higher visibility than red light and blue light, it may be preferable to increase light emitting efficiency of the first LED stack 23 and the third LED stack 43 to the greater extent than that of the second LED stack 33. As such, the first LED stack 23 and the third LED stack 43 may be surface textured to improve light extraction efficiency without surface texturing the second LED stack 33. In this manner, light intensities of red light, green light, and the blue light may be balanced and adjusted to have substantially similar levels.

[0090] The first LED stack 23 is disposed close to the support substrate 51, the second LED stack 33 is disposed on the first LED stack 23, and the third LED stack 43 is disposed on the second LED stack 33. Since the first LED stack 23 may emit light having a longer wavelength than the second and third LED stacks 33 and 43, the light generated from the first LED stack 23 may be transmitted through the second and third LED stacks 33 and 43 and be emitted to the outside. In addition, since the second LED stack 33 may emit light having a longer wavelength than the third LED stack 43, the light generated from the second LED stack 33 may be transmitted through the third LED stack 43 and be emitted to the outside.

[0091] The first reflective electrode 25 is in ohmic contact with the p-type semiconductor layer of the first LED stack 23 and reflects the light generated from the first LED stack 23. For example, the first reflective electrode 25 may include an ohmic contact layer 25a and a reflective layer 25b.

[0092] The ohmic contact layer 25a is partially in contact with the p-type semiconductor layer. In order to prevent absorption of light by the ohmic contact layer 25a, the ohmic contact layer 25a may be formed in a predetermined area. For example, the ohmic contact layer 25a may be disposed near an edge of the first LED stack 23 and may be arranged substantially in an annular shape. A contact area of the ohmic contact layer 25a with respect to the first LED stack 23 may be 25% or less, or may be 10% or less in some exemplary embodiments. Even though the contact area of the ohmic contact layer 25a is relatively small, when an area of the first LED stack 23 is about 200 ?m or less in size, a current may be evenly distributed in the first LED stack 23. The ohmic contact layer 25a may be formed of transparent conductive oxides or Au alloys, such as Au(Zn) or Au(Be).

[0093] The reflective layer 25b may cover the ohmic contact layer 25a and the lower surface of the first LED stack 23. However, as shown in FIG. 1, the reflective layer 25b exposes the lower surface of the first LED stack 23 in regions around where the connectors 59a, 59b, 59c, and 59d are to be formed. More particularly, the reflective layer 25b may expose the lower surface of the first LED stack 23 in a region surrounded by the ohmic contact layer 25a. The reflective layer 25b may include a reflective metal layer formed of Al, Ag, or others. In addition, the reflective layer 25b may include a metal adhesion layer formed of Ti, Ta, Ni, Cr, or others on upper and lower surfaces of the reflective metal layer in order to improve adhesion of the reflective metal layer. The reflective layer 25b may be formed of a metal layer, which has a high reflectance to light generated from the first LED stack 23, for example, red light. Meanwhile, the reflective layer 25b may have a relatively low reflectance to light generated from the second LED stack 33 or the third LED stack 43, for example, green light or blue light. Therefore, the reflective layer 25b may reduce light interference by absorbing light generated from the second and third LED stacks 33 and 43 that is emitted toward the support substrate 51. Au has high reflectance to red light, and low reflectance to green light or blue light, and thus, may be used to form the reflective layer 25b disposed on the first LED stack 23.

[0094] The second transparent electrode 35 is in ohmic contact with the p-type semiconductor layer of the second LED stack 33. The second transparent electrode 35 may be formed of a metal layer or conductive oxide layer transparent to red light and green light. The third transparent electrode 45 is in ohmic contact with the p-type semiconductor layer of the third LED stack 43. The third transparent electrode 45 may be formed of a metal layer or conductive oxide layer transparent to red light, green light, and blue light. The second transparent electrode 35 and the third transparent electrode 45 may be in ohmic contact with the p-type semiconductor layer of each of the LED stacks to assist current distribution. Examples of the conductive oxide layer used for the second and third transparent electrodes 35 and 45 may include Sn02, In02, IT0, Zn0, IZ0 or others.

[0095] The first color filter 37 may be disposed between the first LED stack 23 and the second LED stack 33. In addition, the second color filter 47 may be disposed between the second LED stack 33 and the third LED stack 43. The first color filter 37 may transmit light generated from the first LED stack 23 and reflects the light generated from the second LED stack 33. The second color filter 47 may transmit light generated from the first and second LED stacks 23 and 33 and reflect light generated from the third LED stack 43. As such, light generated from the first LED stack 23 may be emitted to the outside through the second LED stack 33 and the third LED stack 43, and light generated from the second LED stack 33 may be emitted to the outside through the third LED stack 43. Further, it may be possible to prevent light generated from the second LED stack 33 from being incident to the first LED stack 23 and being lost, or to prevent light generated from the third LED stack 43 from being incident to the second LED stack 33 and being lost.

[0096] In some exemplary embodiments, the first color filter 37 may also reflect light generated from the third LED stack 43.

[0097] The first and second color filters 37 and 47 may be, for example, a low pass filter through which only a low wavelength region of light, e.g., light in a long wavelength region, a band pass filter through which only a certain wavelength region of light passes, or a band stop filter only blocking a certain wavelength region of light. More particularly, the first and second color filters 37 and 47 may be formed by alternately stacking insulating layers having different refractive indices. For example, the color filters may be formed by alternately stacking Ti02 and Si02. The first and second color filters 37 and 47 may include a distributed Bragg reflector (DBR). A stop band in the distributed Bragg reflector may be controlled by adjusting the thicknesses of Ti02 and Si02. The low pass filter and the band pass filter may also be formed by alternately stacking insulating layers having different refractive indices one above another.

[0098] The first bonding layer 55 couples the first LED stack 23 to the substrate 51. As shown in the drawings, the first reflective electrode 25 may be in contact with the first bonding layer 55. The first bonding layer 55 may be transmissive or non-transmissive.

[0099] The second bonding layer 65 couples the second LED stack 33 to the first LED stack 23. As shown in the drawings, the second bonding layer 65 may be in contact with the first LED stack 23 and the first color filter 37. The second bonding layer 65 transmits light generated from the first LED stack 23. The second bonding layer 65 may be formed of, for example, spin-on-glass having light transmitting property.

[0100] The third bonding layer 75 couples the third LED stack 43 to the second LED stack 33. As shown in the drawings, the third bonding layer 75 may be in contact with the second LED stack 33 and the second color filter 47. However, the inventive concepts are not limited thereto, and a transparent conductive layer may be disposed on the second LED stack 33. The third bonding layer 75 transmits the light generated from the first LED stack 23 and the second LED stack 33. The third bonding layer 75 may be formed of, for example, spin-on-glass having light transmitting property.

[0101] The bonding layers 55, 65, and 75 may be formed by forming transparent organic layers or transparent inorganic layer on each of the two objects to be bonded, and then bonding the objects with each other. Examples of an organic layer may include SU8, poly(methyl methacrylate) (PMMA), polyimide, parylene, benzocyclobutene (BCB), or others. Examples of an inorganic layer may include Al203, Si02, SiNx, or others. The organic layers may be bonded at high vacuum and high pressure. Surfaces of the inorganic layers may be planarized by, for example, a chemical mechanical polishing (CMP), and then surface energy is lowered by plasma and the like, resulting in bonding at high vacuum.

[0102] A first-1 connector 59d electrically connects the first reflective electrode 25 and the electrode pad 53d to each other. As such, the first-1 connector 59d is electrically connected to the lower surface of the first LED stack 23. As shown in the drawings, the first-1 connector 59d may pass through the first LED stack 23. However, the inventive concepts are not limited thereto, and the first-1 connector 59d may be formed on a side surface of the first LED stack 23. The insulating layer 57 is interposed between the first-1 connector 59d and the first LED stack 23, thereby preventing the first-1 connector 59d from being short-circuited to the upper surface of the first LED stack 23.

[0103] A first-2 connector 59a electrically connects the upper surface of the first LED stack 23 and the electrode pad 53a on the substrate 51 to each other. The first-2 connector 59a may be connected to the upper surface of the first LED stack 23, and may pass through the first LED stack 23 to be connected to the electrode pad 53a. The insulating layer 57 may be interposed between the first LED stack 23 and the first-2 connector 59a in order to prevent the first-2 connector 59a from being short-circuited to the lower surface of the first LED stack 23.

[0104] A first-3 connector 59b and a first-4 connector 59c may pass through the first LED stack 23 to be connected to each of the electrode pads 53b and 53c. The first-3 connector 59b and the first-4 connector 59c are insulated from the first LED stack 23, by the insulating layer 57 interposed between the first LED stack 23 and the connectors 59b and 59c.

[0105] The first-3 connector 59b and the first-4 connector 59c may function as an intermediate connector, or these configurations may be omitted in some exemplary embodiments.

[0106] A second-1 connector 69d is disposed to electrically connect the second transparent electrode 35 to the electrode pad 53d. The second-1 connector 69d is electrically connected to the lower surface of the second LED stack 33 through the second transparent electrode 35. As shown in the drawings, the second-1 connector 69d may pass through the second LED stack 33. However, the inventive concepts are not limited thereto, and the second-1 connector 69d may be formed on a side surface of the second LED stack 33. The insulating layer 67 is interposed between the second-1 connector 69d and the second LED stack 33, thereby preventing the second-1 connector 69d from being short-circuited to the upper surface of the second LED stack 33.

[0107] As shown in FIG. 2, the second-1 connector 69d may be connected to the first-1 connector 59d to be electrically connected to the electrode pad 53d. In this case, the first-1 connector 59d may function as an intermediate connector. In addition, as shown in FIG. 2, the second-1 connector 69d may be stacked on the first-1 connector 59d in a vertical direction.

[0108] A second-2 connector 69b is disposed to electrically connect the upper surface of the second LED stack 33 to the electrode pad 53b. The second-2 connector 69b may be connected to the upper surface of the second LED stack 33, and may pass through the second LED stack 33. As shown in the drawings, the second-2 connector 69b may be connected to the first-3 connector 59b to be electrically connected to the electrode pad 53b. The second-2 connector 69b may be directly connected to the electrode pad 53b. In this case, the first-3 connector 59b is omitted.

[0109] The insulating layer 67 may be interposed between the second LED stack 33 and the second-2 connector 69b in order to prevent the second-2 connector 69b from being short-circuited to the lower surface of the second LED stack 33.

[0110] A second-3 connector 69c may be disposed to pass through the second LED stack 33. The second-3 connector 69c may be electrically connected to the electrode pad 53c, and may be connected to, for example, the first-4 connector 59c. The second-3 connector 69c is insulated from the second LED stack 33 by the insulating layer 67 interposed between the second LED stack 33 and the second-3 connector 69c.

[0111] The second-3 connector 69c may function as an intermediate connector, or these configurations may be omitted in some exemplary embodiments.

[0112] A third-1 connector 79d is disposed to connect the third transparent electrode 45 and the electrode pad 53d to each other. The third-1 connector 79d is electrically connected to the lower surface of the third LED stack 43 through the third transparent electrode 45. As shown in the drawings, the third-1 connector 79d may pass through the third LED stack 43. However, the inventive concepts are not limited thereto, and the third-1 connector 79d may be formed on a side surface of the third LED stack 43. The insulating layer 77 is interposed between the third-1 connector 79d and the third LED stack 43, thereby preventing the third-1 connector 79d from being short-circuited to the upper surface of the third LED stack 43.

[0113] As shown in FIG. 2, the third-1 connector 79d may be connected to the second-1 connector 69d to be electrically connected to the electrode pad 53d. In this case, the second-1 connector 69d and the first-1 connector 59d may function as an intermediate connector. In addition, as shown in FIG. 2, the third-1 connector 79d may be stacked on the second-1 connector 69d in a vertical direction. Therefore, the first-1 connector 59d, the second-1 connector 69d, and the third-1 connector 79d are electrically connected to one another and are stacked in a vertical direction. The connectors are disposed in an emission direction of light to absorb light. In a case where the connectors are disposed to be spaced apart from one another in a lateral direction, a light emission area may be decreased and cause increased light loss. However, the connectors according to an exemplary embodiment are stacked in a vertical direction to reduce loss of light generated from the first LED stack 23 and the second LED stack 33 by the connectors.

[0114] A third-2 connector 79c is disposed to connect the upper surface of the third LED stack 43 and the electrode pad 53c to each other. The third-2 connector 79c may be connected to the upper surface of the third LED stack 43 and may pass through the third LED stack 43. As shown in the drawings, the third-2 connector 79c may be connected to the second-3 connector 69c to be electrically connected to the electrode pad 53c. The third-2 connector 79c may be directly connected to the electrode pad 53c. In this case, the second-3 connector 69c may be omitted.

[0115] Meanwhile, the insulating layer 77 may be interposed between the third LED stack 43 and the third-2 connector 79c in order to prevent the third-2 connector 79c from being short-circuited to the lower surface of the third LED stack 43.

[0116] As shown in the drawings, the third-2 connector 79c, the second-3 connector 69c, and the first-4 connector 59c may be stacked in a vertical direction, which may reduce loss of light.

[0117] To prevent light interference between the pixels due to light emission from the first LED stack 23, the second LED stack 33, and the third LED stack 43 to the side surfaces thereof, a light reflective layer or a light blocking material layer may be formed to cover side surfaces of the first to third LED stacks 23, 33, and 43. Examples of the light reflective layer may include a distributed Bragg reflector, or an insulating layer formed of Si02 with a reflective metal layer or a highly reflective organic layer deposited on the insulating layer. As the light blocking layer, for example, black epoxy may be used. The light blocking materials prevent light interference between light emitting elements to increase a contrast ratio of an image.

[0118] According to an exemplary embodiment, the first LED stack 23 is electrically connected to the electrode pads 53d and 53a, the second LED stack 33 is electrically connected to the electrode pads 53d and 53b, and the third LED stack 43 is electrically connected to the electrode pads 53d and 53c. As such, anodes of the first LED stack 23, the second LED stack 33, and the third LED stack 43 are commonly and electrically connected to the electrode pad 53d, and cathodes thereof are electrically connected to the electrode pads 53a, 53b, and 53c different from one another, respectively. Therefore, the first to third LED stacks 23, 33, and 43 may be independently driven. Further, these LED stacks 23, 33, and 43 may be disposed on the thin film transistor substrate 51 and may be electrically connected to the internal circuit of the substrate 51 to be driven in an active matrix manner.

[0119] FIGS. 3A, 3B, 4A, 4B, 5A, 5B, 6A, 6B, 7A, 7B, 8A, 8B, 9A, 9B, 10A, 10B, 11A, 11B, 12A, 12B, 13A, 13B, 14A, 14B, 15A, 15B, 16A, and 16B are schematic plan views and schematic cross-sectional views illustrating a method of manufacturing a display apparatus not forming part of the invention. In the drawings, each plan view corresponds to the plan view of FIG. 1, and each cross-sectional view is taken along line A-A of FIG. 1.

[0120] First, referring to FIGS. 3A and 3B, a first LED stack 23 is grown on a first substrate 21. The first substrate 21 may be, for example, a GaAs substrate. In addition, the first LED stack 23 is formed of AlGaInP-based semiconductor layers, and includes an n-type semiconductor layer, an active layer, and a p-type semiconductor layer.

[0121] An ohmic contact layer 25a and a reflective layer 25b are formed on the first LED stack 23 to form a first reflective electrode 25. The ohmic contact layer 25a may be formed by using lift-off technique or the like, and may be formed to be disposed near an edge of the first LED stack 23. As shown in the drawings, the ohmic contact layer 25a may be formed to have substantially an annular shape.

[0122] The reflective layer 25b covers the ohmic contact layer 25a and also covers the first LED stack 23. The reflective layer 25b may be formed to expose each of the edges of the first LED stack 23. More particularly, the reflective layer 25b may have an opening 25h exposing the first LED stack 23 with the ohmic contact layer 25a. The reflective layer 25b may be, for example, formed of Au and may be formed by using lift-off technique or the like.

[0123] Referring to FIGS. 4A and 4B, a second LED stack 33 is grown on a second substrate 31, and a second transparent electrode 35 and a first color filter 37 are formed on the second LED stack 33. The second LED stack 33 may be formed of gallium nitride-based semiconductor layers and may include a GaInN-based well layer. The second substrate 31, on which gallium nitride-based semiconductor layers may be grown, is different from the first substrate 21. A composition ratio of GaInN may be determined such that the second LED stack 33 may emit green light. Meanwhile, the second transparent electrode 35 is in ohmic contact with a p-type semiconductor layer.

[0124] Referring to FIGS. 5A and 5B, a third LED stack 43 is grown on a third substrate 41, and a third transparent electrode 45 and a second color filter 47 are formed on the third LED stack 43. The third LED stack 43 may be formed of gallium nitride-based semiconductor layers and may include a GaInN-based well layer. The third substrate 41, on which gallium nitride-based semiconductor layers may be grown, is different from the first substrate 21. A composition ratio of GaInN may be determined such that the third LED stack 43 may emit blue light. Meanwhile, the third transparent electrode 45 is in ohmic contact with a p-type semiconductor layer.

[0125] The first color filter 37 and the second color filter 47 are substantially the same those as described with reference to FIG. 1, therefore detailed descriptions thereof will be omitted to avoid redundancy.

[0126] Referring to FIGS. 6A and 6B, electrode pads 53a, 53b, 53c, and 53d are formed on a substrate 51. The substrate 51 may be a substrate formed of Si, having thin film transistors therein. Each of the electrode pads 53a, 53b, 53c, and 53d corresponding to one pixel area may be disposed in each of the four edge regions of the substrate 51.

[0127] The first LED stack 23, the second LED stack 33, the third LED stack 43, and the electrode pads 53a, 53b, 53c, and 53d are separately formed on different substrates, and the forming sequence thereof is not particularly limited.

[0128] Referring to FIGS. 7A and 7B, the first LED stack 23 is coupled onto the substrate 51 via a first bonding layer 55. The first bonding layer 55 may be disposed on the substrate 51, and the first reflective electrode 25 is disposed to face the substrate 51 so that the first reflective electrode 25 is bonded to the first bonding layer 55. Alternatively, bonding material layers may be formed on each of the substrate 51 and the first LED stack 23, and then the first LED stack 23 may be coupled to the substrate 51 by bonding the bonding material layers to each other. Meanwhile, the first substrate 21 may be removed from the first LED stack 23 by chemical etching, or the like. As such, the n-type semiconductor layer of the first LED stack 23 is exposed on the upper surface. The exposed n-type semiconductor layer may be subjected to surface texturing.

[0129] Referring to FIGS. 8A and 8B, the first LED stack 23 is patterned to expose a part of the first reflective electrode 25. To avoid damages of the reflective layer 25b, the ohmic contact layer 25a may be exposed. In addition, the first LED stack 23 and the first bonding layer 55 are patterned to form openings for exposing the electrode pads 53a, 53b, 53c, and 53d.

[0130] Referring FIGS. 9A and 9B, an insulating layer 57 is formed to cover side surfaces of the first LED stack 23 in the openings. The insulating layer 57 may also partially cover upper surfaces of the first LED stack 23. The insulating layer 57 is formed to expose the first reflective electrode 25 and the electrode pads 53a, 53b, 53c, and 53d.

[0131] Referring FIGS. 10A and 10B, connectors 59a, 59b, 59c, and 59d are formed, which may be connected to the exposed electrode pads 53a, 53b, 53c, and 53d, respectively. A first-1 connector 59d is connected to the first reflective electrode 25 and also to the electrode pad 53d. Therefore, a lower surface of the first LED stack 23 and the electrode pad 53d are electrically connected to each other by the first-1 connector 59d. In addition, a first-2 connector 59a is connected to the upper surface of the first LED stack 23 and also to the electrode pad 53a. Therefore, the upper surface of the first LED stack 23 and the electrode pad 53a are electrically connected to each other by the first-2 connector 59a. A first-3 connector 59b and a first-4 connector 59c are insulated from the first LED stack 23 by the insulating layer 57.

[0132] Referring to FIGS. 11A and 11B, the second LED stack 33 of FIGS. 4A and 4B is coupled onto the first LED stack 23, on which the first-1, first-2, first-3, and first-4 connectors 59d, 59a, 59b, and 59c are formed, via a second bonding layer 65. The first color filter 37 is bonded to the second bonding layer 65 and disposed to face the first LED stack 23. The second bonding layer 65 may be disposed on the first LED stack 23 in advance. The first color filter 37 may be bonded to the second bonding layer 65 and disposed to face the second bonding layer 65 and. Alternatively, the bonding material layers may be formed on each of the first LED stack 23 and the first color filter 37, and the bonding material layers are bonded to each other to couple the second LED stack 33 to the first LED stack 23. Meanwhile, the second substrate 31 may be separated from the second LED stack 33 by using laser lift-off, chemical lift-off techniques, or others. Therefore, the n-type semiconductor layer of the second LED stack 33 is exposed. The exposed n-type semiconductor layer may be subjected to surface texturing by chemical etching or the like. However, the step of surface texturing on the second LED stack 33 may be omitted in some exemplary embodiments.

[0133] Referring to FIGS. 12A and 12B, the second LED stack 33 is patterned to expose the second transparent electrode 35, and the exposed second transparent electrode 35, the first color filter 37, and the second bonding layer 65 are etched to form openings for exposing the first-1 connector 59d. In addition, the openings for exposing the first-3 connector 59b and the first-4 connector 59c may be formed together.

[0134] Referring FIGS. 13A and 13B, an insulating layer 67 covering sides of the exposed openings is formed. The insulating layer 67 exposes the second transparent electrode 35 and also exposes the first-1 connector 59d, the first-3 connector 59b, and the first-4 connector 59c.

[0135] A second-1 connector 69d, a second-2 connector 69b, and a second-3 connector 69c are formed in the openings. The second-1 connector 69d electrically connects the second transparent electrode 35 and the first-1 connector 59d to each other and is insulated from the upper surface of the second LED stack 33 by the insulating layer 67. The second-2 connector 69b is connected to the upper surface of the second LED stack 33 and to the first-3 connector 59b. The second-2 connector 69b is electrically connected to the electrode pad 53b through the first-3 connector 59b. The second-2 connector 69b is insulated from the lower surface of the second LED stack 33 and the second transparent electrode 35 by the insulating layer 67.

[0136] Meanwhile, the second-3 connector 69c is connected to the first-4 connector 59c and is insulated from the second LED stack 33 and the second transparent electrode 35 by the insulating layer 67.

[0137] Referring to FIGS. 14A and 14B, the third LED stack 43 of FIGS. 5A and 5B is coupled onto the second LED stack 33, on which the second-1, second-2, and second-3 connectors 69d, 69b, and 69c are formed via a third bonding layer 75. The second color filter 47 is bonded to the third bonding layer 75 and disposed to face the second LED stack 33. The third bonding layer 75 may be disposed on the second LED stack 33 in advance, and the second color filter 47 may be bonded to the third bonding layer 75 and disposed to face the third bonding layer 75. Alternatively, the bonding material layers may be formed on each of the second LED stack 33 and the second color filter 47, and the bonding material layers to are bonded to each other to bond the third LED stack 43 to the second LED stack 33. Meanwhile, the third substrate 41 may be separated from the third LED stack 43 by using laser lift-off, chemical lift-off techniques, or others. As such, the n-type semiconductor layer of the third LED stack 43 is exposed. The exposed n-type semiconductor layer may be subjected to surface texturing by chemical etching or the like.

[0138] Referring to FIGS. 15A and 15B, the third LED stack 43 is patterned to expose the third transparent electrode 45, and the exposed third transparent electrode 45, the second color filter 47, and the third bonding layer 75 are etched to form openings for exposing the second-1 connector 69d. In addition, the openings for exposing the second-3 connector 69c may be formed together.

[0139] Referring to FIGS. 16A and 16B, an insulating layer 77 covering sides of the exposed openings is formed. The insulating layer 77 exposes the third transparent electrode 45, and also exposes the second-1 connector 69d and the second-3 connector 69c.

[0140] A third-1 connector 79d and a third-2 connector 79c are formed in the openings. The third-1 connector 79d electrically connects the third transparent electrode 45 and the second-1 connector 69d to each other, and is insulated from the upper surface of the third LED stack 43 by the insulating layer 77. The third-2 connector 79c is connected to the upper surface of the third LED stack 43 and to the second-3 connector 69c. The third-2 connector 79c is electrically connected to the electrode pad 53c through the second-3 connector 69c and the first-4 connector 59c. The third-2 connector 79c is insulated from the lower surface of the third LED stack 43 and the third transparent electrode 45 by the insulating layer 77.

[0141] According to an exemplary embodiment, a unit pixel having anodes of the first to third LED stacks 23, 33, and 43 commonly and electrically connected to one another and cathodes thereof independently connected may be provided.

[0142] Although a method of manufacturing one unit pixel has been described above according to an exemplary embodiment, a display apparatus may include a plurality of unit pixels arranged on the substrate 51 in a matrix form. The unit pixels are spaced apart from each other. In this case, regions of the first to third LED stacks 23, 33, and 43 each corresponding to the unit pixels may be isolated, in advance, from one another on the substrates 21, 31, and 41. Alternatively, when each of the LED stacks 23, 33, and 43 is patterned after being bonded onto the substrate 51, the regions of the LED stacks may be isolated into regions corresponding to each pixel region. Accordingly, a display apparatus having a plurality of unit pixels on the substrate 51 according to an exemplary embodiment may obviate the need of individually mount pixels having a small size.

[0143] Further, in order to prevent light interference between pixels, a light reflective layer or a light blocking material layer covering sides of the pixels may be added. Examples of the light reflective layer may include a distributed Bragg reflector, or an insulating layer formed of Si02 with a reflective metal layer or a highly reflective organic layer deposited on the insulating layer. As the light blocking layer, for example, black epoxy may be used. The light blocking materials prevent light interference between light emitting elements to increase a contrast ratio of an image.

[0144] FIG. 17 is a schematic plan view of a display apparatus not forming part of the invention. FIG. 18 is a schematic cross-sectional view taken along line B-B of FIG. 17.

[0145] Referring to FIGS. 17 and 18, the display apparatus according to an exemplary embodiment is generally similar to the display apparatus described with reference to FIGS. 1 and 2, except that cathodes of the first to third LED stacks 23, 33, and 43 are commonly and electrically connected to one another, and anodes thereof are individually connected.

[0146] In particular, a first-1 connector 159d electrically connects the first reflective electrode 25 to an electrode pad 153d. A second-1 connector 169a electrically connects the second transparent electrode 35 to an electrode pad 153a, and a third-1 connector 179b electrically connects the third transparent electrode 45 to an electrode pad 153b.

[0147] In addition, a first-2 connector 159c is connected to the upper surface of the first LED stack 23 and an electrode pad 153c. A second-2 connector 169c is connected to the upper surface of the second LED stack 33 and the first-2 connector 159c. A third-2 connector 179c is connected to the upper surface of the third LED stack 43 and the second-2 connector 169c. As shown in the drawings, the first-2, second-2, and third-2 connectors 159c, 169c, and 179c may be stacked in a vertical direction. In addition, the third-2 connector 179c may be connected to the electrode pad 153b through intermediate connectors 169b and 159b, and the connectors 159b, 169b, and 179b may also be stacked in a vertical direction.

[0148] FIG. 19 is a schematic circuit diagram of a display apparatus according to an exemplary embodiment.

[0149] Referring to FIG. 19, a driving circuit according to an exemplary embodiment includes two or more transistors Tr1 and Tr2 and capacitors. When power is connected to select lines Vrow1 to Vrow3 and a data voltage is applied to data lines Vdata1 to Vdata3, a voltage is applied to the corresponding light emitting diode. Charges are charged to the corresponding capacitor depending on values of the Vdata1 to Vdata3. Since turn-on state of Tr2 is maintained by the charged voltage of the capacitor, a voltage of the capacitor may be maintained even if power is shut off,, and a voltage may be applied to the light emitting diodes LED1 to LED3. In addition, a current flowing in LED1 to LED3 may be changed depending on values of the Vdata1 to Vdata3. A current may be constantly supplied through Vdd, and therefore continuous light emission is possible.

[0150] The transistors Tr1 and Tr2 and the capacitors may be formed in the substrate 51. Here, LED1 to LED3 correspond to the first to third LED stacks 23, 33, and 43, respectively, which are stacked as one pixel. Anodes of the first to third LED stacks are connected to the transistors Tr2 and cathodes thereof are grounded. According to an exemplary embodiment, the first to third LED stacks 23, 33, and 43 may be commonly connected one another to be grounded.

[0151] Although FIG. 19 shows a circuit diagram for driving an active matrix according to an exemplary embodiment, however, the inventive concepts are not limited thereto, and another circuit may be used. In addition, while each of the anodes of the LED1 to LED3 is described as being connected to different transistors Tr2 and cathodes thereof are described as being grounded, the anodes of the first to third LED stacks 23, 33, and 43 may be connected in common and each of cathodes thereof may be connected to different transistors in some exemplary embodiments.

[0152] FIG. 20 is a schematic plan view of a display apparatus according to an exemplary embodiment.

[0153] Referring to FIG. 20, the display apparatus includes a circuit board 201 and a plurality of light emitting devices 200.

[0154] The circuit board 201 may include a circuit for passive matrix driving or active matrix driving. In an exemplary embodiment, the circuit board 201 may include wires and resistors therein. In another exemplary embodiment, the circuit board 201 may include wires, transistors, and capacitors. The circuit board 201 may also have pads on the upper side thereof, such that the circuit disposed therein is allowed to be electrically connected.

[0155] A plurality of light emitting devices 200 are arranged on the circuit board 201. Each light emitting device 200 constitutes one pixel. The light emitting device 200 has electrode pads 281a, 281b, 281c, and 281d, and the electrode pads 281a, 281b, 281c, and 281d are electrically connected to the circuit board 201. The light emitting device 200 may also include a substrate 241 on the upper surface. As the light emitting devices 200 are spaced apart from each other, the substrates 241 disposed on the upper surfaces of the light emitting devices 200 are also spaced apart from each other.

[0156] The specific configuration of the light emitting device 200 will be described in detail with reference to FIGS. 21A and 21B. FIG. 21A is a schematic plan view of the light emitting device 200 according to an exemplary embodiment, and FIG. 21B is a cross-sectional view taken along line A-A of FIG. 21A. Although the electrode pads 281a, 281b, 281c, and 281d are shown as being arranged on the upper side, however, the inventive concepts are not limited thereto, and the light emitting device 200 may be flip-bonded on the circuit board 201 of FIG. 20, and in this case, the electrode pads 281a, 281b, 281c, and 281d will be arranged on the lower side.

[0157] Referring to FIGS. 21A and 21B, the light emitting device 200 includes the substrate 241, the electrode pads 281a, 281b, 281c, and 281d, a first LED stack 223, a second LED stack 233, a third LED stack 243, an insulating layer 271, a first reflective electrode 228, a second transparent electrode 235, a third transparent electrode 245, first ohmic electrodes 228, a first color filter 247, a second color filter 267, a first bonding layer 249, a second bonding layer 269, and an upper insulating layer 273.

[0158] The substrate 241 may support the LED stacks 223, 233, and 243. In addition, the substrate 241 may be a growth substrate for growing the third LED stack 243. For example, the substrate 241 may be a sapphire substrate or a gallium nitride substrate, in particular, a patterned sapphire substrate. The first, second, and third LED stacks are arranged on the substrate 241 in the order of the third LED stack 243, the second LED stack 233, and the first LED stack 223. Single third LED stack is disposed on one substrate 241, and thus, the light emitting device 200 has a single-chip structure of a single pixel. In some exemplary embodiments, the substrate 241 may be omitted and the lower surface of the third LED stack 243 may be exposed. In this case, a rough surface may be formed on the lower surface of the third LED stack 243 by surface texturing.

[0159] The first LED stack 223, the second LED stack 233, and the third LED stack 243 each include a first conductivity type semiconductor layer 223a, 233a, or 243a, a second conductivity type semiconductor layer 223b, 233b, or 243b, and an active layer interposed therebetween. In particular, the active layer may have a multiple quantum well structure.

[0160] The closer to the substrate 241, the shorter wavelength light may be emitted from the LED stack. For example, the first LED stack 223 may be an inorganic light emitting diode emitting red light, the second LED stack 233 may be an inorganic light emitting diode emitting green light, and the third LED stack 243 may be an inorganic light emitting diode emitting blue light. The first LED stack 223 may include a GaInP based well layer and the second LED stack 233 and the third LED stack 243 may include a GaInN based well layer. However, the inventive concepts are not limited thereto, and when the light emitting device 200 includes a micro LED, the first LED stack 223 may emit any one of red, green, and blue light, and second and third LED stacks 233 and 243 may emit different one of red, green, and blue light without adversely affecting operation due to small form factor of a micro LED.

[0161] The first conductivity type semiconductor layers 223a, 233a, and 243a of the respective LED stacks 223, 233, and 243 may be n-type semiconductor layers and the second conductivity type semiconductor layers 223b, 233b, and 243b of the respective LED stacks 223, 233, and 243 may be p-type semiconductor layers. The upper surface of the first LED stack 223 may be a p-type semiconductor layer 223b, the upper surface of the second LED stack 233 may be an n-type semiconductor layer 233a, and the upper surface of the third LED stack 243 may be a p-type semiconductor layer 243b. More particularly, according to an exemplary embodiment, the order of the semiconductor layers is reversed only in the second LED stack 233. The first LED stack 223 and the third LED stack 243 may have the first conductivity type semiconductor layers 223a and 243a with textured surfaces to improve light extraction efficiency. The second LED stack 233 may also have the first conductivity type semiconductor layer 233a with a textured surface, however, since the first conductivity type semiconductor layer 233a is disposed farther away from the substrate 241 than the second conductivity type semiconductor layer 233b, surface texturing may be less effective. More particularly, when the second LED stack 233 emits green light, the green light has higher visibility than red light or blue light. Therefore, it may be preferable to increase the luminous efficiency of the first LED stack 223 and the third LED stack 243 more than the luminous efficiency of the second LED stack 233. In this manner, luminous intensities of red light, green light, and blue light can be adjusted or balanced to be kept at a similar level by applying surface texturing to the first LED stack 223 and the third LED stack 243 to improve light extraction efficiency while using the second LED stack 233 without or less surface texturing.

[0162] In the first LED stack 223 and the third LED stack 243, the second conductivity type semiconductor layers 223b and 243b may be disposed on partial regions of the first conductivity type semiconductor layer 223a and 243a, and thus, the first conductivity type semiconductor layers 223a and 243a are partially exposed. Alternatively, in the case of the second LED stack 233, the first conductivity type semiconductor layer 233a and the second conductivity type semiconductor layer 233b may be completely overlapped.

[0163] The first LED stack 223 is disposed apart from the substrate 241, the second LED stack 233 is disposed below the first LED stack 223, and the third LED stack 243 is disposed below the second LED stack 233. The first LED stack 223 may emit light having a longer wavelength than the second and third LED stacks 233 and 243, so that light generated in the first LED stack 223 is emitted to the outside through the second and third LED stacks 233 and 243 and the substrate 241. In addition, the second LED stack 233 may emit light having a longer wavelength than the third LED stack 243, so that light generated in the second LED stack 233 is emitted to the outside through the third LED stack 243 and the substrate 241. However, the inventive concepts are not limited thereto. For example, when the light emitting device 200 includes a micro LED, the first LED stack 223 may emit any one of red, green, and blue light, and second and third LED stacks 233 and 243 may emit different one of red, green, and blue light without adversely affecting operation due to small form factor of a micro LED

[0164] The insulating layer 271 is disposed on the first LED stack 223 and has an opening for exposing the second conductivity type semiconductor layer 223b of the first LED stack 223. The insulating layer 271 may have, for example, an opening having substantially an annular shape. The insulating layer 271 may be a transparent insulating layer having a lower refractive index than the first LED stack 223.

[0165] The first reflective electrode 228 is in ohmic contact with the second conductivity type semiconductor layer 223b of the first LED stack 223, and reflects light generated in the first LED stack 223 toward the substrate 241. The first reflective electrode 228 is disposed on the insulating layer 271 and is connected to the first LED stack 223 through the opening of the insulating layer 271.

[0166] The first reflective electrode 228 may include an ohmic contact layer 228a and a reflective layer 228b. The ohmic contact layer 228a is in partial contact with the second conductivity type semiconductor layer 223b, for example, a p-type semiconductor layer. The ohmic contact layer 228a may be formed in a predetermined area to prevent the ohmic contact layer 228a from absorbing light. The ohmic contact layer 228a may be formed on the second conductivity type semiconductor layer 223b exposed in the opening of the insulating layer 271. The ohmic contact layer 228a may be formed to have substantially an annular shape. The ohmic contact layer 228a may be formed of a transparent conductive oxide, for example, an Au alloy, such as Au (Zn) or Au (Be).

[0167] The reflective layer 228b covers the ohmic contact layer 228a and the insulating layer 271. When the reflective layer 228b covers the insulating layer 271, the first LED stack 223 may have a stacked structure of the first LED stack 223 having a relatively high refractive index, the insulating layer 271 having a relatively low refractive index, and the reflective layer 228b, which may form an omnidirectional reflector. The reflective layer 228b may include a reflective metal layer such as Al, Ag, or Au. In addition, the reflective layer 228b may include an adhesive metal layer, such as Ti, Ta, Ni, or Cr on the upper and lower surfaces of the reflective metal layer to improve the adhesion of the reflective metal layer. Au is particularly suitable for the reflective layer 228b formed in the first LED stack 223 because of its high reflectance to red light and its low reflectance to blue light or green light. The reflective layer 228b may cover more than about 50% of the area of the first LED stack 223, and may further cover most of the area to improve light efficiency.

[0168] The ohmic contact layer 228a and the reflective layer 228b may be formed of a metal layer containing Au. The reflective layer 228b may be formed of a metal layer having high reflectance of light generated in the first LED stack 223, for example, red light. The reflective layer 228b may have a relatively low reflectance of light generated in the second LED stack 233 and the third LED stack 243, for example, green light or blue light, and accordingly, light generated in the second and third LED stacks 233 and 243 and incident on the reflective layer 228b may be absorbed to reduce optical interference.

[0169] A first ohmic electrode 226 is disposed on the exposed first conductivity type semiconductor layer 223a, and is in ohmic contact with the first conductivity type semiconductor layer 223a. The first ohmic electrode 226 may also be formed of a metal layer containing Au.

[0170] The second transparent electrode 235 is in ohmic contact with the second conductivity type semiconductor layer 233b of the second LED stack 233. As shown in the drawing, the second transparent electrode 235 is in contact with the lower surface of the second LED stack 233 between the second LED stack 233 and the third LED stack 243. The second transparent electrode 235 may be formed of a metal layer or a conductive oxide layer which is transparent to red light and green light.

[0171] In addition, the third transparent electrode 245 is in ohmic contact with the second conductivity type semiconductor layer 243b of the third LED stack 243. The third transparent electrode 245 may be disposed between the second LED stack 233 and the third LED stack 243, and is in contact with the upper surface of the third LED stack 243. The third transparent electrode 245 may be formed of a metal layer or a conductive oxide layer which is transparent to red light and green light. The third transparent electrode 245 may also be transparent to blue light according to some exemplary embodiments. The second transparent electrode 235 and the third transparent electrode 245 may assist current distribution by ohmic contact with the p-type semiconductor layer of each LED stack. Examples of the conductive oxide layer used for the second and third transparent electrodes 235 and 245 include Sn02, In02, IT0, Zn0, IZ0, or others.

[0172] The first color filter 247 may be disposed between the third transparent electrode 245 and the second LED stack 233, and the second color filter 267 may be disposed between the second LED stack 233 and the first LED stack 223. The first color filter 247 may transmit light generated in the first and second LED stacks 223 and 233 and reflect light generated in the third LED stack 243. The second color filter 267 may transmit light generated in the first LED stack 223 and reflect light generated in the second LED stack 233. Accordingly, light generated in the first LED stack 223 can be emitted to the outside through the second LED stack 233 and the third LED stack 243, and light generated in the second LED stack 233 can be emitted to the outside through the third LED stack 243. Furthermore, light generated in the second LED stack 233 may be prevented from being lost by being incident on the first LED stack 223, or light generated in the third LED stack 243 may be prevented from being lost by being incident on the second LED stack 233.

[0173] In some exemplary embodiments, the second color filter 267 may reflect light generated in the third LED stack 243.

[0174] *242The first and second color filters 247 and 267 may be, for example, a low frequency range, such as a low pass filter that passes only a long wavelength band, a band pass filter that passes only a predetermined wavelength band, or a band stop filter that blocks only a predetermined wavelength band. In particular, the first and second color filters 247 and 267 may be formed by alternately stacking insulating layers having refractive indices different from each other, for example, may be formed by alternately stacking Ti02 insulating layer and Si02 insulating layer. In particular, the first and second color filters 247 and 267 may include a distributed Bragg reflector (DBR). The stop band of the distributed Bragg reflector can be controlled by adjusting the thickness of Ti02 and Si02 layers. The low pass filter and the band pass filter may also be formed by alternately stacking insulating layers having refractive indices different from each other.

[0175] The first bonding layer 249 couples the second LED stack 233 to the third LED stack 243. The first bonding layer 249 covers the first color filter 247 and is bonded to the second transparent electrode 235. For example, the first bonding layer 249 may be a transparent organic layer or a transparent inorganic layer. Examples of the organic layer include SU8, poly(methylmethacrylate) (PMMA), polyimide, parylene, and benzocyclobutene (BCB), examples of the inorganic layer include Al203, Si02, SiNx, or others. The organic layers may be bonded at a high vacuum and a high pressure, and the inorganic layers may be bonded under a high vacuum in a state in which the surface energy is lowered by using plasma or the like, after flattening the surface by a chemical mechanical polishing process, for example.

[0176] The second bonding layer 269 couples the second LED stack 233 to the first LED stack 223. As shown in the drawing, the second bonding layer 269 may cover the second color filter 267 and be in contact with the first LED stack 223. However, the inventive concepts are not limited thereto, and another layer such as a transparent electrode layer may further be disposed to the lower surface of the first LED stack 223. The second bonding layer 269 may be formed of substantially the same material as the first bonding layer 249 described above.

[0177] The upper insulating layer 273 covers the side surfaces and upper portions of the first, second, and third LED stacks 223, 233, and 243. The upper insulating layer 273 may be formed of Si02, Si3N4, S0G, or others. Alternatively, the upper insulating layer 273 may contain a light reflecting material or a light blocking material to prevent optical interference with the adjacent light emitting device. For example, the upper insulating layer 273 may include a distributed Bragg reflector that reflects red light, green light, and blue light, or an Si02 layer with a reflective metal layer or a highly reflective organic layer deposited thereon. Alternatively, the upper insulating layer 273 may contain a black epoxy, as the light blocking material, for example. The light blocking material increases the contrast of an image by preventing optical interference between the light emitting devices.

[0178] The upper insulating layer 273 has openings for exposing the first ohmic electrode 26, the first reflective electrode 228, the second and third transparent electrodes 235 and 245, and the second and third LED stacks 233 and 243. Holes may be formed to pass through the first LED stack 223 and the second LED stack 233, and the upper insulating layer 273 may cover the side walls of the holes while exposing the bottom surface of the holes.

[0179] The electrode pads 281a, 281b, 281c, and 281d are disposed above the first LED stack 223 and are electrically connected to the first, second, and third LED stacks 223, 233, and 243. The electrode pads 281a, 281b, 281c, and 281d may be disposed on the upper insulating layer 273 and be connected to the first ohmic electrode 26, the first reflective electrode 228, the second and third transparent electrodes 235 and 245, and the second and third LED stacks 233 and 243, which are exposed through the holes h1, h2, h3, h4, and h5.

[0180] For example, the first electrode pad 281a may be connected to the first ohmic electrode 26 through the hole h4 that passes through the upper insulating layer 273. The first electrode pad 281a is electrically connected to the first conductivity type semiconductor layer 223a of the first LED stack 223.

[0181] The second electrode pad 281b may be connected to the first conductivity type semiconductor layer 233a of the second LED stack 233 through the hole h3 that passes through the upper insulating layer 273 and the first LED stack 223.

[0182] The third electrode pad 281c may be electrically connected to the first conductivity type semiconductor layer 243a of the third LED stack 243 through the hole h2 that passes through the upper insulating layer 273, the first LED stack 223, and the second LED stack 233. The hole h2 may pass through the second conductivity type semiconductor layer 243b of the third LED stack 243 and the active layer.

[0183] Meanwhile, the common electrode pad 281d may be connected in common to the first reflective electrode 228, the second transparent electrode 235, and the third transparent electrode 245 through the holes h1 and h5. The hole h1 passes through the first LED stack 223 and the second LED stack 233 to expose the second transparent electrode 235 and the third transparent electrode 245, and the hole h5 exposes the first reflective electrode 228. Accordingly, the common electrode pad 281d is electrically connected in common to the second conductivity type semiconductor layer 223b of the first LED stack 223, the second conductivity type semiconductor layer 233b of the second LED stack 233, and the second conductivity type semiconductor layer 243b of the third LED stack 243. In addition, as shown in FIG. 21B, the common electrode pad 281d may be connected to the third LED stack 243 through the hole h1 that passes through a hollow portion surrounded by the first reflective electrode 228.

[0184] According to an exemplary embodiment, the first LED stack 223 is electrically connected to the electrode pads 281d and 281a, and the second LED stack 233 is electrically connected to the electrode pads 281d and 281b, and the third LED stack 243 is electrically connected to the electrode pads 281d and 281c. Accordingly, anodes of the first LED stack 223, the second LED stack 233, and the third LED stack 243 are electrically connected in common to the electrode pad 281d, and cathodes thereof are electrically connected to the first, second, and third electrode pads 281a, 281b, and 281c, respectively. Thus, the first, second, and third LED stacks 223, 233, and 243 can be independently driven.

[0185] FIGS. 22, 23, 24, 25, 26A, 26B, 27A, 27B, 28A, 28B, 29, 30A, 30B, 31A, 31B, 32A, 32B, 33A, 33B, 34A, 34B, 35A and 35B are schematic plan views and cross-sectional views illustrating a method of manufacturing the light emitting device 200 according to an exemplary embodiment. In the drawings, each plan view corresponds to a plan view of FIG. 21A, and each cross-sectional view is taken along line A-A of FIG. 21A.

[0186] First, referring to FIG. 22, the first LED stack 223 is grown on a first substrate 221. The first substrate 221 may be a GaAs substrate, for example. The first LED stack 223 is formed of AlGaInP based semiconductor layers, and includes the first conductivity type semiconductor layer 223a, the active layer, and the second conductivity type semiconductor layer 223b. Here, the first conductivity type may be an n-type and the second conductivity type may be a p-type.

[0187] Referring to FIG. 23, the second LED stack 233 is grown on a second substrate 231, and the second transparent electrode 235 is formed on the second LED stack 233. The second LED stack 233 is formed of gallium nitride based semiconductor layers, and may include the first conductivity type semiconductor layer 233a, the active layer, and the second conductivity type semiconductor layer 233b. The active layer may include a GaInN well layer. Here, the first conductivity type may be an n-type and the second conductivity type may be a p-type.

[0188] The second substrate 231 is a substrate on which a gallium nitride based semiconductor layer can be grown, and is different from the first substrate 221. The composition ratio of the GaInN well layer may be determined so that the second LED stack 233 emits green light, for example. The second transparent electrode 235 is in ohmic contact with the second conductivity type semiconductor layer 233b. The second transparent electrode 235 may be formed of a conductive oxide layer such as SnO2, InO2, ITO, ZnO, or IZO.

[0189] Referring to FIG. 24, the third LED stack 243 is grown on a third substrate 241, and the third transparent electrode 245 and the first color filter 247 are formed on the third LED stack 243. The third LED stack 243 is formed of gallium nitride based semiconductor layers, and includes the first conductivity type semiconductor layer 243a, the active layer, and the second conductivity type semiconductor layer 243b. The active layer may also include a GaInN well layer. Here, the first conductivity type may be an n-type and the second conductivity type may be a p-type.

[0190] The third substrate 241 is a substrate on which a gallium nitride based semiconductor layer can be grown, and is different from the first substrate 221. The composition ratio of the GaInN well layer may be determined so that the third LED stack 243 emits blue light, for example. The third transparent electrode 245 is in ohmic contact with the second conductivity type semiconductor layer 243b. The third transparent electrode 245 may be formed of a conductive oxide layer, such as SnO2, InO2, ITO, ZnO, or IZO.

[0191] Since the first color filter 247 is substantially the same as that described with reference to FIGS. 21A and 21B, detailed descriptions thereof will be omitted in order to avoid redundancy.

[0192] Referring to FIG. 25, the second LED stack 233 of FIG. 223 is bonded onto the third LED stack 243 of FIG. 24.

[0193] The first color filter 247 and the second transparent electrode 235 are bonded so as to face each other. For example, bonding material layers are formed on the first color filter 247 and the second transparent electrode 235, respectively, and by bonding the first color filter 247 and the second transparent electrode 235, the first bonding layer 249 may be formed. The bonding material layers may be, for example, a transparent organic layer or a transparent inorganic layer. Examples of the organic layer include SU8, poly (methylmethacrylate) (PMMA), polyimide, parylene, benzocyclobutene (BCB), or others, and examples of the inorganic layer include Al2O3, SiO2, SiNx, or others. The organic layers may be bonded at a high vacuum and a high pressure, and the inorganic layers may be bonded under a high vacuum in a state in which the surface energy is lowered by using plasma or the like, after flattening the surface by a chemical mechanical polishing process, for example.

[0194] Then, the second substrate 231 is removed from the second LED stack 233 using techniques such as laser lift-off or chemical lift-off. Accordingly, the first conductivity type semiconductor layer 233a of the second LED stack 233 is exposed from above. The surface of the exposed first conductivity type semiconductor layer 233a may be textured.

[0195] Meanwhile, before coupling the first LED stack 223 to the second LED stack, a reflective electrode and an ohmic electrode are first formed on the first LED stack 223, and the substrate 221 is removed using a carrier substrate. This will be described in more detail below with reference to FIGS. 26A, 26B, 27A, 27B, 28A, 28B, and 29.

[0196] Referring to FIGS. 26A and 26B, the second conductivity type semiconductor layer 223b of the first LED stack 223 of FIG. 22 is patterned to expose the first conductivity type semiconductor layer 223a. A light emitting device region may have substantially a rectangular shape as shown in FIG. 26A. Here, the second conductivity type semiconductor layer 223b is removed in the vicinity of four corners in one light emitting device region. As shown in FIG. 26A, all of the second conductivity type semiconductor layer 223b may be removed in the vicinity of three corners, and a hole that passes through the second conductivity type semiconductor layer 223b may be formed in the vicinity of one corner. Here, although one light emitting device region is shown, a plurality of light emitting device regions may be provided on the substrate 241, and the second conductivity type semiconductor layer 223b may be patterned in each light emitting device region according to some exemplary embodiments.

[0197] Referring to FIGS. 27A and 27B, the first ohmic electrode 226 is formed in the vicinity of one corner. The first ohmic electrode 26 is in ohmic contact with the first conductivity type semiconductor layer 223a.

[0198] Then, the insulating layer 271 covering the first ohmic electrode 226 and the first LED stack 223 is formed and patterned to form an opening for exposing the second conductivity type semiconductor layer 223b. For example, SiO2 is formed on the first LED stack 223, a photoresist is applied thereto, and then a photoresist pattern is formed using photolithography and development. Then, SiO2 is patterned using the photoresist pattern as an etching mask to form the insulating layer 271 having an opening.

[0199] The opening may be formed around the hole that passes through the second conductivity type semiconductor layer 223b, and may surround the hole having substantially an annular shape.

[0200] Then, the ohmic contact layer 228a is formed in the opening of the insulating layer 271. The ohmic contact layer 228a may be formed using a lift-off technique or the like. The ohmic contact layer 228a may be formed to have substantially an annular shape along the shape of the opening.

[0201] Referring to FIGS. 28A and 28B, after the ohmic contact layer 228a is formed, the reflective layer 228b covering the ohmic contact layer 228a and the insulating layer 271 is formed. The reflective layer 228b may be formed using a lift-off technique or the like. The first reflective electrode 228 is formed by the ohmic contact layer 228a and the reflective layer 228b.

[0202] The first reflective electrode 228 may have a shape in which four corner portions are removed in one rectangular light emitting device region, as shown in the drawing. In particular, at one corner portion, the first reflective electrode 228 may have a hollow portion above a hole formed in the second conductivity type semiconductor layer 223b. Here, although one light emitting device region is shown, a plurality of light emitting device regions may be provided on the substrate 221, and the first reflective electrode 228 may be formed in each light emitting device region according to some exemplary embodiments.

[0203] Referring to FIG. 29, the carrier substrate 251 is bonded onto the first LED stack 223 of FIGS. 28A and 28B. The first reflective electrode 228 is disposed to face the carrier substrate 251, and the first LED stack 223 may be bonded to the carrier substrate 251 using the adhesive layer 253. Then, the substrate 221 is removed from the first LED stack 223. Accordingly, the first conductivity type semiconductor layer 223a is exposed. The surface of the exposed first conductivity type semiconductor layer 223a may be textured to improve light extraction efficiency, so that a roughened surface or a light extracting structure may be formed on the surface of the first conductivity type semiconductor layer 223a.

[0204] Hereinafter, with reference to FIG. 25, a method of manufacturing the light emitting device 200 by bonding the first LED stack 223 onto the second LED stack 233 will be described.

[0205] Referring to FIGS. 30A and 30B, first, the second color filter 267 is formed on the exposed first conductivity type semiconductor layer 233a of the second LED stack 233 of FIG.25. Since the second color filter 267 is substantially the same as that described with reference to FIGS. 21A and 21B, detailed descriptions thereof will be omitted.

[0206] The first LED stack 223 is bonded onto the second LED stack 233. The second color filter 267 and the first LED stack 223 may be bonded to face each other. For example, bonding material layers are formed on the second color filter 267 and the first LED stack 223, respectively, and by bonding the second color filter 267 and the first LED stack 223, the second bonding layer 269 may be formed. The bonding material layers may be a transparent organic layer or a transparent inorganic layer as described above.

[0207] Then, the carrier substrate 251 and the adhesive layer 253 are removed. Accordingly, the first reflective electrode 228 is exposed.

[0208] Referring to FIGS. 31A and 31B, the insulating layer 271 is patterned to expose the first LED stack 223 around the first reflective electrode 228, and then the first LED stack 223, the second bonding layer 269, and the second color filter 269 are sequentially patterned to form holes h1, h2, and h3 through which the first conductivity type semiconductor layer 233a of the second LED stack 233 is exposed. Further, the second LED stack 233 is patterned so that the holes h1 and h2 pass through the second LED stack 233 to expose the second transparent electrode 235. The hole h3 is maintained to expose the first conductivity type semiconductor layer 233a of the second LED stack 233.

[0209] In addition, the insulating layer 271, the first LED stack 223, the second bonding layer 269, the second color filter 267, and the second LED stack 233 are sequentially removed so that the second transparent electrode 235 is exposed at edge portions of the light emitting device regions.

[0210] Referring to FIGS. 32A and 32B, the second transparent electrode 235, the first bonding layer 249, and the first color filter 247 are removed to expose the third transparent electrode 245 through the holes h1 and h2. The upper surface of the second transparent electrode 235 is partially exposed in the hole h1.

[0211] In addition, the second transparent electrode 235, the first bonding layer 249, and the first color filter 247 are also removed at the edge portions of the light emitting device regions to expose the third transparent electrode 245.

[0212] Referring to FIGS. 33A and 33B, the third transparent electrode 245 and the second conductivity type semiconductor layer 243b are patterned to expose the first conductivity type semiconductor layer 243a of the third LED stack 243 through the hole h2. The hole h1 is maintained to expose the third transparent electrode 245.

[0213] In addition, the third transparent electrode 245 and the third LED stack 243 are removed so that the substrate 241 is exposed at the edge portions of the light emitting device regions. The exposed regions of the substrate 241 may be dicing regions for dividing the light emitting devices.

[0214] As shown in FIG. 33B, the hole h1 is formed to pass through the hollow portion of the first reflective electrode 228 and exposes the second transparent electrode 235 and the second transparent electrode 245. The hole h2 passes through both the first and second LED stacks 223 and 233 and exposes the first conductivity type semiconductor layer 243a by passing through the second conductivity type semiconductor layer 243b. The hole h3 passes through the first LED stack 223 and exposes the first conductivity type semiconductor layer 233a of the second LED stack 233.

[0215] Referring to FIGS. 34A and 34B, the upper insulating layer 273 is formed to cover side surfaces and an upper region of the first, second, and third LED stacks 223, 233, and 243. The upper insulating layer 273 may be formed of a single layer or multiple layers of SiO2, Si3N4, SOG, or others. Alternatively, the upper insulating layer 273 may contain a light reflecting material or a light blocking material to prevent optical interference between adjacent light emitting devices. For example, the upper insulating layer 273 may include a distributed Bragg reflector that reflects red light, green light, and blue light, or SiO2 layer with a reflective metal layer or a highly reflective organic layer deposited thereon. Alternatively, the upper insulating layer 273 may contain a black epoxy, as the light blocking material, for example. The light blocking material may increase the contrast of an image by preventing optical interference between the light emitting devices. The distributed Bragg reflector may be formed, for example, by alternately depositing SiO2 and TiO2 layers.

[0216] Then, the upper insulating layer 273 is patterned using photolithography and etching techniques to form openings in the holes h1, h2, and h3, and openings h4 and h5 are further formed. The upper insulating layer 273 exposes the second transparent electrode 235 and the third transparent electrode 245 in the hole h1, and covers the sides of the first LED stack 223 and the second LED stack 233. In addition, the upper insulating layer 273 covers the side wall in the hole h2 while exposing the first conductivity type semiconductor layer 243a. Further, the upper insulating layer 273 exposes the first conductivity type semiconductor layer 233a of the second LED stack 233 in the hole h3. Meanwhile, the hole h4 passes through the upper insulating layer 273 and the insulating layer 271 to expose the first ohmic electrode 226, and the hole h5 passes through the upper insulating layer 273 to expose the first reflective electrode 228. The hole h5 may be formed to have substantially an annular shape as shown in FIG. 34A.

[0217] Referring to FIGS. 35A and 35B, the electrode pads 281a, 281b, 281c, and 281d are formed on the upper insulating layer 273. The electrode pads 281a, 281b, 281c, and 281d include the first electrode pad 281a, the second electrode pad 281b, the third electrode pad 281c, and the common electrode pad 281d.

[0218] The common electrode pad 281d is connected to the second transparent electrode 235 and the second transparent electrode 245 through the hole h1, and to the first reflective electrode 228 through the hole h5. Thus, the common electrode pad 281d is electrically connected in common to the anodes of the first, second, and third LED stacks 223, 233, and 243.

[0219] The first electrode pad 281a is connected to the first ohmic electrode 226 through the hole h4, and electrically connected to the cathode of the first LED stack 223, e.g., the first conductivity type semiconductor layer 223a. Meanwhile, the second electrode pad 281b is electrically connected to the cathode of the second LED stack 233, e.g., the first conductivity type semiconductor layer 233a through the hole h3, and the third electrode pad 281c is electrically connected to the cathode of the third LED stack 243, e.g., the first conductivity type semiconductor layer 243a through the hole h2

[0220] Meanwhile, the electrode pads 281a, 281b, 281c, and 281d are electrically separated from each other, so that each of the first, second, and third LED stacks 223, 233, and 243 is electrically connected to two electrode pads, and is adapted to be independently driven.

[0221] Subsequently, the light emitting device 200 according to an exemplary embodiment is provided by dividing the substrate 241 into light emitting device regions. As shown in FIG. 35A, the electrode pads 281a, 281b, 281c, and 281d may be disposed at four corners of each light emitting device 200. In addition, the electrode pads 281a, 281b, 281c, and 281d may have substantially a rectangular shape, but are not limited thereto.

[0222] Although the substrate 241 is described above as being divided, according to some exemplary embodiments, the substrate 241 may be removed so that the surface of the exposed first conductivity type semiconductor layer 243 may be textured. The substrate 241 may be removed after bonding the first LED stack 223 on the second LED stack 233, or may be removed after forming the electrode pads 281a, 281b, 281c, and 281d.

[0223] According to the exemplary embodiments, a light emitting device includes anodes of the first, second, and third LED stacks 223, 233, and 243 that are electrically connected in common, and cathodes thereof are independently connected. However, the inventive concepts are limited thereto, and for example, the anodes of the first, second, and third LED stacks 223, 233, and 243 may be independently connected to the electrode pads, and the cathodes may be electrically connected in common.

[0224] The light emitting device 200 may include the first, second, and third LED stacks 223, 233, and 243 to emit red, green, and blue light, and thus, may be used as a single pixel in a display apparatus. As described with reference to FIG. 20, a display apparatus may be provided by aligning a plurality of light emitting devices 200 on the circuit board 201. Since the light emitting device 200 includes the first, second, and third LED stacks 223, 233, and 243, the area of the subpixel in one pixel may be increased. Further, the first, second, and third LED stacks 223, 233, and 243 may be mounted by mounting one light emitting device 200, thereby reducing the number of mounting processes.

[0225] As described with reference to FIG. 20, the light emitting devices 200 mounted on the circuit board 201 may be driven by a passive matrix method or an active matrix method.

[0226] FIG. 36 is a schematic cross-sectional view of a light emitting diode stack for a display not forming part of the invention.

[0227] Referring to FIG. 36, the light emitting diode stack 1000 includes a support substrate 1510, a first LED stack 1230, a second LED stack 1330, a third LED stack 1430, a reflective electrode 1250, an ohmic electrode 1290, a second-p transparent electrode 1350, a third-p transparent electrode 1450, an insulation layer 1270, a first color filter 1370, a second color filter 1470, a first bonding layer 1530, a second bonding layer 1550, and a third bonding layer 1570. In addition, the first LED stack 1230 may include an ohmic contact portion 1230a for ohmic contact.

[0228] The support substrate 1510 supports the semiconductor stacks 1230, 1330, and 1430. The support substrate 1510 may include a circuit on a surface thereof or therein, but the inventive concepts are not limited thereto. The support substrate 1510 may include, for example, a Si substrate or a Ge substrate.

[0229] Each of the first LED stack 1230, the second LED stack 1330, and the third LED stack 1430 includes an n-type semiconductor layer, a p-type semiconductor layer, and an active layer interposed therebetween. The active layer may have a multi-quantum well structure.

[0230] For example, the first LED stack 1230 may be an inorganic light emitting diode configured to emit red light, the second LED stack 1330 may be an inorganic light emitting diode configured to emit green light, and the third LED stack 1430 may be an inorganic light emitting diode configured to emit blue light. The first LED stack 1230 may include a GaInP-based well layer, and each of the second LED stack 1330 and the third LED stack 1430 may include a GaInN-based well layer.

[0231] In addition, both surfaces of each of the first to third LED stacks 1230, 1330, 1430 are an n-type semiconductor layer and a p-type semiconductor layer, respectively. In the illustrated exemplary embodiment, each of the first to third LED stacks 1230, 1330, and 1430 has an n-type upper surface and a p-type lower surface. Since the third LED stack 1430 has an n-type upper surface, a roughened surface may be formed on the upper surface of the third LED stack 1430 through chemical etching. However, the inventive concepts are not limited thereto, and the semiconductor types of the upper and lower surfaces of each of the LED stacks can be alternatively arranged.

[0232] The first LED stack 1230 is disposed near the support substrate 1510, the second LED stack 1330 is disposed on the first LED stack 1230, and the third LED stack 1430 is disposed on the second LED stack 1330. Since the first LED stack 1230 emits light having a longer wavelength than the second and third LED stacks 1330 and 1430, light generated from the first LED stack 1230 can be emitted outside through the second and third LED stacks 1330 and 1430. In addition, since the second LED stack 1330 emits light having a longer wavelength than the third LED stack 1430, light generated from the second LED stack 1330 can be emitted outside through the third LED stack 1430.

[0233] The reflective electrode 1250 forms ohmic contact with the p-type semiconductor layer of the first LED stack 1230, and reflects light generated from the first LED stack 1230. For example, the reflective electrode 1250 may include an ohmic contact layer 1250a and a reflective layer 1250b.

[0234] The ohmic contact layer 1250a partially contacts the p-type semiconductor layer of the first LED stack 1230. In order to prevent absorption of light by the ohmic contact layer 1250a, a region in which the ohmic contact layer 1250a contacts the p-type semiconductor layer may not exceed 50% of the total area of the p-type semiconductor layer. The reflective layer 1250b covers the ohmic contact layer 1250a and the insulation layer 1270. As shown in FIG. 36, the reflective layer 1250b may cover substantially the entire ohmic contact layer 1250a, without being limited thereto. Alternatively, the reflective layer 1250b may cover a portion of the ohmic contact layer 1250a.

[0235] Since the reflective layer 1250b covers the insulation layer 1270, an omnidirectional reflector can be formed by the stacked structure of the first LED stack 1230 having a relatively high index of refraction, and the insulation layer 1270 and the reflective layer 1250b having a relatively low index of refraction. The reflective layer 1250b may cover 50% or more of the area of the first LED stack 1230, or most of the first LED stack 1230, thereby improving luminous efficacy.

[0236] The ohmic contact layer 1250a and the reflective layer 1250b may be metal layers, which may include Au. The reflective layer 1250b may be formed of a metal having relatively high reflectance with respect to light generated from the first LED stack 1230, for example, red light. On the other hand, the reflective layer 1250b may be formed of a metal having relatively low reflectance with respect to light generated from the second LED stack 1330 and the third LED stack 1430, for example, green light or blue light, to reduce interference of light having been generated from the second and third LED stacks 1330 and 1430 and traveling toward the support substrate 1510.

[0237] The insulation layer 1270 is interposed between the support substrate 1510 and the first LED stack 1230 and has openings that expose the first LED stack 1230. The ohmic contact layer 1250a is connected to the first LED stack 1230 in the openings of the insulation layer 1270.

[0238] The ohmic electrode 1290 is disposed on the upper surface of the first LED stack 1230. In order to reduce ohmic contact resistance of the ohmic electrode 1290, the ohmic contact portion 1230a may protrude from the upper surface of the first LED stack 1230. The ohmic electrode 1290 may be disposed on the ohmic contact portion 1230a.

[0239] The second-p transparent electrode 1350 forms ohmic contact with the p-type semiconductor layer of the second LED stack 1330. The second-p transparent electrode 1350 may include a metal layer or a conductive oxide layer that is transparent to red light and green light.

[0240] The third-p transparent electrode 1450 forms ohmic contact with the p-type semiconductor layer of the third LED stack 1430. The third-p transparent electrode 1450 may include a metal layer or a conductive oxide layer that is transparent to red light, green light, and blue light.

[0241] The reflective electrode 1250, the second-p transparent electrode 1350, and the third-p transparent electrode 1450 may assist in current spreading through ohmic contact with the p-type semiconductor layer of corresponding LED stack.

[0242] The first color filter 1370 may be interposed between the first LED stack 1230 and the second LED stack 1330. The second color filter 1470 may be interposed between the second LED stack 1330 and the third LED stack 1430. The first color filter 1370 transmits light generated from the first LED stack 1230 while reflecting light generated from the second LED stack 1330. The second color filter 1470 transmits light generated from the first and second LED stacks 1230 and 1330, while reflecting light generated from the third LED stack 1430. As such, light generated from the first LED stack 1230 can be emitted outside through the second LED stack 1330 and the third LED stack 1430, and light generated from the second LED stack 1330 can be emitted outside through the third LED stack 1430. Further, light generated from the second LED stack 1330 may be prevented from entering the first LED stack 1230, and light generated from the third LED stack 1430 may be prevented from entering the second LED stack 1330, thereby preventing light loss.

[0243] In some exemplary embodiments, the first color filter 1370 may reflect light generated from the third LED stack 1430.

[0244] The first and second color filters 1370 and 1470 may be, for example, a low pass filter that transmits light in a low frequency band, that is, in a long wavelength band, a band pass filter that transmits light in a predetermined wavelength band, or a band stop filter that prevents light in a predetermined wavelength band from passing therethrough. In particular, each of the first and second color filters 1370 and 1470 may include a distributed Bragg reflector (DBR). The distributed Bragg reflector may be formed by alternately stacking insulation layers having different indices of refraction one above another, for example, TiO2 and SiO2. In addition, the stop band of the distributed Bragg reflector can be controlled by adjusting the thicknesses of TiO2 and SiO2 layers. The low pass filter and the band pass filter may also be formed by alternately stacking insulation layers having different indices of refraction one above another.

[0245] The first bonding layer 1530 couples the first LED stack 1230 to the support substrate 1510. As shown in FIG. 36, the reflective electrode 1250 may adjoin the first bonding layer 1530. The first bonding layer 1530 may be a light transmissive or opaque layer.

[0246] The second bonding layer 1550 couples the second LED stack 1330 to the first LED stack 1230. As shown in FIG. 36, the second bonding layer 1550 may adjoin the first LED stack 1230 and the first color filter 1370. The ohmic electrode 1290 may be covered by the second bonding layer 1550. The second bonding layer 1550 transmits light generated from the first LED stack 1230. The second bonding layer 1550 may be formed of, for example, light transmissive spin-on-glass.

[0247] The third bonding layer 1570 couples the third LED stack 1430 to the second LED stack 1330. As shown in FIG. 36, the third bonding layer 1570 may adjoin the second LED stack 1330 and the second color filter 1470. However, the inventive concepts are not limited thereto. For example, a transparent conductive layer may be disposed on the second LED stack 1330. The third bonding layer 1570 transmits light generated from the first LED stack 1230 and the second LED stack 1330. The third bonding layer 1570 may be formed of, for example, light transmissive spin-on-glass.

[0248] FIGS. 37A, 37B, 37C, 37D, and 37E are schematic cross-sectional views illustrating a method of manufacturing a light emitting diode stack for a display not forming part of the invention.

[0249] Referring to FIG. 37A, a first LED stack 1230 is grown on a first substrate 1210. The first substrate 1210 may be, for example, a GaAs substrate. The first LED stack 1230 may be formed of AlGaInP-based semiconductor layers and includes an n-type semiconductor layer, an active layer, and a p-type semiconductor layer.

[0250] An insulation layer 1270 is formed on the first LED stack 1230, and is patterned to form opening(s). For example, a SiO2 layer is formed on the first LED stack 1230 and a photoresist is deposited onto the SiO2 layer, followed by photolithography and development to form a photoresist pattern. Then, the SiO2 layer is patterned through the photoresist pattern used as an etching mask, thereby forming the insulation layer 1270.

[0251] Then, an ohmic contact layer 1250a is formed in the opening(s) of the insulation layer 1270. The ohmic contact layer 1250a may be formed by a lift-off process or the like. After the ohmic contact layer 1250a is formed, a reflective layer 1250b is formed to cover the ohmic contact layer 1250a and the insulation layer 1270. The reflective layer 1250b may be formed by a lift-off process or the like. The reflective layer 1250b may cover a portion of the ohmic contact layer 1250a or the entirety thereof, as shown in FIG. 37A. The ohmic contact layer 1250a and the reflective layer 1250b form a reflective electrode 1250.

[0252] The reflective electrode 1250 forms ohmic contact with the p-type semiconductor layer of the first LED stack 1230, and thus, will hereinafter be referred to as a first-p reflective electrode 1250.

[0253] Referring to FIG. 37B, a second LED stack 1330 is grown on a second substrate 1310, and a second-p transparent electrode 1350 and a first color filter 1370 are formed on the second LED stack 1330. The second LED stack 1330 may be formed of GaN-based semiconductor layers and include a GaInN well layer. The second substrate 1310 is a substrate on which GaN-based semiconductor layers may be grown thereon, and is different from the first substrate 1210. The composition ratio of GaInN for the second LED stack 1330 may be determined such that the second LED stack 1330 emits green light. The second-p transparent electrode 1350 forms ohmic contact with the p-type semiconductor layer of the second LED stack 1330.

[0254] Referring to FIG. 37C, a third LED stack 1430 is grown on a third substrate 1410, and a third-p transparent electrode 1450 and a second color filter 1470 are formed on the third LED stack 1430. The third LED stack 1430 may be formed of GaN-based semiconductor layers and include a GaInN well layer. The third substrate 1410 is a substrate on which GaN-based semiconductor layers may be grown thereon, and is different from the first substrate 1210. The composition ratio of GaInN for the third LED stack 1430 may be determined such that the third LED stack 1430 emits blue light. The third-p transparent electrode 1450 forms ohmic contact with the p-type semiconductor layer of the third LED stack 1430.

[0255] The first color filter 1370 and the second color filter 1470 are substantially the same as those described with reference to FIG. 36, and thus, repeated descriptions thereof will be omitted to avoid redundancy.

[0256] As such, the first LED stack 1230, the second LED stack 1330 and the third LED stack 1430 may be grown on different substrates, and the formation sequence thereof is not limited to a particular sequence.

[0257] Referring to FIG. 37D, the first LED stack 1230 is coupled to the support substrate 1510 via a first bonding layer 1530. The first bonding layer 1530 may be previously formed on the support substrate 1510, and the reflective electrode 1250 may be bonded to the first bonding layer 1530 to face the support substrate 1510. The first substrate 1210 is removed from the first LED stack 1230 by chemical etching or the like. Accordingly, the upper surface of the n-type semiconductor layer of the first LED stack 1230 is exposed.

[0258] Then, an ohmic electrode 1290 is formed in the exposed region of the first LED stack 1230. In order to reduce ohmic contact resistance of the ohmic electrode 1290, the ohmic electrode 1290 may be subjected to heat treatment. The ohmic electrode 1290 may be formed in each pixel region so as to correspond to the pixel regions.

[0259] Referring to FIG. 37E, the second LED stack 1330 is coupled to the first LED stack 1230, on which the ohmic electrode 1290 is formed, via a second bonding layer 1550. The first color filter 1370 is bonded to the second bonding layer 1550 to face the first LED stack 1230. The second bonding layer 1550 may be previously formed on the first LED stack 1230 so that the first color filter 1370 may face and be bonded to the second bonding layer 1550. The second substrate 31 may be separated from the second LED stack 1330 by a laser lift-off or chemical lift-off process.

[0260] Then, referring to FIG. 36 and FIG. 37C, the third LED stack 1430 is coupled to the second LED stack 1330 via a third bonding layer 1570. The second color filter 1470 is bonded to the third bonding layer 1570 to face the second LED stack 1330. The third bonding layer 1570 may be previously disposed on the second LED stack 1330 so that the second color filter 1470 may face and be bonded to the third bonding layer 1570. The third substrate 1410 may be separated from the third LED stack 1430 by a laser lift-off or chemical lift-off process. As such a light emitting diode stack for a display may be formed as shown in FIG. 36, which has the n-type semiconductor layer of the third LED stack 1430 exposed to the outside.

[0261] A display apparatus according to an exemplary embodiment may be provided by patterning the stack of the first to third LED stacks 1230, 1330, and 1430 on the support substrate 1510 in pixel units, followed by connecting the first to third LED stacks to one another through interconnections. Hereinafter, a display apparatus according to exemplary embodiments will be described.

[0262] FIG. 38 is a schematic circuit diagram of a display apparatus not forming part of the invention, and FIG. 39 is a schematic plan view of the display apparatus not forming part of the invention.

[0263] Referring to FIG. 38 and FIG. 39, a display apparatus according to an exemplary embodiment may be operated in a passive matrix manner.

[0264] For example, since the light emitting diode stack for a display of FIG. 36 includes the first to third LED stacks 1230, 1330, and 1430 stacked in the vertical direction, one pixel may include three light emitting diodes R, G, and B. A first light emitting diode R may correspond to the first LED stack 1230, a second light emitting diode G may correspond to the second LED stack 1330, and a third light emitting diode B may correspond to the third LED stack 1430.

[0265] In FIGS. 36 and 39, one pixel includes the first to third light emitting diodes R, G, and B, each of which corresponds to a subpixel. Anodes of the first to third light emitting diodes R, G, and B are connected to a common line, for example, a data line, and cathodes thereof are connected to different lines, for example, scan lines. More particularly, in a first pixel, the anodes of the first to third light emitting diodes R, G, and B are commonly connected to a data line Vdata1 and the cathodes thereof are connected to scan lines Vscan1-1, Vscan1-2, and Vscan1-3, respectively. As such, the light emitting diodes R, G, and B in each pixel can be driven independently.

[0266] In addition, each of the light emitting diodes R, G, and B may be driven by a pulse width modulation or by changing the magnitude of electric current, thereby controlling the brightness of each subpixel.

[0267] Referring to FIG. 39, a plurality of pixels is formed by patterning the light emitting diode stack 1000 of FIG. 36, and each of the pixels is connected to the reflective electrodes 1250 and interconnection lines 1710, 1730, and 1750. As shown in FIG. 38, the reflective electrode 1250 may be used as the data line Vdata and the interconnection lines 1710, 1730, and 1750 may be formed as the scan lines.

[0268] The pixels may be arranged in a matrix form, in which the anodes of the light emitting diodes R, G, and B of each pixel are commonly connected to the reflective electrode 1250, and the cathodes thereof are connected to the interconnection lines 1710, 1730, and 1750 separated from one another. Here, the interconnection lines 1710, 1730, and 1750 may be used as the scan lines Vscan.

[0269] FIG. 40 is an enlarged plan view of one pixel of the display apparatus of FIG. 39, FIG. 41 is a schematic cross-sectional view taken along line A-A of FIG. 40, and FIG. 42 is a schematic cross-sectional view taken along line B-B of FIG. 40.

[0270] Referring to FIG. 39, FIG. 40, FIG. 41, and FIG. 42, in each pixel, a portion of the reflective electrode 1250, the ohmic electrode 1290 formed on the upper surface of the first LED stack 1230 (see FIG. 43H), a portion of the second-p transparent electrode 1350 (see also FIG. 43H), a portion of the upper surface of the second LED stack 1330 (see FIG. 43J), a portion of the third-p transparent electrode 1450 (see FIG. 43H), and the upper surface of the third LED stack 1430 are exposed to the outside.

[0271] The third LED stack 1430 may have a roughened surface 1430a on the upper surface thereof. The roughened surface 1430a may be formed over the entirety of the upper surface of the third LED stack 1430 or may be formed in some regions thereof, as shown in FIG. 41.

[0272] A lower insulation layer 1610 may cover a side surface of each pixel. The lower insulation layer 1610 may be formed of a light transmissive material, such as SiO2. In this case, the lower insulation layer 1610 may cover the entire upper surface of the third LED stack 1430. Alternatively, the lower insulation layer 1610 may include a distributed Bragg reflector to reflect light traveling towards the side surfaces of the first to third LED stacks 1230, 1330, and 1430. In this case, the lower insulation layer 1610 partially exposes the upper surface of the third LED stack 1430.

[0273] The lower insulation layer 1610 may include an opening 1610a which exposes the upper surface of the third LED stack 1430, an opening 1610b which exposes the upper surface of the second LED stack 1330, an opening 1610c (see FIG. 43H) which exposes the ohmic electrode 1290 of the first LED stack 1230, an opening 1610d which exposes the third-p transparent electrode 1450, an opening 1610e which exposes the second-p transparent electrode 1350, and openings 1610f which expose the first-p reflective electrode 1250.

[0274] The interconnection lines 1710 and 1750 may be formed near the first to third LED stacks 1230, 1330, and 1430 on the support substrate 1510, and may be disposed on the lower insulation layer 1610 to be insulated from the first-p reflective electrode 1250. A connecting portion 1770a connects the third-p transparent electrode 1450 to the reflective electrode 1250, and a connecting portion 1770b connects the second-p transparent electrode 1350 to the reflective electrode 1250, such that the anodes of the first LED stack 1230, the second LED stack 1330, and the third LED stack 1430 are commonly connected to the reflective electrode 1250.

[0275] A connecting portion 1710a connects the upper surface of the third LED stack 1430 to the interconnection line 1710, and a connecting portion 1750a connects the ohmic electrode 1290 on the first LED stack 1230 to the interconnection line 1750.

[0276] An upper insulation layer 1810 may be disposed on the interconnection lines 1710 and 1730 and the lower insulation layer 1610 to cover the upper surface of the third LED stack 1430. The upper insulation layer 1810 may have an opening 1810a which partially exposes the upper surface of the second LED stack 1330.

[0277] The interconnection line 1730 may be disposed on the upper insulation layer 1810, and the connecting portion 1730a may connect the upper surface of the second LED stack 1330 to the interconnection line 1730. The connecting portion 1730a may pass through an upper portion of the interconnection line 1750, and is insulated from the interconnection line 1750 by the upper insulation layer 1810.

[0278] Although the electrodes of each pixel according to the illustrated exemplary embodiment are described as being connected to the data line and the scan lines, various implementations are possible. In addition, although the interconnection lines 1710 and 1750 are described as being formed on the lower insulation layer 1610, and the interconnection line 1730 is formed on the upper insulation layer 1810, the inventive concepts are not limited thereto. For example, each of the interconnection lines 1710, 1730, and 1750 may be formed on the lower insulation layer 1610, and covered by the upper insulation layer 1810, which may have openings to expose the interconnection line 1730. In this structure, the connecting portion 1730a may connect the upper surface of the second LED stack 1330 to the interconnection line 1730 through the openings of the upper insulation layer 1810.

[0279] Alternatively, the interconnection lines 1710, 1730, and 1750 may be formed inside the support substrate 1510, and the connecting portions 1710a, 1730a, and 1750a on the lower insulation layer 1610 may connect the ohmic electrode 1290, the upper surface of the second LED stack 1330, and the upper surface of the third LED stack 1430 to the interconnection lines 1710, 1730, and 1750.

[0280] FIG. 43A to FIG. 43K are schematic plan views illustrating a method of manufacturing a display apparatus including the pixel of FIG. 40 not forming part of the invention.

[0281] First, the light emitting diode stack 1000 described in FIG. 36 is prepared.

[0282] Then, referring to FIG. 43A, a roughened surface 1430a may be formed on the upper surface of the third LED stack 1430. The roughened surface 1430a may be formed on the upper surface of the third LED stack 1430 so as to correspond to each pixel region. The roughened surface 1430a may be formed by chemical etching, for example, photo-enhanced chemical etching (PEC) or the like.

[0283] The roughened surface 1430a may be partially formed in each pixel region by taking into account a region of the third LED stack 1430 to be etched in the subsequent process, without being limited thereto. Alternatively, the roughened surface 1430a may be formed over the entire upper surface of the third LED stack 1430.

[0284] Referring to FIG. 43B, a surrounding region of the third LED stack 1430 in each pixel is removed by etching to expose the third-p transparent electrode 1450. As shown in FIG. 43B, the third LED stack 1430 may be remained to have a rectangular shape or a square shape. The third LED stack 1430 may have a plurality of depressions along edges thereof.

[0285] Referring to FIG. 43C, the upper surface of the second LED stack 1330 is exposed by removing the exposed third-p transparent electrode 1450 in areas other than one depression of the third LED stack 1430. Accordingly, the upper surface of the second LED stack 1330 is exposed around the third LED stack 1430 and in other depressions excluding the depression in which the third-p transparent electrode 1450 partially remains.

[0286] Referring to FIG. 43D, the second-p transparent electrode 1350 is exposed by removing the exposed second LED stack 1330 in areas other than another depression of the third LED stack 1430.

[0287] Referring to FIG. 43E, the ohmic electrode 1290 is exposed together with the upper surface of the first LED stack 1230 by removing the exposed second-p transparent electrode 1350 in areas other than still another depression of the third LED stack 1430. In this case, the ohmic electrode 1290 may be exposed in one depression. Accordingly, the upper surface of the first LED stack 1230 is exposed around the third LED stack 1430, and an upper surface of the ohmic electrode 1290 is exposed in at least one of the depressions formed in the third LED stack 1430.

[0288] Referring to FIG. 43F, the reflective electrode 1250 is exposed by removing an exposed portion of the first LED stack 1230 other than the ohmic electrode 1290 exposed in one depression. The reflective electrode 1250 is exposed around the third LED stack 1430.

[0289] Referring to FIG. 43G, linear interconnection lines are formed by patterning the reflective electrode 1250. Here, the support substrate 1510 may be exposed. The reflective electrode 1250 may connect pixels arranged in one row to each other among pixels arranged in a matrix (see FIG. 39).

[0290] Referring to FIG. 43H, a lower insulation layer 1610 (see FIG. 41 and FIG. 42) is formed to cover the pixels. The lower insulation layer 1610 covers the reflective electrode 1250 and side surfaces of the first to third LED stacks 1230, 1330, and 1430. In addition, the lower insulation layer 1610 may at least partially cover the upper surface of the third LED stack 1430. If the lower insulation layer 1610 is a transparent layer such as a SiO2 layer, the lower insulation layer 1610 may cover the entire upper surface of the third LED stack 1430. Alternatively, when the lower insulation layer 1610 includes a distributed Bragg reflector, the lower insulation layer 1610 may at least partially expose the upper surface of the third LED stack 1430 such that light may be emitted to the outside.

[0291] The lower insulation layer 1610 may include an opening 1610a which exposes the third LED stack 1430, an opening 1610b which exposes the second LED stack 1330, an opening 1610c which exposes the ohmic electrode 1290, an opening 1610d which exposes the third-p transparent electrode 1450, an opening 1610e which exposes the second-p transparent electrode 1350, and an opening 1610f which exposes the reflective electrode 1250. One or more openings 1610f may be formed to expose the reflective electrode 1250.

[0292] Referring to FIG. 43I, interconnection lines 1710, 1750 and connecting portions 1710a, 1750a, 1770a, and 1770b are formed. These may be formed by a lift-off process or the like. The interconnection lines 1710 and 1750 are insulated from the reflective electrode 1250 by the lower insulation layer 1610. The connecting portion 1710a electrically connects the third LED stack 1430 to the interconnection line 1710, and the connecting portion 1750a electrically connects the ohmic electrode 1290 to the interconnection line 1750 such that the first LED stack 1230 is electrically connected to the interconnection line 1750. The connecting portion 1770a electrically connects the third-p transparent electrode 1450 to the first-p reflective electrode 1250, and the connecting portion 1770b electrically connects the second-p transparent electrode 1350 to the first-p reflective electrode 1250.

[0293] Referring to FIG. 43J, an upper insulation layer 1810 (see FIG. 41 and FIG. 42) covers the interconnection lines 1710 and 1750 and the connecting portions 1710a, 1750a, 1770a, and 1770b. The upper insulation layer 1810 may also cover the entire upper surface of the third LED stack 1430. The upper insulation layer 1810 has an opening 1810a which exposes the upper surface of the second LED stack 1330. The upper insulation layer 1810 may be formed of, for example, silicon oxide or silicon nitride, and may include a distributed Bragg reflector. When the upper insulation layer 1810 includes the distributed Bragg reflector, the upper insulation layer 1810 may expose at least part of the upper surface of the third LED stack 1430 such that light may be emitted to the outside.

[0294] Referring to FIG. 43K, an interconnection line 1730 and a connecting portion 1730a are formed. An interconnection line 1750 and a connecting portion 1750a may be formed by a lift-off process or the like. The interconnection line 1730 is disposed on the upper insulation layer 1810, and is insulated from the reflective electrode 1250 and the interconnection lines 1710 and 1750. The connecting portion 1730a electrically connects the second LED stack 1330 to the interconnection line 1730. The connecting portion 1730a may pass through an upper portion of the interconnection line 1750 and is insulated from the interconnection line 1750 by the upper insulation layer 1810.

[0295] As such, a pixel region as shown in FIG. 40 may be formed. In addition, as shown in FIG. 39, a plurality of pixels may be formed on the support substrate 1510 and may be connected to one another by the first-p the reflective electrode 1250 and the interconnection lines 1710, 1730, and 1750 to be operated in a passive matrix manner.

[0296] Although the display apparatus above has been described as being configured to be operated in the passive matrix manner, the inventive concepts are not limited thereto. More particularly, a display apparatus according to some exemplary embodiments may be manufactured in various ways so as to be operated in the passive matrix manner using the light emitting diode stack shown in FIG. 36.

[0297] For example, although the interconnection line 1730 is illustrated as being formed on the upper insulation layer 1810, the interconnection line 1730 may be formed together with the interconnection lines 1710 and 1750 on the lower insulation layer 1610, and the connecting portion 1730a may be formed on the upper insulation layer 1810 to connect the second LED stack 1330 to the interconnection line 1730. Alternatively, the interconnection lines 1710, 1730, and 1750 may be disposed inside the support substrate 1510.

[0298] FIG. 44 is a schematic circuit diagram of a display apparatus not forming part of the invention. The display apparatus according to the illustrated exemplary embodiment may be driven in an active matrix manner.

[0299] Referring to FIG. 44, the drive circuit according to an exemplary embodiment includes at least two transistors Tr1, Tr2 and a capacitor. When a power source is connected to selection lines Vrow1 to Vrow3, and voltage is applied to data lines Vdata1 to Vdata3, the voltage is applied to the corresponding light emitting diode. In addition, the corresponding capacitor is charged according to the values of Vdata1 to Vdata3. Since a turned-on state of a transistor Tr2 can be maintained by the charged voltage of the capacitor, the voltage of the capacitor can be maintained and applied to the light emitting diodes LED1 to LED3 even when power supplied to Vrow1 is cut off. In addition, electric current flowing in the light emitting diodes LED1 to LED3 can be changed depending upon the values of Vdata1 to Vdata3. Electric current can be continuously supplied through Vdd, such that light may be emitted continuously.

[0300] The transistors Tr1, Tr2 and the capacitor may be formed inside the support substrate 1510. For example, thin film transistors formed on a silicon substrate may be used for active matrix driving.

[0301] The light emitting diodes LED1 to LED3 may correspond to the first to third LED stacks 1230, 1330, and 1430 stacked in one pixel, respectively. The anodes of the first to third LED stacks are connected to the transistor Tr2 and the cathodes thereof are connected to the ground.

[0302] Although FIG. 44 shows the circuit for active matrix driving according to an exemplary embodiment, other various types of circuits may be used. In addition, although the anodes of the light emitting diodes LED1 to LED3 are described as being connected to different transistors Tr2, and the cathodes thereof are described as being connected to the ground, the inventive concepts are not limited thereto, and the anodes of the light emitting diodes may be connected to current supplies Vdd and the cathodes thereof may be connected to different transistors.

[0303] FIG. 45 is a schematic plan view of a pixel of a display apparatus not forming part of the invention. The pixel described herein may be one of a plurality of pixels arranged on the support substrate 1511.

[0304] Referring to FIG. 45, the pixels according to the illustrated exemplary embodiment are substantially similar to the pixels described with reference to FIG. 39 to FIG. 42, except that the support substrate 1511 is a thin film transistor panel including transistors and capacitors, and the reflective electrode is disposed in a lower region of the first LED stack.

[0305] The cathode of the third LED stack is connected to the support substrate 1511 through the connecting portion 1711a. For example, as shown in FIG. 45, the cathode of the third LED stack may be connected to the ground through electrical connection to the support substrate 1511. The cathodes of the second LED stack and the first LED stack may also be connected to the ground through electrical connection to the support substrate 1511 via the connecting portions 1731a and 1751a.

[0306] The reflective electrode is connected to the transistors Tr2 (see FIG. 44) inside the support substrate 1511. The third-p transparent electrode and the second-p transparent electrode are also connected to the transistors Tr2 (see FIG. 44) inside the support substrate 1511 through the connecting portions 1771a and 1731b.

[0307] In this manner, the first to third LED stacks are connected to one another, thereby constituting a circuit for active matrix driving, as shown in FIG. 44.

[0308] Although FIG. 45 shows electrical connection of a pixel for active matrix driving according to an exemplary embodiment, the inventive concepts are not limited thereto, and the circuit for the display apparatus can be modified into various circuits for active matrix driving in various ways.

[0309] In addition, while the reflective electrode 1250, the second-p transparent electrode 1350, and the third-p transparent electrode 1450 of FIG. 36 are described as forming ohmic contact with the corresponding p-type semiconductor layer of each of the first LED stack 1230, the second LED stack 1330, and the third LED stack 1430, and the ohmic electrode 1290 forms ohmic contact with the n-type semiconductor layer of the first LED stack 1230, the n-type semiconductor layer of each of the second LED stack 1330 and the third LED stack 1430 is not provided with a separate ohmic contact layer. When the pixels have a small size of 200 µm or less, there is less difficulty in current spreading even without formation of a separate ohmic contact layer in the n-type semiconductor layer. However, according to some exemplary embodiments, a transparent electrode layer may be disposed on the n-type semiconductor layer of each of the LED stacks in order to secure current spreading.

[0310] In addition, although the first to third LED stacks 1230, 1330, and 1430 are coupled to each other via bonding layers 1530, 1550, and 1570, the inventive concepts are not limited thereto, and the first to third LED stacks 1230, 1330, and 1430 may be connected to one another in various sequences and using various structures.

[0311] According to exemplary embodiments, since it is possible to form a plurality of pixels at the wafer level using the light emitting diode stack 1000 for a display, individual mounting of light emitting diodes may be obviated. In addition, the light emitting diode stack according to the exemplary embodiments has the structure in which the first to third LED stacks 1230, 1330, and 1430 are stacked in the vertical direction, thereby securing an area for subpixels in a limited pixel area. Furthermore, the light emitting diode stack according to the exemplary embodiments allows light generated from the first LED stack 1230, the second LED stack 1330, and the third LED stack 1430 to be emitted outside therethrough, thereby reducing light loss.

[0312] FIG. 46 is a schematic cross-sectional view of a light emitting diode stack for a display not forming part of the invention.

[0313] Referring to FIG. 46, the light emitting diode stack 2000 includes a support substrate 2510, a first LED stack 2230, a second LED stack 2330, a third LED stack 2430, a reflective electrode 2250, an ohmic electrode 2290, a second-p transparent electrode 2350, a third-p transparent electrode 2450, an insulation layer 2270, a first bonding layer 2530, a second bonding layer 2550, and a third bonding layer 2570. In addition, the first LED stack 2230 may include an ohmic contact portion 2230a for ohmic contact.

[0314] In general, light may be generated from the first LED stack by the light emitted from the second LED stack, and light may be generated from the second LED stack by the light emitted from the third LED stack. As such, a color filter may be interposed between the second LED stack and the first LED stack, and between the third LED stack and the second LED stack.

[0315] However, while the color filters may prevent interference of light, forming color filters increases manufacturing complexity. A display apparatus according to exemplary embodiments may suppress generation of secondary light between the LED stacks without arrangement of the color filters therebetween.

[0316] Accordingly, in some exemplary embodiments, interference of light between the LED stacks can be reduced by controlling the bandgap of each of the LED stacks, which will be described in more detail below.

[0317] The support substrate 2510 supports the semiconductor stacks 2230, 2330, and 2430. The support substrate 2510 may include a circuit on a surface thereof or therein, but the inventive concepts are not limited thereto. The support substrate 2510 may include, for example, a Si substrate, a Ge substrate, a sapphire substrate, a patterned sapphire substrate, a glass substrate, or a patterned glass substrate.

[0318] Each of the first LED stack 2230, the second LED stack 2330, and the third LED stack 2430 includes an n-type semiconductor layer, a p-type semiconductor layer, and an active layer interposed therebetween. The active layer may have a multi-quantum well structure.

[0319] Light L1 generated from the first LED stack 2230 has a longer wavelength than light L2 generated from the second LED stack 2330, which has a longer wavelength than light L3 generated from the third LED stack 2430.

[0320] The first LED stack 2230 may be an inorganic light emitting diode configured to emit red light, the second LED stack 2330 may be an inorganic light emitting diode configured to emit green light, and the third LED stack 2430 may be an inorganic light emitting diode configured to emit blue light. The first LED stack 2230 may include a GaInP-based well layer, and each of the second LED stack 2330 and the third LED stack 2430 may include a GaInN-based well layer.

[0321] Although the light emitting diode stack 2000 of FIG. 46 is illustrated as including three LED stacks 2230, 2330, and 2430, the inventive concepts are not limited to a particular number of LED stacks one over the other. For example, an LED stack for emitting yellow light may be further added between the first LED stack 2230 and the second LED stack 2330.

[0322] Both surfaces of each of the first to third LED stacks 2230, 2330, and 2430 are an n-type semiconductor layer and a p-type semiconductor layer, respectively. In FIG. 46, each of the first to third LED stacks 2230, 2330, and 2430 is described as having an n-type upper surface and a p-type lower surface. Since the third LED stack 2430 has an n-type upper surface, a roughened surface may be formed on the upper surface of the third LED stack 2430 through chemical etching or the like. However, the inventive concepts are not limited thereto, and the semiconductor types of the upper and lower surfaces of each of the LED stacks can be formed alternatively.

[0323] The first LED stack 2230 is disposed near the support substrate 2510, the second LED stack 2330 is disposed on the first LED stack 2230, and the third LED stack 2430 is disposed on the second LED stack. Since the first LED stack 2230 emits light having a longer wavelength than the second and third LED stacks 2330 and 2430, light L1 generated from the first LED stack 2230 can be emitted to the outside through the second and third LED stacks 2330 and 2430. In addition, since the second LED stack 2330 emits light having a longer wavelength than the third LED stack 2430, light L2 generated from the second LED stack 2330 can be emitted to the outside through the third LED stack 2430. Light L3 generated in the third LED stack 2430 is directly emitted outside from the third LED stack 2430.

[0324] In an exemplary embodiment, the n-type semiconductor layer of the first LED stack 2230 may have a bandgap wider than the bandgap of the active layer of the first LED stack 2230, and narrower than the bandgap of the active layer of the second LED stack 2330. Accordingly, a portion of light generated from the second LED stack 2330 may be absorbed by the n-type semiconductor layer of the first LED stack 2230 before reaching the active layer of the first LED stack 2230. As such, the intensity of light generated in the active layer of the first LED stack 2230 may be reduced by the light generated from the second LED stack 2330.

[0325] In addition, the n-type semiconductor layer of the second LED stack 2330 has a bandgap wider than the bandgap of the active layer of each of the first LED stack 2230 and the second LED stack 2330, and narrower than the bandgap of the active layer of the third LED stack 2430. Accordingly, a portion of light generated from the third LED stack 2430 may be absorbed by the n-type semiconductor layer of the second LED stack 2330 before reaching the active layer of the second LED stack 2330. As such, the intensity of light generated in the second LED stack 2330 or the first LED stack 2230 may be reduced by the light generated from the third LED stack 2430.

[0326] The p-type semiconductor layer and the n-type semiconductor layer of the third LED stack 2430 has wider bandgaps than the active layers of the first LED stack 2230 and the second LED stack 2330, thereby transmitting light generated from the first and second LED stacks 2230 and 2330 therethrough.

[0327] According to an exemplary embodiment, it is possible to reduce interference of light between the LED stacks 2230, 2330, and 2430 by adjusting the bandgaps of the n-type semiconductor layers or the p-type semiconductor layers of the first and second LED stacks 2230 and 2330, which may obviate the need for other components, such as color filters. For example, the intensity of light generated from the second LED stack 2330 and emitted to the outside may be about 10 times or more than the intensity of the light generated from the first LED stack 2230 by the light generated from the second LED stack 2330. Likewise, the intensity of light generated from the third LED stack 2430 and emitted to the outside may be about 10 times or more the intensity of the light generated from the second LED stack 2330 caused by the light generated from the third LED stack 2430. In this case, the intensity of the light generated from the third LED stack 2430 and emitted to the outside may be about 10 times or more the intensity of the light generated from the first LED stack 2230 caused by the light generated from the third LED stack 2430. Accordingly, it is possible to realize a display apparatus free from color contamination caused by interference of light.

[0328] The reflective electrode 2250 forms ohmic contact with the p-type semiconductor layer of the first LED stack 2230 and reflects light generated from the first LED stack 2230. For example, the reflective electrode 2250 may include an ohmic contact layer 2250a and a reflective layer 2250b.

[0329] The ohmic contact layer 2250a partially contacts the p-type semiconductor layer of the first LED stack 2230. In order to prevent absorption of light by the ohmic contact layer 2250a, a region in which the ohmic contact layer 2250a contacts the p-type semiconductor layer may not exceed about 50% of the total area of the p-type semiconductor layer. The reflective layer 2250b covers the ohmic contact layer 2250a and the insulation layer 2270. As shown in FIG. 46, the reflective layer 2250b may cover substantially the entire ohmic contact layer 2250a, without being limited thereto. Alternatively, the reflective layer 2250b may cover a portion of the ohmic contact layer 2250a.

[0330] Since the reflective layer 2250b covers the insulation layer 2270, an omnidirectional reflector can be formed by the stacked structure of the first LED stack 2230 having a relatively high index of refraction and the insulation layer 2270 having a relatively low index of refraction, and the reflective layer 2250b. The reflective layer 2250b may cover about 50% or more of the area of the first LED stack 2230 or most of the first LED stack 2230, thereby improving luminous efficacy.

[0331] The ohmic contact layer 2250a and the reflective layer 2250b may be formed of metal layers, which may include Au. The reflective layer 2250b may include metal having relatively high reflectance with respect to light generated from the first LED stack 2230, for example, red light. On the other hand, the reflective layer 2250b may include metal having relatively low reflectance with respect to light generated from the second LED stack 2330 and the third LED stack 2430, for example, green light or blue light, to reduce interference of light having been generated from the second and third LED stacks 2330, 2430 and traveling toward the support substrate 2510.

[0332] The insulation layer 2270 is interposed between the support substrate 2510 and the first LED stack 2230, and has openings that expose the first LED stack 2230. The ohmic contact layer 2250a is connected to the first LED stack 2230 in the openings of the insulation layer 2270.

[0333] The ohmic electrode 2290 is disposed on the upper surface of the first LED stack 2230. In order to reduce ohmic contact resistance of the ohmic electrode 2290, the ohmic contact portion 2230a may protrude from the upper surface of the first LED stack 2230. The ohmic electrode 2290 may be disposed on the ohmic contact portion 2230a.

[0334] The second-p transparent electrode 2350 forms ohmic contact with the p-type semiconductor layer of the second LED stack 2330. The second-p transparent electrode 2350 may be formed of a metal layer or a conductive oxide layer that is transparent to red light and green light.

[0335] The third-p transparent electrode 2450 forms ohmic contact with the p-type semiconductor layer of the third LED stack 2430. The third-p transparent electrode 2450 may be formed of a metal layer or a conductive oxide layer that is transparent to red light, green light, and blue light.

[0336] The reflective electrode 2250, the second-p transparent electrode 2350, and the third-p transparent electrode 2450 may assist in current spreading through ohmic contact with the p-type semiconductor layer of corresponding LED stacks.

[0337] The first bonding layer 2530 couples the first LED stack 2230 to the support substrate 2510. As shown in FIG. 46, the reflective electrode 2250 may adjoin the first bonding layer 2530. The first bonding layer 2530 may be a light transmissive or opaque layer.

[0338] The second bonding layer 2550 couples the second LED stack 2330 to the first LED stack 2230. As shown in FIG. 46, the second bonding layer 2550 may adjoin the first LED stack 2230 and the second-p transparent electrode 2350. The ohmic electrode 2290 may be covered by the second bonding layer 2550. The second bonding layer 2550 transmits light generated from the first LED stack 2230. The second bonding layer 2550 may be formed of a light transmissive bonding material, for example, a light transmissive organic bonding agent or light transmissive spin-on-glass. Examples of the light transmissive organic bonding agent may include SU8, poly(methyl methacrylate) (PMMA), polyimide, Parylene, benzocyclobutene (BCB), and the like. In addition, the second LED stack 2330 may be bonded to the first LED stack 2230 by plasma bonding or the like.

[0339] The third bonding layer 2570 couples the third LED stack 2430 to the second LED stack 2330. As shown in FIG. 46, the third bonding layer 2570 may adjoin the second LED stack 2330 and the third-p transparent electrode 2450. However, the inventive concepts are not limited thereto. For example, a transparent conductive layer may be disposed on the second LED stack 2330. The third bonding layer 2570 transmits light generated from the first LED stack 2230 and the second LED stack 2330, and may be formed of, for example, light transmissive spin-on-glass.

[0340] Each of the second bonding layer 2550 and the third bonding layer 2570 may transmit light generated from the third LED stack 2430 and light generated from the second LED stack 2330.

[0341] FIG. 47A to FIG. 47E are schematic cross-sectional views illustrating a method of manufacturing a light emitting diode stack for a display not forming part of the invention.

[0342] Referring to FIG. 47A, a first LED stack 2230 is grown on a first substrate 2210. The first substrate 2210 may be, for example, a GaAs substrate. The first LED stack 2230 is formed of AlGaInP-based semiconductor layers, and includes an n-type semiconductor layer, an active layer, and a p-type semiconductor layer. In some exemplary embodiments, the n-type semiconductor layer may have an energy bandgap capable absorbing light generated from the second LED stack 2330, and the p-type semiconductor layer may have an energy bandgap capable absorbing light generated from the second LED stack 2330.

[0343] An insulation layer 2270 is formed on the first LED stack 2230 and patterned to form opening(s) therein. For example, a Si02 layer is formed on the first LED stack 2230, and a photoresist is deposited onto the SiO2 layer, followed by photolithography and development to form a photoresist pattern. Then, the SiO2 layer is patterned through the photoresist pattern used as an etching mask, thereby forming the insulation layer 2270 having the opening(s).

[0344] Then, an ohmic contact layer 2250a is formed in the opening(s) of the insulation layer 2270. The ohmic contact layer 2250a may be formed by a lift-off process or the like. After the ohmic contact layer 2250a is formed, a reflective layer 2250b is formed to cover the ohmic contact layer 2250a and the insulation layer 2270. The reflective layer 2250b may be formed by a lift-off process or the like. The reflective layer 2250b may cover a portion of the ohmic contact layer 2250a or the entirety thereof. The ohmic contact layer 2250a and the reflective layer 2250b form a reflective electrode 2250.

[0345] The reflective electrode 2250 forms ohmic contact with the p-type semiconductor layer of the first LED stack 2230, and thus, will hereinafter be referred to as a first-p reflective electrode 2250.

[0346] Referring to FIG. 47B, a second LED stack 2330 is grown on a second substrate 2310, and a second-p transparent electrode 2350 is formed on the second LED stack 2330. The second LED stack 2330 may be formed of GaN-based semiconductor layers and may include a GaInN well layer. The second substrate 2310 is a substrate on which GaN-based semiconductor layers may be grown thereon, and is different from the first substrate 2210. The composition ratio of GaInN for the second LED stack 2330 may be determined such that the second LED stack 2330 emits green light. The second-p transparent electrode 2350 forms ohmic contact with the p-type semiconductor layer of the second LED stack 2330. The second LED stack 2330 may include an n-type semiconductor layer, an active layer, and a p-type semiconductor layer. In some exemplary embodiments, the n-type semiconductor layer of the second LED stack 2330 may have an energy bandgap capable of absorbing light generated from the third LED stack 2430, and the p-type semiconductor layer of the second LED stack 2330 may have an energy bandgap capable of absorbing light generated from the third LED stack 2430.

[0347] Referring to FIG. 47C, a third LED stack 2430 is grown on a third substrate 2410, and a third-p transparent electrode 2450 is formed on the third LED stack 2430. The third LED stack 2430 may be formed of GaN-based semiconductor layers and may include a GaInN well layer. The third substrate 2410 is a substrate on which GaN-based semiconductor layers may be grown thereon, and is different from the first substrate 2210. The composition ratio of GaInN for the third LED stack 2430 may be determined such that the third LED stack 2430 emits blue light. The third-p transparent electrode 2450 forms ohmic contact with the p-type semiconductor layer of the third LED stack 2430.

[0348] As such, the first LED stack 2230, the second LED stack 2330, and the third LED stack 2430 are grown on different substrates, and the formation sequence thereof is not limited to a particular sequence.

[0349] Referring to FIG. 47D, the first LED stack 2230 is coupled to the support substrate 2510 via a first bonding layer 2530. The first bonding layer 2530 may be previously formed on the support substrate 2510 and the reflective electrode 2250 may be bonded to the first bonding layer 2530 to face the support substrate 2510. The first substrate 2210 is removed from the first LED stack 2230 by chemical etching or the like. Accordingly, the upper surface of the n-type semiconductor layer of the first LED stack 2230 is exposed.

[0350] Then, an ohmic electrode 2290 is formed in the exposed region of the first LED stack 2230. In order to reduce ohmic contact resistance of the ohmic electrode 2290, the ohmic electrode 2290 may be subjected to heat treatment. The ohmic electrode 2290 may be formed in each pixel region so as to correspond to the pixel regions.

[0351] Referring to FIG. 47E, the second LED stack 2330 is coupled to the first LED stack 2230, on which the ohmic electrode 2290 is formed, via a second bonding layer 2550. The second-p transparent electrode 2350 is bonded to the second bonding layer 2550 to face the first LED stack 2230. The second bonding layer 2550 may be previously formed on the first LED stack 2230 such that the second-p transparent electrode 2350 may face and be bonded to the second bonding layer 2550. The second substrate 2310 may be separated from the second LED stack 2330 by a laser lift-off or chemical lift-off process.

[0352] Then, referring to FIG. 46 and FIG. 47C, the third LED stack 2430 is coupled to the second LED stack 2330 via a third bonding layer 2570. The third-p transparent electrode 2450 is bonded to the third bonding layer 2570 to face the second LED stack 2330. The third bonding layer 2570 may be previously formed on the second LED stack 2330 such that the third-p transparent electrode 2450 may face and be bonded to the third bonding layer 2570. The third substrate 2410 may be separated from the third LED stack 2430 by a laser lift-off or chemical lift-off process. As such, the light emitting diode stack for a display as shown in FIG. 46 may be formed, which has the n-type semiconductor layer of the third LED stack 2430 exposed to the outside.

[0353] A display apparatus may be formed by patterning the stack of the first to third LED stacks 2230, 2330, and 2430 disposed on the support substrate 2510 in pixel units, followed by connecting the first to third LED stacks 2230, 2330, and 2430 to one another through interconnections. However, the inventive concepts are not limited thereto. For example, a display apparatus may be manufactured by dividing the stack of the first to third LED stacks 2230, 2330, and 2430 into individual units, and transferring the first to third LED stacks 2230, 2330, and 2430 to other support substrates, such as a printed circuit board.

[0354] FIG. 48 is a schematic circuit diagram of a display apparatus not forming part of the invention. FIG. 49 is a schematic plan view of the display apparatus not forming part of the invention.

[0355] Referring to FIG. 48 and FIG. 49, the display apparatus according to an exemplary embodiment may be implemented to be driven in a passive matrix manner.

[0356] The light emitting diode stack for a display shown in FIG. 46 has the structure including the first to third LED stacks 2230, 2330, and 2430 stacked in the vertical direction. Since one pixel includes three light emitting diodes R, G, and B, a first light emitting diode R may correspond to the first LED stack 2230, a second light emitting diode G may correspond to the second LED stack 2330, and a third light emitting diode B may correspond to the third LED stack 2430.

[0357] Referring to FIGS. 48 and 49, one pixel includes the first to third light emitting diodes R, G, and B, each of which may correspond to a subpixel. Anodes of the first to third light emitting diodes R, G, and B are connected to a common line, for example, a data line, and cathodes thereof are connected to different lines, for example, scan lines. For example, in a first pixel, the anodes of the first to third light emitting diodes R, G, and B are commonly connected to a data line Vdata1, and the cathodes thereof are connected to scan lines Vscan1-1, Vscan1-2, and Vscan1-3, respectively. As such, the light emitting diodes R, G, and B in each pixel can be driven independently.

[0358] In addition, each of the light emitting diodes R, G, and B may be driven by a pulse width modulation or by changing the magnitude of electric current to control the brightness of each subpixel.

[0359] Referring to FIG. 49, a plurality of pixels is formed by patterning the stack of FIG. 46, and each of the pixels is connected to the reflective electrodes 2250 and interconnection lines 2710, 2730, and 2750. As shown in FIG. 48, the reflective electrode 2250 may be used as the data line Vdata and the interconnection lines 2710, 2730, and 2750 may be formed as the scan lines.

[0360] The pixels may be arranged in a matrix form, in which the anodes of the light emitting diodes R, G, and B of each pixel are commonly connected to the reflective electrode 2250, and the cathodes thereof are connected to the interconnection lines 2710, 2730, and 2750 separated from one another. Here, the interconnection lines 2710, 2730, and 2750 may be used as the scan lines Vscan.

[0361] FIG. 50 is an enlarged plan view of one pixel of the display apparatus of FIG. 49. FIG. 51 is a schematic cross-sectional view taken along line A-A of FIG. 50, and FIG. 52 is a schematic cross-sectional view taken along line B-B of FIG. 50.

[0362] Referring to FIGS. 49 to 52, in each pixel, a portion of the reflective electrode 2250, the ohmic electrode 2290 formed on the upper surface of the first LED stack 2230 (see FIG. 53H), a portion of the second-p transparent electrode 2350 (see FIG. 53H), a portion of the upper surface of the second LED stack 2330 (see FIG. 53J), a portion of the third-p transparent electrode 2450 (see FIG. 53H), and the upper surface of the third LED stack 2430 are exposed to the outside.

[0363] The third LED stack 2430 may have a roughened surface 2430a on the upper surface thereof. The roughened surface 2430a may be formed over the entirety of the upper surface of the third LED stack 2430 or may be formed in some regions thereof.

[0364] A lower insulation layer 2610 may cover a side surface of each pixel. The lower insulation layer 2610 may be formed of a light transmissive material, such as SiO2. In this case, the lower insulation layer 2610 may cover substantially the entire upper surface of the third LED stack 2430. Alternatively, the lower insulation layer 2610 may include a distributed Bragg reflector to reflect light traveling towards the side surfaces of the first to third LED stacks 2230, 2330, and 2430. In this case, the lower insulation layer 2610 may partially expose the upper surface of the third LED stack 2430. Still alternatively, the lower insulation layer 2610 may be a black-based insulation layer that absorbs light. Furthermore, an electrically floating metallic reflective layer may be further formed on the lower insulation layer 2610 to reflect light emitted through the side surfaces of the first to third LED stacks 2230, 2330, and 2430.

[0365] The lower insulation layer 2610 may include an opening 2610a which exposes the upper surface of the third LED stack 2430, an opening 2610b which exposes the upper surface of the second LED stack 2330, an opening 2610c (see FIG. 53H) which exposes the ohmic electrode 2290 of the first LED stack 2230, an opening 2610d which exposes the third-p transparent electrode 2450, an opening 2610e which exposes the second-p transparent electrode 2350, and openings 2610f which expose the first-p reflective electrode 2250.

[0366] The interconnection lines 2710 and 2750 may be formed near the first to third LED stacks 2230, 2330, and 2430 on the support substrate 2510, and may be disposed on the lower insulation layer 2610 to be insulated from the first-p reflective electrode 2250. A connecting portion 2770a connects the third-p transparent electrode 2450 to the reflective electrode 2250, and a connecting portion 2770b connects the second-p transparent electrode 2350 to the reflective electrode 2250, such that the anodes of the first LED stack 2230, the second LED stack 2330, and the third LED stack 2430 are commonly connected to the reflective electrode 2250.

[0367] A connecting portion 2710a connects the upper surface of the third LED stack 2430 to the interconnection line 2710, and a connecting portion 2750a connects the ohmic electrode 2290 on the first LED stack 2230 to the interconnection line 2750.

[0368] An upper insulation layer 2810 may be disposed on the interconnection lines 2710 and 2730 and the lower insulation layer 2610 to cover the upper surface of the third LED stack 2430. The upper insulation layer 2810 may have an opening 2810a which partially exposes the upper surface of the second LED stack 2330.

[0369] The interconnection line 2730 may be disposed on the upper insulation layer 2810, and the connecting portion 2730a may connect the upper surface of the second LED stack 2330 to the interconnection line 2730. The connecting portion 2730a may pass through an upper portion of the interconnection line 2750 and is insulated from the interconnection line 2750 by the upper insulation layer 2810.

[0370] Although the electrodes of each pixel are described as being connected to the data line and the scan lines, the inventive concepts are not limited thereto. Further, while the interconnection lines 2710 and 2750 are described as being formed on the lower insulation layer 2610 and the interconnection line 2730 is described as being formed on the upper insulation layer 2810, the inventive concepts are not limited thereto. For example, all of the interconnection lines 2710, 2730, and 2750 may be formed on the lower insulation layer 2610, and may be covered by the upper insulation layer 2810, which may have openings that expose the interconnection line 2730. In this manner, the connecting portion 2730a may connect the upper surface of the second LED stack 2330 to the interconnection line 2730 through the openings of the upper insulation layer 2810.

[0371] Alternatively, the interconnection lines 2710, 2730, and 2750 may be formed inside the support substrate 2510, and the connecting portions 2710a, 2730a, and 2750a on the lower insulation layer 2610 may connect the ohmic electrode 2290, the upper surface of the first LED stack 2230, and the upper surface of the third LED stack 2430 to the interconnection lines 2710, 2730, and 2750.

[0372] According to an exemplary embodiment, light L1 generated from the first LED stack 2230 is emitted to the outside through the second and third LED stacks 2330 and 2430, and light L2 generated from the second LED stack 2330 is emitted to the outside through the third LED stack 2430. Furthermore, a portion of light L3 generated from the third LED stack 2430 may enter the second LED stack 2330, and a portion of light L2 generated from the second LED stack 2330 may enter the first LED stack 2230. Furthermore, a secondary light may be generated from the second LED stack 2330 by the light L3, and a secondary light may also be generated from the first LED stack 2230 by the light L2. However, such secondary light may have a low intensity.

[0373] FIG. 53A to FIG. 53K are schematic plan views illustrating a method of manufacturing a display apparatus not forming part of the invention. Hereinafter, the following descriptions will be given with reference to the pixel of FIG. 50.

[0374] First, the light emitting diode stack 2000 described in FIG. 46 is prepared.

[0375] Referring to FIG. 53A, a roughened surface 2430a may be formed on the upper surface of the third LED stack 2430. The roughened surface 2430a may be formed on the upper surface of the third LED stack 2430 to correspond to each pixel region. The roughened surface 2430a may be formed by chemical etching, for example, photo-enhanced chemical etching (PEC) or the like.

[0376] The roughened surface 2430a may be partially formed in each pixel region by taking into account a region of the third LED stack 2430 to be etched in the subsequent process, without being limited thereto. Alternatively, the roughened surface 2430a may be formed over the entire upper surface of the third LED stack 2430.

[0377] Referring to FIG. 53B, a surrounding region of the third LED stack 2430 in each pixel is removed by etching to expose the third-p transparent electrode 2450. As shown in FIG. 53B, the third LED stack 2430 may be remained to have a rectangular shape or a square shape. The third LED stack 2430 may have a plurality of depressions formed along edges thereof.

[0378] Referring to FIG. 53C, the upper surface of the second LED stack 2330 is exposed by removing the exposed third-p transparent electrode 2450 in areas other than in one depression. Accordingly, the upper surface of the second LED stack 2330 is exposed around the third LED stack 2430 and in other depressions other than the depression where the third-p transparent electrode 2450 is partially remained.

[0379] Referring to FIG. 53D, the second-p transparent electrode 2350 is exposed by removing the exposed second LED stack 2330 exposed in areas other than one depression.

[0380] Referring to FIG. 53E, the ohmic electrode 2290 is exposed together with the upper surface of the first LED stack 2230 by removing the exposed second-p transparent electrode 2350 in areas other than in one depression. Here, the ohmic electrode 2290 may be exposed in one depression. Accordingly, the upper surface of the first LED stack 2230 is exposed around the third LED stack 2430, and an upper surface of the ohmic electrode 2290 is exposed in at least one of the depressions formed in the third LED stack 2430.

[0381] Referring to FIG. 53F, the reflective electrode 2250 is exposed by removing an exposed portion of the first LED stack 2230 in areas other than in one depression. As such, the reflective electrode 2250 is exposed around the third LED stack 2430.

[0382] Referring to FIG. 53G, linear interconnection lines are formed by patterning the reflective electrode 2250. Here, the support substrate 2510 may be exposed. The reflective electrode 2250 may connect pixels arranged in one row to each other among pixels arranged in a matrix (see FIG. 49).

[0383] Referring to FIG. 53H, a lower insulation layer 2610 (see FIG. 51 and FIG. 52) is formed to cover the pixels. The lower insulation layer 2610 covers the reflective electrode 2250 and side surfaces of the first to third LED stacks 2230, 2330, and 2430. In addition, the lower insulation layer 2610 may partially cover the upper surface of the third LED stack 2430. If the lower insulation layer 2610 is a transparent layer such as a SiO2 layer, the lower insulation layer 2610 may cover substantially the entire upper surface of the third LED stack 2430. Alternatively, the lower insulation layer 2610 may include a distributed Bragg reflector. In this case, the lower insulation layer 2610 may partially expose the upper surface of the third LED stack 2430 to allow light to be emitted to the outside.

[0384] The lower insulation layer 2610 may include an opening 2610a which exposes the third LED stack 2430, an opening 2610b which exposes the second LED stack 2330, an opening 2610c which exposes the ohmic electrode 2290, an opening 2610d which exposes the third-p transparent electrode 2450, an opening 2610e which exposes the second-p transparent electrode 2350, and an opening 2610f which exposes the reflective electrode 2250. The opening 2610f that exposes the reflective electrode 2250 may be formed singularly or in plural.

[0385] Referring to FIG. 53I, interconnection lines 2710 and 2750, and connecting portions 2710a, 2750a, 2770a, and 2770b are formed by a lift-off process or the like. The interconnection lines 2710 and 2750 are insulated from the reflective electrode 2250 by the lower insulation layer 2610. The connecting portion 2710a electrically connects the third LED stack 2430 to the interconnection line 2710, and the connecting portion 2750a electrically connects the ohmic electrode 2290 to the interconnection line 2750 such that the first LED stack 2230 is electrically connected to the interconnection line 2750. The connecting portion 2770a electrically connects the third-p transparent electrode 2450 to the first-p reflective electrode 2250, and the connecting portion 2770b electrically connects the second-p transparent electrode 2350 to the first-p reflective electrode 2250.

[0386] Referring to FIG. 53J, an upper insulation layer 2810 (see FIG. 51 and FIG. 52) covers the interconnection lines 2710, 2750 and the connecting portions 2710a, 2750a, 2770a, and 2770b. The upper insulation layer 2810 may also cover substantially the entire upper surface of the third LED stack 2430. The upper insulation layer 2810 has an opening 2810a which exposes the upper surface of the second LED stack 2330. The upper insulation layer 2810 may be formed of, for example, silicon oxide or silicon nitride, and may include a distributed Bragg reflector. When the upper insulation layer 2810 includes the distributed Bragg reflector, the upper insulation layer 2810 may expose at least a part of the upper surface of the third LED stack 2430 to allow light to be emitted to the outside.

[0387] Referring to FIG. 53K, an interconnection line 2730 and a connecting portion 2730a are formed. An interconnection line 2750 and a connecting portion 2750a may be formed by a lift-off process or the like. The interconnection line 2730 is disposed on the upper insulation layer 2810, and is insulated from the reflective electrode 2250 and the interconnection lines 2710 and 2750. The connecting portion 2730a electrically connects the second LED stack 2330 to the interconnection line 2730. The connecting portion 2730a may pass through an upper portion of the interconnection line 2750, and is insulated from the interconnection line 2750 by the upper insulation layer 2810.

[0388] As such, a pixel region shown in FIG. 50 may be formed. In addition, as shown in FIG. 49, a plurality of pixels may be formed on the support substrate 2510 and may be connected to one another by the first-p the reflective electrode 2250 and the interconnection lines 2710, 2730 and 2750, to be operated in a passive matrix manner.

[0389] Although the above describes a method of manufacturing a display apparatus that may be operated in the passive matrix manner, the inventive concepts are not limited thereto. More particularly, the display apparatus according to exemplary embodiments may be manufactured in various ways so as to be operated in the passive matrix manner using the light emitting diode stack shown in FIG. 46.

[0390] For example, while the interconnection line 2730 is described as being formed on the upper insulation layer 2810, the interconnection line 2730 may be formed together with the interconnection lines 2710 and 2750 on the lower insulation layer 2610, and the connecting portion 2730a may be formed on the upper insulation layer 2810 to connect the second LED stack 2330 to the interconnection line 2730. Alternatively, the interconnection lines 2710, 2730, 2750 may be disposed inside the support substrate 2510.

[0391] FIG. 54 is a schematic circuit diagram of a display apparatus not forming part of the invention. The circuit diagram of FIG. 54 relates to a display apparatus driven in an active matrix manner.

[0392] Referring to FIG. 54, the drive circuit according to an exemplary embodiment includes at least two transistors Tr1, Tr2 and a capacitor. When a power source is connected to selection lines Vrow1 to Vrow3 and voltage is applied to data lines Vdata1 to Vdata3, the voltage is applied to the corresponding light emitting diode. In addition, the corresponding capacitors are charged according to the values of Vdata1 to Vdata3. Since a turned-on state of the transistor Tr2 can be maintained by the charged voltage of the capacitor, the voltage of the capacitor can be maintained and applied to the light emitting diodes LED1 to LED3, even when power supplied to Vrow1 is cut off. In addition, electric current flowing in the light emitting diodes LED1 to LED3 can be changed depending upon the values of Vdata1 to Vdata3. Electric current can be continuously supplied through Vdd, and thus, light may be emitted continuously.

[0393] The transistors Tr1, Tr2 and the capacitor may be formed inside the support substrate 2510. For example, thin film transistors formed on a silicon substrate may be used for active matrix driving.

[0394] Here, the light emitting diodes LED1 to LED3 may correspond to the first to third LED stacks 2230, 2330, and 2430 stacked in one pixel, respectively. The anodes of the first to third LED stacks 2230, 2330, and 2430 are connected to the transistor Tr2 and the cathodes thereof are connected to the ground.

[0395] Although FIG. 54 shows the circuit for active matrix driving according to an exemplary embodiment, other types of circuits may be variously used. In addition, although the anodes of the light emitting diodes LED1 to LED3 are described as being connected to different transistors Tr2 and the cathodes thereof are described as being connected to the ground, the anodes of the light emitting diodes may be connected to current supplies Vdd and the cathodes thereof may be connected to different transistors in some exemplary embodiments.

[0396] FIG. 55 is a schematic plan view of a display apparatus not forming part of the invention. Hereinafter, the following description will be given with reference to one pixel among a plurality of pixels arranged on the support substrate 2511.

[0397] Referring to FIG. 55, the pixel according to an exemplary embodiment are substantially similar to the pixel described with reference to FIG. 49 to FIG. 52, except that the support substrate 2511 is a thin film transistor panel including transistors and capacitors and the reflective electrode 2250 is disposed in a lower region of the first LED stack 2230.

[0398] The cathode of the third LED stack 2430 is connected to the support substrate 2511 through the connecting portion 2711a. For example, as shown in FIG. 54, the cathode of the third LED stack 2430 may be connected to the ground through electrical connection to the support substrate 2511. The cathodes of the second LED stack 2330 and the first LED stack 2230 may also be connected to the ground through electrical connection to the support substrate 2511 via the connecting portions 2731a and 2751a.

[0399] The reflective electrode is connected to the transistors Tr2 (see FIG. 54) inside the support substrate 2511. The third-p transparent electrode and the second-p transparent electrode are also connected to the transistors Tr2 (see FIG. 54) inside the support substrate 2511 through the connecting portions 2711b and 2731b.

[0400] In this manner, the first to third LED stacks are connected to one another, thereby forming a circuit for active matrix driving, as shown in FIG. 54.

[0401] Although FIG. 55 shows a pixel having an electrical connection for active matrix driving according to an exemplary embodiment, the inventive concepts are not limited thereto, and the circuit for the display apparatus can be modified into various circuits for active matrix driving in various ways.

[0402] In addition, the reflective electrode 2250, the second-p transparent electrode 2350, and the third-p transparent electrode 2450 of FIG. 46 are described as forming ohmic contact with the p-type semiconductor layer of each of the first LED stack 2230, the second LED stack 2330, and the third LED stack 2430, and the ohmic electrode 2290 is described as forming ohmic contact with the n-type semiconductor layer of the first LED stack 2230, the n-type semiconductor layer of each of the second LED stack 2330, and the third LED stack 2430 is not provided with a separate ohmic contact layer. Although there is less difficulty in current spreading even without formation of a separate ohmic contact layer in the n-type semiconductor layer when the pixels have a small size of 200 µm or less, however, a transparent electrode layer may be disposed on the n-type semiconductor layer of each of the LED stacks in order to secure current spreading according to some exemplary embodiments.

[0403] In addition, although FIG. 46 shows the coupling of the first to third LED stacks 2230, 2330, and 2430 to one another via a bonding layers, the inventive concepts are not limited thereto, and the first to third LED stacks 2230, 2330, and 2430 may be connected to one another in various sequences and using various structures.

[0404] According to exemplary embodiments, since it is possible to form a plurality of pixels at the wafer level using the light emitting diode stack 2000 for a display, the need for individual mounting of light emitting diodes may be obviated. In addition, the light emitting diode stack according to exemplary embodiments has the structure in which the first to third LED stacks 2230, 2330, and 2430 are stacked in the vertical direction, and thus, an area for subpixels may be secured in a limited pixel area. Furthermore, the light emitting diode stack according to the exemplary embodiments allows light generated from the first LED stack 2230, the second LED stack 2330, and the third LED stack 2430 to be emitted outside therethrough, thereby reducing light loss.

[0405] FIG. 56 is a schematic plan view of a display apparatus not forming part of the invention, and FIG. 57 is a schematic cross-sectional view of a light emitting diode pixel for a display not forming part of the invention.

[0406] Referring to FIG. 56 and FIG. 57, the display apparatus includes a circuit board 3510 and a plurality of pixels 3000. Each of the pixels 3000 includes a substrate 3210 and first to third subpixels R, G, and B disposed on the substrate 3210.

[0407] The circuit board 3510 may include a passive circuit or an active circuit. The passive circuit may include, for example, data lines and scan lines. The active circuit may include, for example, a transistor and a capacitor. The circuit board 3510 may have a circuit on a surface thereof or therein. The circuit board 3510 may include, for example, a glass substrate, a sapphire substrate, a Si substrate, or a Ge substrate.

[0408] The substrate 3210 supports first to third subpixels R, G, and B. The substrate 3210 is continuous over the plurality of pixels 3000 and electrically connects the subpixels R, G, and B to the circuit board 3510. For example, the substrate 3210 may be a GaAs substrate.

[0409] The first subpixel R includes a first LED stack 3230, the second subpixel G includes a second LED stack 3330, and the third subpixel B includes a third LED stack 3430. The first subpixel R is configured to allow the first LED stack 3230 to emit light, the second subpixel G is configured to allow the second LED stack 3330 to emit light, and the third subpixel B is configured to allow the third LED stack 3430 to emit light. The first to third LED stacks 3230, 3330, and 3430 may be driven independently.

[0410] The first LED stack 3230, the second LED stack 3330, and the third LED stack 3430 are stacked to overlap one another in the vertical direction. Here, as shown in FIG. 57, the second LED stack 3330 may be disposed in a portion of the first LED stack 3230. For example, the second LED stack 3330 may be disposed towards one side on the first LED stack 3230. The third LED stack 3430 may be disposed in a portion of the second LED stack 3330. For example, the third LED stack 3430 may be disposed towards one side on the second LED stack 3330. Although FIG. 57 shows that the third LED stack 3430 is disposed towards right side, the inventive concepts are not limited thereto. Alternatively, the third LED stack 3430 may be disposed towards the left side of the second LED stack 3330.

[0411] Light R generated from the first LED stack 3230 may be emitted through a region not covered by the second LED stack 3330, and light G generated from the second LED stack 3330 may be emitted through a region not covered by the third LED stack 3430. More particularly, light generated from the first LED stack 3230 may be emitted to the outside without passing through the second LED stack 3330 and the third LED stack 3430, and light generated from the second LED stack 3330 may be emitted to the outside without passing through the third LED stack 3430.

[0412] The region of the first LED stack 3230 through which the light R is emitted, the region of the second LED stack 3330 through which the light G is emitted, and the region of the third LED stack 3340 may have different areas, and the intensity of light emitted from each of the LED stacks 3230, 3330, and 3430 may be adjusted by adjusting the areas thereof.

[0413] However, the inventive concepts are not limited thereto. Alternatively, light generated from the first LED stack 3230 may be emitted to the outside after passing through the second LED stack 3330 or after passing through the second LED stack 3330 and the third LED stack 3430, and light generated from the second LED stack 3330 may be emitted to the outside after passing through the third LED stack 3430.

[0414] Each of the first LED stack 3230, the second LED stack 3330, and the third LED stack 3430 may include a first conductivity type (for example, n-type) semiconductor layer, a second conductivity type (for example, p-type) semiconductor layer, and an active layer interposed therebetween. The active layer may have a multi-quantum well structure. The first to third LED stacks 3230, 3330, and 3430 may include different active layers to emit light having different wavelengths. For example, the first LED stack 3230 may be an inorganic light emitting diode configured to emit red light, the second LED stack 3330 may be an inorganic light emitting diode configured to emit green light, and the third LED stack 3430 may be an inorganic light emitting diode configured to emit blue light. To this end, the first LED stack 3230 may include an AlGaInP-based well layer, the second LED stack 3330 may include an AlGaInP or AlGaInN-based well layer, and the third LED stack 3430 may include an AlGaInN-based well layer. However, the inventive concepts are not limited thereto. The wavelengths of light generated from the first LED stack 3230, the second LED stack 3330, and the third LED stack 3430 may be varied. For example, the first LED stack 3230, the second LED stack 3330, and the third LED stack 3430 may emit green light, red light, and blue light, respectively, or may emit green light, blue light, and red light, respectively.

[0415] In addition, a distributed Bragg reflector may be interposed between the substrate 3210 and the first LED stack 3230 to prevent loss of light generated from the first LED stack 3230 through absorption by the substrate 3210. For example, a distributed Bragg reflector formed by alternately stacking AlAs and AlGaAs semiconductor layers one above another may be interposed therebetween.

[0416] FIG. 58 is a schematic circuit diagram of a display apparatus not forming part of the invention.

[0417] Referring to FIG. 58, the display apparatus according to an exemplary embodiment may be driven in an active matrix manner. As such, the circuit board may include an active circuit.

[0418] For example, the drive circuit may include at least two transistors Tr1, Tr2 and a capacitor. When a power source is connected to selection lines Vrow1 to Vrow3 and voltage is applied to data lines Vdata1 to Vdata3, the voltage is applied to the corresponding light emitting diode. In addition, the corresponding capacitors are charged according to the values of Vdata1 to Vdata3. Since a turned-on state of the transistor Tr2 can be maintained by the charged voltage of the capacitor, the voltage of the capacitor can be maintained and applied to the light emitting diodes LED1 to LED3 even when power supplied to Vrow1 is cut off. In addition, electric current flowing in the light emitting diodes LED1 to LED3 can be changed depending upon the values of Vdata1 to Vdata3. Electric current can be continuously supplied through Vdd, and thus, light may be emitted continuously.

[0419] The transistors Tr1, Tr2 and the capacitor may be formed inside the support substrate 3510. Here, the light emitting diodes LED1 to LED3 may correspond to the first to third LED stacks 3230, 3330, and 3430 stacked in one pixel, respectively. The anodes of the first to third LED stacks 3230, 3330, and 3430 are connected to the transistor Tr2 and the cathodes thereof are connected to the ground. The cathodes of the first to third LED stacks 3230, 3330, and 3430, for example, may be commonly connected to the ground.

[0420] Although FIG. 58 shows the circuit for active matrix driving according to an exemplary embodiment, other types of circuits may also be used. In addition, although the anodes of the light emitting diodes LED1 to LED3 are described as being connected to different transistors Tr2 and the cathodes thereof are described as being connected to the ground, the anodes of the light emitting diodes may be commonly connected and the cathodes thereof may be connected to different transistors in some exemplary embodiments.

[0421] Although the active circuit for active matrix driving is illustrated above, the inventive concepts are not limited thereto, and the pixels according to an exemplary embodiment may be driven in a passive matrix manner. As such, 0the circuit board 3510 may include data lines and scan lines arranged thereon, and each of the subpixels may be connected to the data line and the scan line. In an exemplary embodiment, the anodes of the first to third LED stacks 3230, 3330, and 3430 may be connected to different data lines and the cathodes thereof may be commonly connected to a scan line. In other exemplary embodiments, the anodes of the first to third LED stacks 3230, 3330, and 3430 may be connected to different scan lines and the cathodes thereof may be commonly connected to a data line.

[0422] In addition, each of the LED stacks 3230, 3330, and 3430 may be driven by a pulse width modulation or by changing the magnitude of electric current, thereby controlling the brightness of each subpixel. Furthermore, the brightness may be adjusted by adjusting the areas of the first to third LED stacks 3230, 3330, and 3430, and the areas of the regions of the LED stacks 3230, 3330, and 3430 through which light R, G, and B is emitted. For example, an LED stack emitting light having low visibility, for example, the first LED stack 3230, has a larger area than the second LED stack 3330 or the third LED stack 3430, and thus, can emit light with a higher intensity under the same current density. In addition, since the area of the second LED stack 3330 is larger than the area of the third LED stack 3430, the second LED stack 3330 can emit light with a higher intensity under the same current density than the third LED stack 3430. In this manner, light output can be adjusted based on the visibility of light emitted from the first to third LED stacks 3230, 3330, and 3430 by adjusting the areas of the first LED stack 3230, the second LED stack 3330, and the third LED stack 3430.

[0423] FIG. 59A and FIG. 59B are a top view and a bottom view of one pixel of a display apparatus not forming part of the invention, and FIG. 60A, FIG. 60B, FIG. 60C, and FIG. 60D are schematic cross-sectional views taken along lines A-A, B-B, C-C, and D-D of FIG. 59A, respectively.

[0424] In the display apparatus, pixels are arranged on a circuit board 3510 (see FIG. 56) and each of the pixel includes a substrate 3210 and subpixels R, G, and B. The substrate 3210 may be continuous over the plurality of pixels. Hereinafter, a configuration of a pixel according to an exemplary embodiment will be described.

[0425] Referring to FIG. 59AA, FIG. 59B, FIG. 60A, FIG. 60B, FIG. 60C, and FIG. 60D, the pixel includes a substrate 3210, a distributed Bragg reflector 3220, an insulation layer 3250, through-hole vias 3270a, 3270b, 3270c, a first LED stack 3230, a second LED stack 3330, a third LED stack 3430, a first-1 ohmic electrode 3290a, a first-2 ohmic electrode 3290b, a second-1 ohmic electrode 3390, a second-2 ohmic electrode 3350, a third-1 ohmic electrode 3490, a third-2 ohmic electrode 3450, a first bonding layer 3530, a second bonding layer 3550, an upper insulation layer 3610, connectors 3710, 3720, 3730, a lower insulation layer 3750, and electrode pads 3770a, 3770b, 3770c, 3770d.

[0426] Each of subpixels R, G, and B includes the LED stacks 3230, 3330, and 3430 and ohmic electrodes. In addition, anodes of the first to third subpixels R, G, and B may be electrically connected to the electrode pads 3770a, 3770b, and 3770c, respectively, and cathodes thereof may be electrically connected to the electrode pad 3770d, thereby allowing the first to third subpixels R, G, and B to be driven independently.

[0427] The substrate 3210 supports the LED stacks 3230, 3330, and 3430. The substrate 3210 may be a growth substrate on which AlGaInP-based semiconductor layers may be grown thereon, for example, a GaAs substrate. In particular, the substrate 3210 may be a semiconductor substrate exhibiting n-type conductivity.

[0428] The first LED stack 3230 includes a first conductivity type semiconductor layer 3230a and a second conductivity type semiconductor layer 3230b, the second LED stack 3330 includes a first conductivity type semiconductor layer 3330a and a second conductivity type semiconductor layer 3330b, and the third LED stack 3430 includes a first conductivity type semiconductor layer 3430a and a second conductivity type semiconductor layer 3430b. An active layer may be interposed between the first conductivity type semiconductor layer 3230a, 3330a, or 3430a and the second conductivity type semiconductor layer 3230b, 3330b, or 3430b.

[0429] According to an exemplary embodiment, each of the first conductivity type semiconductor layers 3230a, 3330a, 3430a may be an n-type semiconductor layer, and each of the second conductivity type semiconductor layers 3230b, 3330b, 3430b may be a p-type semiconductor layer. A roughened surface may be formed on an upper surface of each of the first conductivity type semiconductor layers 3230a, 3330a, 3430a by surface texturing. However, the inventive concepts are not limited thereto and the first and second conductivity types can be changed vice versa.

[0430] The first LED stack 3230 is disposed near the support substrate 3510, the second LED stack 3330 is disposed on the first LED stack 3230, and the third LED stack 3430 is disposed on the second LED stack 3330. The second LED stack 3330 is disposed in some region on the first LED stack 3230, so that the first LED stack 3230 partially overlaps the second LED stack 3330. The third LED stack 3430 is disposed in some region on the second LED stack 3330, so that the second LED stack 3330 partially overlaps the third LED stack 3430. Accordingly, light generated from the first LED stack 3230 can be emitted to the outside without passing through the second and third LED stacks 3330 and 3430. In addition, light generated from the second LED stack 3330 can be emitted to the outside without passing through the third LED stack 3430.

[0431] Materials for the first LED stack 3230, the second LED stack 3330, and the third LED stack 3430 are substantially the same as those described with reference to FIG. 57, and thus, detailed descriptions thereof will be omitted to avoid redundancy.

[0432] The distributed Bragg reflector 3220 is interposed between the substrate 3210 and the first LED stack 3230. The distributed Bragg reflector 3220 may include a semiconductor layer grown on the substrate 3210. For example, the distributed Bragg reflector 3220 may be formed by alternately stacking AlAs layers and AlGaAs layers. The distributed Bragg reflector 3220 may include a semiconductor layer that electrically connects the substrate 3210 to the first conductivity type semiconductor layer 3230a of the first LED stack 3230.

[0433] Through-hole vias 3270a, 3270b, 3270c are formed through the substrate 3210. The through-hole vias 3270a, 3270b, 3270c may be formed to pass through the first LED stack 3230. The through-hole vias 3270a, 3270b, 3270c may be formed of conductive pastes or by plating.

[0434] The insulation layer 3250 is disposed between the through-hole vias 3270a, 3270b, and 3270c and an inner wall of a through-hole formed through the substrate 3210 and the first LED stack 3230 to prevent short circuit between the first LED stack 3230 and the substrate 3210.

[0435] The first-1 ohmic electrode 3290a forms ohmic contact with the first conductivity type semiconductor layer 3230a of the first LED stack 3230. The first-1 ohmic electrode 3290a may be formed of, for example, Au-Te or Au-Ge alloys.

[0436] In order to form the first-1 ohmic electrode 3290a, the second conductivity type semiconductor layer 3230b and the active layer may be partially removed to expose the first conductivity type semiconductor layer 3230a. The first-1 ohmic electrode 3290a may be disposed apart from the region where the second LED stack 3330 is disposed. Furthermore, the first-1 ohmic electrode 3290 may include a pad region and an extension, and the connector 3710 may be connected to the pad region of the first-1 ohmic electrode 3290, as shown in FIG. 59A.

[0437] The first-2 ohmic electrode 3290b forms ohmic contact with the second conductivity type semiconductor layer 3230b of the first LED stack 3230. As shown in FIG. 59A, the first-2 ohmic electrode 3290b may be formed to partially surround the first-1 ohmic electrode 3290a in order to assist in current spreading. The first-2 ohmic electrode 3290b may not include the extension. The first-2 ohmic electrode 3290b may be formed of, for example, Au-Zn or Au-Be alloys. Furthermore, the first-2 ohmic electrode 3290b may have a single layer or multiple layers structure.

[0438] The first-2 ohmic electrode 3290b may be connected to the through-hole via 3270a such that the through-hole via 3270a can be electrically connected to the second conductivity type semiconductor layer 3230b.

[0439] The second-1 ohmic electrode 3390 forms ohmic contact with the first conductivity type semiconductor layer 3330a of the second LED stack 3330. The second-1 ohmic electrode 3390 may also include a pad region and an extension. As shown in FIG. 59A, the connector 3710 may electrically connect the second-1 ohmic electrode 3390 to the first-1 ohmic electrode 3290a. The second-1 ohmic electrode 3390 may be disposed apart from the region where the third LED stack 3430 is disposed.

[0440] The second-2 ohmic electrode 3350 forms ohmic contact with the second conductivity type semiconductor layer 3330b of the second LED stack 3330. The second-2 ohmic electrode 3350 may include a reflective layer 3350a and a barrier layer 3350b. The reflective layer 3350a reflects light generated from the second LED stack 3330 to improve luminous efficacy of the second LED stack 3330. The barrier layer 3350b may act as a connection pad, which provides the reflective layer 3350a, and is connected to the connector 3720. Although the second-2 ohmic electrode 3350 is described as including a metal layer in this exemplary embodiment, the inventive concepts are not limited thereto. For example, the second-2 ohmic electrode 3350 may be formed of a transparent conductive oxide, such as a conductive oxide semiconductor layer.

[0441] The third-1 ohmic electrode 3490 forms ohmic contact with the first conductivity type semiconductor layer 3430a of the third LED stack 3430. The third-1 ohmic electrode 3490 may also include a pad region and an extension, and the connector 3710 may connect the third-1 ohmic electrode 3490 to the first-1 ohmic electrode 3290a, as shown in FIG. 59A.

[0442] The third-2 ohmic electrode 3450 may form ohmic contact with the second conductivity type semiconductor layer 3430b of the third LED stack 3430. The third-2 ohmic electrode 3450 may include a reflective layer 3450a and a barrier layer 3450b. The reflective layer 3450a reflects light generated from the third LED stack 3430 to improve luminous efficacy of the third LED stack 3430. The barrier layer 3450b may act as a connection pad, which provides the reflective layer 3450a, and is connected to the connector 3730. Although the third-2 ohmic electrode 3450 is described as including a metal layer, the inventive concepts are not limited thereto. Alternatively, the third-2 ohmic electrode 3450 may be formed of a transparent conductive oxide, such as a conductive oxide semiconductor layer.

[0443] The first-2 ohmic electrode 3290b, the second-2 ohmic electrode 3350, and the third-2 ohmic electrode 3450 may form ohmic contact with the p-type semiconductor layers of the corresponding LED stacks to assist in current spreading, and the first-1 ohmic electrode 3290a, the second-1 ohmic electrode 3390, and the third-1 ohmic electrode 3490 may form ohmic contact with the n-type semiconductor layers of the corresponding LED stacks to assist in current spreading.

[0444] The first bonding layer 3530 couples the second LED stack 3330 to the first LED stack 3230. As shown in the drawings, the second-2 ohmic electrode 3350 may adjoin the first bonding layer 3530. The first bonding layer 3530 may be a light transmissive layer or an opaque layer. The first bonding layer 3530 may be formed of an organic material or an inorganic material. Examples of the organic material may include SU8, poly(methyl methacrylate) (PMMA), polyimide, Parylene, benzocyclobutene (BCB), or others, and examples of the inorganic material may include Al203, Si02, SiNx, or others. The organic material layer may be bonded under high vacuum, and the inorganic material layer may be bonded under high vacuum after flattening the surface of the first bonding layer by, for example, chemical mechanical polishing, followed by adjusting surface energy through plasma treatment. The first bonding layer 3530 may be formed of spin-on-glass or may be a metal bonding layer formed of AuSn or the like. For the metal bonding layer, an insulation layer may be disposed on the first LED stack 3230 to secure electrical insulation between the first LED stack 3230 and the metal bonding layer. Furthermore, a reflective layer may be further disposed between the first bonding layer 3530 and the first LED stack 3230 to prevent light generated from the first LED stack 3230 from entering the second LED stack 3330.

[0445] The second bonding layer 3550 couples the second LED stack 3330 to the third LED stack 3430. The second bonding layer 3550 may be interposed between the second LED stack 3330 and the third-2 ohmic electrode 3450 to bond the second LED stack 3330 to the third-2 ohmic electrode 3450. The second bonding layer 3550 may be formed of substantially the same bonding material as the first bonding layer 3530. Furthermore, an insulation layer and / or a reflective layer may be further disposed between the second LED stack 3330 and the second bonding layer 3550.

[0446] When the first bonding layer 3530 and the second bonding layer 3550 are formed of a light transmissive material, and the second-2 ohmic electrode 3350 and the third-2 ohmic electrode 3450 are formed of a transparent oxide material, some fractions of light generated from the first LED stack 3230 may be emitted through the second LED stack 3330 after passing through the first bonding layer 3530 and the second-2 ohmic electrode 3350, and may also be emitted through the third LED stack 3430 after passing through the second bonding layer 3550 and the third-2 ohmic electrode 3450. In addition, some fractions of light generated from the second LED stack 3330 may be emitted through the third LED stack 3430 after passing through the second bonding layer 3550 and the third-2 ohmic electrode 3450.

[0447] In this case, light generated from the first LED stack 3230 should be prevented from being absorbed by the second LED stack 3330 while passing through the second LED stack 3330. As such, light generated from the first LED stack 3230 may have a smaller bandgap than the second LED stack 3330, and thus, may have a longer wavelength than light generated from the second LED stack 3330.

[0448] In addition, in order to prevent light generated from the second LED stack 3330 from being absorbed by the third LED stack 3430 while passing through the third LED stack 3430, light generated from the second LED stack 3330 may have a longer wavelength than light generated from the third LED stack 3430.

[0449] When the first bonding layer 3530 and the second bonding layer 3550 are formed of opaque materials, the reflective layers are interposed between the first LED stack 3230 and the first bonding layer 3530, and between the second LED stack 3330 and the second bonding layer 3550, respectively, to reflect light having been generated from the first LED stack 3230 and entering the first bonding layer 3530, and light having been generated from the second LED stack 3330 and entering the second bonding layer 3550. The reflected light may be emitted through the first LED stack 3230 and the second LED stack 3330.

[0450] The upper insulation layer 3610 may cover the first to third LED stacks 3230, 3330, and 3430. In particular, the upper insulation layer 3610 may cover side surfaces of the second LED stack 3330 and the third LED stack 3430, and may also cover the side surface of the first LED stack 3230.

[0451] The upper insulation layer 3610 has openings that expose the first to third the through-hole vias 3270a, 3270b, 3270c, and openings that expose the first conductivity type semiconductor layer 3330a of the second LED stack 3330, the first conductivity type semiconductor layer 3430a of the third LED stack 3430, the second-2 ohmic electrode 3350, and the third-2 ohmic electrode 3450.

[0452] The upper insulation layer 3610 may be formed of any insulation material, for example, silicon oxide or silicon nitride, without being limited thereto.

[0453] The connector 3710 electrically connects the first-1 ohmic electrode 3290a, the second-1 ohmic electrode 3390, and the third-1 ohmic electrode 3490 to one another. The connector 3710 is formed on the upper insulation layer 3610, and is insulated from the second conductivity type semiconductor layer 3430b of the third LED stack 3430, the second conductivity type semiconductor layer 3330b of the second LED stack 3330, and the second conductivity type semiconductor layer 3230b of the first LED stack 3230.

[0454] The connector 3710 may be formed of substantially the same material as the second-1 ohmic electrode 3390 and the third-1 ohmic electrode 3490, and thus, may be formed together with the second-1 ohmic electrode 3390 and the third-1 ohmic electrode 3490. Alternatively, the connector 3710 may be formed of a different conductive material from the second-1 ohmic electrode 3390 or the third-1 ohmic electrode 3490, and thus, may be separately formed in a different process from the second-1 ohmic electrode 3390 and / or the third-1 ohmic electrode 3490.

[0455] The connector 3720 may electrically connect the second-1 ohmic electrode 3350, for example, the barrier layer 3350b, to the second through-hole via 3270b. The connector 3730 electrically connects the third-1 ohmic electrode, for example, the barrier layer 3450b, to the third through-hole via 3270c. The connector 3720 may be electrically insulated from the first LED stack 3230 by the upper insulation layer 3610. The connector 3730 may also be electrically insulated from the second LED stack 3330 and the first LED stack 3230 by the upper insulation layer 3610.

[0456] The connectors 3720, 3730 may be formed together by the same process. The connector 3720, 3730 may also be formed together with the connector 3710. Furthermore, the connectors 3720, 3730 may be formed of substantially the same material as the second-1 ohmic electrode 3390 and the third-1 ohmic electrode 3490, and may be formed together therewith. Alternatively, the connectors 3720, 3730 may be formed of a different conductive material from the second-1 ohmic electrode 3390 or the third-1 ohmic electrode 3490, and thus may be separately formed by a different process from the second-1 ohmic electrode 3390 and / or the third-1 ohmic electrode 3490.

[0457] The lower insulation layer 3750 covers a lower surface of the substrate 3210. The lower insulation layer 3750 may include openings which expose the first to third through-hole vias 3270a, 3270b, 3270c at a lower side of the substrate 3210, and may also include openings which expose the lower surface of the substrate 3210.

[0458] The electrode pads 3770a, 3770b, 3770c, and 3770d are disposed on the lower surface of the substrate 3210. The electrode pads 3770a, 3770b, and 3770c are connected to the through-hole vias 3270a, 3270b, and 3270c through the openings of the insulation layer 3750, and the electrode pad 3770d is connected to the substrate 3210.

[0459] The electrode pads 3770a, 3770b, and 3770c are provided to each pixel to be electrically connected to the first to third LED stacks 3230, 3330, and 3430 of each pixel, respectively. Although the electrode pad 3770d may also be provided to each pixel, the substrate 3210 is continuously disposed over a plurality of pixels, which may obviate the need for providing the electrode pad 3770d to each pixel.

[0460] The electrode pads 3770a, 3770b, 3770c, 3770d are bonded to the circuit board 3510, thereby providing a display apparatus.

[0461] Next, a method of manufacturing the display apparatus according to an exemplary embodiment will be described.

[0462] FIG. 61A to FIG. 61B are schematic plan views and cross-sectional views illustrating a method of manufacturing the display apparatus not forming part of the invention. Each of the cross-sectional views is taken along a line shown in each corresponding plan view.

[0463] Referring to FIG. 61A and 61B, a first LED stack 3230 is grown on a substrate 3210. The substrate 3210 may be, for example, a GaAs substrate. The first LED stack 3230 is formed of AlGaInP-based semiconductor layers, and includes a first conductivity type semiconductor layer 3230a, an active layer, and a second conductivity type semiconductor layer 3230b. A distributed Bragg reflector 3220 may be formed prior to growth of the first LED stack 3230. The distributed Bragg reflector 3220 may have a stack structure formed by repeatedly stacking, for example, AlAs / AlGaAs layers.

[0464] Then, grooves are formed on the first LED stack 3230 and the substrate 3210 through photolithography and etching. The grooves may be formed to pass through the substrate 3210 or may be formed to a predetermined depth in the substrate 3210, as shown in FIG. 61B.

[0465] Then, an insulation layer 3250 is formed to cover sidewalls of the grooves and through-hole vias 3270a, 3270b, 3270c are formed to fill the grooves. The through-hole vias 3270a, 3270b, and 3270c may be formed by, for example, forming an insulation layer to cover the sidewalls of the grooves, filling the groove with a conductive material layer or conductive pastes through plating, and removing the insulation and the conductive material layer from an upper surface of the first LED stack 3230 through chemical mechanical polishing.

[0466] Referring to FIG. 62A and FIG. 62B, a second LED stack 3330 and a second-2 ohmic electrode 3350 may be coupled to the first LED stack 3230 via the first bonding layer 3530.

[0467] The second LED stack 3330 is grown on a second substrate, and the second-2 ohmic electrode 3350 is formed on the second LED stack 3330. The second LED stack 3330 is formed of AlGaInP-based or AlGaInN-based semiconductor layers, and may include a first conductivity type semiconductor layer 3330a, an active layer, and a second conductivity type semiconductor layer 3330b. The second substrate may be a substrate on which AlGaInP-based semiconductor layers may be grown thereon, for example, a GaAs substrate, or a substrate on which AlGaInN-based semiconductor layers may be grown thereon, for example, a sapphire substrate. The composition ratio of Al, Ga, and In for the second LED stack 3330 may be determined such that the second LED stack 3330 can emit green light. The second-2 ohmic electrode 3350 forms ohmic contact with the second conductivity type semiconductor layer 3330b, for example, a p-type semiconductor layer. The second-2 ohmic electrode 3350 may include a reflective layer 3350a, which reflects light generated from the second LED stack 3330, and a barrier layer 3350b.

[0468] The second-2 ohmic electrode 3350 is disposed to face the first LED stack 3230 and is coupled to the first LED stack 3230 by the first bonding layer 3530. Thereafter, the second substrate is removed from the second LED stack 3330 to expose the first conductivity type semiconductor layer 3330a by chemical etching or laser lift-off. A roughened surface may be formed on the exposed first conductivity type semiconductor layer 3330a by surface texturing.

[0469] According to an exemplary embodiment, an insulation layer and a reflective layer may be further formed on the first LED stack 3230 before formation of the first bonding layer 3530.

[0470] Referring to FIG. 63A and FIG. 63B, a third LED stack 3430 and a third-2 ohmic electrode 3450 may be coupled to the second LED stack 3330 via the second bonding layer 3550.

[0471] The third LED stack 3430 is grown on a third substrate, and the third-2 ohmic electrode 3450 is formed on the third LED stack 3430. The third LED stack 3430 is formed of AlGaInN-based semiconductor layers, and may include a first conductivity type semiconductor layer 3430a, an active layer, and a second conductivity type semiconductor layer 3430b. The third substrate is a substrate on which GaN-based semiconductor layers may be grown thereon, and is different from the first substrate 3210. The composition ratio of AlGaInN for the third LED stack 3430 may be determined such that the third LED stack 3430 can emit blue light. The third-2 ohmic electrode 3450 forms ohmic contact with the second conductivity type semiconductor layer 3430b, for example, a p-type semiconductor layer. The third-2 ohmic electrode 3450 may include a reflective layer 3450a, which reflects light generated from the third LED stack 3430, and a barrier layer 3450b.

[0472] The third-2 ohmic electrode 3450 is disposed to face the second LED stack 3330 and is coupled to the second LED stack 3330 by the second bonding layer 3550. Thereafter, the third substrate is removed from the third LED stack 3430 to expose the first conductivity type semiconductor layer 3430a by chemical etching or laser lift-off. A roughened surface may be formed on the exposed first conductivity type semiconductor layer 3430a by surface texturing.

[0473] According to an exemplary embodiment, an insulation layer and a reflective layer may be further formed on the second LED stack 3330 before formation of the second bonding layer 3550.

[0474] Referring to FIG. 64A and FIG. 64B, in each of pixel regions, the third LED stack 3430 is patterned to remove the third LED stack 3430 other than in the third subpixel B. In a region of the third subpixel B, an indentation is formed on the third LED stack 3430 to expose the barrier layer 3450b through the indentation.

[0475] Then, in regions other than the third subpixel B, the third-2 ohmic electrode 3450 and the second bonding layer 3550 are removed to expose the second LED stack 3330. As such, the third-2 ohmic electrode 3450 is restrictively placed near the region of the third subpixel B.

[0476] In each pixel region, the second LED stack 3330 is patterned to remove the second LED stack 3330 in regions other than the second subpixel G. In the region of the second subpixel G, the second LED stack 3330 partially overlaps the third LED stack 3430.

[0477] By patterning the second LED stack 3330, the second-2 ohmic electrode 3350 is exposed. The second LED stack 3330 may include an indentation, and the second-2 ohmic electrode 3350, for example, the barrier layer 3350b, may be exposed through the indentation.

[0478] Thereafter, the second-2 ohmic electrode 3350 and the first bonding layer 3530 are removed to expose the first LED stack 3230. As such, the second-2 ohmic electrode 3350 is disposed near the region of the second subpixel G. On the other hand, the first to third through-hole vias 3270a, 3270b, and 3270c are also exposed together with the first LED stack 3230.

[0479] In each pixel region, the first conductivity type semiconductor layer 3230a is exposed by patterning the second conductivity type semiconductor layer 3230b of the first LED stack 3230. As shown in FIG. 64A, the first conductivity type semiconductor layer 3230a may be exposed in an elongated shape, without being limited thereto.

[0480] Furthermore, the pixel regions are divided from one another by patterning the first LED stack 3230. As such, a region of the first subpixel R is defined. Here, the distributed Bragg reflector 3220 may also be divided. Alternatively, the distributed Bragg reflector 3220 may be continuously disposed over the plurality of pixels, rather than being divided. Further, the first conductivity type semiconductor layer 3230a may also be continuously disposed over the plurality of pixels.

[0481] Referring to FIG. 65A and FIG. 65B, a first-1 ohmic electrode 3290a and a first-2 ohmic electrode 3290b are formed on the first LED stack 3230. The first-1 ohmic electrode 3290a may be formed of, for example, Au-Te or Au-Ge alloys on the exposed first conductivity type semiconductor layer 3230a. The first-2 ohmic electrode 3290b may be formed of, for example, Au-Be or Au-Zn alloys on the second conductivity type semiconductor layer 3230b. The first-2 ohmic electrode 3290b may be formed prior to the first-1 ohmic electrode 3290a, or vice versa. The first-2 ohmic electrode 3290b may be connected to the first through-hole via 3270a. On the other hand, the first-1 ohmic electrode 3290a may include a pad region and an extension, which may extend from the pad region towards the first through-hole via 3270a.

[0482] For current spreading, the first-2 ohmic electrode 3290b may be disposed to at least partially surround the first-1 ohmic electrode 3290a. Although each of the first-1 ohmic electrode 3290a and the first-2 ohmic electrode 3290b is being illustrated as having an elongated shape in FIG. 65A, the inventive concepts are not limited thereto. Alternatively, each of the first-1 ohmic electrode 3290a and the first-2 ohmic electrode 3290b may have a circular shape, for example.

[0483] Referring to FIG. 66A and FIG. 66B, an upper insulation layer 3610 is formed to cover the first to third LED stacks 3230, 3330, 3430. The upper insulation layer 3610 may cover the first-1 ohmic electrode 3290a and the first-2 ohmic electrode 3290b. The upper insulation layer 3610 may also cover side surfaces of the first to third LED stacks 3230, 3330, and 3430, and a side surface of the distributed Bragg reflector 3220.

[0484] The upper insulation layer 3610 may have an opening 3610a which exposes the first-1 ohmic electrode 3290a, openings 3610b, 3610c which expose the barrier layers 3350b, 3450b, openings 3610d, 3610e which expose the second and third through-hole vias 3270b, 3270c, and openings 3610f, 3610g which expose the first conductivity type semiconductor layers 3330a, 3430a of the second LED stack 3330 and the third LED stack 3430.

[0485] Referring to FIG. 67A and FIG. 67B, a second-1 ohmic electrode 3390, a third-1 ohmic electrode 3490 and connectors 3710, 3720, 3730 are formed. The second-1 ohmic electrode 3390 is formed in the opening 3610f to form ohmic contact with the first conductivity type semiconductor layer 3330a, and the third-1 ohmic electrode 3490 is formed in the opening 3610g to form ohmic contact with the first conductivity type semiconductor layer 3430a.

[0486] The connector 3710 electrically connects the second-1 ohmic electrode 3390 and the third-1 ohmic electrode 3490 to the first-1 ohmic electrode 3290a. The connector 3710 may be connected to, for example, the first-1 ohmic electrode 3290a exposed in the opening 3610a. The connector 3710 is formed on the upper insulation layer 3610 to be insulated from the second conductivity type semiconductor layers 3230b, 3330b, and 3430b.

[0487] The connector 3720 electrically connects the second-2 ohmic electrode 3350 to the second through-hole via 3270b, and the connector 3730 electrically connects the third-2 ohmic electrode 3450 to the third through-hole via 3270c. The connectors 3720, 3730 are disposed on the upper insulation layer 3610 to prevent short circuit to the first to third LED stacks 3230, 3330, and 3430.

[0488] The second-1 ohmic electrode 3390, the third-1 ohmic electrode 3490, and the connectors 3710, 3720, 3730 may be formed of substantially the same material by the same process. However, the inventive concepts are not limited thereto. Alternatively, the second-1 ohmic electrode 3390, the third-1 ohmic electrode 3490, and the connectors 3710, 3720, 3730 may be formed of different materials by different processes.

[0489] Thereafter, referring to FIG. 68A and FIG. 68B, a lower insulation layer 3750 is formed on a lower surface of the substrate 3210. The lower insulation layer 3750 has openings which expose the first to third the through-hole vias 3270a, 3270b, 3270c, and may also have opening(s) which expose the lower surface of the substrate 3210.

[0490] Electrode pads 3770a, 3770b, 3770c, 3770d are formed on the lower insulation layer 3750. The electrode pads 3770a, 3770b, 3770c are connected to the first to third the through-hole vias 3270a, 3270b, 3270c, respectively, and the electrode pad 3770d is connected to the substrate 3210.

[0491] Accordingly, the electrode pad 3770a is electrically connected to the second conductivity type semiconductor layer 3230b of the first LED stack 3230 through the first through-hole via 3270a, the electrode pad 3770b is electrically connected to the second conductivity type semiconductor layer 3330b of the second LED stack 3330 through the second through-hole via 3270b, and the electrode pad 3770c is electrically connected to the second conductivity type semiconductor layer 3430b of the third LED stack 3430 through the third through-hole via 3270c. The first conductivity type semiconductor layers 3230a, 3330a, 3430a of the first to third LED stacks 3230, 3330, 3430 are commonly electrically connected to the electrode pad 3770d.

[0492] In this manner, a display apparatus according to an exemplary embodiment may be formed by bonding the electrode pads 3770a, 3770b, 3770c, 3770d of the substrate 3210 to the circuit board 3510 shown in FIG. 56. As described above, the circuit board 3510 may include an active circuit or a passive circuit, whereby the display apparatus can be driven in an active matrix manner or in a passive matrix manner.

[0493] FIG. 69 is a cross-sectional view of a light emitting diode pixel for a display not forming part of the invention.

[0494] Referring to FIG. 69, the light emitting diode pixel 3001 of the display apparatus according to an exemplary embodiment is generally similar to the light emitting diode pixel 3000 of the display apparatus of FIG. 57, except that the second LED stack 3330 covers most of the first LED stack 3230 and the third LED stack 3430 covers most of the second LED stack 3330. In this manner, light generated from the first subpixel R is emitted to the outside after substantially passing through the second LED stack 3330 and the third LED stack 3430, and light generated from the second LED stack 3330 is emitted to the outside after substantially passing through the third LED stack 3430.

[0495] The first LED stack 3230 may include an active layer having a narrower bandgap than the second LED stack 3330 and the third LED stack 3430 to emit light having a longer wavelength than the second LED stack 3330 and the third LED stack 3430, and the second LED stack 3330 may include an active layer having a narrower bandgap than the third LED stack 3430 to emit light having a longer wavelength than the third LED stack 3430.

[0496] FIG. 70 is an enlarged top view of one pixel of a display apparatus not forming part of the invention, and FIG. 71A and FIG. 71B are cross-sectional views taken along lines G-G and H-H of FIG. 70, respectively.

[0497] Referring to FIG. 70, FIG. 71A, and FIG. 71B, the pixel according to an exemplary embodiment is generally similar to the pixel of FIG. 59, FIG. 60A, FIG. 60B, and FIG. 60C, except that the second LED stack 3330 covers most of the first LED stack 3230 and the third LED stack 3430 covers most of the second LED stack 3330. The first to third through-hole vias 3270a, 3270b, 3270c may be disposed outside the second LED stack 3330 and the third LED stack 3430.

[0498] In addition, a portion of the first-1 ohmic electrode 3290a and a portion of the second-1 ohmic electrode 3390 may be disposed under the third LED stack 3430. As such, the first-1 ohmic electrode 3290a may be formed before the second LED stack 3330 is coupled to the first LED stack 3230, and the second-1 ohmic electrode 3390 may also be formed before the third LED stack 3430 is coupled to the second LED stack 3330.

[0499] Furthermore, light generated from the first LED stack 3230 is emitted to the outside after substantially passing through the second LED stack 3330 and the third LED stack 3430, and light generated from the second LED stack 3330 is emitted to the outside after substantially passing through the third LED stack 3430. Accordingly, the first bonding layer 3530 and the second bonding layer 3550 are formed of light transmissive materials, and the second-2 ohmic electrode 3350 and the third-2 ohmic electrode 3450 are composed of transparent conductive layers.

[0500] On the other hand, as shown in FIGS. 71A and 71B, an indentation may be formed on the third LED stack 3430 to expose the third-2 ohmic electrode 3450, and an indentation is continuously formed on the third LED stack 3430 and the second LED stack 3330 to expose the second-2 ohmic electrode 3350. The second-2 ohmic electrode 3350 and the third-2 ohmic electrode 3450 are electrically connected to the second through-hole via 3270b, and the third through-hole via 3270c through the connectors 3720, 3730, respectively.

[0501] Furthermore, the indentation may be formed on the third LED stack 3430 to expose the second-1 ohmic electrode 3390 formed on the first conductivity type semiconductor layer 3330a of the second LED stack 3330, and the indentation may be continuously formed on the third LED stack 3430 and the second LED stack 3330 to expose the first-1 ohmic electrode 3290a formed on the first conductivity type semiconductor layer 3230a of the first LED stack 3230. The connector 3710 may connect the first-1 ohmic electrode 3290a and the second-1 ohmic electrode 3390 to the third-1 ohmic electrode 3490. The third-1 ohmic electrode 3490 may be formed together with the connector 3710 and may be connected to the pad regions of the first-1 ohmic electrode 3290a and the second-1 ohmic electrode 3390.

[0502] The first-1 ohmic electrode 3290a and the second-1 ohmic electrode 3390 are partially disposed under the third LED stack 3430, but the inventive concepts are not limited thereto. For example, the portions of the first-1 ohmic electrode 3290a and the second-1 ohmic electrode 3390 disposed under the third LED stack 3430 may be omitted. Furthermore, the second-1 ohmic electrode 3390 may be omitted and the connector 3710 may form ohmic contact with the first conductivity type semiconductor layer 3330a.

[0503] According to exemplary embodiments, a plurality of pixels may be formed at the wafer level through wafer bonding, and thus, the process of individually mounting light emitting diodes may be obviated or substantially reduced.

[0504] Furthermore, since the through-hole vias 3270a, 3270b, 3270c are formed in the substrate 3210 and used as current paths, the substrate 3210 may not need to be removed. Accordingly, a growth substrate used for growth of the first LED stack 3230 can be used as the substrate 3210 without being removed from the first LED stack 3230.

[0505] FIG. 72 is a schematic cross-sectional view of a light emitting diode (LED) stack for a display not forming part of the invention.

[0506] Referring to FIG. 72, the light emitting diode stack 4000 for a display may include a support substrate 4051, a first LED stack 4023, a second LED stack 4033, a third LED stack 4043, a reflective electrode 4025, an ohmic electrode 4026, a first insulating layer 4027, a second insulating layer 4028, a interconnection line 4029, a second-p transparent electrode 4035, a third-p transparent electrode 4045, a first color filter 4037, a second color filter 4047, hydrophilic material layers 4052, 4054, and 4056, a first bonding layer 4053 (a lower bonding layer), a second bonding layer 4055 (an intermediate bonding layer), and a third bonding layer 4057 (an upper bonding layer).

[0507] The support substrate 4051 supports semiconductor stacks 4023, 4033, and 4043. The support substrate 4051 may have a circuit on a surface thereof or an inside thereof, but is not limited thereto. The support substrate 4051 may include, for example, a glass, a sapphire substrate, a Si substrate, or a Ge substrate.

[0508] The first LED stack 4023, the second LED stack 4033, and the third LED stack 4043 each include first conductivity type semiconductor layers 4023a, 4033a, and 4043a, second conductivity type semiconductor layers 4023b, 4033b, and 4043b, and active layers interposed between the first conductivity type semiconductor layers and the second conductivity type semiconductor layers. The active layer may have a multiple quantum well structure.

[0509] The first LED stack 4023 may be an inorganic LED that emits red light, the second LED stack 4033 may be an inorganic LED that emits green light, and the third LED stack 4043 may be an inorganic LED that emits blue light. The first LED stack 4023 may include a GaInP-based well layer, and the second LED stack 4033 and the third LED stack 4043 may include a GaInN-based well layer. However, the inventive concepts are limited thereto, and when the LED stacks include micro LEDs, the first LED stack 4023 may emit any one of red, green, and blue light, and the second and third LED stacks 4033 and 4043 may emit a different one of the red, green, and blue light without adversely affecting operation or requiring color filters due to its small form factor.

[0510] Opposite surfaces of each LED stack 4023, 4033, or 4043 are an n-type semiconductor layer and a p-type semiconductor layer, respectively. The illustrated exemplary embodiment describes a case in which the first conductivity type semiconductor layers 4023a, 4033a, and 4043a of each of the first to third LED stacks 4023, 4033, and 4043 are n-type, and the second conductivity type semiconductor layers 4023b, 4033b, and 4043b thereof are p-type. A roughened surface may be formed on upper surfaces of the first to third LED stacks 4023, 4033, and 4043. However, the inventive concepts are not limited thereto, and the type of the semiconductor types of the upper surface and the lower surface of each of the LED stacks may be reversed.

[0511] The first LED stack 4023 is disposed to be adjacent to the support substrate 4051, the second LED stack 4033 is disposed on the first LED stack 4023, and the third LED stack 4043 is disposed on the second LED stack 4033. Since the first LED stack 4023 emits light of the wavelength longer than the wavelengths of the second and third LED stacks 4033 and 4043, light generated in the first LED stack 4023 may be transmitted through the second and third LED stacks 4033 and 4043 and may be emitted to the outside. In addition, since the second LED stack 4033 emits light of the wavelength longer than the wavelength of the third LED stack 4043, light generated in the second LED stack 4033 may be transmitted through the third LED stack 4043 and may be emitted to the outside.

[0512] The reflective electrode 4025 is in ohmic contact with the second conductivity type semiconductor layer of the first LED stack 4023 and reflects light generated in the first LED stack 4023. For example, the reflective electrode 4025 may include an ohmic contact layer 4025a and a reflective layer 4025b.

[0513] The ohmic contact layer 4025a is partially in contact with the second conductivity type semiconductor layer, that is, a p-type semiconductor layer. In order to prevent light absorption by the ohmic contact layer 4025a, an area in which the ohmic contact layer 4025a is in contact with the p-type semiconductor layer may not exceed about 50% of a total area of the p-type semiconductor layer. The reflective layer 4025b covers the ohmic contact layer 4025a and also covers the first insulating layer 4027. As illustrated, the reflective layer 4025b may substantially cover the entirety of the ohmic contact layer 4025a, or a portion of the ohmic contact layer 4025a.

[0514] The reflective layer 4025b covers the first insulating layer 4027, such that an omnidirectional reflector may be formed by a stack of the first LED stack 4023 having a relatively high refractive index and the first insulating layer 4027 and the reflective layer 4025b having a relatively low refractive index. The reflective layer 4025b covers about 50% or more of the area of the first LED stack 4023, preferably, most of the region of the first LED stack 4023, thereby improving light efficiency.

[0515] The ohmic contact layer 4025a and the reflective layer 4025b may be formed of a metal layer containing gold (Au). The ohmic contact layer 4025a may be formed of, for example, an Au-Zn alloy or an Au-Be alloy. The reflective layer 4025b may be formed of a metal layer having high reflectivity with respect to light generated in the first LED stack 4023, for example, red light, such as aluminum (Al), silver (Ag), or gold (Au). In particular, Au may have relatively low reflectivity with respect to light generated in the second LED stack 4033 and the third LED stack 4043, for example, green light or blue light, and thus, may reduce light interference by absorbing light generated in the second and third LED stacks 4033 and 4043 and traveling toward the support substrate 4051.

[0516] The first insulating layer 4027 is disposed between the support substrate 4051 and the first LED stack 4023, and has an opening exposing the first LED stack 4023. The ohmic contact layer 4025a is connected to the first LED stack 4023 within the opening of the first insulating layer 4027.

[0517] The ohmic electrode 4026 is in ohmic contact with the first conductivity type semiconductor layer 4023a of the first LED stack 4023. The ohmic electrode 4026 may be disposed on the first conductivity type semiconductor layer 4023a exposed by partially removing the second conductivity type semiconductor layer 4023b. Although FIG. 72 illustrates one ohmic electrode 4026, a plurality of ohmic electrodes 4026 are aligned on a plurality of regions on the support substrate 4051. The ohmic electrode 4026 may be formed of, for example, an Au-Te alloy or an Au-Ge alloy.

[0518] The second insulating layer 4028 is disposed between the support substrate 4051 and the reflective electrode 4025 to cover the reflective electrode 4025. The second insulating layer 4028 has an opening exposing the ohmic electrode 4026. The second insulating layer 4028 may be formed of Si02 or SOG.

[0519] The interconnection line 4029 is disposed between the second insulating layer 4028 and the support substrate 4051, and is connected to the ohmic electrode 4026 through the opening of the second insulating layer 4028. The interconnection line 4026 may connect a plurality of ohmic electrodes 4026 to one another on the support substrate 4051.

[0520] The second-p transparent electrode 4035 is in ohmic contact with the second conductivity type semiconductor layer 4033b of the second LED stack 4033, that is, the p-type semiconductor layer. The second-p transparent electrode 4035 may be formed of a metal layer or a conductive oxide layer which is transparent to red light and green light.

[0521] The third-p transparent electrode 4045 is in ohmic contact with the second conductivity type semiconductor layer 4043b of the third LED stack 4043, that is, the p-type semiconductor layer. The third-p transparent electrode 4045 may be formed of a metal layer or a conductive oxide layer which is transparent to red light, green light, and blue light.

[0522] The reflective electrode 4025, the second-p transparent electrode 4035, and the third-p transparent electrode 4045 may be in ohmic contact with the p-type semiconductor layer of each LED stack to assist in current dispersion.

[0523] The first color filter 4037 may be disposed between the first LED stack 4023 and the second LED stack 4033. In addition, the second color filter 4047 may be disposed between the second LED stack 4033 and the third LED stack 4043. The first color filter 4037 transmits light generated in the first LED stack 4023 and reflects light generated in the second LED stack 4033. The second color filter 4047 transmits light generated in the first and second LED stacks 4023 and 4033 and reflects light generated in the third LED stack 4043. Accordingly, light generated in the first LED stack 4023 may be emitted to the outside through the second LED stack 4033 and the third LED stack 4043, and light generated in the second LED stack 4033 may be emitted to the outside through the third LED stack 4043. Further, it is possible to prevent light generated in the second LED stack 4033 from being incident on the first LED stack 4023 and lost, or light generated in the third LED stack 4043 from being incident on the second LED stack 4033 and lost.

[0524] According to some exemplary embodiments, the first color filter 4037 may also reflect light generated in the third LED stack 4043. According to some exemplary embodiments, when the LED stacks include micro LEDs, the color filters may be omitted due to the small form factor of the micro LEDs.

[0525] The first and second color filters 4037 and 4047 may be, for example, a low pass filter that passes only a low frequency region, that is, a long wavelength region, a band pass filter that passes only a predetermined wavelength band, or a band stop filter that blocks only the predetermined wavelength band. In particular, the first and second color filters 4037 and 4047 may be formed by alternately stacking insulating layers having different refractive indices, and may be formed by alternately stacking, for example, Ti02 and Si02, Ta205 and Si02, Nb205 and Si02, Hf02 and Si02, or Zr02 and SiO2. Further, the first and / or second color filter 4037 and / or 4047 may include a distributed Bragg reflector (DBR). The distributed Bragg reflector may be formed by alternately stacking insulating layers having different refractive indices. Further, a stop band of the distributed Bragg reflector may be controlled by adjusting a thickness of Ti02 and Si02.

[0526] The first bonding layer 4053 couples the first LED stack 4023 to the support substrate 4051. As illustrated, the interconnection line 4029 may be in contact with the first bonding layer 4053. In addition, the interconnection line 4029 is disposed below some regions of the second insulating layer 4028, and a region of the second insulating layer 4028 that does not have the interconnection line 4029 may be in contact with the first bonding layer 4053. The first bonding layer 4053 may be light transmissive or light non-transmissive. In particular, a contrast of the display apparatus may be improved by using an adhesive layer that absorbs light, such as black epoxy, as the first bonding layer 4053.

[0527] The first bonding layer 4053 may be in direct contact with the support substrate 4051, but as illustrated, the hydrophilic material layer 4052 may be disposed on an interface between the support substrate 4051 and the first bonding layer 4053. The hydrophilic material layer 4052 may change a surface of the support substrate 4051 to be hydrophilic to improve adhesion of the first bonding layer 4053. As used herein, the bonding layer and the hydrophilic material layer may collectively be referred to as a buffer layer.

[0528] The first bonding layer 4053 has a strong adhesion to the hydrophilic material layer, while it has a weak adhesion to a hydrophobic material layer. Therefore, peeling may occur at a portion in which the adhesion is weak. The hydrophilic material layer 4052 according to an exemplary embodiment may change a hydrophobic surface to be hydrophilic to enhance the adhesion of the first bonding layer 4053, thereby preventing the occurrence of the peeling.

[0529] The hydrophilic material layer 4052 may also be formed by depositing, for example, Si02, or others on the surface of the support substrate 4051, and may also be formed by treating the surface of the support substrate 4051 with plasma to modify the surface. The surface modified layer increases surface energy to change hydrophobic property into hydrophilic property. In a case in which the second insulating layer 4028 has hydrophobic property, the hydrophilic material layer may also be disposed on the second insulating layer 4028, and the first bonding layer 4052 may be in contact with the hydrophilic material layer on the second insulating layer 4028.

[0530] The second bonding layer 4055 couples the second LED stack 4033 to the first LED stack 4023. The second bonding layer 4055 may be disposed between the first LED stack 4023 and the first color filter 4037 and may be in contact with the first color filter 4037. The second bonding layer 4055 may transmit light generated in the first LED stack 4023. A hydrophilic material layer 4054 may be disposed in an interface between the first LED stack 4023 and the second bonding layer 4055. The first conductivity type semiconductor layer 4023a of the first LED stack 4023 generally exhibits hydrophobic property. Therefore, in a case in which the second bonding layer 4055 is in direct contact with the first conductivity type semiconductor layer 4023a, the peeling is likely to occur at an interface between the second bonding layer 4055 and the first conductivity type semiconductor layer 4023a.

[0531] The hydrophilic material layer 4054 according to an exemplary embodiment changes the surface of the first LED stack 4023 from having hydrophobic properties to having hydrophilic properties, and thus, improves the adhesion of the second bonding layer 4055, thereby reducing or preventing the occurrence of the peeling. The hydrophilic material layer 4054 may be formed by depositing Si02 or modifying the surface of the first LED stack 4023 with plasma as described above.

[0532] A surface layer of the first color filter 4037 which is in contact with the second bonding layer 4055 may be a hydrophilic material layer, for example, Si02. In a case in which the surface layer of the first color filter 4037 is not hydrophilic, the hydrophilic material layer may be formed on the first color filter 4037, and the second bonding layer 4055 may be in contact with the hydrophilic material layer.

[0533] The third bonding layer 4057 couples the third LED stack 4043 to the second LED stack 4033. The third bonding layer 4057 may be disposed between the second LED stack 4033 and the second color filter 4047 and may be in contact with the second color filter 4047. The third bonding layer 4057 transmits light generated in the first LED stack 4023 and the second Led stack 4033. A hydrophilic material layer 4056 may be disposed in an interface between the second LED stack 4033 and the third bonding layer 4057. The second LED stack 4033 may exhibit hydrophobic property, and as a result, in a case in which the third bonding layer 4057 is in direct contact with the second LED stack 4033, the peeling is likely to occur at an interface between the third bonding layer 4057 and the second LED stack 4033.

[0534] The hydrophilic material layer 4056 according to an exemplary embodiment changes the surface of the second LED stack 4033 from hydrophobic property into hydrophilic property, and thus, improves the adhesion of the third bonding layer 4057, thereby preventing the occurrence of the peeling. The hydrophilic material layer 4056 may be formed by depositing Si02 or modifying the surface of the second LED stack 4033 with plasma as described above.

[0535] A surface layer of the second color filter 4047 which is in contact with the third bonding layer 4057 may be a hydrophilic material layer, for example, Si02. In a case in which the surface layer of the second color filter 4047 is not hydrophilic, the hydrophilic material layer may be formed on the second color filter 4047 and the third bonding layer 4057 may be in contact with the hydrophilic material layer.

[0536] The first to third bonding layers 4053, 4055, and 4057 may be formed of light transmissive SOC, but is not limited thereto, and other transparent organic material layers or transparent inorganic material layers may be used. Examples of the organic material layer may include SU8, poly (methylmethacrylate) (PMMA), polyimide, parylene, benzocyclobutene (BCB), or others, and examples of the inorganic material layer may include Al203, Si02, SiNx, or others. The organic material layers may be bonded at high vacuum and high pressure, and the inorganic material layers may be bonded by planarizing a surface with, for example, a chemical mechanical polishing process, changing surface energy using plasma or others, and then using the changed surface energy.

[0537] FIGS. 73A to 73F are schematic cross-sectional views illustrating a method of manufacturing the light emitting diode stack 4000 for a display not forming part of the invention.

[0538] Referring to FIG. 73A, a first LED stack 4023 is first grown on a first substrate 4021. The first substrate 4021 may be, for example, a GaAs substrate. The first LED stack 4023 is formed of an AlGaInP based semiconductor layers, and includes a first conductivity type semiconductor layer 4023a, an active layer, and a second conductivity type semiconductor layer 4023b.

[0539] Next, the second conductivity type semiconductor layer 4023b is partially removed to expose the first conductivity type semiconductor layer 4023a. Although FIG. 73A shows only one pixel region, the first conductivity type semiconductor layer 4023a is partially exposed for each of the pixel regions.

[0540] A first insulating layer 4027 is formed on the first LED stack 4023 and is patterned to form openings. For example, Si02 is formed on the first LED stack 4023, a photoresist is applied thereto, and a photoresist pattern is formed through photolithograph and development. Next, the first insulating layer 4027 in which the openings are formed may be formed by patterning Si02 using the photoresist pattern as an etching mask. One of the openings of the first insulating layer 4027 may be disposed on the first conductivity type semiconductor layer 4023a, and other openings may be disposed on the second conductivity type semiconductor layer 4023b.

[0541] Thereafter, an ohmic contact layer 4025a and an ohmic electrode 4026 are formed in the openings of the first insulating layer 4027. The ohmic contact layer 4025a and the ohmic electrode 4026 may be formed using a lift-off technique. The ohmic contact layer 4025a may be first formed and the ohmic electrode 4026 may be then formed, or vice versa. In addition, according to an exemplary embodiment, the ohmic electrode 4026 and the ohmic contact layer 4025a may be simultaneously formed of the same material layer.

[0542] After the ohmic contact layer 4025a is formed, a reflective layer 4025b covering the ohmic contact layer 4025a and the first insulating layer 4027 is formed. The reflective layer 4025b may be formed using a lift-off technique. The reflective layer 4025b may also cover a portion of the ohmic contact layer 4025a, and may also cover substantially the entirety of the ohmic contact layer 4025a as illustrated. A reflective electrode 4025 is formed by the ohmic contact layer 4025a and the reflective layer 4025b.

[0543] The reflective electrode 4025 may be in ohmic contact with a p-type semiconductor layer of the first LED stack 4023, and may be thus referred to as a first p-type reflective electrode 4025. The reflective electrode 4025 is spaced apart from the ohmic electrode 4026, and is thus electrically insulated from the first conductivity type semiconductor layer 4023a.

[0544] A second insulating layer 4028 covering the reflective electrode 4025 and having an opening exposing the ohmic electrode 4026 is formed. The second insulating layer 4028 may be formed of, for example, Si02 or SOG.

[0545] Then, a interconnection line 4029 is formed on the second insulating layer 4028. The interconnection line 4029 is connected to the ohmic electrode 4026 through the opening of the second insulating layer 4028, and is thus electrically connected to the first conductivity type semiconductor layer 4023a.

[0546] Although the interconnection line 4029 is illustrated in FIG. 73A as covering the entire surface of the second insulating layer 4028, the interconnection line 4029 may be partially disposed on the second insulating layer 4028, and an upper surface of the second insulating layer 4028 may be exposed around the interconnection line 4029.

[0547] Although the illustrated exemplary embodiment shows one pixel region, the first LED stack 4023 disposed on the substrate 4021 may cover a plurality of pixel regions, and the interconnection line 4029 may be commonly connected to the ohmic electrodes 4026 formed on a plurality of regions. In addition, a plurality of interconnection lines 4029 may be formed on the substrate 4021.

[0548] Referring to FIG. 73B, a second LED stack 4033 is grown on a second substrate 4031 and a second-p transparent electrode 4035 and a first color filter 4037 are formed on the second LED stack 4033. The second LED stack 4033 may include a gallium nitride-based first conductivity type semiconductor layer 4033a, a second conductivity type semiconductor layer 4033b, and an active layer disposed therebetween, and the active layer may include a GaInN well layer. The second substrate 4031 is a substrate on which a gallium nitride-based semiconductor layer may be grown, and is different from the first substrate 4021. A combination ratio of GaInN may be determined so that the second LED stack 4033 may emit green light. The second-p transparent electrode 4035 is in ohmic contact with the second conductivity type semiconductor layer 4033b.

[0549] The first color filter 4037 may be formed on the second-p transparent electrode 4035, and since details thereof are substantially the same as those described with reference to FIG. 72, detailed descriptions thereof will be omitted in order to avoid redundancy.

[0550] Referring to FIG. 73C, a third LED stack 4043 is grown on a third substrate 4041 and a third-p transparent electrode 4045 and a second color filter 4047 are formed on the third LED stack 4043. The third LED stack 4043 may include a gallium nitride-based first conductivity type semiconductor layer 4043a, a second conductivity type semiconductor layer 4043b, and an active layer disposed therebetween, and the active layer may include a GaInN well layer. The third substrate 4041 is a substrate on which a gallium nitride-based semiconductor layer may be grown, and is different from the first substrate 4021. A combination ratio of GaInN may be determined so that the third LED stack 4043 emits blue light. The third-p transparent electrode 4045 is in ohmic contact with the second conductivity type semiconductor layer 4043b.

[0551] Since the second color filter 4047 is substantially the same as that described with reference to FIG. 72, detailed descriptions thereof will be omitted in order to avoid redundancy.

[0552] Meanwhile, since the first LED stack 4023, the second LED stack 4033, and the third LED stack 4043 are grown on different substrates, the order of formation thereof is not particularly limited.

[0553] Referring to FIG. 73D, next, the first LED stack 4023 is coupled onto a support substrate 4051 through the first bonding layer 4053. Bonding material layers may be disposed on the support substrate 4051 and the second insulating layer 4028 and may be bonded to each other to form the first bonding layer 4053. The interconnection line 4029 is disposed to face the support substrate 4051.

[0554] Meanwhile, in a case in which a surface of the support substrate 4051 has hydrophobic property, a hydrophilic material layer 4052 may be first formed on the support substrate 4051. The hydrophilic material layer 4052 may also be formed by depositing a material layer such as Si02 on the surface of the support substrate 4051, or treating the surface of the support substrate 4051 with plasma or the like to increase surface energy. The surface of the support substrate 4051 is modified by the plasma treatment, and a surface modified layer having high surface energy may be formed on the surface of the support substrate 4051. The first bonding layer 4053 may be bonded to the hydrophilic material layer 4052, and adhesion of the first bonding layer 4053 is thus improved.

[0555] The first substrate 4021 is removed from the first LED stack 4023 using a chemical etching technique. Accordingly, the first conductivity type semiconductor layer of the first LED stack 4023 is exposed on the top surface. The exposed surface of the first conductivity type semiconductor layer 4023a may be textured to increase light extraction efficiency, and a light extraction structure, such as a roughened surface or others, may be thus formed on the surface of the first conductivity type semiconductor layer 4023a.

[0556] Referring to FIG. 73E, the second LED stack 4033 is coupled to the first LED stack 4023 through the second bonding layer 4055. The first color filter 4037 is disposed to face the first LED stack 4023 and is bonded to the second bonding layer 4055. The bonding material layers are disposed on the first LED stack 4023 and the first color filter 4037 and are bonded to each other to form the second bonding layer 4055.

[0557] Meanwhile, before the second bonding layer 4055 is formed, a hydrophilic material layer 4054 may be first formed on the first LED stack 4023. The hydrophilic material layer 4054 changes the surface of the first LED stack 4023 from having a hydrophobic property to a hydrophilic property and thus improves the adhesion of the second bonding layer 4055. The hydrophilic material layer 4054 may also be formed by depositing a material layer such as Si02, or treating the surface of the first LED stack 4023 with plasma or others to increase surface energy. The surface of the first LED stack 4023 is modified by the plasma treatment, and a surface modified layer having high surface energy may be formed on the surface of the first LED stack 4023. The second bonding layer 4055 may be bonded to the hydrophilic material layer 4054, and adhesion of the second bonding layer 4055 is thus improved.

[0558] The second substrate 4031 may be separated from the second LED stack 4033 using a technique such as a laser lift-off or a chemical lift-off. In addition, in order to improve light extraction, a roughened surface may be formed on the exposed surface of the first conductivity type semiconductor layer 4033a using a surface texturing.

[0559] Referring to FIG. 73F, a hydrophilic material layer 4056 may be then formed on the second LED stack 4033. The hydrophilic material layer 4056 changes the surface of the second LED stack 4033 to a hydrophilic property and thus improves adhesion of the third bonding layer 4057. The hydrophilic material layer 4056 may also be formed by depositing a material layer such as Si02, or treating the surface of the second LED stack 4033 with plasma or the like to increase surface energy. However, in a case in which the surface of the second LED stack 4033 has a hydrophilic property, the hydrophilic material layer 4056 may be omitted.

[0560] Next, referring to FIGS. 72 and 73C, the third LED stack 4043 is coupled onto the second LED stack 4033 through the third bonding layer 4057. The second color filter 4047 is disposed to face the second LED stack 4033 and is bonded to the third bonding layer 4057. The bonding material layers are disposed on the second LED stack 4033 (or the hydrophilic material layer 4056) and the third color filter 4047, and are bonded to each other to form the third bonding layer 4057.

[0561] The third substrate 4041 may be separated from the third LED stack 4043 using a technique such as a laser lift-off or a chemical lift-off. Accordingly, as illustrated in FIG. 72, the LED stack for a display in which the first conductive layer 4043a of the third LED stack 4043 is exposed is provided. In addition, a roughened surface may be formed on the exposed surface of the first conductivity type semiconductor layer 4043a by a surface texturing.

[0562] A stack of the first to third LED stacks 4023, 4033, and 4043 disposed on the support substrate 4051 is patterned in a unit of pixel, and the patterned stacks are connected to each other using the interconnection lines, thereby making it possible to provide a display apparatus. Hereinafter, a display apparatus according to exemplary embodiments will be described.

[0563] FIG. 74 is a schematic circuit diagram of a display apparatus not forming part of the invention, and FIG. 75 is a schematic plan view of a display apparatus not forming part of the invention.

[0564] Referring to FIGS. 74 and 75, the display apparatus according to an exemplary embodiment may be implemented to be driven in a passive matrix manner.

[0565] For example, since the LED stack for a display described with reference to FIG. 72 has a structure in which the first to third LED stacks 4023, 4033, and 4044 are stacked in a vertical direction, one pixel includes three light emitting diodes R, G, and B. Here, a first light emitting diode R may correspond to the first LED stack 4023, a second light emitting diode G may correspond to the second LED stack 4033, and a third light emitting diode B may correspond to the third LED stack 4043.

[0566] In FIGS. 74 and 75, one pixel includes the first to third light emitting diodes R, G, and B, and each light emitting diode corresponds to a sub-pixel. Anodes of the first to third light emitting diodes R, G, and B are connected to a common line, for example, a data line, and cathodes thereof are connected to different lines, for example, scan lines. For a first pixel, as an example, the anodes of the first to third light emitting diodes R, G, and B are commonly connected to a data line Vdata1, and cathodes thereof are connected to scan lines Vscan1-1, Vscan1-2, and Vscan1-3, respectively. Accordingly, the light emitting diodes R, G, and B in the same pixel may be separately driven.

[0567] In addition, each of the light emitting diodes R, G, and B may be driven by using pulse width modulation or change current intensity, thereby making it possible to adjust brightness of each sub-pixel.

[0568] Referring to again FIG. 75, a plurality of patterns are formed by patterning the stack described with reference to FIG. 72, and the respective pixels are connected to reflective electrodes 4025 and interconnection lines 4071, 4073, and 4075. As illustrated in FIG. 74, the reflective electrode 4025 may be used as a data line Vdata, and the interconnection lines 4071, 4073, and 4075 may be formed as the scan lines. Here, the interconnection line 4075 may be formed by the interconnection line 4029. The reflective electrode 4025 may electrically connect the first conductivity type semiconductor layers 4023a, 4033a, and 4043a of the first to third LED stacks 4023, 4033, and 4043 of the plurality of pixels to one another, and the interconnection line 4029 may be disposed to be substantially perpendicular to the reflective electrode 4025 to electrically connect the first conductivity type semiconductor layers 4023a of the plurality of pixels to each other.

[0569] The pixels may be arranged in a matrix form, and the anodes of the light emitting diodes R, G, and B of each pixel are commonly connected to the reflective electrode 4025 and the cathodes thereof are each connected to the interconnection lines 4071, 4073, and 4075 which are spaced apart from each other. Here, the interconnection lines 4071, 4073, and 4075 may be used as scan lines Vscan.

[0570] FIG. 76 is an enlarged plan view of one pixel of the display apparatus of FIG. 75, FIG. 77 is a schematic cross-sectional view taken along line A-A of FIG. 76, and FIG. 78 is a schematic cross-sectional view taken along line B-B of FIG. 76.

[0571] Referring back to FIGS. 75 to 78, in each pixel, a portion of the reflective electrode 4025, a portion of the second-p transparent electrode 4035, a portion of an upper surface of the second LED stack 4033, a portion of the third-p transparent electrode 4045, and an upper surface of the third LED stack 4043 are exposed to the outside.

[0572] The third LED stack 4043 may have a roughened surface 4043r formed on the upper surface thereof. The roughened surface 4043r may also be formed on the entirety of the upper surface of the third LED stack 4043, or on a portion of the upper surface of the third LED stack 4043.

[0573] A lower insulating layer 4061 may cover a side surface of each pixel. The lower insulating layer 4061 may be formed of a light transmissive material such as Si02, and in this case, the lower insulating layer 4061 may also cover substantially the entirety of the upper surface of the third LED stack 4043. Alternatively, the lower insulating layer 4061 according to an exemplary embodiment may include a light reflective layer or a light absorption layer to prevent light traveling from the first to third LED stacks 4023, 4033, and 4043 to the side surface, and in this case, the lower insulating layer 4061 at least partially exposes the upper surface of the third LED stack 4043. The lower insulating layer 4061 may include, for example, a distribution Bragg reflector or a metallic reflective layer, or an organic reflective layer on a transparent insulating layer, and may also include a light absorption layer such as black epoxy. The light absorption layer, such as black epoxy, may prevent light from being emitted to the outside of the pixels, thereby improving a contrast ratio between the pixels in the display apparatus.

[0574] The lower insulating layer 4061 may have an opening 4061a exposing the upper surface of the third LED stack 4043, an opening 4061b exposing the upper surface of the second LED stack 4033, an opening 4061c exposing the third-p transparent electrode 4045, an opening 4061d exposing the second-p transparent electrode 4035, and an opening 4061e exposing the first p-type reflective electrode 4025. The upper surface of the first LED stack 4023 may not be exposed to the outside.

[0575] The interconnection line 4071 and the interconnection line 4073 may be formed on the support substrate 4051 in the vicinity of the first to third LED stacks 4023, 4033, and 4043, and may be disposed on the lower insulating layer 4061 to be insulated from the first p-type reflective electrode 4025. A connector 4077ab connects the second-p transparent electrode 4035 and the third-p transparent electrode 4045 to the reflective electrode 4025. Accordingly, the anodes of the first LED stack 4023, the second LED stack 4033, and the third LED stack 4043 are commonly connected to the reflective electrode 4025.

[0576] The interconnection line 4075 or 4029 may be disposed to be substantially perpendicular to the reflective electrode 4025 below the reflective electrode 4025, and is connected to the ohmic electrode 4026, thereby being electrically connected to the first conductivity type semiconductor layer 4023a. The ohmic electrode 4026 is connected to the first conductivity type semiconductor layer 4023a below the first LED stack 4023. The ohmic electrode 4026 may be disposed outside a lower region of the roughened surface 4043r of the third LED stack 4043 as illustrated in FIG. 76, and light loss may be thus reduced.

[0577] The connector 4071a connects the upper surface of the third LED stack 4043 to the interconnection line 4071, and the connector 4073a connects the upper surface of the second LED stack 4033 to the interconnection line 4073.

[0578] An upper insulating layer 4081 may be disposed on the interconnection lines 4071 and 4073 and the lower insulating layer 4061 to protect the interconnection lines 4071, 4073, and 4075. The upper insulating layer 4081 may have openings that expose the interconnection lines 4071, 4073, and 4075, and a bonding wire and the like may be connected thereto through the openings.

[0579] According to an exemplary embodiment, the anodes of the first to third LED stacks 4023, 4033, and 4043 are commonly and electrically connected to the reflective electrode 4025, and the cathodes thereof are electrically connected to the interconnection lines 4071, 4073, and 4075, respectively. Accordingly, the first to third LED stacks 4023, 4033, and 4043 may be independently driven. However, the inventive concepts are not limited thereto, and connections of the electrodes and wirings can be variously modified.

[0580] FIGS. 79A to 79H are schematic plan views for describing a method for manufacturing a display apparatus not forming part of the invention. Hereinafter, a method for manufacturing the pixel of FIG. 76 will be described.

[0581] First, the light emitting diode stack 4000 as described with reference to FIG. 72 is prepared.

[0582] Next, referring to FIG. 79A, the roughened surface 4043r may be formed on the upper surface of the third LED stack 4043. The roughened surface 4043r may be formed to correspond to each pixel region on the upper surface of the third LED stack 4043. The roughened surface 4043r may be formed using a chemical etching technique, for example, using a photo-enhanced chemical etch (PEC) technique.

[0583] The roughened surface 4043r may be partially formed within each pixel region in consideration of a region in which the third LED stack 4043 is to be etched in the future. In particular, the roughened surface 4043r may be formed so that the ohmic electrode 4026 is disposed outside the roughened surface 4043r. However, the inventive concepts are limited thereto, and the roughened surface 4043r may also be formed over substantially the entirety of the upper surface of the third LED stack 4043.

[0584] Referring to FIG. 79B, a peripheral region of the third LED stack 4043 is then etched in each pixel region to expose the third-p transparent electrode 4045. The third LED stack 4043 may be left to have substantially a rectangular or square shape as illustrated, but at least two depression parts may be formed along the edges. In addition, as illustrated, one depression part may be formed to be greater than another depression part.

[0585] Referring to FIG. 79C, the exposed third-p transparent electrode 4045 is then removed except for a portion of the third-p transparent electrode 4045 exposed in a relatively large depression part, to thereby expose the upper surface of the second LED stack 4033. The upper surface of the second LED stack 4033 is exposed around the third LED stack 4043 and is also exposed in another depression part. A region in which the third-p transparent electrode 4045 is exposed and a region in which the second LED stack 4033 is exposed are formed in the relatively large depression part.

[0586] Referring to FIG. 79D, the second LED stack 4033 exposed in the remaining region is removed except for the second LED stack 4033 formed in a relatively small depression part to thereby expose the second-p transparent electrode 4035. The second-p transparent electrode is exposed around the third LED stack 4043 and the second-p transparent electrode 4035 is also exposed in the relatively large depression part.

[0587] Referring to FIG. 79E, the second-p transparent electrode 4035 exposed around the second LED stack 4043 is then removed except for the second-p transparent electrode 4035 exposed in the relatively large depression part, to thereby expose the upper surface of the first LED stack 4023.

[0588] Referring to FIG. 79F, the first LED stack 4023 exposed around the third LED stack 4043 continues to be removed and the first insulating layer 4027 is removed to thereby expose the reflective electrode 4025. Accordingly, the reflective electrode 4025 is exposed around the third LED stack 4043. The exposed reflective electrode 4025 is patterned so as to have substantially an elongated shape in a vertical direction to thereby form a linear interconnection line. The patterned reflective electrode 4025 is disposed over the plurality of pixel regions in the vertical direction and is spaced apart from a neighboring pixel in a horizontal direction.

[0589] In the illustrated exemplary embodiment, it is described the reflective electrode 4025 is patterned after removing the first LED stack 4023, but the reflective electrode 4025 may also be formed in advance to have the patterned shape when the reflective electrode 4025 is formed on the substrate 4021. In this case, it is not necessary to pattern the reflective electrode 4025 after removing the first LED stack 4023.

[0590] By patterning the reflective electrode 4025, the second insulating layer 4028 may be exposed. The interconnection line 4029 is disposed to be perpendicular to the reflective electrode 4025, and is insulated from the reflective electrode 4025 by the second insulating layer 4028.

[0591] Referring to FIG. 79G, the lower insulating layer 4061 (FIGS. 83 and 84) covering the pixels is then formed. The lower insulating layer 4061 covers the reflective electrode 4025 and covers the side surfaces of the first to third LED stacks 4023, 4033, and 4043. In addition, the lower insulating layer 4061 may at least partially cover the upper surface of the third LED stack 4043. In a case in which the lower insulating layer 4061 is a transparent layer such as Si02, the lower insulating layer 4061 may also cover substantially the entirety of the upper surface of the third LED stack 4043. Alternatively, the lower insulating layer 4061 may also include a reflective layer or a light absorption layer, and in this case, the lower insulating layer 4061 at least partially exposes the upper surface of the third LED stack 4043 so that light is emitted to the outside.

[0592] The lower insulating layer 4061 may have an opening 4061a exposing the third LED stack 4043, an opening 4061b exposing the second LED stack 4033, an opening 4061c exposing the third-p transparent electrode 4045, an opening 4061d exposing the second-p transparent electrode 4035, and an opening 4061e exposing the reflective electrode 4025. One or a plurality of openings 4061e exposing the reflective electrode 4025 may be formed.

[0593] Referring to FIG. 79H, the interconnection lines 4071 and 4073 and the connectors 4071a, 4073a, and 77ab are then formed by a lift-off technique. The interconnection lines 4071 and 4073 are insulated from the reflective electrode 4025 by the lower insulating layer 4061. The connector 4071a electrically connects the third LED stack 4043 to the interconnection line 4071 and the connector 4073a connects the second LED stack 4033 to the interconnection line 4073. The connector 77ab electrically connects the third-p transparent electrode 4045 and the second-p transparent electrode 4035 to the first p-type reflective electrode 4025.

[0594] The interconnection lines 4071 and 4073 may be disposed to be substantially perpendicular to the reflective electrode 4025 and may connect the plurality of pixels to each other.

[0595] Next, the upper insulating layer 4081 (FIGS. 83 and 84) covers the interconnection lines 4071 and 4073 and the connectors 4071a, 4073a, and 4077ab. The upper insulating layer 4081 may also cover substantially the entirety of the upper surface of the third LED stack 4043. The upper insulating layer 4081 may be formed of, for example, silicon oxide film or silicon nitride film, and may also include a distribution Bragg reflector. In addition, the upper insulating layer 4081 may include a transparent insulating film and a reflective metal layer, or an organic reflective layer of a multilayer structure thereon to reflect light, or may include a light absorption layer such as black based epoxy to thereby shield light.

[0596] In a case in which the upper insulating layer 4081 reflects or shields light, in order to emit light to the outside, it is necessary to at least partially expose the upper surface of the third LED stack 4043. Meanwhile, in order to allow an electrical connection from the outside, the upper insulating layer 4081 is partially removed to thereby partially expose the interconnection lines 4071, 4073, and 4075. Further, the upper insulating layer 4081 may also be omitted.

[0597] As the upper insulating layer 4081 is formed, the pixel region illustrated in FIG. 76 is provided. In addition, as illustrated in FIG. 75, the plurality of pixels may be formed on the support substrate 4051, and those pixels may be connected to each other by the first p-type reflective electrode 4025 and the interconnection lines 4071, 4073, and 4075, and may be driven in a passive matrix manner.

[0598] In the illustrated exemplary embodiment, the method for manufacturing the display apparatus that may be driven in the passive matrix manner is described, but the inventive concepts are not limited thereto, and a display apparatus including the light emitting diode stack illustrated in FIG. 72 may be configured to be driven in various manners.

[0599] For example, it is described that the interconnection lines 4071 and 4073 are formed together on the lower insulating layer 4061, but the interconnection line 4071 may be formed on the lower insulating layer 4061 and the interconnection line 4073 may also be formed on the upper insulating layer 4081.

[0600] Meanwhile, in FIG. 72, it is described that the reflective electrode 4025, the second-p transparent electrode 4035, and the third-p transparent electrode 4045 are in ohmic contact with the second conductivity type semiconductor layers 4023b, 4033b, and 4043b of the first LED stack 4023, the second LED stack 4033, and the third LED stack 4043, respectively, and it is described that the ohmic electrode 4026 is in ohmic contact with the first conductivity type semiconductor layer 4023a of the first LED stack 4023, but the ohmic contact layer is not separately provided to the first conductivity type semiconductor layers 4033a and 4033b of the second LED stack 4033 and the third LED stack 4043. When a size of a pixel is as small as 200 micrometers or less, according to some exemplary embodiments, there is no difficulty in current dispersion even in a case in which a separate ohmic contact layer is not formed in the first conductivity type semiconductor layers 4033a and 4043a, which are n-type. However, for current dispersion, transparent electrode layers may be disposed on the n-type semiconductor layers of the second and third LED stacks 4033 and 4043.

[0601] According to exemplary embodiments, the plurality of pixels may be formed at a wafer level by using the light emitting diode stack 4000 for a display, and thus the steps of individually mounting the light emitting diodes may be obviated. Furthermore, since the light emitting diode stack has a structure that the first to third LED stacks 4023, 4033, and 4043 are vertically stacked, an area of the sub-pixel may be secured within a limited pixel area. In addition, since light generated in the first LED stack 4023, the second LED stack 4033, and the third LED stack 4043 is transmitted through these LED stacks and emitted to the outside, it is possible to reduce light loss.

[0602] However, the inventive concepts are not limited thereto, and light emitting devices in which the respective pixels are separated from each other may also be provided, and those light emitting devices are individually mounted on a circuit board, thereby making it possible to provide the display apparatus.

[0603] In addition, it is described that the ohmic electrode 4026 is formed on the first conductivity type semiconductor layer 4023a adjacent to the second conductivity type semiconductor layer 4023b, but the ohmic electrode 4026 may also be formed on the surface of the first conductivity type semiconductor layer 4023a opposite to the second conductivity type semiconductor layer 4023b. In this case, the third LED stack 4043 and the second LED stack 4033 are patterned to expose the ohmic electrode 4026, and instead of the interconnection line 4029, a separate interconnection line connecting the ohmic electrode 4026 to the circuit board is provided.

[0604] FIG. 80 is a cross-sectional view of a light emitting stacked structure not forming part of the invention.

[0605] Referring to FIG. 80, a light emitting stacked structure not forming part of the invention includes a plurality of sequentially stacked epitaxial stacks. A plurality of epitaxial stacks are provided on the substrate 5010.

[0606] The substrate 5010 has a substantially a plate shape having an upper surface and a lower surface.

[0607] A plurality of epitaxial stacks can be mounted on the upper surface of the substrate 5010, and the substrate 5010 may be provided in various forms. The substrate 5010 may be formed of an insulating material. Examples of the material of the substrate 5010 include glass, quartz, silicon, organic polymer, organic / inorganic composite, or others. However, the material of the substrate 5010 is not limited thereto, and is not particularly limited as long as it has an insulation property. In an exemplary embodiment, the substrate 5010 may further include a wiring part that may provide a light emitting signal and a common voltage to the respective epitaxial stacks. In an exemplary embodiment, in addition to the wiring part, the substrate 5010 may further include a drive element including a thin film transistor, in which case the respective epitaxial stacks may be driven in the active matrix type. To this end, the substrate 5010 may be provided as a printed circuit board 5010 or as a composite substrate having a wiring part and / or a drive element formed on glass, silicon, quartz, organic polymer, or organic / inorganic composite.

[0608] A plurality of epitaxial stacks are sequentially stacked on an upper surface of the substrate 5010, and respectively emit light.

[0609] In an exemplary embodiment, two or more epitaxial stacks may be provided, each emitting light of different wavelength bands from each other. That is, a plurality of epitaxial stacks may be provided, respectively having different energy bands from each other. In an exemplary embodiment, the epitaxial stack on the substrate 5010 is illustrated as being provided with three sequentially stacked layers, including first to third epitaxial stacks 5020, 5030, and 5040.

[0610] Each of the epitaxial stacks may emit a color light of a visible light band of various wavelength bands. Light emitted from the lowermost epitaxial stack is a color light of the longest wavelength having the lowest energy band, and the wavelength of the emitted color light becomes shorter in the order from lower to upper sides. The light emitted from the epitaxial stack disposed at the top is a color light of the shortest wavelength having the highest energy band. For example, the first epitaxial stack 5020 may emit the first color light L1, the second epitaxial stack 5030 may emit the second color light L2, and the third epitaxial stack 5040 may emit the third color light L3. The first to third color light L1, L2, and L3 correspond to different color light from each other, and the first to third color light L1, L2, and L3 may be color light of different wavelength bands from each other which have sequentially decreasing wavelengths. That is, the first to third color light L1, L2, and L3 may have different wavelength bands from each other, and the color light may be a shorter wavelength band of a higher energy in an order of the first color light L1 to the third color light L3. However, the inventive concepts are not limited thereto, and when the light emitting stacked structure include micro LEDs, the lowermost epitaxial stack may emit a color of light having any energy band, and the epitaxial stacks disposed thereon may emit a color of light having different energy band than that of the lowermost epitaxial stack due to the small form factor of micro LEDs.

[0611] In the exemplary embodiment, the first color light L1 may be red light, the second color light L2 may be green light, and the third color light L3 may be blue light, for example.

[0612] Each of the epitaxial stacks emits light to a front direction of the substrate 5010. In particular, light emitted from one epitaxial stack is passed through another epitaxial stack located in the light path, and travels to the front direction. The front direction may correspond to a direction along which the first to third epitaxial stacks 5020, 5030 and 5040 are stacked.

[0613] Hereinafter, in addition to the front direction and the back direction mentioned above, the "front" direction of the substrate 5010 will be referred to as the "upper" direction, and "back" direction of the substrate 5010 will be referred to as the "lower" direction. Of course, the terms "upper" or "lower" refer to relative directions, which may vary according to the placement and the direction of the light emitting stacked structure.

[0614] Each of the epitaxial stacks emits light in an upper direction, and each of the epitaxial stacks transmits most of light emitted from the underlying epitaxial stacks. In particular, light emitted from the first epitaxial stack 5020 passes through the second epitaxial stack 5030 and the third epitaxial stack 5040 and travels to the front direction, and the light emitted from the second epitaxial stack 5030 passes through the third epitaxial stack 5040 and travels to the front direction. To this end, at least some, or desirably, all of the epitaxial stacks other than the lowermost epitaxial stack may include an optically transmissive material. As used herein, the material being "optically transmissive" not only includes a transparent material that transmits the entire light, but also a material that transmits light of a predetermined wavelength or transmitting a portion of light of a predetermined wavelength. In an exemplary embodiment, each of the epitaxial stacks may transmit about 60% or more of light emitted from the epitaxial stack disposed thereunder, or about 80% or more in another exemplary embodiment, or about 90% or more in yet another exemplary embodiment.

[0615] In the light emitting stacked structure according to an exemplary embodiment, the signal lines for applying emitting signals to the respective epitaxial stacks are independently connected, and accordingly, the respective epitaxial stacks can be independently driven and the light emitting stacked structure can implement various colors according to whether light is emitted from each of the epitaxial stacks. In addition, the epitaxial stacks for emitting light of different wavelengths from each other are overlapped vertically on one another, and thus can be formed in a narrow area.

[0616] FIGS. 81A and 81B are cross-s...

Claims

1. A light emitting device for a display, comprising: a first LED sub-unit (223); a second LED sub-unit (233) disposed below and adjacent to the first LED sub-unit (223); a third LED sub-unit (243) disposed below and adjacent to the second LED sub-unit (233); electrode pads (281) disposed on the first LED sub-unit (223) and electrically connected to the first, second, and third LED sub-units (223, 233, 243), the electrode pads comprising a common electrode pad (281d) electrically connected to each of the first, second, and third LED sub-units (223, 233, 243), and first, second, and third electrode pads (281a, 281b, 281c) connected to a respective one of the first, second, and third LED sub-units (223, 233, 243); and a first reflective electrode (228) disposed between the electrode pads (281) and the first LED sub-unit (223), a second transparent electrode (235) being interposed between the second LED sub-unit (233) and the third LED sub (243), a third transparent electrode (245) in ohmic contact with an upper surface of the third LED sub-unit (243), wherein: the common electrode pad (281d), the second electrode pad (281b), and the third electrode pad (281c) are electrically connected to the second LED sub-unit (233) and the third LED sub-unit (243) through holes that pass through the first LED sub-unit (223); the first LED sub-unit (223), the second LED sub-unit (233), and the third LED sub-unit (243) are configured to be independently driven; the first reflective electrode (228) is disposed between the electrode pads (281) and the first LED sub-unit (223) and in ohmic contact with the first LED sub-unit (223); the common electrode pad (281d) is connected to the first reflective electrode (228); light generated in the first LED sub-unit (223) is configured to be emitted to the outside of the light emitting device through the second LED sub-unit (233) and the third LED sub-unit (243); the first reflective electrode (228) comprises an ohmic contact layer (228a) in ohmic contact with an upper surface of the first LED sub-unit (223) and a reflective layer (228b) that covers the ohmic contact layer light generated in the second LED sub-unit (233) is configured to be emitted to the outside of the light emitting device through the third LED sub-unit (243); the common electrode pad (281d) being connected to the second transparent electrode (235), the second transparent electrode (235) being in ohmic contact with a lower surface of the second LED sub-unit (233), and electrically connected to the third transparent electrode (245).

2. The light emitting device of claim 1, wherein: the first, second, and third LED sub-units (223, 233, 243) comprise a first LED stack, a second, LED stack, and a third LED stack (223, 233, 243), respectively; and the first, second, and third LED stacks (223, 233, 243) are configured to emit red light, green light, and blue light, respectively.

3. The light emitting device of claim 1, wherein: the first reflective electrode (228) has a hollow portion defined by a substantially annular-shaped member; and the common electrode pad (281d) passes through the hollow portion of the substantially annular-shaped member.

4. The light emitting device of claim 1, wherein the common electrode pad (281d) is connected to an upper surface of the second transparent electrode (235) and an upper surface of the third transparent electrode (245).

5. The light emitting device of claim 4, wherein: each of the first LED sub-unit (223) and the third LED sub-unit (243) comprises a first conductivity type semiconductor layer (223a, 243a) and a second conductivity type semiconductor layer (223b, 243b) disposed on a partial region of the first conductivity type semiconductor layer (223a, 243a); and the first electrode pad (281a) and the third electrode pad (281c) are electrically connected to the first conductivity type semiconductor layer (223a, 243a) of the first LED sub-unit and the third LED sub-unit, respectively.

6. The light emitting device of claim 5, further comprising a first ohmic electrode (226) disposed on the first conductivity type semiconductor layer (223a) of the first LED sub-unit, wherein the first electrode pad (281a) is connected to the first ohmic electrode (226).

7. The light emitting device of claim 6, wherein the third electrode pad (281c) is directly connected to the first conductivity type semiconductor layer (243a) of the third LED sub-unit.

8. The light emitting device of claim 5, further comprising: a first color filter (247) disposed between the third transparent electrode (245) and the second LED sub-unit (233); and a second color filter (267) disposed between the first and second LED sub-units (223, 233).

9. The light emitting device of claim 8, wherein the first color filter (247) and the second color filter (267) comprise insulating layers having different refractive indices.

10. The light emitting device of claim 1, wherein the common electrode pad (281d) and the third electrode pad (281c) are electrically connected to the third LED sub-unit (243) through holes that pass through the second LED sub-unit (233).

11. The light emitting device of claim 1, further comprising a substrate (241) on which the third LED sub-unit (243) is disposed.

12. The light emitting device of claim 11, wherein the substrate (241) comprises a sapphire substrate or a gallium nitride substrate.