Light emitting device
By introducing and exiting the coupling texture on the pixel epitaxial surface of the light emitting device, the crosstalk and poor contrast performance when the pixel spacing is less than 40 μm in the light emitting device is solved, and higher contrast performance and illuminance uniformity are achieved.
Patent Information
- Application Number
- CN202380071224.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-10-06
- Filing Date
- 2023-10-06
- Publication Date
- 2025-05-16
AI Technical Summary
In the light emitting device, since the pixel pitch is less than 40 μm, the crosstalk and contrast performance between adjacent pixels are poor, and there is a problem of illuminance unevenness.
By introducing coupling textures into the central region of the interface between the pixel epitaxial surface and the environment or conversion layer, the area where light escapes from the pixels of the light emitting device is physically reduced, limiting the area where light escapes without reducing the physical area where current flows.
It effectively improves the contrast performance of the light emitting device, reduces crosstalk between adjacent pixels, and ensures illumination uniformity in the pixel array.
Smart Images
Figure CN120019737A_ABST
Abstract
Description
[0001] This application claims the priority of German patent application DE 10 2022 125869.6 filed on October 6, 2022, the disclosure of which is incorporated herein by reference in its entirety.
[0002] The present invention relates to a light emitting device, in particular to a micro light emitting diode (μLED) having a common conversion layer arranged on top, wherein the light emitting device provides improved contrast performance of the light emitted by each pixel and reduced crosstalk between adjacent pixels compared to known light emitting devices. Background Art
[0003] In case the size of light emitting devices is reduced due to the desire to provide displays with increasing resolution and thus decreasing pixel pitch of the pixels of the light emitting devices (typically <40 μm), crosstalk between adjacent pixels may increase significantly due to diffusion of light through a conversion layer arranged, for example, on top of the light emitting device and / or poor contrast performance of the pixels of the light emitting device. Achieving perfect separation of the individual pixels of the light emitting device can usually only be easily achieved in the epitaxial (epi) layer, but when the conversion layer is arranged on top of the light emitting device, this is difficult to achieve when the pixel pitch is less than 40 microns. In this size range, due to manufacturing limitations, the conversion layer must therefore remain undivided, covering several pixels as a common converter, or protruding a single pixel. However, an undivided conversion layer covering multiple pixels as a common conversion layer or a conversion layer protruding a single pixel may lead to the above-mentioned problems of crosstalk and poor contrast performance.
[0004] Furthermore, light emitting devices with pixels arranged in an array with a pitch less than 40 μm (tiling small "monolithic" pixels in an array of, for example, 5 x 5 pixels) tend to have illumination non-uniformity between "inside" and "edge" pixels at the stitching grooves.
[0005] It is therefore an object of the present application to overcome at least one of the above problems and to provide a light emitting device with enhanced contrast performance. Summary of the invention
[0006] This and other objects are solved by the subject matter of the independent claims. Characteristics and further aspects of the proposed principle are outlined in the dependent claims.
[0007] The idea proposed by the inventors is to physically reduce the area where light escapes from the epitaxial structure of the pixel of the light-emitting device, for example into the environment or conversion layer, by introducing an outcoupling texture only in the central area of the interface between the epitaxial surface of the pixel and the environment or conversion layer. By doing so, the area where light escapes from the pixel is effectively limited without actually reducing the physical area where current flows, thereby avoiding problems associated with current crowding. Therefore, with this approach, it is easier to meet forward voltage requirements and avoid current crowding effects that may significantly reduce the internal quantum efficiency (IQE) (such current crowding effects would occur if the pixel size was physically reduced). Selectively texturing only the central area of the interface between the epitaxial surface of the pixel and the environment or conversion layer also allows for more flexibility in ensuring illumination uniformity in pixel arrays constructed by splicing groups of multiple pixels together.
[0008] In one aspect, a light emitting device is provided, which includes a semiconductor layer stack having a first layer of a first doping type, a second layer of a second doping type, and an active region arranged between the first layer and the second layer. The light emitting device also includes a first electrical contact connected to an electrical contact via, the electrical contact via extending electrically isolated through the second layer and the active region and contacting the first layer; and a second electrical contact contacting the second layer, the first electrical contact and the second electrical contact being arranged on the second layer on the bottom surface of the semiconductor layer stack. In order to ensure that the area where light escapes from the semiconductor layer stack to the environment or, for example, in the conversion layer is smaller than the top surface of the semiconductor layer stack, the interface between the first layer and the medium above the top surface of the semiconductor layer stack is roughened in an area smaller than the area of the top surface, in particular, in an area at least 10% smaller than the area of the top surface. In this way, the area where light escapes from the semiconductor layer stack to the medium, such as the environment or the conversion layer, is effectively limited to improve the contrast performance of the light emitting device.
[0009] In some embodiments, the medium is a conversion layer disposed on the first layer on the top surface of the semiconductor layer stack, which is configured to convert the light of the first wavelength generated in the active region into light of the second wavelength. However, the medium can also be the environment surrounding the light emitting device, such as air.
[0010] The roughened interface may be, for example, away from the periphery of the top surface and, in particular, arranged in a central region above the active area. However, in this context, the term "central" region should not be understood as the roughened interface being arranged in the exact center of the top surface, but may also be positioned away from the periphery of the top surface, with, for example, different distances from, for example, the opposite edges of the top surface.
[0011] In some embodiments, the interface between the first layer and the environment or conversion layer is roughened in a central region above the active region, wherein the central region is at least 5%, 10% or 15% smaller than a projection of the active region when viewed from a direction perpendicular to the top surface.
[0012] In some embodiments, the roughened interface provides better outcoupling of light generated in the active region from the top surface to the environment or conversion layer compared to the unroughened interface surrounding the roughened interface. In this way, the region where light escapes from the semiconductor layer stack to the environment or conversion layer is effectively limited. Due to the different refractive indices of the semiconductor layer stack and the environment or conversion layer, the unroughened interface can simultaneously act as a reflector, especially for light incident on the top surface at a shallow angle. In addition, this can further enhance the effect of limiting the region where light escapes from the semiconductor layer stack to the environment or conversion layer.
[0013] To further enhance the effect of limiting the area where light escapes from the semiconductor layer stack to the environment or the conversion layer, a coating may be arranged on the top surface surrounding the roughened interface, the coating comprising a higher transmittance for light incident on the coating perpendicular to the top surface compared to light incident on the coating at a shallower angle relative to the top surface. The coating may be specifically configured to transmit light incident on the coating perpendicular to the top surface and absorb or reflect light incident on the coating at a shallower angle relative to the top surface to suppress the emission of light "to the side" of the light emitting device, while transmitting the emission of light in a direction substantially perpendicular to the top surface. In this way, the area where light escapes from the semiconductor layer stack to the environment or the conversion layer is once again effectively limited to improve the contrast performance of the light emitting device.
[0014] In some embodiments, the reflective sidewall is arranged on at least one side surface of the semiconductor layer stack, which connects the top surface and the bottom surface to each other. In particular, the reflective sidewall or several reflective sidewalls can surround / enclose the semiconductor layer stack, and can therefore be arranged on all side surfaces of the semiconductor layer stack. The reflective sidewall can be configured to reflect the light generated in the active area in the direction of the top surface to enhance the luminous efficiency of the light emitting device. In addition, the reflective sidewall can be configured to reflect the light reflected at the unroughened surface or coating to the roughened surface to enhance the luminous efficiency of the light emitting device again, and ensure that the light blocked by the unroughened surface or coating at the first moment still comes out of the light emitting device via the roughened interface.
[0015] In some embodiments, a reflective layer is disposed on the bottom surface of the layer stack, the reflective layer surrounding the first electrical contact and the second electrical contact. The reflective layer can be configured to reflect light generated in the active region in the direction of the top surface to enhance the luminous efficiency of the light emitting device. In addition, the reflective layer can be configured to reflect light reflected at the unroughened surface or coating to the roughened surface to again enhance the luminous efficiency of the light emitting device and ensure that light blocked by the unroughened surface or coating at the first moment still exits the light emitting device via the roughened interface.
[0016] By increasing the reflectivity of the side surfaces of the semiconductor layer stack and / or the bottom surface of the semiconductor layer stack, the possible output brightness loss can be particularly minimized compared to arranging the outcoupling structure on the entire top surface of the light emitting device. For example, the reflectivity of the reflective sidewalls and / or the reflective layer can be increased by selecting a material with low losses (e.g. aluminum or silver) for the sidewalls and additionally applying a single layer coating (e.g. SiO2) with a thickness sufficient to allow total internal reflection with minimal losses. As an alternative, a multilayer coating acting as a distributed Bragg mirror can be applied to increase the reflectivity at all angles of incidence.
[0017] In some embodiments, at least the second layer and the active area are divided into a first portion and at least a second portion of the semiconductor layer stack, each portion forming a pixel of the light emitting device. The first portion and at least the second portion can be formed in particular by etching a groove in the semiconductor stack, the groove extending at least through the second layer and the active area, and optionally through a portion of the first layer or through the entire first layer. The first portion and at least the second portion can be arranged adjacent to each other in particular, and in the case of more than two portions, can be arranged in an array corresponding to the pixel pitch of the light emitting device. In some embodiments, the groove can be filled with a reflective separator, wherein the reflective separator can be similar to the above-mentioned sidewall.
[0018] However, the first part and at least the second part may also be separated by an electrical contact via, whereby the electrical contact via fills a trench separating the first part and at least the second part from each other. In the case where the first part and at least the second part are separated by the electrical contact via, in a preferred embodiment, the trench may extend through the second layer and the active area, as well as through a portion of the first layer, such that the electrical contact via contacts the first layer. Thus, the first layer may include a portion providing a common electrical contact for portions of the layer stack, which portion is not completely separated but still connects the first part and at least the second part of the semiconductor layer stack.
[0019] In some embodiments, over each first portion and at least the second portion, the interface between the first layer and the environment or conversion layer is roughened in separate regions, the separate regions being separated from each other. In other words, each pixel of the light-emitting device is associated with its own roughened interface region, limiting the region where light escapes from the corresponding pixel of the light-emitting device to the environment or the common conversion layer, thereby improving the contrast performance of the light-emitting device.
[0020] In some embodiments, the top surface is theoretically divided into surface areas, one surface area in each of the surface areas is allocated to the first portion and at least the second portion, and wherein the separate roughened interface areas are each located within the theoretically divided surface areas, each away from the periphery of the corresponding surface area.
[0021] In some embodiments, a separate roughened interface region is further from an adjacent edge of an adjacent surface region than from an opposite edge of the corresponding surface region. In particular, a separate roughened interface region is further from an "inner" edge of a surface region than from an "outer" edge of the surface region, wherein the "outer" edge of the surface region is closer to the side surface of the semiconductor layer stack than the "inner" edge. This results in a more uniform pixel illumination of the light-emitting device on the "inner" pixels and the "edge" pixels.
[0022] In some embodiments, each second electrical contact contacts a separate portion of the second layer of the first portion and at least the second portion. Thus, each pixel of the light-emitting device comprises its own separate electrical contact on one side of the semiconductor layer stack and, in particular, a common electrical contact on the other side of the semiconductor layer stack. Thus, each pixel of the light-emitting device is individually electrically controllable.
[0023] In some embodiments, the light emitting device or the pixel of the light emitting device is formed by an LED, in particular an LED chip. In particular, the LED can be referred to as a μLED. μLEDs are small LEDs, for example with an edge length of less than 100 μm, in particular less than 40 μm, and in particular in the range of 40 μm to 5 μm. Another range is between 100 μm and 10 μm. Within these spatial ranges, the optoelectronic semiconductor device is barely visible to the human eye.
[0024] In some embodiments, the μLED or μLED chip can be an unpackaged semiconductor chip. Unpackaged means that there is no packaging around the semiconductor layer of the chip, such as a "bare chip". In some embodiments, unpackaged can mean that the chip does not contain any organic material. Therefore, an unpackaged device does not include any organic compound containing carbon in a covalent bond. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Further aspects and embodiments according to the proposed principles will become apparent through the various embodiments and examples described in detail in conjunction with the accompanying drawings, in which:
[0026] Figure 1 A light emitting device having outcoupling structures over its entire top surface is shown.
[0027] Figure 2 A light emitting device according to some aspects of the proposed principles is shown;
[0028] Figure 3 Another embodiment of a light emitting device according to some aspects of the proposed principles is shown;
[0029] Figure 4 Further embodiments of light emitting devices according to some aspects of the proposed principles are shown;
[0030] Figure 5A is a top view of an embodiment of a light emitting device according to some aspects of the proposed principles; and
[0031] Figure 5B is a top view of another embodiment of a light emitting device according to some aspects of the proposed principles. DETAILED DESCRIPTION
[0032] The following embodiments and examples disclose various aspects and combinations thereof according to the proposed principles. Embodiments and examples are not always drawn to scale. Likewise, different elements may be displayed in enlarged or reduced sizes to emphasize various aspects. It is obvious that the various aspects of the embodiments and examples shown in the drawings can be combined with each other without saying anything more, and will not contradict the principles of the present invention. Some aspects show regular structures or forms. It should be noted that in practice, slight differences and deviations from the ideal form may occur, but this will not contradict the concept of the present invention.
[0033] In addition, the various drawings and aspects are not necessarily shown in the correct scale, and the ratios between the various elements are not necessarily substantially correct. Some aspects are highlighted by being shown enlarged. However, terms such as "above", "above", "below", "below", "larger", "smaller", etc. are accurately represented in relation to the elements in the drawings. Therefore, such relationships between the elements can be inferred based on the drawings.
[0034] Figure 1 A diagram of a reference pixel of a light emitting device having an outcoupling structure over the entire top surface 11 of the semiconductor layer stack 2 is shown. Light L2 escaping from the conversion layer 10 arranged on the semiconductor stack of the light emitting device at the edge of the pixel will typically leak to adjacent pixels (see Figure 1L2 on the right), resulting in crosstalk between adjacent pixels and / or poor contrast performance of the light-emitting device pixels.
[0035] However, if light extraction into the conversion layer 10 at the edge of a pixel can be minimized, crosstalk between adjacent pixels will be reduced, and higher contrast performance of the pixel can be achieved.
[0036] Therefore, the inventors propose to limit the outcoupling structure at the interface between the semiconductor layer stack 2 and the conversion layer to the central region above the pixel of the light emitting device to allow light L2 to be emitted from the light emitting device pixel in only the central region of the pixel of the light emitting device.
[0037] Figure 2 A corresponding light emitting device 1 is shown, which comprises a semiconductor layer stack 2 having a first layer 3 of a first doping type, a second layer 4 of a second doping type and an active region 5 arranged between the first layer and the second layer. The light emitting device 1 further comprises a first electrical contact connected to an electrical contact via (both not shown here), which extends electrically isolated through the second layer 4 and the active region 5 and contacts the first layer 3. Furthermore, a second electrical contact 8 contacts the second layer, and the same is true for a not shown first electrical contact on the second layer 4 arranged on the bottom surface 9 of the semiconductor layer stack 2. A conversion layer 10 is arranged on the first layer 3 on the top surface 11 of the semiconductor layer stack 2, wherein the conversion layer 10 is configured to convert the light L1 of the first wavelength generated in the active region 5 into light L2 of the second wavelength.
[0038] In order to ensure that the area where light escapes from the semiconductor layer stack 2 to the conversion layer 10 is smaller than the area of the top surface 11 of the semiconductor layer stack 2, the interface 12 between the first layer 3 and the conversion layer 10 is roughened in an area smaller than the area of the top surface 11. In this way, the area where light escapes from the semiconductor layer stack 2 to the conversion layer 10 is effectively limited to improve the contrast performance of the light-emitting device 1. The roughened interface 12 is particularly far away from the periphery 13 of the top surface 11, and is particularly arranged in the central area above the active area 5.
[0039] like Figure 2 As shown, the roughened interface 12 is confined to an area smaller than the area of the top surface 11 so that light L1 incident on the unroughened interface surrounding the roughened interface 12 is reflected back into the semiconductor layer stack 2 and is Figure 1Compared to the light emitting device shown in FIG. 1 , light L1 does not escape from the conversion layer 10 at the edge of the pixel of the light emitting device 1 shown. This is because due to the different refractive indices of the semiconductor layer stack 2 and the conversion layer 10 at the unroughened interface, the roughened interface 12 provides better outcoupling of light generated in the active region 5 from the top surface 11 into the conversion layer 10 compared to the unroughened interface surrounding the roughened interface 12. Therefore, the unroughened interface acts as a reflector, especially for light incident on the top surface 11 at a shallow angle.
[0040] However, in order to ensure that the back-reflected light at the unroughened interface still escapes from the light-emitting device, a reflective sidewall 15 at the side surface 16 of the semiconductor layer stack 2 and a reflective layer 17 arranged on the bottom surface 9 of the semiconductor layer stack 2 are provided to guide the back-reflected light in the direction of the roughened interface 12 (see Figure 2 arrow on the right).
[0041] Figure 3 Another embodiment of the light emitting device 1 is shown, except that Figure 2 In addition to the embodiment of the present invention, this embodiment also includes a coating 14 located on the top surface 11 surrounding the roughened interface 12. With respect to the light incident on the coating 14 at a shallow angle relative to the top surface 11 (see Figure 3 ) compared to the light incident on the coating 14 substantially perpendicular to the top surface 11 (see Figure 3 ), the coating 14 has a higher transmittance. In this way, light emitted to the "side" of the light-emitting device 1 can be further reduced, but light emission in a direction substantially perpendicular to the top surface 11 can be allowed. This effectively limits the area where light escapes from the semiconductor layer stack 2 to the conversion layer 10 to improve the contrast performance of the light-emitting device 1. The coating 14 can, for example, be a thin film (multilayer) coating to manage the optical response at the unroughened interface, thereby further improving the contrast or light extraction by reducing the transmittance of the area at a specific angle or wavelength range and increasing its transmittance at another specific angle or wavelength range. The coating 14 can, for example, be an interference filter or a dichroic filter, etc.
[0042] Figure 4 Another embodiment of a light emitting device is shown, comprising several pixels arranged next to each other and a common conversion layer 10 arranged on the pixels. Such a design may for example be referred to as a so-called "cloverleaf" design, where for example 4 pixels are connected to each other like a cloverleaf.
[0043] In order to form a pixel, the semiconductor layer stack 2, and in particular the second layer 4, the active area 5 and a part of the first layer 3, is divided into individual parts 2a, 2b, ... of the semiconductor layer stack 2, each part forming a pixel of the light emitting device 1. The individual parts 2a, 2b, ... can in particular be formed by trenches etched into the semiconductor stack 2, which extend through the second layer 4 and the active area 5, and through a part of the first layer 3. Each individual part 2a, 2b, ... and thus each pixel comprises its own active area 5a, 5b, ... to generate light L1 when excited.
[0044] The individual parts 2a, 2b, ..... are separated by electrical contact vias 7, so that the electrical contact 7 vias fill the grooves that separate the parts 2a, 2b, ... from each other. Thus, the electrical contact vias contact the first layer 3, wherein the first layer 3 includes a portion that provides a common electrical contact for the parts 2a, 2b, ... in the semiconductor layer stack 2, which is not completely separated but still connects the individual parts 2a, 2b, ... of the semiconductor layer stack 2. On the electrical contact 7 on the bottom surface 9 of the semiconductor layer stack, a first electrical contact is arranged, through which the pixel can be controlled in combination with the second electrical contact 8a, 8b, ... on the bottom surface 9 of each individual part 2a, 2b, ... of the semiconductor layer stack 2. Therefore, each pixel of the light-emitting device 2 includes its own individual second electrical contact 8a, 8b, ... on one side of the semiconductor layer stack 2, and a common electrical contact on the other side of the semiconductor layer stack 2. Therefore, each pixel of the light-emitting device 1 can be individually electrically controlled.
[0045] Above each individual portion 2a, 2b, ... and thus above each pixel, the interface between the first layer 3 and the conversion layer 10 is roughened in individual regions 12a, 12b, ..., wherein the roughened interface regions 12a, 12b, ... are spaced apart from one another. Thus, each pixel of the light-emitting device 1 is associated with its own roughened interface region 12a, 12b, ..., limiting the escape of light from the individual pixels of the light-emitting device to the region of the common conversion layer 10, thereby improving the contrast performance of the light-emitting device 1.
[0046] The top surface 11 is theoretically divided into surface areas 11a, 11b, ..., one of each of which is assigned to a separate portion 2a, 2b, ... of the semiconductor layer stack 2. The theoretical division is performed between two adjacent pixels along a dividing line / plane 18 passing through the semiconductor layer stack 2. The separate roughened interface areas 12a, 12b, ... are all located within the theoretically divided surface areas 11a, 11b, ..., and each separate roughened interface area is away from the periphery 13a, 13b, ... of the corresponding surface area 11a, 11b, ...
[0047] like Figure 4 As shown, individual roughened interface regions 12a, 12b, ... are farther from adjacent edges of adjacent surface regions (distance D2) than from opposite edges of corresponding surface regions (distance D1). In particular, individual roughened interface regions 12a, 12b, ... are farther from the "inner" edge of the surface region (distance D2) than from the "outer" edge of the surface region (distance D1), wherein the "outer" edge of the surface region is closer to the side surface 16 of the semiconductor layer stack 2 than the "inner" edge. This results in more uniform pixel illumination of the light-emitting device on the "inner" pixels and the "edge" pixels. Figure 4 , which is indicated by distance D1 and distance D2, where D1 is the distance from the outer edge of the light emitting device to the roughened interface of one of the pixels, and D2 is the distance from the inner edge or separation line / plane 18 to the roughened interface of the pixel.
[0048] However, Figure 2 and Figure 3 The embodiments shown in the should be understood as exemplary embodiments only and may be used in conjunction with Figure 4 The embodiment shown in is similarly extended to the left or right thereof to form an array of pixels arranged adjacent to each other with a common conversion layer arranged on top of the pixels.
[0049] Figure 5A and Figure 5B Each shows a top view of an embodiment of a light emitting device according to some aspects of the proposed principles, and in particular a light emitting device comprising several pixels arranged in a four-leaf clover design.
[0050] Figure 5AAn embodiment is shown in which each individual part 2a, 2b, ... of the semiconductor layer stack 2 is assigned its own contact via 7a, 7b, ... along the two edges of the respective individual part 2a, 2b, ... In the embodiment shown, the individual parts 2a, 2b, ... are separated in a cross-wise manner by reflective side walls 15, which extend through the entire semiconductor layer stack 2, completely separating the first layer, the second layer and the active area from each other. The top surface 11 of the semiconductor layer stack 2 is theoretically divided into surface areas 11a, 11b, ... along the dividing line / plane 18, and the individual roughened interface areas 12a, 12b, ... are all located within the theoretically divided surface areas 11a, 11b, ..., and each individual roughened interface area is away from the periphery 13a, 13b, ... of the respective surface area 11a, 11b, ...
[0051] Figure 5B An embodiment is shown in which individual parts 2a, 2b, ... of the semiconductor layer stack 2 are electrically connected via a common electrical contact through contact vias 7 extending in a cross-shaped manner through a first layer, an active area, and a portion of a second layer. The top surface 11 of the semiconductor layer stack 2 is theoretically divided into surface areas 11a, 11b, ... along a dividing line / plane 18, and individual roughened interface areas 12a, 12b, ... are all located within the theoretically divided surface areas 11a, 11b, ..., and each individual roughened interface area is away from the periphery 13a, 13b, ... of the corresponding surface area 11a, 11b, ...
[0052] Reference numerals
[0053] 1 Light-emitting device
[0054] 2Semiconductor layer stacking
[0055] 2a, 2b, ... separate parts
[0056] 3First floor
[0057] 4 Second floor
[0058] 5 Active Area
[0059] 5a, 5b, ... Active area
[0060] 6First electrical contact
[0061] 7 Contact vias
[0062] 7a, 7b, ... contact vias
[0063] 8 Second electrical contact
[0064] 8a, 8b, ... second electrical contact
[0065] 9 Bottom surface
[0066] 10 Conversion Layers
[0067] 11 Top surface
[0068] 11a, 11b, ... surface area
[0069] 12 Roughening the interface
[0070] 12a, 12b, ... Roughened interface region
[0071] 13. Periphery
[0072] 13a, 13b, ... periphery
[0073] 14 Coating
[0074] 15 Reflective sidewalls
[0075] 16 Side surface
[0076] 17Reflection layer
[0077] 18 dividing line
[0078] L1 has light of the first wavelength
[0079] L2 has light of the second wavelength
[0080] D1 distance
[0081] D2 distance
Claims
1. A light emitting device (1), comprising: A semiconductor layer stack (2), the semiconductor layer stack (2) comprising a first layer (3) of a first doping type, a second layer (4) of a second doping type, and an active region (5) arranged between the first layer and the second layer; a first electrical contact (6) connected to an electrical contact via (7) extending electrically isolated through the second layer (4) and the active area (5) and contacting the first layer (3); and a second electrical contact (8) contacting the second layer (4), the first electrical contact (6) and the second electrical contact (8) being arranged on the second layer (4) on a bottom surface (9) of the semiconductor layer stack (2); The interface (12) between the top surface (11) of the semiconductor layer stack (2) and the medium above the top surface (11) is roughened in an area smaller than the area of the top surface (11), in particular in an area at least 10% smaller than the area of the top surface (11).
2. The light emitting device according to claim 1, in, The medium above the top surface (11) is a conversion layer (10) arranged on the first layer (3) on the top surface (11) of the semiconductor layer stack (2), and the conversion layer (10) is configured to convert the first wavelength light (L1) generated in the active area (5) into a second wavelength light (L2).
3. The light emitting device according to claim 1 or 2, in, The roughened interface (12) is away from the periphery (13) of the top surface (11).
4. The light emitting device according to claim 2 or 3, in, The interface (12) between the first layer (3) and the conversion layer (10) is roughened in a central region above the active region (5), wherein the central region is at least 10% smaller than a projection of the active region when viewed in a direction perpendicular to the top surface (11).
5. A light emitting device according to any one of the preceding claims, in, The roughened interface (12) provides better outcoupling of light from the top surface (11) to the conversion (10) layer compared to an unroughened interface.
6. A light emitting device according to any one of the preceding claims, in, A coating (14) is disposed on the top surface (11) surrounding the roughened interface (12), the coating (14) comprising a higher transmittance for light incident on the coating perpendicular to the top surface (11) than for light incident on the coating at a shallow angle relative to the top surface.
7. A light emitting device according to any one of the preceding claims, in, A reflective side wall (15) is arranged on at least one side surface (16) of the semiconductor layer stack (2), the side surface (16) connecting the top surface (9) and the bottom surface (11) to each other.
8. A light emitting device according to any one of the preceding claims, in, A reflective layer (17) is arranged on the bottom surface (9) of the semiconductor layer stack (2), the reflective layer (17) surrounding the first electrical contact (6) and the second electrical contact (8).
9. A light emitting device according to any one of the preceding claims, in, At least the second layer (4) and the active area (5) are divided into a first part and at least a second part (2a, 2b, . . . ).
10. The light emitting device according to claim 9, in, The first portion and the at least second portion (2a, 2b, ...) are separated by the electrical contact via (7).
11. The light emitting device according to claim 9 or 10, in, Above each of the first portion and the at least second portion (2a, 2b, ...), the interface (12) between the first layer (3) and the conversion layer (10) is roughened in separate areas (12a, 12b, ...), the separate areas (12a, 12b, ...) being spaced apart from one another.
12. The light emitting device according to claim 11, in, The top surface (11) is theoretically divided into surface areas (11a, 11b, ...), one surface area in each of the surface areas is allocated to the first part and the at least second part (2a, 2b, ...), and wherein the individual roughened interface areas (12a, 12b, ...) are each away from the periphery (13a, 13b, ...) of the corresponding surface area (11a, 11b, ...).
13. The light emitting device according to claim 12, in, The individual roughened interface regions (12a, 12b, ...) are further from adjacent edges of adjacent surface regions (11a, 11b, ...) than from opposing edges of the respective surface regions (11a, 11b, ...).
14. The light emitting device according to any one of claims 9 to 13, in, Each second electrical contact (8a, 8b, ...) contacts a separate portion of the second layer (4) of the first portion and the at least second portion (2a, 2b, ...).
15. A light emitting device according to any one of the preceding claims, in, The light emitting device (1) comprises at least one μLED.