Enhanced Color Conversion

Abstract

1. A method of forming a light emitting structure, the light emitting structure comprising: a light emitting region configured to emit light having a primary peak wavelength; a partially reflective region; a reflective region; and a color conversion region, wherein the light emitting region is positioned at least partially between a partially reflective layer and a reflective layer, the partially reflective region is positioned at least partially between the color conversion region and the light emitting region, the partially reflective region is configured to reflect light in a predetermined range of wavelengths and to pass light outside the predetermined range of wavelengths through the partially reflective region, and the primary peak wavelength is outside the predetermined range of wavelengths.

Description

Technical Field

[0001] The present invention relates to a light emitting structure and a method of forming the light emitting structure. In particular, but not limited thereto, the present invention relates to improved color conversion in a light emitting diode structure.

Background Art

[0002] Light emitting diode (LED) devices are known to be efficient light sources for a wide range of applications. LED light sources are used to provide conventional white light and / or multi-color light emissions. For example, multi-color light emissions include red, green, and / or blue emissions suitable for display applications. The light of a desired wavelength provided by an LED is typically realized by using a combination of an excitation source LED and a color conversion material such as a phosphor or a quantum dot (QD). Such an excitation source LED generates light having an output of a primary peak wavelength to excite the emission of light of different wavelengths in the color conversion material. For example, a blue light nitride material LED (emitting light having a primary peak wavelength of about 450 nm) is used to provide an LED emission of light converted to white. The blue nitride material LED is also used to provide an LED emission of light color-converted to red and an LED emission of light color-converted to green.

[0003] However, although excitation source LEDs such as blue nitride-based material LEDs are available with high-quality and efficient light emission, when a color conversion material is applied to obtain light of a desired color, the efficiency of light emission in the color-converted LED is usually lower than that of the excitation source LED used to excite the color conversion material. Such a decrease in efficiency is caused, for example, by the light generated by the excitation source LED being absorbed by the color conversion material. Therefore, various optical coating methods are used to reduce the loss due to the absorption of light by the color conversion material. However, such conventional optical coatings are expensive and difficult to implement in mass production.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, in a color-converted LED using a color-conversion technique to provide light of a desired wavelength, it is beneficial to enable more efficient light extraction.

Means for Solving the Problems

[0005] To mitigate at least some of the above problems, the following is provided, namely, A method of forming a light-emitting structure, the light-emitting structure including a light-emitting region configured to emit light having a primary peak wavelength, a partial reflection region, a reflection region, and a color-conversion region, the light-emitting region being at least partially positioned between the partial reflection region and the reflection region, the partial reflection region being at least partially positioned between the color-conversion region and the light-emitting region, the partial reflection region being configured to reflect light within a predetermined range of wavelengths and allow light outside the predetermined range of wavelengths to pass through the partial reflection region, and the primary peak wavelength being outside the predetermined range of wavelengths. A method is provided.

[0006] Furthermore, a light-emitting structure including a light-emitting region configured to emit light having a primary peak wavelength, a partial reflection region, a reflection region, and a color-conversion region, the light-emitting region being at least partially positioned between the partial reflection region and the reflection region, the partial reflection region being at least partially positioned between the color-conversion region and the light-emitting region, the partial reflection region being configured to reflect light within a predetermined range of wavelengths and allow light outside the predetermined range of wavelengths to pass through the partial reflection region, and the primary peak wavelength being outside the predetermined range of wavelengths. A light-emitting structure is provided.

[0007] Conveniently, the light-emitting structure thus formed provides improved color conversion efficiency, minimizes the required amount of color conversion material, and is suitable for mass production. Advantageously, the present method is applicable to LEDs of various sizes such as micro-LEDs that can realize white LED displays or multi-color LED displays, and is also suitable for mass transfer of individual LEDs, micro-LEDs, and / or monolithic LED arrays.

[0008] Preferably, the partial reflection region includes a Distributed Bragg Reflector (DBR). Advantageously, by incorporating the DBR into the growth process, it is possible to form a crystalline semiconductor layer that provides the necessary partial reflection function without degrading the crystal quality required for the formation of high-quality and efficient light-emitting diode devices.

[0009] Preferably, the reflection region includes a silver (Ag)-based mirror. Conveniently, by incorporating a layer with high reflectivity into the structure, the reuse of backscattered light and the light that is not emitted by the color conversion region but propagates through the structure and returns to be incident on the Ag-based mirror increases. Advantageously, Ag is suitable for dual purposes by being used simultaneously for forming a mirror layer and providing a eutectic bond to the carrier device.

[0010] Preferably, the present method includes depositing a reflection region on a light-emitting device having a light-emitting region. Conveniently, it is possible to provide a light-emitting device such as a light-emitting diode device, and known deposition techniques can be used to provide a reflection region while enabling at least visible light and / or ultraviolet light to be reflected for color conversion and / or light emission without degrading the quality of the light-emitting device.

[0011] Preferably, the present method includes growing a light-emitting device having a light-emitting region on a substrate. Conveniently, by forming the structure on the substrate using known techniques, high-quality materials for light generation and extraction are provided.

[0012] Preferably, the method includes growing a partial reflection region in front of the light-emitting region. Advantageously, growing the structure in this way means that a high-quality material can be provided that uses a continuous process to provide the crystal quality necessary to form the LED structure while providing the function of the partial reflection region.

[0013] Preferably, the method includes removing the substrate, preferably by wet etching. Advantageously, when provided in this way, the processing load required to provide the resulting structure is reduced by forming a high-quality structure on the substrate that is subsequently removed in order to provide a structure having improved photochromic conversion efficiency.

[0014] Preferably, the method includes depositing a color conversion region following removal of the substrate. Advantageously, by reusing the same region of the structure used to initiate high-quality material growth for color conversion, it becomes possible to form the structure without prohibiting color conversion at relatively similar positions of the structure.

[0015] Preferably, the method includes roughening the light-emitting device after removal of the substrate and before forming the color conversion region. Advantageously, roughening the substrate helps with the adhesion of the color conversion region and the extraction of light without impairing the effect of light emission from the structure.

[0016] Preferably, the method includes bonding a carrier device to the reflection region. Advantageously, the structure is conveyed from the side opposite the original growth substrate.

[0017] Preferably, the light-emitting structure includes a GaN-based structure. Advantageously, the GaN-based structure provides highly efficient light emission suitable for color conversion.

[0018] Preferably, the light emitting region comprises one or more epitaxial quantum wells. Advantageously, a high-quality epitaxial quantum well structure enables efficient light emission in an epitaxial stacked device.

[0019] Preferably, the light emitting region is configured to emit light having a primary peak wavelength corresponding to blue light. Advantageously, blue light has a shorter wavelength than red light and green light and can be used to excite light emission at various wavelengths including the emission of multicolor light and white light.

[0020] Preferably, a wavelength range includes wavelengths of light longer than 500 nm such that wavelengths shorter than 500 nm are outside the predetermined range. Advantageously, light having a wavelength of 500 nm or less passes through the partial reflection layer, and light having a wavelength longer than 500 nm is reflected by the partial reflection layer. Thus, for example, when blue light excites red and green light emission from a color conversion material, the red and green light emissions are reflected from the structure, and light having a wavelength of less than 500 nm passes through the structure for reuse. Thus, improvement in output and efficiency from the color conversion material is enabled.

[0021] A further aspect of the present invention should become apparent from the following description and the appended claims.

[0022] For purposes of illustration only, a detailed description of embodiments of the present invention will be described with reference to the drawings.

Brief Description of the Drawings

[0023]

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 1E

Figure 2

Figure 3A

Figure 3B

[0024] In a light-emitting structure having a color conversion region, by simply and advantageously implementing a reflective layer and a partial reflective layer, an LED device such as a micro LED device capable of realizing a white or multicolor LED display suitable for the mass transfer process of both individual micro LEDs and monolithic LED arrays is provided. By synergistically combining various regions or layers in the light-emitting structure, a solution for improving light conversion and extraction is obtained compared to known structures. Advantageously, implementation enables improvement of functions while maintaining the structural crystal integrity of the epitaxial compound semiconductor light-emitting structure and reducing processing requirements.

[0025] With reference to FIGS. 1A to 1E, a method of forming the light-emitting structure 100 will be described. The light-emitting structure 100 is an LED structure that uses a color conversion material to provide light having a desired wavelength. The resulting light-emitting structure is an LED structure having an excitation light source LED and a color conversion region. The method is described based on cross-sectional views through the layers of the light-emitting structure 100 at different stages of the process that provides a light-emitting structure with improved color conversion. The layers shown in FIGS. 1A to 1E represent regions having different functional characteristics of the light-emitting structure. Regions having different functional characteristics of the light-emitting structure are formed from one or more layers of different materials that cooperate to provide the functional characteristics (for example, the light-emitting region may comprise a multiple quantum well structure, and the partial reflection region may comprise a plurality of layers having different refractive indices). In a further example, additional or alternative layers are used to assist in the concepts described herein.

[0026] Figure 1A shows a light-emitting structure 100A which is an LED structure that emits blue light. What is shown is a stack of epitaxial compound semiconductor crystal layers. The epitaxial compound semiconductor crystal layers are provided by sequentially growing layers on a growth substrate 102. Advantageously, such epitaxial compound semiconductor crystal layers formed in this way are precisely controlled to provide high-quality materials and can efficiently emit light when carriers are injected from the n-type region and the p-type region into the light-emitting region.

[0027] In Figure 1A, the growth substrate 102 is shown, and on the growth substrate 102, a layer 104 of an undoped material which is a buffer layer or a buffer region is growing. The undoped material 104 is a layer of undoped gallium nitride (u-GaN). Conveniently, using such undoped GaN is used to promote the growth of III-V nitride-based LED devices with high luminous efficiency and to provide an efficient light source for color conversion using a color conversion material. Further, the undoped material provides a region that is transparent to at least visible light and ultraviolet light and is further processed so that a color conversion material can be incorporated into the final light-emitting structure.

[0028] On the undoped material 104, a layer which is a partial reflection region 106 is shown. The growth substrate 102 is a growth silicon substrate. The partial reflection region 106 is a distributed Bragg reflector (DBR). In one example, the DBR is formed on an n-type semiconductor layer using the method described in Zhang et al., ACS Photonics, 2, 980 (2015). The partial reflection region 106 is formed to reflect all wavelengths greater than 500 nm. Light with a longer wavelength, for example, green light having a wavelength of 520 nm is reflected by the partial reflection region 106, and red light having a wavelength of 620 nm is reflected by the partial reflection region 106.

[0029] The partially reflective region 106 is formed from alternating epitaxial crystalline layers having different refractive indices. The refractive indices of the layers and the layer thicknesses are selected to provide a reflectance response as a function of wavelength of light incident on the partially reflective region 106. Additionally, the porosity of the epitaxial crystalline layers forming the partially reflective region 106, as related to its refractive index, is controlled to provide the desired reflectance response as a function of wavelength.

[0030] In one example, alternating high and low refractive index layers form the partially reflective region 106, where the high refractive index (n H ) layer and low refractive index (n L ) The thickness of each of the layers is chosen so that the product of the layer thickness and the inverse of the refractive index is λ / 4, where λ is the central wavelength of high reflectance response at ±λ around λ according to the following equation:

number

[0031] FIG. 3A illustrates such alternating high and low index layers forming partially reflective regions 106. 3B shows a cross-sectional view of an example 300A of a quartz-insulated quartz-based ...

[0032] Although a particular structure configured to provide a desired effect can be implemented in various ways, in one example, the partial reflection region 106 has a structure 300A as described in connection with FIG. 3A. The partial reflection region 106 comprises alternating high refractive index and low refractive index layers. When the structure is formed for light of a wavelength of λ0 = 570 nm, the first layer has a thickness of 121.8 nm (1.3λ0 / 4 rather than λ / 4) and is formed from gallium nitride having a porosity of 70%. The next layer is formed from a gallium nitride layer that is not porous and is 61.7 nm thick. The next layer is another gallium nitride layer having a porosity of 70% and a thickness of 93.7 nm. The next layer is another gallium nitride layer that is not porous and is 61.7 nm thick. Additionally, 4 more pairs of alternating 93.7 nm thick gallium nitride with 70% porosity and 61.7 nm thick non-porous gallium nitride are formed. The last layer, a 121.8 nm (1.3λ0 / 4 rather than λ0 / 4) gallium nitride layer with 70% porosity, terminates the structure. The structure described in connection with FIG. 3A provides a reflectivity at normal incidence as a function of wavelength as shown by the reflectivity response 300B in FIG. 3B.

[0033] While the partial reflection region 106 is formed as described above, alternatively or additionally, the structure and / or layers of the partial reflection region 106 are formed from various layers and materials having various porosities and thicknesses that provide the required reflectivity response. For example, it is known that the porosity of a material can be varied to change the refractive index (see, for example, M.M. Braun, L. Pilon, “Effective optical properties of non-absorbing nanoporous thin Films”, This Solid Films 496 (2006) 505 - 514). For example, the refractive index of porous gallium nitride can vary as a function of percent porosity according to the following equation.

Equation

[0034] Advantageously, the partial reflection region 106 is formed as part of a continuous process for forming the light-emitting structure 100A, providing a higher-quality material and reducing the processing load. Beneficially, the partial reflection region 106 is grown prior to the light-emitting region 110. This provides a structure that can be grown in a continuous process, is of high quality, and can be used as described later.

[0035] The partial reflection region 106 is a distributed Bragg reflector (DBR), but in a further example, the partial re flection region 106 is formed using different methods while maintaining the function of enabling reflection of light of one wavelength and transmission of light of a different wavelength.

[0036] There is an n-type region 108 on the partial reflection region 106. The n-type region 108 is n-type doped gallium nitride (n-GaN). There is a light-emitting region 110 on the n-type region 108. The light-emitting region 110 is a blue light-emitting region 110. A p-type region 112 is grown on the blue light-emitting region 110. The p-type region is p-type doped gallium nitride (p-GaN). The light-emitting structure 100A is based on a general blue LED structure. In a further example, an alternative blue light-emitting structure having additional or alternative layers is used.

[0037] The n-type region 108 is n-type doped GaN, but in further examples, additionally or alternatively, the n-type region 108 includes a different material. The p-type region 112 is p-type doped GaN, but in further examples, additionally or alternatively, the p-type region 112 includes a different material.

[0038] The growth of epitaxial GaN-based materials on the silicon growth substrate 102 is shown, but in further examples, additional or alternative intervening layers are used to account for the lattice mismatch between the silicon substrate 102 and subsequent grown layers such as the partial reflection region 106, the n-type region 108, the light emitting region 110, and the p-type region 112. In one example, the growth substrate 102 includes silicon having an aluminum nitride (AlN) buffer layer. In further examples, the growth substrate 102 includes an undoped GaN region.

[0039] When the light-emitting structure 100A of FIG. 1A is provided, the light-emitting structure 100A is bonded to the carrier device 116. This is shown in FIG. 1B. FIG. 1B shows a cross-sectional view of the light-emitting structure 100A processed to provide the processed light-emitting structure 100B of FIG. 1B. The light-emitting structure 100A is bonded to the carrier device 116 by the reflective region 114. The reflective region 114 is deposited on the p-type region 112 and includes a highly reflective Ag (silver)-based mirror processed to enable eutectic bonding of the carrier device 116 to the p-type region 112. The carrier device 116 is a silicon wafer and, in one example, is beneficially used for physical properties such as thermal and structural properties. In a further example, additional and / or alternative materials are used to form the carrier device 116. In a further example, additional and / or alternative materials are used to form the reflective region 114. For example, the reflective region 114 may use a different method to enable bonding to the carrier device 116. For example, separate bonding and reflective layers may be used. In a further example, the reflective region 114 is a mirror formed from other materials. The reflective region 114 is configured to reflect light having at least visible wavelengths and / or ultraviolet wavelengths, including light at the primary peak wavelength emitted by the light-emitting region 110. Advantageously, the light emitted from the light-emitting region 110 and backscattered toward the reflective region 114, and the light reused into the light-emitting structure through the partial reflection region 106 are reflected in the directions of the partial reflection region 106 and the color conversion region 118, thereby enhancing color conversion and light output from the light-emitting structure.

[0040] When the light-emitting structure 100B of FIG. 1B is provided, the light-emitting structure 100B can be transported using the transport device 116 to enable further processing of the structure. The light-emitting structure 100B is processed to remove the growth substrate 102. This is shown in FIG. 1C. FIG. 1C shows a cross-sectional view of the light-emitting structure 100B processed to provide the processed light-emitting structure 100C of FIG. 1C. The growth substrate 102, which is a silicon growth wafer, is removed by wet etching using a KOH solution, hydrofluoric acid and nitric acid, BOE, or a similar wet etching solution. If a buffer layer is formed on the growth substrate 102 prior to the growth of the subsequent light-emitting structure, the buffer layer is optionally removed by dry etching.

[0041] When the light-emitting structure 100C of FIG. 1C is provided, the light-emitting structure 100C is processed to roughen the undoped material 10 4. This is shown in FIG. 1D. FIG. 1D shows a cross-sectional view of the light-emitting structure 100C processed to provide the processed light-emitting structure 100D of FIG. 1D.

[0042] When the light-emitting structure 100D of FIG. 1D is provided, the light-emitting structure 100D is processed to provide a color conversion material on the roughened undoped region 104. This is shown in FIG. 1E. FIG. 1E shows a cross-sectional view of the light-emitting structure 100D processed to provide the processed light-emitting structure 100E of FIG. 1E. The color conversion material 118 is a phosphor. Alternatively or additionally, the color conversion material 118 comprises different means of converting the wavelength of light from an excitation light source LED, using, for example, quantum dots (QD), or other quantum confinement structures such as quantum wells.

[0043] Advantageously, removing the growth substrate 102 to deposit the color conversion material 118 enables increasing the light output and efficiency from the color - converted light in combination with the use of the partial reflection region 106 and the reflection region 114. Advantageously, the simple configuration of the structure provides for the growth of a high - quality light - emitting structure and improved light conversion, resulting in an efficient process flow suitable for mass production. Advantageously, the improvement in the light conversion efficiency means a reduction in the amount of color conversion material used. This is advantageous in terms of cost and processing, meaning that thinner and more efficient layers of the color conversion material 118 are used.

[0044] The light - emitting structure 100A of FIG. 1A is formed using epitaxial compound semiconductor growth techniques such as metalorganic chemical vapour deposition (MOCVD) and molecular beam epitaxy (MBE). Additionally or alternatively, the light - emitting structure 100A is formed using any suitable technique. The light - emitting structure 100A is an LED structure, but in further examples, additionally or alternatively, the light - emitting structure 100A is a different light - emitting structure that benefits from the selective use of partial reflection layers to control the wavelength of light passing through the entire light - emitting structure. The growth of the above - mentioned epitaxial crystal compound semiconductor layer is performed using growth / deposition on a silicon wafer used as the growth substrate 102. Alternatively or additionally, other wafers such as sapphire wafers or free - standing gallium nitride (GaN) wafers are used.

[0045] In FIGS. 1A - 1E, specific epitaxial crystal compound semiconductor layers are shown, but in further examples, it will be understood by those skilled in the art that alternative or additional layers may be used. Further, in some examples, a portion of the epitaxial crystal compound semiconductor layer is removed while maintaining the essence of the concepts described herein.

[0046]

[0047] ​The light-emitting structure described in relation to FIGS. 1A to 1E is formed from a nitride-based material. In particular, the epitaxial crystal compound semiconductor layer is a gallium nitride (GaN)-based material. Although the structures described in relation to FIGS. 1A to 1E relate to nitride-based semiconductor compound materials, those skilled in the art will understand that the concepts described herein are applicable to other materials, particularly other semiconductor materials, such as other group III-V compound semiconductor materials or group II-VI compound semiconductor materials.

[0048] The light-emitting region 110 is formed to include multiple quantum wells (MQWs). The blue light-emitting region 110 includes MQWs configured to emit light having a primary peak wavelength that is blue when carriers recombine radiatively in the MQWs. The MQWs are formed from indium gallium nitride ( InGaN) epitaxially grown between GaN-based layers, and the composition of each individual quantum well is adjusted to provide light of a desired wavelength that can be emitted therefrom. Although MQWs are described in the context of the light-emitting region 110, alternatively, a single quantum well (SQW) layer can be used. In a further example, the light-emitting region 110 includes quantum dots (QDs), and the QDs are configured to emit light when carriers recombine radiatively in the QDs. The light having the primary peak wavelength emitted from the light-emitting region 110 described in relation to FIGS. 1A to 1E is configured to be blue, but in a further example, the light-emitting region 108 is configured to emit light having a different primary peak wavelength, such as ultraviolet light, additionally or alternatively.

[0049] Furthermore, by providing the light-emitting structure as described, in any of the processing steps involved in the process of forming the individual light-emitting structures or in processing the resulting structure formed by bringing together those individual light-emitting structures, it will be understood by those skilled in the art that the material is produced efficiently and with high quality while reducing the processing steps by incorporating layers into the structure. However, in a further example, it will be further understood by those skilled in the art that additional or alternative steps may be used to form the structure, the order of the steps may be different, or the steps may be selected to provide additional advantages.

[0050] FIG. 2 shows the light-emission concept from the light-emitting structure 100E described in FIG. 1E. The light-emitting structure 100E is configured such that carriers are injected into the light-emitting region 110, whereby radiative recombination occurs and light having a primary peak wavelength of blue (about 450 nm) is emitted. Carrier injection occurs by electrically contacting the n-type region and the p-type region. Such electrical contact is provided by the formation of an anode and a cathode (not shown).

[0051] When the activated light-emitting region 110 is excited, light (blue light) having a primary peak wavelength of 450 nm is emitted. The light emission from the light-emitting region 110 is non-uniform and has a higher intensity in a direction perpendicular to the lateral surface formed by the quantum wells of the light-emitting region 110. As indicated by the arrows in FIG. 2, a part of the blue light emitted by the light-emitting region 110 passes through the n-type region 108 and the partial reflection region 106 in order to excite the carriers of the color conversion material 118. This is indicated by arrow 204. The backward-scattered blue light emitted from the light-emitting region 110 passing through the p-type region 112 is reflected by the reflection region 114 and passes through the remaining part of the light-emitting structure 100A in order to excite the carriers of the color conversion material 118.

[0052] In contrast, light generated and / or reflected by the color conversion material 118 and incident on the partial reflection region 106 (e.g., when not passing through other surfaces) is reflected by the partial reflection region 106 or transmitted through the partial reflection region 106. When the blue light from the light emitting region 110 generates red light from the color conversion material 118, the red light incident on the partial reflection region 106 is reflected by the partial reflection region 106 and exits the structure, providing light emission from the defined upper surface. This is indicated by arrow 202. When the blue light from the light emitting region 110 generates green light from the color conversion material 118, the green light incident on the partial reflection region 106 is reflected by the partial reflection region 106 and exits the structure, providing light emission from the defined upper surface. This is indicated by arrow 206. When the blue light from the light emitting region 110 emits (including generating or reflecting) blue light from the color conversion material 118, the blue light incident on the partial reflection region 106 is transmitted through the partial reflection region 106 and passes through the structure, whereby the light incident on the bottom region 114 is reflected and passes through the partial reflection region 106, so that this light can excite light emission in the color conversion material or provide an opportunity to exit the structure. This is indicated by arrow 208. Advantageously, the light from the color conversion material 118 is directed to leave the light emitting structure 100 through the same defined upper surface, while the downwardly directed light (light that leaves the upper surface and returns to the light emitting structure from the location where light is generated by the excitation light source LED) is reflected out or reused to generate further light emission by leaving the light emitting structure through the defined upper surface.

[0053] The color conversion material has been described in relation to the generation of red, green, and blue light, but alternatively or additionally, the light generated by the color conversion material 118 has a broad spectrum such as white light. In that case, the partial reflection region 106 provides selective transmission and reflection of light based on the wavelength of the light incident on the partial reflection region 106 such that the partial reflection layer is configured to reflect a predetermined range of wavelengths. The predetermined range of wavelengths includes wavelengths longer than 500 nm.

[0054] In a further example, alternatively or additionally, a predetermined range of wavelengths includes wavelengths of visible light longer than 500 nm, such as wavelengths of light from 500 nm to 740 nm. In a further example, a predetermined range of wavelengths includes wavelengths longer than 400 nm. Advantageously, a light source with a shorter wavelength (e.g., a UV light source of about 380 nm) is used to excite the color conversion material in such a way that, for example, the partial reflection region 106 reflects blue light as well as red and green light, and benefits are obtained by the partial reflection region 106 and the mirror region 114 in enhancing the efficiency of light conversion and light extraction from the light-emitting structure. Thus, in the example, the wavelengths of light in a beneficial predetermined range reflected by the partial reflection region 106 include all wavelengths from 400 to 740 nm, from 500 to 740 nm, all wavelengths longer than 400 nm, and all wavelengths longer than 500 nm.

[0055] The partial reflection region 106 is configured to reflect light at a predetermined range of wavelengths. However, in some examples, less than 100% of the light incident on the partial reflection region 106 (e.g., due to absorption / slight transmission) is reflected at the predetermined range of wavelengths, and the partial reflection region 106 is optimized to reflect light at the predetermined range of wavelengths as efficiently as possible to provide the effect of selective transmission of light from the light-emitting region 110 to the color conversion region 118, so that light of the wavelength of the excitation light source from the color conversion region is recycled in the light-emitting structure, hits the reflection region, and exits to the color conversion region again.

[0056] Advantageously, light that does not contribute to the emission from the color conversion material 118 on the side of the light-emitting region 110 of the structure opposite thereto is provided with a further chance to be emitted from the structure, either by reflection in the partial reflection region 106 or by reflection by the bottom mirror region 114. Advantageously, the amount of light emitted by a color-converted LED with such a structure increases, and the light conversion efficiency also increases by using the partial reflection region 106 and the mirror region 114 in combination.

[0057] The reflectance profile 200B of the partial reflection region 106 described in relation to the LED structure 200A of FIG. 2 is shown. In the reflectance profile, light having a wavelength longer than 500 nm is substantially reflected by the partial reflection region 106, and light having a wavelength less than 500 nm is substantially transmitted through the partial reflection region 106. The partial reflection region 106 having such characteristics can be implemented using various methods and structures. An example of a structure that provides a function that can be used in such a manner has been described above with reference to FIGS. 3A and 3B as well.

[0058] The blue light from the light emitting region excites the color conversion material 118 so that the wavelength reflected by the partial reflection region 106 becomes longer in order to improve the emission of longer and shorter wavelengths passing through the partial reflection region 106 and being reflected by the reflection region 114 to enhance the opportunity for color conversion and light emission from the color conversion LED structure 200A. Although the above structure has been described in relation to the emission of blue light from the light emitting region and the functions of the partial reflection region 106 and the reflection region 114, those skilled in the art will understand that these concepts are also applicable to light having different primary peak wavelengths emitted by the light emitting region so that the total amount of color-converted light emitted from the color conversion material 118 is improved.

Claims

1. A method for forming a light-emitting structure, comprising: the light-emitting structure including: a light-emitting region configured to emit light having a primary peak wavelength; a partial reflection region; a reflection region; a color conversion region; wherein the light-emitting region is at least partially positioned between the partial reflection region and the reflection region, the partial reflection region is at least partially positioned between the color conversion region and the light-emitting region, the partial reflection region is configured to reflect light having wavelengths within a predetermined range and allow light having wavelengths outside the predetermined range to pass therethrough, and the primary peak wavelength is outside the predetermined range; the method for forming the light-emitting structure including: forming a light-emitting device including the light-emitting region on a substrate; forming the partial reflection region in front of the light-emitting region; forming an undoped material between the substrate and the partial reflection region; removing the substrate; roughening the undoped material subsequent to the removal of the substrate, the roughening of the undoped material being performed before forming the color conversion region on the roughened undoped material; a method comprising the above steps.

2. The method according to claim 1, wherein the partial reflection region includes a distributed Bragg reflector.

3. The method according to claim 1 or 2, wherein the reflection region includes an Ag-based mirror.

4. The method according to any one of claims 1 to 3, including depositing the reflection region on a light-emitting device including the light-emitting region.

5. The method according to any one of claims 1 to 4, including removing the substrate by wet etching.

6. The method according to any one of claims 1 to 5, including bonding a transfer device to the reflection region.

7. The method according to any one of claims 1 to 6, wherein the light-emitting structure includes a GaN-based structure.

8. The method according to any one of claims 1 to 7, wherein the light-emitting region includes one or more epitaxial quantum wells.

9. The method according to any one of claims 1 to 8, wherein the light-emitting region is configured to emit light having a primary peak wavelength corresponding to blue light.

10. The method according to any one of claims 1 to 9, wherein the predetermined range of wavelengths includes wavelengths of light longer than 500 nm such that wavelengths shorter than 500 nm are outside the predetermined range of wavelengths.

Images