Selective optical filters for RGB LEDs

Abstract

1. A method of forming a light emitting structure, the light emitting structure comprising: an emissive layer configured to emit light having a primary peak wavelength; a partially reflective layer; a reflective layer; and a color conversion layer, wherein the emissive layer is located at least partially between the partially reflective layer and the reflective layer; the color conversion layer is located at least partially between the emissive layer and the partially reflective layer; the partially reflective layer is configured to reflect light of wavelengths within a predetermined range and transmit light of wavelengths outside the predetermined range; and the primary peak wavelength is a wavelength within the predetermined range.

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 exclusively, the present invention relates to improved color conversion in light emitting diode structures.

Background Art

[0002] Light emitting diode (LED) devices are known to provide an efficient light source for a wide range of applications. LED light sources are used to produce conventional white light and / or multicolor light emissions. For example, multicolor light emissions include red, green, and / or blue light emissions suitable for display applications. The light of the desired wavelength provided by the LED is typically achieved using a combination of a pump source LED having a color conversion layer such as, for example, a phosphor, quantum dots (QD), or an organic semiconductor. Such a pump source LED generates light having a primary peak wavelength output and induces light emissions of different wavelengths in the color conversion layer. For example, a blue light nitride material LED (which emits light having a primary peak wavelength of about 450 nm) is used to produce white converted light LED emissions. The blue nitride material LED is also used to produce red converted light LED emissions and green converted light LED emissions.

[0003] However, while pump source LEDs such as blue nitride-based material LEDs are available for high-quality and efficient light emission, the application of a color conversion layer to achieve light of the desired color typically results in a reduction in the light emission efficiency of the color-converted LED compared to the source LED used to pump the color conversion layer. Such reduced efficiency is due, for example, to the light generated by the source LED being absorbed in the color conversion layer. Therefore, various optical coating methods are used to reduce the losses due to absorption of light in the light conversion layer. However, such conventional optical coatings are costly and difficult to implement in mass production.

[0004] Therefore, it is beneficial to enable more efficient light extraction in color-converted LEDs that use color conversion techniques to produce light of a desired wavelength. [Overview of the project] [Means for solving the problem]

[0005] To mitigate at least some of the problems described above, a method is provided for forming a light-emitting structure, wherein the light-emitting structure includes a light-emitting layer configured to emit light having a primary peak wavelength, a partial reflection layer, a reflection layer, and a color conversion layer, wherein the light-emitting layer is at least partially located between the partial reflection layer and the reflection layer, the color conversion layer is at least partially located between the light-emitting layer and the partial reflection layer, the partial reflection layer is configured to reflect light of wavelengths within a predetermined range and transmit light of wavelengths outside the predetermined range, and the primary peak wavelength is within a predetermined range.

[0006] Furthermore, a light-emitting structure is provided, comprising a light-emitting layer configured to emit light having a primary peak wavelength, a partial reflection layer, a reflection layer, and a color conversion layer, wherein the light-emitting layer is at least partially located between the partial reflection layer and the reflection layer, the color conversion layer is at least partially located between the light-emitting layer and the partial reflection layer, the partial reflection layer is configured to reflect light of wavelengths within a predetermined range and transmit light of wavelengths outside the predetermined range, and the primary peak wavelength is a wavelength within a predetermined range.

[0007] Advantageously, the light-emitting structures formed in this way result in improved color conversion efficiency, minimize the amount of color conversion material required, and are suitable for mass production. Beneficially, the method is: Applicable to LEDs of different sizes, including microLEDs, capable of realizing white LED or multi-color LED displays, and suitable for mass transfer of individual LEDs, microLEDs, and / or monolithic LED arrays.

[0008] Preferably, the color conversion layer includes a first lateral separation layer and a second lateral separation layer, wherein the first layer is configured to convert incident light having a primary peak wavelength into light having wavelengths outside a predetermined range, and the second layer is configured to transmit incident light having a primary peak wavelength, and a partial reflection layer extends over the first layer of the color conversion layer but not over the second layer.

[0009] Preferably, the first layer of the color conversion layer further includes a first lateral separation sublayer and a second lateral separation sublayer, wherein the first sublayer is configured to convert incident light having a primary peak wavelength into light having a first wavelength outside a predetermined range, and the second sublayer is configured to convert incident light having a primary peak wavelength into light having a second wavelength outside a predetermined range.

[0010] Advantageously, this allows some of the light having the primary wavelength to exit the light-emitting structure by directly passing through the second layer of the color conversion layer, while the light converted to wavelengths outside a predetermined range is emitted from the first layer of the color-converted layer and exits the light-emitting structure via the partial reflection layer. Any light that passes through the first layer of the color conversion layer without being converted is reflected by the partial reflection layer for reuse, thereby improving efficiency.

[0011] Preferably, the partial reflective layer includes a distributed Bragg reflector (DBR), the DBR comprising porous GaN. Advantageously, the DBR is incorporated into the growth process, thereby enabling the formation of a crystalline semiconductor layer that provides the required partial reflective function without compromising the crystal quality necessary for forming high-quality, efficient light-emitting diode devices.

[0012] Preferably, the reflective layer includes a silver (Ag)-based mirror. Advantageously, the highly reflective layer is incorporated into the structure, thereby increasing the reuse of backscattered light and light that is not emitted by the color conversion layer but propagates back through the structure and incident on the Ag-based mirror. Beneficially, Ag is used simultaneously to form the mirror layer and to provide a eutectic junction to the handling device, thereby serving a dual purpose.

[0013] Preferably, the method further comprises depositing a reflective layer on a light-emitting device including a light-emitting layer. Advantageously, a light-emitting device such as a light-emitting diode device may be provided, and known deposition techniques may be used to provide a reflective layer that allows at least visible light and / or ultraviolet light to be reflected for color conversion and / or emission without impairing the quality of the light-emitting device.

[0014] Preferably, the method further comprises growing a light-emitting device including a light-emitting layer on a substrate, and then removing the substrate, preferably by wet etching. Advantageously, the structure is formed on the substrate using known techniques, thereby providing a high-quality material for light generation and extraction, and when provided in this manner, the high-quality structure is formed on the substrate that is subsequently removed in order to provide a structure having improved light color conversion efficiency, thereby reducing the processing burden required to provide the resulting structure.

[0015] Preferably, the method further includes depositing a color conversion layer after substrate removal, and the light-emitting structure is roughened after substrate removal and before the color conversion layer is formed. Advantageously, the same layer of the structure used to initiate the growth of high-quality material is reused for color conversion, enabling the formation of the structure at relatively similar locations on the structure without interfering with color conversion. Furthermore, roughening the substrate aids in the adhesion and light extraction of the color conversion layer without impairing the light-emitting effect from the structure.

[0016] Preferably, the method further includes bonding the handling device to the reflective layer. Advantageously, the structure is handled from the opposite side to 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 layer includes one or more epitaxial quantum wells. Advantageously, high-quality epitaxial quantum well structures enable efficient light emission in epitaxial stacked devices.

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

[0020] Preferably, the predetermined wavelength range includes wavelengths of light shorter than 500 nm, such that wavelengths exceeding 500 nm are outside the predetermined range. Therefore, for example, when blue light pumps red and green emission from the first layer of the color conversion layer, the red and green emission is transmitted away from the structure, and light with wavelengths less than 500 nm is reflected through the structure for reuse. Thus, it is possible to increase the output and efficiency from the color conversion layer.

[0021] Preferably, the color conversion layer is separated by reflective sidewalls extending through the light-emitting layer, and these sidewalls include aluminum sidewalls coated with silicon dioxide. Advantageously, this serves to divide the light-emitting device into electronically isolated, individually addressable elements, improving the efficiency of each element by internally reflecting light directed away from the light-emitting surface while reducing optical crosstalk between elements.

[0022] Further aspects of the invention will become apparent from the description and the attached claims.

[0023] A detailed description of embodiments of the invention is given with reference to the drawings, merely as examples. [Brief explanation of the drawing]

[0024] [Figure 1] A cross-sectional view of a portion of the light-emitting structure, including the DBR, is shown. [Figure 2]Shows a cross-sectional view of the light-emitting structure. [Figure 3] Shows a further processed version of the cross-sectional view of the light-emitting structure in FIG. 2. [Figure 4] Shows the light emission and reflection profiles of the DBR. [Figure 5] FIGS. 5(a) and 5(b) show an exemplary DBR structure, and FIG. 5(c) shows an exemplary reflectivity profile at normal incidence for the DBR of FIG. 5(a).

Embodiments for Carrying Out the Invention

[0025] A concise and advantageous embodiment of the reflective layer and the partial reflective layer in a light-emitting structure having a color conversion layer provides an LED device such as a micro-LED device capable of realizing a white LED or a multi-color LED display, which is suitable for both the individual micro-LED transfer process and the monolithic LED array. The synergistic combination of different layers within the light-emitting structure provides a solution for improved light conversion and extraction compared to known structures. Advantageously, the embodiment maintains the structural crystalline integrity of the epitaxial compound semiconductor light-emitting structure while enabling improved functionality and reducing processing requirements.

[0026] The present invention uses a distributed Bragg reflector (DBR) to improve the performance of light-emitting devices such as RGB LEDs and micro-LED devices. Methods for creating DBRs using GaN materials are disclosed in Zhang et al. ACS Photonics, 2, 980 (2015), and more recently in "Wafer-scale Fabrication of Non-Polar Mesoporous GaN Distributed Bragg Reflectors via Electrochemical Porosification" by Tongtong et al., Scientific Reports 7, article number 45344, 2017.

[0027] A method for forming the light-emitting structure 100 will be described with reference to Figures 1 to 3. The light-emitting structure 100 is an LED structure that provides light having a desired wavelength using a color conversion layer. The resulting light-emitting structure is an LED structure having a pump-source LED and a color conversion layer. The method will be described by cross-sectional views through the layers of the light-emitting structure 100 at different stages in the process of providing improved color conversion to the light-emitting structure. The layers shown in Figures 1 to 3 provide layers of the light-emitting structure having different functional properties. Layers of the light-emitting structure having different functional properties are formed from one or more layers of different materials working together to provide the functional properties (for example, the light-emitting layer may include multiple quantum well structures, and the partial reflection layer may include multiple layers with different refractive indices). In further embodiments, additional or alternative layers are used to facilitate the concepts described herein.

[0028] Figures 1(a) and 1(b) illustrate the steps in providing the DBR filter 100A. A stack of epitaxial compound semiconductor crystalline layers is shown. The epitaxial compound semiconductor crystalline layers are provided by the sequential growth of layers on a growth substrate 102. Conveniently, such epitaxial compound semiconductor crystalline layers formed in this manner can be controlled with high precision to provide a high-quality material.

[0029] A layer of undoped material 104, which serves as a buffer layer, or a growth substrate 102 on which the buffer layer grows, is shown. The undoped material 104 is a layer of undoped gallium nitride (u-GaN). Advantageously, the undoped material provides a layer that is transparent to at least visible and ultraviolet light.

[0030] A layer, which is a partial reflective layer 106, is shown above the undoped material 104. The growth substrate 102 is a growth silicon substrate. The partial reflective layer 106 is a distributed Bragg reflector (DBR). In this 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 reflective layer 106 is formed to reflect all wavelengths less than 500 nm. Light with longer wavelengths, such as green light with a wavelength of 520 nm, is transmitted, but unconverted blue pump light is reflected by the partial reflective layer 106, and red light with a wavelength of 620 nm is transmitted, but unconverted blue pump light is reflected by the partial reflective layer 106.

[0031] The partial reflective layer 106 is formed from alternating epitaxial crystalline layers with different refractive indices. The refractive indices and thicknesses of the layers are selected to provide a reflectivity response as a function of the wavelength of light incident on the partial reflective layer 106. Furthermore, since the porosity of the epitaxial crystalline layers is linked to the refractive index of the partial reflective layer 106, the porosity of the epitaxial crystalline layers forming the partial reflective layer 106 is controlled to provide a desired reflectivity response as a function of wavelength.

[0032] In this embodiment, alternating high-refractive-index layers and low-refractive-index layers form a partial reflective layer 106, and the high-refractive-index (n H ) layer and low refractive index (n L The thickness of each layer is selected such that the product of the layer thickness and the reciprocal of the layer's refractive index is λ0 / 4, and λ0 is calculated according to the following formula, with + / around λ0. -λ e This is the center wavelength for high reflectivity response between [the specified ranges].

number

[0033] Figure 5(a) shows a cross-sectional view of an example of such alternating high-refractive-index and low-refractive-index layers forming a partial reflective layer 106, and Figure 5(c) shows the associated reflectivity response as a function of wavelength. The alternating high-refractive-index and low-refractive-index layers begin at the bottom of the structure and end at the top with a low-refractive-index layer that is half the thickness of the other low-refractive-index layer in the other alternating layers in the structure (λ0 / 8 instead of λ0 / 4), resulting in the reflectivity response at perpendicular incidence shown in Figure 5(c).

[0034] A particular structure configured to produce the desired effect may be carried out in different ways, and in this embodiment, the partial reflection layer 106 has a structure as described with respect to Figure 5(b). The partial reflection layer 106 includes alternating high refractive index layers and low refractive index layers. When the structure is formed for a wavelength of light λ0 = 430 nm, the first layer is 21.3 nm thick and is formed from non-porous gallium nitride. The next layer is a gallium nitride layer with 70% porosity and a thickness of 66 nm. The next layer is another non-porous gallium nitride layer with a thickness of 42.6 nm. Four more pairs are formed, alternating between 66 nm thick gallium nitride with 70% porosity and non-porous gallium nitride with a thickness of 42.6 nm. A final layer of 33 nm thick gallium nitride with 70% porosity forms the end of the structure. The structures described with respect to Figures 5(a) and 5(b) provide reflectance at perpendicular incidence as a function of wavelength, as shown in the reflectance response of Figure 4.

[0035] The partial reflective layer 106 is formed by the method described above, and, as an alternative or addition, the structure and / or layers of the partial reflective layer 106 are formed from different layers and materials having different porosities and thicknesses to produce the desired reflectivity response. For example, it is known that the porosity of a material can be changed to alter its refractive index (see, e.g., MMBraun, 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 the percentage of porosity according to the following formula.

number

[0036] The partial reflective layer 106 is a distributed Bragg reflector (DBR), and in further embodiments, the partial reflective layer 106 is formed by a different method, either additionally or alternatively. It maintains the functionality to allow reflection of light of one wavelength and transmission of light of different wavelengths.

[0037] An n-type layer 108 is located above the partial reflective layer 106. The n-type layer 108 is made of n-doped gallium nitride (n-GaN).

[0038] While the growth of epitaxial GaN-based materials on a silicon growth substrate 102 is shown, in further embodiments, additional or alternative intervening layers are used to account for lattice mismatch between the silicon substrate 102 and the subsequent growth layer. In the embodiment, the growth substrate 102 includes an aluminum nitride (AlN)-containing silicon buffer layer. In further embodiments, the growth substrate 102 includes an undoped GaN layer.

[0039] Given the structure of Figure 1(a), selective portions of the partial reflective layer 106 and the n-GaN layer 108 are removed. In this embodiment, this is achieved by selective dry etching, but those skilled in the art will understand that any suitable alternative process may be applied. Advantageously, the anisotropic etching process provides a clearer distinction between the different colored emission regions of the light-emitting structure 100 (shown in Figure 3) than was possible with conventional optical coatings, further enhancing the performance of small devices.

[0040] As shown in Figure 2, the DBR filter 100A is bonded to the underlying RGB LED device 100B. In an alternative embodiment, the DBR filter 100A and the RGB LED device 100B are attached by mechanical means.

[0041] The RGB LED device 100B includes an emissive layer 110 sandwiched between an n-type layer 109 and a p-type layer 112. In a preferred embodiment, the emissive layer 110 is a blue emissive layer 110. In embodiments, these layers are epitaxial compound semiconductor crystalline layers resulting from the sequential growth of layers on a growth substrate (not shown) which is subsequently removed. Advantageously, such epitaxial compound semiconductor crystalline layers formed in this manner can be controlled with high precision to provide high-quality material and efficient light emission during carrier injection from the n-type and p-type layers to the emissive layer. In embodiments, the n-type layer 109 is n-doped GaN (n-GaN) and the p-type layer is p-doped gallium nitride (p-GaN), but any suitable material may be used. The illustrated RGB LED 100B is based on a typical blue LED structure. In further embodiments, alternative blue emissive structures having additional or alternative layers are used.

[0042] The RGB LED device 100B further includes a color conversion layer 118 formed on an n-type layer 109. In an embodiment, the color conversion layer 118 is formed on the surface of the n-type layer 109 that is exposed after the removal of the substrate on which the n-type layer 109, the light-emitting layer 110, and the p-type layer were grown. In a further embodiment, the surface of the n-type layer is roughened before the deposition of the color conversion layer 118 to improve the adhesion of the color conversion layer 118.

[0043] The color conversion layer 118 is formed from three regions 118A-C that are laterally separated along the plane of the layer 118, and regions 118A and 118B are configured to generate light of different wavelengths using light emitted by the light-emitting layer 110. In a preferred embodiment, regions 118A and 118B generate red and green light, respectively, using incident blue light generated by the light-emitting layer 110. In an embodiment, regions 118A and 118B are phosphors. Alternatively, or additionally, regions 118A and 118B include any suitable means for converting the wavelength of light from the pump-source LED, for example, using quantum dots (QDs) or other quantum confinement structures such as organic semiconductors or quantum wells. Region 118C is configured to allow blue light from the light-emitting layer to pass through. In an embodiment, region 118C is provided by a colorless transparent material such as a resin or transparent oxide, but any suitable material is It may be used.

[0044] In the illustrated embodiment, each region 118A-C of the color conversion layer 118, along with the lower portion of the light-emitting layer 110, is surrounded by reflective sidewalls. In a preferred embodiment, the reflective sidewalls are formed by aluminum sidewalls 300 coated with an insulating material such as silicon dioxide 302. As shown in Figures 2 and 3, the sidewalls 300 extend through the color conversion layer 118, the n-type layer 109, the light-emitting layer 110, and the p-type layer. These sidewalls are formed by conventional means and serve to reduce optical crosstalk between the elements of the RGB LED device 100B while separating the RGB LED 100B into three electrically isolated (and thereby individually addressable) elements. In a preferred embodiment, the elements correspond to the portions of the RGB LED 100B that generate red light, green light, and blue light.

[0045] The RGB LED device 100B is formed from a highly reflective Ag (silver)-based mirror deposited on a p-type layer 112 and further includes a mirror layer 114 configured to block light emitted to the p-type layer 112 by the light-emitting layer. The mirror layer 114 is processed to enable the formation of a eutectic bond with a handling device 116. The handling device 116 is a silicon wafer, which in this embodiment is used for its physical properties such as thermal and structural properties. In further embodiments, additional and / or alternative materials are used to form the handling device 116. In further embodiments, additional and / or alternative materials are used to form the reflective mirror layer 114, which, for example, may enable bonding to the handling device 116 using different methods, for example, using a separate bonding layer and a reflective layer. In further embodiments, the reflective mirror layer 114 is a mirror formed from another material. The reflective mirror layer 114 is configured to reflect at least visible light wavelengths and / or ultraviolet light wavelengths, including the primary peak wavelength of the light emitted by the light-emitting layer 110. Beneficially, the light emitted by the light-emitting layer 110, which is backscattered toward the reflective mirror layer 114, and the light reused within the light-emitting structure through the partially reflective layer 106, are reflected toward the color conversion layer 118, thereby enhancing the color conversion and light output from the light-emitting structure.

[0046] Through-silicon vias (TSVs) 120A-C and 122A-C extending from the handling device 116 into the light-emitting structure 100 are also shown. These allow separate electrical contacts to be created for each insulating portion of the light-emitting layer 110, enabling the color selection operation of the light-emitting structure 100.

[0047] The DBR filter 100A and RGB LED device 100B are positioned such that a region 118C of the RGB LED 100B aligns with a selectively etched portion of the DBR filter 100A. Advantageously, this step of the process can be performed simultaneously across multiple devices 100 when the devices are provided in an array. Although shown as a single DBR filter 100A added to a single underlying RGB LED device 100B, the DBR filter 100A may be provided as a continuous layer across the entire first wafer / handling device, having regularly etched portions corresponding to a region 118C of the array of RGB LED devices on a second wafer / handling device. Aligning such a DBR filter 100A with the underlying array in a single all-wafer step greatly simplifies the manufacturing process and benefits further from associated economies of scale. Additionally, the growth substrate 102 provides a uniform outer layer from which the DBR filter can be safely and controllably handled, enabling precise positioning of the filter relative to the region of the RGB LED device.

[0048] The light-emitting structure 100 is processed to remove the growth substrate 102 for the DBR filter 100A. Again, in embodiments where the RGB LED device is provided as an array, this A single step can be performed simultaneously for each device in the array. The resulting structure is shown in Figure 3. Figure 3 shows a cross-sectional view of the light-emitting structure 100. The growth substrate 102 is a silicon growth wafer and 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 before the growth of subsequent light-emitting structures, the buffer layer is optionally removed by dry etching. If the RGB LED devices are arranged in an array of repeating structures across the wafer, this etching step can be performed once for all devices in the array.

[0049] Advantageously, the illustrated structure allows for increased light output and efficiency from color-converted light. Beneficially, the simple configuration of the structure leads to an efficient process flow suitable for mass production, as it results in the growth of high-quality light-emitting structures and improved light conversion. Beneficially, the increased light conversion efficiency means that fewer color conversion layers are used. This is advantageous in terms of cost and processing, as it means that thinner and more efficient layers of the color conversion layer 118 are used.

[0050] The light-emitting structure 100 is formed using epitaxial compound semiconductor growth techniques such as metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). Additionally, or alternatively, the light-emitting structure 100 may be formed using any suitable technique. The light-emitting structure 100 is an LED structure, but in further embodiments, additionally, or alternatively, the light-emitting structure 100 is a different light-emitting structure that benefits from the use of a selectively reflective layer to control the wavelength of light passing through the entire light-emitting structure.

[0051] The growth of the epitaxial crystalline compound semiconductor layer described above is carried out by growth / deposition on a silicon wafer used as the growth substrate. Alternatively, or additionally, other wafers such as sapphire wafers or self-supporting gallium nitride (GaN) wafers may be used.

[0052] While certain epitaxial crystalline compound semiconductor layers are shown in Figures 1 to 3, those skilled in the art will understand that alternative or additional layers may be used in further embodiments. Furthermore, in some embodiments, some of the epitaxial crystalline compound semiconductor layers are removed while maintaining the essence of the concepts described herein.

[0053] The light-emitting structures described with respect to Figures 1 to 5 are formed from nitride-based materials. In particular, the epitaxial crystalline compound semiconductor layer is a gallium nitride (GaN)-based material. Although the structures described with respect to Figures 1 to 5 relate to nitride-based semiconductor compound materials, those skilled in the art will understand that the concepts described herein are applicable to other materials, in particular other semiconductor materials, such as other III-V compound semiconductor materials or II-VI compound semiconductor materials.

[0054] The light-emitting layer 110 is formed to include multiple quantum wells (MQWs). The blue light-emitting layer 110 includes MQWs configured to emit light having a primary peak wavelength that is blue when carriers radiate-couple to the MQWs. The MQWs are formed from indium gallium nitride (InGaN) epitaxially grown between GaN-based layers having individual quantum well compositions adapted to provide light of a desired wavelength that can be emitted from them. Although MQWs are described in light-emitting layer 110, single quantum well (SQW) layers are used as an alternative. In further embodiments, the light-emitting layer 110 includes quantum dots (QDs) configured to emit light when carriers radiate-couple to the QDs. The primary peak wavelength of the light emitted from the light-emitting layer 110 described with respect to Figures 1 to 3 is configured to be blue, but in further embodiments, the light-emitting layer 110 may, as an addition or alternative, have a different primary peak wavelength. It is configured to emit light having a next peak wavelength, such as ultraviolet light.

[0055] Furthermore, those skilled in the art will understand that providing luminescent structures in the described manner by incorporating layers into the structure in either the process of forming individual luminescent structures or the processing steps involved in transporting those individual luminescent structures together and processing the resulting structure results in an efficient and high-quality production of material with reduced processing steps. However, those skilled in the art will further understand that in further embodiments, additional or alternative steps are used to form the structure, and the order of the steps is selected to yield different or additional benefits.

[0056] Figure 3 further illustrates the concept of light emission from the light-emitting structure 100. The light-emitting structure 100 is configured such that carriers are injected into the light-emitting layer 110, thereby resulting in radiative recombination and emission of light having a primary peak wavelength (approximately 450 nm) which is blue. Carrier injection occurs as a result of providing electrical contacts in the n-type and p-type layers. Such electrical contacts are provided by forming anodes and cathodes (not shown) using biases 120A~C and 122A~C.

[0057] When the active light-emitting layer 110 is excited, light (blue light) with a primary peak wavelength of 450 nm is emitted. The light emission from the light-emitting layer 110 is non-uniform and has a higher brightness in the direction perpendicular to the side plates formed by the quantum wells in the light-emitting layer 110. As shown by the arrows in Figure 3, the blue light emitted by the light-emitting layer 110 passes through the n-type layer 109 and is incident on the color conversion layer. The light incident on region 118C of the color conversion layer is transmitted through the color conversion layer 118 and passes through a portion of the DBR filter 100A corresponding to the gap in the partial reflection layer 106, exiting the light-emitting structure 100 as blue light and resulting in emission from the defined upper surface. This is shown by arrow 200.

[0058] Light incident on region 118A or 118B excites carriers having wavelengths corresponding to red or green light, respectively. Backscattered blue light emitted by the light-emitting layer 110 passing through the p-type layer 112 is reflected by the reflection layer mirror 114 and passes through the rest of the light-emitting structure 100 to excite carriers in the color conversion layer 118.

[0059] In contrast, light generated and / or transmitted by the color conversion layer 118, and light incident on the partial reflection layer 106 (for example, when not passing through other surfaces) are reflected by the partial reflection layer 106 or transmitted through the partial reflection layer 106 depending on their wavelength. When blue light from the light-emitting layer 110 generates red light from region 118A of the color conversion layer 118, the red light incident on the partial reflection layer 106 is transmitted by the partial reflection layer 106, exits the structure, and results in emission from the defined upper surface. This is indicated by arrow 202. When blue light from the light-emitting layer 110 generates green light from region 118B of the color conversion layer 118, the green light incident on the partial reflection layer 106 is transmitted by the partial reflection layer 106, exits the structure, and results in emission from the defined upper surface. This is indicated by arrow 204. When blue light from the light-emitting layer 110 results in blue light being emitted (including being generated or transmitted) from region 118A or 118B of the color conversion layer 118, the blue light incident on the partial reflection layer 106 is reflected by the partial reflection layer 106, passes through the structure, and is thus reflected in such a way that any light incident on the lower mirror layer 114 may be given an opportunity to excite luminescence in the color conversion layer. This is indicated by arrow 206. Beneficially, the light from the color conversion layer 118 is directed away from the light-emitting structure 100 through the same defined upper surface, and the light directed downward (away from the upper surface and returning into the light-emitting structure from where the light is generated by the pump-source LED) is reused to generate further luminescence away from the light-emitting structure through the defined upper surface.

[0060] The color conversion layer is described in relation to the generation of red, green, and blue light, but alternatively or additionally, the light generated in the color conversion layer 118 may have a broad spectrum, such as white light. In such cases, the partial reflection layer 106 provides selective transmission and reflection of light based on the wavelength of light incident on the partial reflection layer 106, such that the partial reflection layer is configured to reflect wavelengths within a predetermined range. The predetermined range of wavelengths includes wavelengths less than 500 nm.

[0061] In an alternative embodiment, a light source with a shorter wavelength (e.g., a UV light source of about 380 nm) is used to pump the color conversion layer in a manner that benefits from the partial reflection layer 106 and the mirror layer 114, which increase the efficiency of light conversion and light extraction from the light-emitting structure, for example, when the partial reflection layer 106 transmits blue light as well as red and green light. Thus, in the embodiment, a predetermined beneficial range of wavelengths of light reflected by the partial reflection layer 106 includes all wavelengths below 380 nm, and any higher wavelengths are transmitted through the partial reflection layer 106.

[0062] The partial reflective layer 106 is configured to reflect light in a predetermined range of wavelengths, and in some embodiments, less than 100% of the incident light in the partial reflective layer 106 is reflected in the predetermined range of wavelengths (e.g., due to absorption / minor transmission). The partial reflective layer 106 is optimized to reflect light as efficiently as possible in a predetermined range of wavelengths to give the effect of selective transmission of light from the light-emitting structure 100, so that the pump-source wavelength light from the conversion layer is reused in the light-emitting structure and strikes the reflective layer before exiting to the color conversion layer again.

[0063] Advantageously, light that does not contribute to the radiation from the color conversion layer 118 on the side of the structure facing the light-emitting layer 110 is given an additional opportunity to be emitted from the structure by the reflectivity of the lower mirror layer 114. Beneficially, the use of a partial reflective layer 106 in combination with the reflective mirror layer 114 increases the amount of light emitted by a color conversion LED using such a structure, and also increases the light conversion efficiency.

[0064] For micro-LED display applications, the size of the light-emitting area of ​​each individual color is preferably less than 5 microns, and therefore the thickness of the color conversion layer 118 is preferably less than 5 microns to reduce light absorption loss due to multiple reflections from the aluminum sidewall 300. Most preferably, the aspect ratio of the thickness of the layer 118 to the size of the light-emitting area of ​​each micro-LED is less than 1:1. For example, a micro-LED display having a subpixel size (individual color) of 3 microns preferably has a color conversion layer 118 that is thinner than 3 microns.

[0065] The supply of the DBR filter 100A allows for a reduction in the thickness of layer 118 without negatively impacting the performance of device 100. This also reduces light absorption from the sidewall 300, further increasing performance.

[0066] Figure 4 shows the reflectance profile of the partial reflective layer 106 described with respect to the structure of Figure 3. The reflectance profile indicates the extent to which light with wavelengths less than 500 nm is substantially reflected by the partial reflective layer 106, while light with wavelengths greater than 500 nm is substantially transmitted by the partial reflective layer 106. A partial reflective layer 106 having such properties can be implemented using different methods and structures. Examples of such structures that provide functionality that can be used in such a manner are described above with respect to Figures 1 to 5.

[0067] Although the above structure is described in relation to the emission of blue light from the light-emitting layer, those skilled in the art will understand that these concepts are applicable to light having different primary peak wavelengths emitted by the light-emitting layer so as to improve the total amount of color-converted light emitted from the color-converting layer 118.

Claims

1. A method for forming a light-emitting structure, wherein the light-emitting structure is A light-emitting layer configured to emit light having a primary peak wavelength λ0, Partial reflective layer, The reflective layer, Color conversion layer, Equipped with, The above method involves forming the light-emitting layer such that the light-emitting layer is at least partially located between the partial reflection layer and the reflection layer, and forming the color conversion layer such that the color conversion layer is at least partially located between the light-emitting layer and the partial reflection layer. The partial reflection layer is configured to reflect light of wavelengths within a predetermined range and transmit light of wavelengths outside the predetermined range, and the primary peak wavelength is a wavelength within the predetermined range. The aforementioned partial reflective layer has a refractive index of n Ｈ The thickness is (λ ０ / 8) × n Ｈ The first sublayer is defined as having a refractive index of n Ｌ The thickness is (λ ０ / 8) × n Ｌ A distributed Bragg reflector having a second sublayer, n Ｈ gan Ｌ Larger, The first sublayer and the second sublayer have a refractive index of n Ｈ and a third sublayer with a thickness of (λ ０ / 4)×n Ｈ and a fourth sublayer with a refractive index of n Ｌ and a thickness of (λ ０ / 4)×n Ｌ are separated by, The color conversion layer includes a first lateral separation layer and a second lateral separation layer, wherein the first lateral separation layer is configured to convert incident light having the primary peak wavelength into light having a wavelength outside the predetermined range, and the second lateral separation layer is configured to transmit incident light having the primary peak wavelength. A method wherein the partial reflective layer extends over the first lateral separation layer of the color conversion layer, but not over the second lateral separation layer.

2. The method according to claim 1, wherein the first lateral separation layer of the color conversion layer further comprises a first lateral separation sublayer and a second lateral separation sublayer, wherein the first sublayer is configured to convert incident light having the primary peak wavelength into light having a first wavelength outside the predetermined range, and the second sublayer is configured to convert incident light having the primary peak wavelength into light having a second wavelength outside the predetermined range.

3. The method according to claim 1 or 2, wherein the partial reflective layer comprises porous GaN and / or the reflective layer comprises an Ag-based mirror.

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

5. The method according to any one of claims 1 to 4, comprising growing a light-emitting device including the light-emitting layer on a substrate, and subsequently removing the substrate by wet etching.

6. The method according to claim 5, comprising depositing the color conversion layer after removing the substrate, wherein the light-emitting structure is roughened after the removal of the substrate and before the formation of the color conversion layer.

7. The method according to any one of claims 1 to 6, comprising bonding a handling device to the reflective layer.

8. The method according to any one of claims 1 to 7, wherein the light-emitting structure includes a GaN-based structure, and / or the light-emitting layer includes one or more epitaxial quantum wells, and / or the light-emitting layer is configured to emit light having a primary peak wavelength corresponding to blue light.

9. The method according to any one of claims 1 to 8, wherein the wavelengths in the predetermined range include wavelengths of light shorter than 500 nm, such that wavelengths exceeding 500 nm are wavelengths outside the predetermined range.

10. The method according to claim 1, wherein the first lateral separation layer and the second lateral separation layer of the color conversion layer are separated by a reflective sidewall extending through the light-emitting layer, and the reflective sidewall includes an aluminum sidewall coated with silicon dioxide.

11. A light-emitting structure, wherein the light-emitting structure is A light-emitting layer configured to emit light having a primary peak wavelength λ0, Partial reflective layer, The reflective layer, Color conversion layer, Equipped with, The light-emitting layer is at least partially located between the partial reflection layer and the reflection layer, and the color conversion layer is at least partially located between the light-emitting layer and the partial reflection layer. The partial reflection layer is configured to reflect light of wavelengths within a predetermined range and transmit light of wavelengths outside the predetermined range, and the primary peak wavelength is a wavelength within the predetermined range. The aforementioned partial reflective layer has a refractive index of n Ｈ The thickness is (λ ０ / 8) × n Ｈ The first sublayer is defined as having a refractive index of n Ｌ The thickness is (λ ０ / 8) × n Ｌ A distributed Bragg reflector having a second sublayer, n Ｈ gan Ｌ Larger, The first sublayer and the second sublayer have a refractive index of n Ｈ The thickness is (λ ０ / 4) × n Ｈ The third sublayer has a refractive index of n. Ｌ The thickness is (λ ０ / 4) × n Ｌ It is separated from the fourth sublayer, The color conversion layer includes a first lateral separation layer and a second lateral separation layer, wherein the first lateral separation layer is configured to convert incident light having the primary peak wavelength into light having a wavelength outside the predetermined range, and the second lateral separation layer is configured to transmit incident light having the primary peak wavelength. A light-emitting structure in which the partial reflective layer extends over the first lateral separation layer of the color conversion layer, but does not extend over the second lateral separation layer.

12. The light-emitting structure according to claim 11, wherein the first lateral separation layer of the color conversion layer further comprises a first lateral separation sublayer and a second lateral separation sublayer, wherein the first sublayer is configured to convert incident light having the primary peak wavelength into light having a first wavelength outside the predetermined range, and the second sublayer is configured to convert incident light having the primary peak wavelength into light having a second wavelength outside the predetermined range.

13. The light-emitting structure according to claim 11 or 12, wherein the partial reflective layer comprises porous GaN and / or the reflective layer comprises an Ag-based mirror.

14. The light-emitting structure according to any one of claims 11 to 13, wherein the light-emitting structure includes a GaN-based structure, and / or the light-emitting layer includes one or more epitaxial quantum wells, and / or the light-emitting layer is configured to emit light having a primary peak wavelength corresponding to blue light.

15. The light-emitting structure according to any one of claims 11 to 14, wherein the wavelengths within the predetermined range include wavelengths of light shorter than 500 nm, such that wavelengths exceeding 500 nm are outside the predetermined range.

16. The light-emitting structure according to any one of claims 11 to 15, wherein the first lateral separation layer and the second lateral separation layer of the color conversion layer are separated by a reflective sidewall extending through the light-emitting layer, and the reflective sidewall includes an aluminum sidewall coated with silicon dioxide.

17. A method for forming an array of light-emitting structures comprising any one of claims 1 to 10.

18. An array of light-emitting structures according to any one of claims 11 to 16.

Images