deformation relaxation layer

Abstract

A method for forming a strain relaxation layer within an epitaxial crystalline structure, comprising: providing a crystalline template layer comprising a material having a first natural relaxation in-plane lattice parameter; forming a first epitaxial crystalline layer on the crystalline template layer, wherein the first epitaxial crystalline layer has an initial electrical conductivity higher than the electrical conductivity of the crystalline template layer; forming a second epitaxial crystalline layer on the first epitaxial crystalline layer, wherein the second epitaxial crystalline layer comprises a material having an electrical conductivity lower than the initial electrical conductivity of the first epitaxial crystalline layer and having a second natural relaxation in-plane lattice parameter different from the first natural relaxation in-plane lattice parameter of the crystalline template layer; A method comprising: forming pores in a first epitaxial crystalline layer by electrochemical etching of the first epitaxial crystalline layer to enable strain relief in the second epitaxial crystalline layer by plastic deformation of bonds at the interface between the first epitaxial crystalline layer and the second epitaxial crystalline layer and / or within the first epitaxial crystalline layer; and forming one or more channels comprising a conductive material through at least the first epitaxial crystalline layer and the second epitaxial crystalline layer to enable electrical connection to a crystalline template layer through the first epitaxial crystalline layer and the second epitaxial crystalline layer.

Description

Technology Field

[0001] The present invention relates to a template and a method for forming a template. Specifically, but not exclusively, the present invention relates to a template and a method for forming a template that enables the growth of a deformation-relaxed crystalline material for forming a practical device. Background Technology

[0002] Epitaxially grown crystalline devices, such as light-emitting diode (LED) devices, are typically formed using techniques such as metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) to provide crystalline structures with layers of variable composition. For example, variable composition of layers, which may be required to achieve specific emission recombination, can cause mismatch between the crystalline lattice parameters of the layers. Such mismatch can typically lead to high strain, which can subsequently lead to a decrease in internal quantum efficiency (IQE). This is a known problem in the formation of InGaN-based LED structures, particularly when a high indium content in indium gallium nitride (InGaN) quantum wells (QWs) is used to provide longer wavelength light emission, e.g., red light emission.

[0003] In such cases, attempts to reduce strain on the underlying layer to improve the characteristics of the devices often present other challenges. For example, in InGaN-based devices, growing QWs on a relaxed InGaN layer having an in-plane lattice constant greater than that of gallium nitride (GaN) will reduce strain and consequently improve IQE. However, achieving high-quality relaxed InGaN layers while also enabling carrier injection into the QWs to form functional devices is problematic because high-quality n-type layers with desirable doping levels are typically and advantageously formed from n-type doped GaN, and this is not easily achieved for materials having the composition required to reduce strain and consequently improve the IQE of red light-emitting InGaN-based LEDs.

[0004] Porous GaN is compliant and rich in broken bonds that enable the propagation of misfit dislocations at the porous GaN / InGaN interface; therefore, it has been proposed as a mechanism for porous GaN layers to reduce strain in subsequently grown layers. However, such porous GaN is highly resistive and is consequently generally unsuitable for the formation of functional devices.

[0005] A method for forming a strain-relaxing layer within an epitaxial crystalline structure to alleviate at least some of the aforementioned problems, comprising: providing a crystalline template layer comprising a material having a first natural relaxation in-plane lattice parameter; forming a first epitaxial crystalline layer on the crystalline template layer, wherein the first epitaxial crystalline layer has an initial electrical conductivity higher than the electrical conductivity of the crystalline template layer; forming a second epitaxial crystalline layer on the first epitaxial crystalline layer, wherein the second epitaxial crystalline layer comprises a material having an electrical conductivity lower than the initial electrical conductivity of the first epitaxial crystalline layer and having a second natural relaxation in-plane lattice parameter different from the first natural relaxation in-plane lattice parameter of the crystalline template layer; A method is provided comprising: forming pores in a first epitaxial crystalline layer by electrochemical etching of the first epitaxial crystalline layer to enable strain relief in the second epitaxial crystalline layer by plastic deformation of bonds at the interface between the first epitaxial crystalline layer and the second epitaxial crystalline layer and / or within the first epitaxial crystalline layer; and forming one or more channels comprising a conductive material through at least the first epitaxial crystalline layer and the second epitaxial crystalline layer to enable electrical connection to a crystalline template layer through the first epitaxial crystalline layer and the second epitaxial crystalline layer.

[0006] Additionally, as an epitaxial crystalline structure, a crystalline template layer comprising a material having a first natural relaxation in-plane lattice parameter; a first epitaxial crystalline layer formed on the crystalline template layer; a second epitaxial crystalline layer formed on the first epitaxial crystalline layer comprising a material having a second natural relaxation in-plane lattice parameter different from the first natural relaxation in-plane lattice parameter of the crystalline template layer; and one or more pores formed in the first epitaxial crystalline layer such that strain within the second epitaxial crystalline layer is relieved by plastic deformation of bonds at the interface between the first epitaxial crystalline layer and the second epitaxial crystalline layer and / or within the first epitaxial crystalline layer; An epitaxial crystalline structure is provided, comprising one or more channels including a conductive material formed through at least the first epitaxial crystalline layer and the second epitaxial crystalline layer to enable electrical connection to a crystalline template layer through the first epitaxial crystalline layer and the second epitaxial crystalline layer.

[0007] Advantageously, the porosity of the initial high-electrical conductive layer, along with the formation of one or more channels, enables the relaxation of the crystalline layer having different intrinsic relaxation in-plane lattice parameters compared to the intrinsic relaxation in-plane lattice parameters of the underlying template layer. This relaxation enables the formation of devices that would otherwise be difficult to achieve, while also enabling electrical connection to the underlying template layer in a manner that improves device formation.

[0008] Preferably, the pores are formed such that the bulk density of the first epitaxial layer between the crystalline template layer and the second epitaxial crystalline layer is greater than 50%, preferably greater than 60%, and more preferably greater than 70%. Advantageously, the density of the pores within the first epitaxial crystalline layer is controlled to facilitate plastic deformation of the bonds at the interface between the first epitaxial crystalline layers and / or within the first epitaxial crystalline layer.

[0009] Preferably, the second epitaxial crystalline layer comprises at least one V-pit, and preferably, the depth of the at least one V-pit is substantially the combined thickness of the first epitaxial crystalline layer and the second epitaxial crystalline layer. Advantageously, V-pits of such depth enable electrical connection to the underlying crystalline template layer.

[0010] Preferably, the method comprises the step of enlarging at least one V-pit, and preferably, the step of enlarging at least one V-pit comprises the step of etching material from the sidewalls of at least one V-pit to expose at least a portion of the crystalline template layer. Advantageously, the V-pits facilitate electrical connection between the crystalline template layer and layers subsequently formed on the second epitaxial crystalline layer through the porous high-electrical-resistive porous first epitaxial crystalline layer.

[0011] Preferably, the method comprises the step of etching through at least the second epitaxial crystalline layer to form one or more islands within the second epitaxial crystalline layer. Advantageously, the formation of the islands controls the relaxation of the second epitaxial crystalline layer.

[0012] Preferably, the method comprises the step of patterning a second epitaxial crystalline layer, and the patterning step comprises at least one of a lithography technique and a self-assembled Ni hard mask. Advantageously, the step of patterning the second epitaxial crystalline layer with a self-assembled Ni hard mask enables the formation of narrow channels for electrical connection and strain relief to an underlying crystalline template layer.

[0013] Preferably, the method comprises the step of forming a crystalline template layer on a patterned template layer. Advantageously, by controlling the underlying morphology of the crystalline template layer, improved device formation is facilitated. Advantageously, the formation of LED devices having improved light deformation control, more efficient light generation, and more efficient light extraction, and the formation of arrays of LED devices such as high-resolution micro-LED arrays may be provided.

[0014] Preferably, the patterned template layer is patterned to provide trenches, and preferably, the step of forming a crystalline template layer comprises forming an overgrown material in the trenches to provide V-grooves to enable the formation of two-dimensional domains that are at least partially defined by valleys within the second epitaxial crystalline layer. Advantageously, the formation of the trenches makes it possible for the size of the valleys to be adjusted by the overgrowth of the material in the trenches.

[0015] Preferably, the patterned template layer is patterned to provide one or more overgrowth structures, and preferably, the step of forming the patterned crystalline template layer comprises at least partially masking the crystalline template layer to provide one or more openings, and forming an overgrowth material within one or more openings to provide one or more overgrowth structures. Advantageously, overgrowth on the patterned substrate can be used to provide structures protruding from an initially substantially flat planar substrate. This morphology can be used to enable improved light emission characteristics from LED devices, along with improved strain control of the underlying crystalline material on which the LED devices are formed.

[0016] Preferably, when a patterned template layer is patterned to provide one or more overgrowth structures, the step of forming one or more channels comprising a conductive material through at least a first epitaxial crystalline layer and a second epitaxial crystalline layer comprises the step of removing material from one or more sidewalls of the one or more overgrowth structures. Advantageously, removing material to form channels through at least the first epitaxial crystalline layer and the second epitaxial crystalline layer enables electrical connection to the crystalline template layer through the first epitaxial crystalline layer and the second epitaxial crystalline layer.

[0017] Preferably, the method comprises the step of planarizing at least a portion of the second epitaxial crystalline layer to form the second epitaxial crystalline layer and a third epitaxial crystalline layer that is pseudomorphic. Advantageously, the third epitaxial crystalline layer provides a surface for forming functional devices.

[0018] Preferably, the method comprises the step of forming a material within one or more channels, and preferably, the material forms part of a third epitaxial crystalline layer. Preferably, the third epitaxial crystalline layer is an electrically conductive layer, and preferably, the third epitaxial crystalline layer electrically communicates with a crystalline template layer and / or the third epitaxial layer forms part of an active region configured to emit light in response to carrier recombination. Advantageously, devices formed on the third epitaxial crystalline layer may be in contact with and electrically connected to the underlying crystalline template layer. Advantageously, when the third epitaxial layer forms part of an active region configured to emit light in response to carrier recombination, the light generation efficiency is improved. Advantageously, when the third epitaxial layer forms part of an active region on the sidewalls of the feature portions of the patterned crystalline template layer, improved electrical connection and carrier injection into the third epitaxial crystalline layer are provided, and together, the strain-relaxed second epitaxial crystalline layer provides improved light generation from devices formed at least partially on the second epitaxial crystalline layer.

[0019] Preferably, at least one of the crystalline template layer, the first epitaxial crystalline layer, the second epitaxial crystalline layer, and the third epitaxial crystalline layer comprises a semiconductor material, preferably the semiconductor material is a III-V material, and more preferably the III-V material is a nitride material. Advantageously, a technique for providing such a material can provide a high-quality crystalline material having a low defect density.

[0020] Preferably, the epitaxial crystalline structure forms part of the light-emitting device. Advantageously, strain relief is managed together with electrical conductivity to form high-quality, practical devices.

[0021] Preferably, the light-emitting device forms part of an array of light-emitting pixels. Advantageously, the array of light-emitting pixels can be formed on a strain-relaxed layer, and thus the in-plane lattice parameters are suitable for material requirements, thereby providing higher quality devices that can be electrically connected on both sides to increase the density of pixels within the array.

[0022] Further aspects of the present invention will become apparent from the detailed description and accompanying drawings. Brief explanation of the drawing

[0023] The detailed description of the embodiments of the present invention is provided with reference to the drawings merely for illustrative purposes. Figure 1a shows a cross-sectional view of an epitaxial crystalline structure. FIG. 1b shows a cross-sectional view of the epitaxial crystalline structure of FIG. 1a that has been further processed. FIG. 2a illustrates a cross-sectional view of an epitaxial crystalline structure containing V-pits. FIG. 2b shows a cross-sectional view of the epitaxial crystalline structure of FIG. 2a that has been further processed. FIG. 2c shows a cross-sectional view of the structure of FIG. 2b that has been further processed. FIG. 3a illustrates a cross-sectional view of an epitaxial structure including V-pits and V-grooves. FIG. 3b shows a cross-sectional view of the structure of FIG. 3a that has been further processed. Figure 3c shows a plan view of the structure of Figure 3b. Figure 3d shows a cross-sectional view of the structure of Figure 3b that has been further processed. FIG. 4a shows a cross-sectional view of the structure of FIG. 1b that has been further processed. FIG. 4b shows a cross-sectional view of the structure of FIG. 4a that has been further processed. FIG. 5a illustrates a cross-sectional view of an epitaxial structure formed on a template. FIG. 5b shows a cross-sectional view of the structure of FIG. 5a that has been further processed. Specific details for implementing the invention

[0024] The formation of strain-relaxed epitaxial crystalline layers, upon which functional solid-state devices can be formed, is described. The structure and the method of forming the structure solve at least some of the problems described above. FIGS. 1 through 5 illustrate the formation of strain-relaxed layers within epitaxial crystalline structures, wherein the strain-relaxed layers have intrinsic natural lattice parameters different from the intrinsic natural lattice parameters of the substrate on which the strain-relaxed layers are formed. The formation of such strain-relaxed layers implies that layers having intrinsic crystalline lattice parameters that are more closely aligned with the strain-relaxed layers can subsequently be formed, and thus formed with higher crystallinity and reduced defects.

[0025] The methods and structures described herein are based on III-V crystalline materials, particularly nitride-based semiconductor materials. However, those skilled in the art understand that in other examples, the techniques described herein may be applied to different crystalline structures and semiconductor materials, for example, other III-V crystalline materials or II-VI crystalline materials. Advantageously, the structure not only provides a template layer for forming a material having natural lattice parameters that are more closely aligned with the template than underlying bulk substrate layers, but also enables the formation of a material having natural lattice parameters that are more closely aligned with the template on an electrically conductive template, thereby enabling the formation of high-resolution arrays of highly crystalline practical functional devices, for example, light-emitting diode (LED) devices.

[0026] FIG. 1a illustrates a cross-sectional view of an epitaxial structure (100A). The epitaxial structure (100A) provides an initial template for forming devices and is formed by metal-organic chemical vapor deposition (MOCVD). In other examples, alternative and / or additional growth and / or deposition techniques are used to provide the epitaxial layers described herein. In one example, molecular beam epitaxy (MBE) is used. Light-emitting diode (LED) devices are typically formed by providing a growth substrate on which a plurality of epitaxial layers of a semiconductor crystalline material are grown and / or deposited to form functional devices. In the case of gallium nitride (GaN)-based LED devices, n-type doped n-GaN is typically provided as a base layer for forming pn junctions. The epitaxial structure (100A) provides a structure that is fabricated to enable devices such as LED devices to be formed from high-quality crystalline materials, while also enabling the devices to be formed on an electrically conductive layer.

[0027] In FIG. 1a, a growth substrate (102) is illustrated. The growth substrate (102) is formed of silicon. In other examples, alternative and / or additional materials, such as sapphire, silicon carbide, or any other suitable substrate material, are used to form the substrate. On the growth substrate (102), n-type doped n-GaN is provided and effectively serves as a crystalline template layer (104). Although the crystalline template layer (104) is illustrated as an n-type GaN layer, in other examples, alternative and / or additional layers, such as a buffer layer, are included to control the characteristics of the n-GaN layer (such as crystallinity, doping level, thickness, etc.). The crystalline template layer (104) has a thickness of about 1000 nm and 5 x 10⁻⁶ 18 atoms / cm 3It is doped at a concentration of . In another example, the crystalline template layer (104) is formed to different thicknesses and has different doping concentrations, but still enables the function described herein. In another example, the crystalline template layer (104) is a p-type doping layer formed to provide the function described herein, and the composition of the subsequently formed layers is adjusted accordingly.

[0028] On the n-type crystalline template layer (104), a first epitaxial crystalline layer (106) is formed, and the first epitaxial crystalline layer (106) is formed of gallium nitride (GaN). Thus, the first epitaxial crystalline layer (106) has the same natural relaxation in-plane lattice constant as the crystalline template layer (104). In another example, the first epitaxial crystalline layer (106) is formed of a different material and is non-normalized with respect to the crystalline template layer (104). The first epitaxial crystalline layer (106) is formed as a highly doped layer, wherein the doping causes an initial doping contrast to exist between the highly doped first epitaxial crystalline layer (106) and the n-type crystalline template layer (104). This contrast enables the porosity of the first epitaxial crystalline layer (106) in the subsequent steps described below in relation to FIG. 1b. The first epitaxial crystalline layer has a thickness of about 30 nm and initially 1 x 10⁻⁶ 20 atoms / cm 3It is doped to a concentration of approximately [amount]. This doping concentration is achieved using Si. In other examples, co-doping using Si and Al is used to achieve this doping concentration while preventing excessive surface roughening. In other examples, different techniques, concentrations, and thicknesses are alternatively and / or additionally used to form the first epitaxial crystalline layer (106). Advantageously, the use of a thin first epitaxial crystalline layer (106) of about 30 nm provides a solidification layer after porosity treatment, where the broken bonds enable the movement of mismatched dislocations. In other examples, the first epitaxial crystalline layer (106) has a thickness of 1 nm to 300 nm, preferably 20 nm to 50 nm. In other examples, the first epitaxial crystalline layer (106) is initially 8 x 10 18 atoms / cm 3 Up to 5 x 10 20 atoms / cm 3 , preferably 3 x 10 19 atoms / cm 3 Up to 1 x 10 20 atoms / cm 3 It is doped with Si at a concentration of . In another example, the first epitaxial crystalline layer (106) is co-doped with Al and Si at a mole fraction of 0.5% to 10%, preferably 1% to 3%.

[0029] On the first epitaxial crystalline layer (106), a second epitaxial crystalline layer, which is an undoped layer (108), is provided, and the undoped second epitaxial crystalline layer (108) is a layer having an intrinsic lattice constant different from that of the crystalline template layer (104) and the first epitaxial crystalline layer (106). In the example of FIG. 1a, the second epitaxial crystalline layer (108) is an undoped layer of indium gallium nitride (InGaN). The undoped second epitaxial crystalline layer (108) has a thickness of about 100 nm to 150 nm. Advantageously, the second epitaxial crystalline layer (108) has a thickness that enables elastic relaxation. Accordingly, the growth of the second epitaxial crystalline layer (108) results in the second epitaxial crystalline layer (108) being initially deformed by the underlying material of the crystalline template layer (104) and the first epitaxial crystalline layer (106), thereby causing the different intrinsic natural in-plane lattice parameters of the second epitaxial crystalline layer (108) to be non-normalized with the intrinsic natural in-plane lattice parameters of the first epitaxial crystalline layer (106). In other examples, the second epitaxial crystalline layer (108) is formed with different thicknesses but enables the functions described herein. In one example, the second epitaxial crystalline layer (108) has a thickness of 100 nm to 500 nm. In another example, the second epitaxial crystalline layer (108) preferably has a thickness of 150 nm to 200 nm. The second epitaxial crystalline layer (108) is a bulk layer of InGaN having an In composition of 0% to 25%, preferably 6% to 15%. Although the second epitaxial crystalline layer (108) is a bulk InGaN layer, in other examples, the second epitaxial crystalline layer (108) is a superlattice structure of multiple layers having an alternating chemical composition providing an average indium composition of 0% to 25%, preferably 6% to 15%, in InGaN.In one example, when the second epitaxial crystalline layer of InGaN is a superlattice structure, the intrinsic lattice constant different from the crystalline template layer (104) is related to the average composition across the entire superlattice layer forming the second epitaxial crystalline layer.

[0030] Providing an epitaxial structure (100A) having a high-doping contrast between a first epitaxial crystalline layer (106), a crystalline template layer (104), and a second epitaxial crystalline layer (108) enables porosity of the first epitaxial crystalline layer (106) with an initial high-doping contrast. Porosity of the first epitaxial crystalline layer (106) occurs by an electrochemical process. The electrochemical etching process may be used to selectively etch the epitaxial layers so that the layer with the highest conductivity is etched first. Porosity of the buried layers within an epitaxial structure such as the epitaxial structure (100A) of FIG. 1a may occur through through-dislocation cores within the second epitaxial crystalline layer (108). Advantageously, the uppermost second epitaxial crystalline layer (108) does not need to be attacked, and the second epitaxial crystalline layer (108) does not need to be patterned to porous the subsurface layers. Although the second epitaxial crystalline layer (108) is described as an undoped layer (108), in other examples, the undoped second epitaxial crystalline layer (108) has a doping level that provides sufficient conductivity contrast to enable porous porous subsurface layers according to the method described herein.

[0031] Electrochemical etching of the epitaxial structure (100A) causes porosity of the first epitaxial crystalline layer (106) through penetrating dislocations or other openings of the undoped InGaN within the second epitaxial crystalline layer (108), thereby enabling such electrochemical processing of the subsurface first epitaxial crystalline layer (106). This is facilitated by the high-doping contrast between the n-type crystalline template layer (104) and the first epitaxial crystalline layer (106), which means that only the first epitaxial crystalline layer (106) becomes porous during the electrochemical etching of this layer. Advantageously, the doping contrast enables control of the porosity process as pores are formed in the first epitaxial crystalline layer (106), the porous first epitaxial crystalline layer (106') becomes highly resistant, and accordingly, the electrochemical process used to porous the first epitaxial crystalline layer (106) stops the formation of pores.

[0032] Accordingly, when the epitaxial structure (100A) is processed by electrochemical etching to provide a porous first epitaxial crystalline layer (106'), the first epitaxial crystalline layer (106) becomes a porous and conformal epitaxial crystalline layer (106').

[0033] FIG. 1b illustrates a fabricated form of the epitaxial structure (100A). The epitaxial structure (100B) is a fabricated form of the epitaxial structure (100A), so that the first epitaxial crystalline layer (106) is porous to provide pores throughout the porous first epitaxial crystalline layer (106'). This porousing enables strain relief of the second epitaxial crystalline layer (108) of undoped InGaN. This strain relief requires the second epitaxial crystalline layer (108) to expand. As described below, the lateral expansion of the second epitaxial crystalline layer (108) is controlled to provide advantageous structures. The apparent density, porosity, and degree of porosity of the first epitaxial crystalline layer (106') by the GaN material depend on the electrochemical etching process. The electrochemical etching process advantageously provides a conforming material within the subsurface layer, while resulting in the porous first epitaxial crystalline layer (106') having reduced electrical conductivity compared to the high-doping conductivity of the first epitaxial crystalline layer (106) at the time of initial formation.

[0034] As described above, the second epitaxial crystalline layer (108), which is initially deformed to the first epitaxial crystalline layer (106), must be expanded to be relaxed. As described with reference to FIGS. 2 through 5, the expansion of the second epitaxial crystalline layer (108) is controlled by the formation of appropriate gaps and / or channels.

[0035] FIG. 2a shows a cross-sectional view of an epitaxial structure (200A) provided according to the processed epitaxial structure (100B) described in relation to FIG. 1b, and accordingly there is a crystalline template layer (104), a porous first epitaxial crystalline layer (106'), and a second epitaxial crystalline layer (108). The epitaxial structure (200A) further shows V-pits (202) within the surface of the second epitaxial crystalline layer (108). These V-pits (202) are formed during the formation of the n-type crystalline template layer (104). FIG. 2a shows the top layer (105) of the crystalline template layer (104). The top layer (105) is also formed of GaN, but the formation of V-pits within the top layer (105) is made possible by changing the growth conditions when forming the crystalline template layer (104). For example, V-pits within the top layer (105) of the crystalline template layer (104) can be initiated by lowering the growth temperature. This top layer (105) has a thickness of about 50 nm. Advantageously, this thickness forms V-pits within subsequent layers of appropriate thickness to enable channels to be formed through the epitaxial structure (200A). In another example, the top layer (105) has a configuration designed to provide the function described herein. A cross-sectional view of the epitaxial structure (200A) shows one V-pit, but in another example, additional V-pits are formed across the flat surface of the top layer (105) of the crystalline template layer. In one example, these V-pits are formed randomly across the top layer (105) of the crystalline template layer.

[0036] The formation of V-pits within the top layer (105) of the crystalline template layer (104) results in the V-pits propagating through the subsequently grown layers. Thus, V-pits (202) are formed within the surface of the second epitaxial crystalline layer (108) according to the V-pits formed within the top layer (105) of the crystalline template layer (104). In other examples, additional and / or alternative techniques are used to form V-pits (202) within the second epitaxial crystalline layer (108).

[0037] When one or more V-pits (202) are formed within the second epitaxial crystalline layer (108), the epitaxial structure (200A) is processed to enlarge the V-pits (202), thereby opening one or more channels and exposing the top layer (105) of the crystalline template layer (104) and / or at least a portion of the crystalline template layer (104). This is illustrated in FIG. 2b, where the sidewalls of the V-pits (202) are shown as etched.

[0038] FIG. 2b illustrates a cross-sectional view of an epitaxial structure (200B) which is an epitaxial structure (200A) of FIG. 2a that has been further processed. FIG. 2b illustrates the enlargement of the V-pit (202) by etching the sidewalls of the V-pit (202). Processing of the epitaxial structure (200A) of FIG. 2a by wet etching enables anisotropic etching of the epitaxial structure (200A). Wet etching is performed using potassium hydroxide (KOH) at a high temperature. In other examples, additional and / or alternative techniques are used to etch and enlarge the V-pits (202). For example, tetramethylammonium hydroxide (TMAh) is used.

[0039] As illustrated in FIG. 2b, the sidewalls (208) of the second epitaxial crystalline layer (108) of undoped InGaN are etched to provide an open path to the conductive GaN. Subsequently, the sidewalls (206) of the porous first epitaxial crystalline layer (106) and the sidewalls (205) of the V-pit top layer (105) are enlarged. Consequently, the etched V-pit (202) is substantially the combined depth of the thickness of the porous first epitaxial crystalline layer (106') and the thickness of the second epitaxial crystalline layer (108) of undoped InGaN. Advantageously, this enlargement provides an electrical connection route to the n-type crystalline template layer (104) through the epitaxial structure (200B). When the sidewalls (205, 206, 208) of the V-pit (202) are etched to provide one or more channels through at least the porous first epitaxial crystalline layer (106') and the second epitaxial crystalline layer (108), the epitaxial structure (200B) is further processed as shown in FIG. 2c.

[0040] FIG. 2c illustrates a cross-sectional view of an epitaxial structure (200C), which is an epitaxial structure (200B) of FIG. 2b that has been further processed. FIG. 2c illustrates a conductive material, which is an n-type material (210), formed within a channel provided by the enlarged V-pit (202) described with reference to FIG. 2a and FIG. 2d. The n-type material (210) also forms a third epitaxial crystalline layer, which is a thin, irregular layer of the n-type material (210), on a second epitaxial crystalline layer (108) of undoped InGaN. The n-type material (210) is electrically in contact with the n-type material of the crystalline template layer (104), thereby advantageously enabling contact capability and current diffusion through the n-doped side of the epitaxial structure (200C) in subsequently formed devices. The n-type material (210) flattens the structure. When formed with GaN, the flattened layer of the n-type material (210) is subjected to tensile stress when the second epitaxial crystalline layer (108) of undoped InGaN is relaxed. Although the conductive n-type material (210) is formed with GaN, in other examples, the conductive material (210) is formed with a different material. In one example, the conductive n-type material (210) is formed with InGaN having an In composition of 0% to 6%. The conductive material (210) is formed as a layer having a thickness of 5 nm to 300 nm, preferably 20 nm to 100 nm.

[0041] The conductive material formed within one or more channels provided by the V-pits (202) is an n-type material (210) shown as flattening the structure, but in other examples, alternatively or additionally, the conductive n-type material (210) partially flattens the second epitaxial crystalline layer (108) or does not flatten the second epitaxial crystalline layer (108), while still filling at least one or more channels provided by the V-pits (202) with the conductive material, thereby providing conductivity to relatively strain-relaxed regions formed after the relaxation of the second epitaxial crystalline layer (108).

[0042] On the n-type material (210), an additional layer (212) is formed. In one example, the additional layer (212) is a multi-layer epitaxial structure having an active region associated with providing red light from InGaN-based quantum wells (QW). Advantageously, the additional layer (212) has the advantage of being formed on the second epitaxial crystalline layer (108) and the non-normalized electrical conductive layer. Although the additional layer (212) is shown as being provided on the n-type material (210), in other examples, the additional layer (212) is provided on both the n-type material (210) and the second epitaxial crystalline layer (108). In other examples, the additional layer (212) includes one or more LED devices, which in another example forms an array of devices such as a high-resolution array of micro-LED devices. In another example, the additional layer (212) alternatively and / or additionally forms a part of the n-type material (210) and / or replaces the n-type material, thereby enabling direct carrier injection into a part of the strain-relaxed material formed on the second epitaxial crystalline layer (108) through the additional layer (212), which is formed at least partially on the sidewall of the crystalline template layer (104), such as the V-foot top layer (105) of the n-type crystalline template layer (104).

[0043] To provide a route that enables a conductive material to be formed on the second epitaxial crystalline layer (108) and to facilitate strain relief of the second epitaxial crystalline layer (108), enlarged V-pits (202) of the structures (200) are described in relation to FIGS. 2a through 2c, but the location and density of the V-pits (202) within the top layer (105) of the crystalline template layer (104) are somewhat random. The density of the V-pits (202) within the top layer (105) is controlled using an appropriate growth technique to enable electrical connection in a controlled manner.

[0044] FIGS. 3a through 3d illustrate other structures incorporated into the epitaxial structures (200A to 200C) of FIGS. 2a through 2c to provide additional control of the resulting template structure.

[0045] FIG. 3a shows a cross-sectional view of an epitaxial structure (300A). The epitaxial structure (300A) is the structure (200A) of FIG. 2a processed using additional steps.

[0046] FIG. 3a illustrates a trench (304) formed within a crystalline template layer (104). The trench (304) is formed using a lithography technique, which uses patterning and etching steps to form the trench (304). In another example, the crystalline template layer (104) is processed using a different technique to provide the trench (304). The trench (304) is formed according to any beneficial structure within the crystalline template layer (104) to be subsequently processed.

[0047] When a trench (304) is formed within the crystalline template layer (104), subsequent layers (105, 106, 108) are formed epitaxially. This formation results in a V-groove (302) within the epitaxial structure (300A) corresponding to the trench (304). V-pits are additionally formed within the top layer (105) of the crystalline template layer (104) and propagate through the layers to provide V-pits (202) in addition to the V-groove (302). In another example, the V-groove (302) is provided without V-pits (202).

[0048] Although it is illustrated that a trench (304) is formed within the crystalline template layer (104) before forming subsequent epitaxial layers, thereby enabling the formation of channels through at least the porous first epitaxial crystalline layer (106') and the second epitaxial crystalline layer (108), in other examples, the trench (304) is formed by patterning the crystalline template layer (104) with a mask and forming an overgrowth material on the mask-patterned crystalline template layer (104). This technique is used to provide an array of columns having regular trapezoidal cross-sections, each normal to the substrate, as described, for example, in WO 2020 / 008200 A1. In other examples, this overgrowth on the mask-patterned crystalline template layer (104) is used to provide base layers for forming an array of light-emitting devices, which is described in more detail in relation to FIGS. 5a and 5b. In another example, the morphology of the crystalline template layer (104) is controlled by other techniques that provide a suitable underlying substrate for patterning and / or improved device formation.

[0049] When the V-grooves (302) are formed, the process proceeds similarly to that illustrated in relation to FIG. 2. FIG. 3b shows a cross-sectional view of an epitaxial structure (300B) which is an additionally processed epitaxial structure (300A) of FIG. 3a.

[0050] In FIG. 3b, a V-pit (202) enlarged by etching of the sidewalls and a V-groove (302) enlarged by etching of the sidewalls are shown. Processing of the epitaxial structure (300A) of FIG. 3a by wet etching enables anisotropic etching of the epitaxial structure (300A). As shown in FIG. 3b, the sidewalls (308) of the second epitaxial crystalline layer (108) are etched. Subsequently, the sidewalls (306) of the porous first epitaxial crystalline layer (106') and the sidewalls (305) of the V-pit type top layer (105) are enlarged. Advantageously, this expansion not only provides room for the second epitaxial crystalline layer (108) of the undoped InGaN to be expanded and strain-relieving, but also provides an electrical connection route to the n-type crystalline template layer (104) through the epitaxial structure (300B). Advantageously, forming V-grooves (302) in this way provides a method for adjusting the width of the gap that the material subsequently forms. This is beneficial, for example, when a lithography technique for forming V-grooves within an already formed epitaxial structure to provide a conduction path for the n-type material is not practical for forming V-grooves on a sufficiently small scale.

[0051] Strain relief is facilitated by annealing the structure (300B) of FIG. 3b. In other examples, strain relief is facilitated by using additional and / or alternative techniques. When the sidewalls (305, 306, 308) of the V-grooves (302) are etched, the epitaxial structure (300B) is further processed as shown in FIG. 3d. FIG. 3c shows a top view (300C) of the structure of FIG. 3b. V-pits (202) randomly distributed within the surface of the second epitaxial crystalline layer (108) are shown. V-grooves (302) forming a hexagonal pattern are also shown. Accordingly, the V-groove (302) isolates a portion of the second epitaxial crystalline layer (108) to form an island or domain by valleys that at least partially form the outer periphery of one or more islands within the second epitaxial crystalline layer (108) of InGaN, and accordingly, the valleys at least partially surround one or more islands within the second epitaxial crystalline layer (108). Although the V-groove (302) is illustrated in a hexagonal configuration, in other examples, the V-groove (302) is formed in any suitable configuration alternatively and / or additionally. Advantageously, the formation of two-dimensional islands within the second epitaxial crystalline layer (108) based on such lithographic patterning and etching of the crystalline template layer (104) provides strain-relaxed islands having lateral dimensions of about 1 μm to 10 μm. These island formations are highly controllable and provide relaxed island domains comparable in size to devices that can be formed on the relaxed island domains, such as micro LED devices having pixel sizes of about 1 μm to 10 μm. In another example, the lateral dimensions of the islands are controlled to provide deformation-relaxed islands of suitable dimensions for forming devices based on subsequently formed crystalline layers.

[0052] When the epitaxial structure (300B) of FIG. 3b is provided, the epitaxial structure (300B) is subsequently flattened. This is illustrated in FIG. 3d. FIG. 3d illustrates a structure (300D) which is the epitaxial structure (300B) of FIG. 3b that has been further processed. An n-type material (210) formed within channels provided by V-grooves (302) and V-pits (202) is illustrated. Random V-pits (202) filled with the n-type material (210) provide uniform electron injection into subsequent layers. As with the epitaxial structure (200C) of FIG. 2c, a subsequent irregular layer (212) is formed on the flattened layer of the n-type material (210). When the flattened layer of the n-type material (210) is formed as n-GaN, the second epitaxial crystalline layer (108) underneath is subjected to tensile stress as it relaxes. Although the conductive n-type material (210) is depicted as flattening the structure with a conductive material formed within one or more channels provided by V-grooves (302) and / or etched V-grooves (302), in other examples, alternatively or additionally, the conductive n-type material (210) partially flattens the second epitaxial crystalline layer (108) or does not flatten the second epitaxial crystalline layer (108), while still filling at least one or more channels provided by V-grooves (202) and / or V-grooves (302) with the conductive material, thereby providing conductivity to relatively strain-relaxed regions formed after the relaxation of the second epitaxial crystalline layer (108).

[0053] Although the additional layer (212) is illustrated as being provided on the n-type material (210), in other examples, the additional layer (212) is provided on both the n-type material (210) and the second epitaxial crystalline layer (108). In other examples, the additional layer (212) comprises one or more LED devices, which form an array of devices such as a high-resolution array of micro-LED devices in another example. In other examples, the additional layer (212) alternatively and / or additionally forms a part of the n-type material (210) and / or replaces the n-type material, thereby enabling direct carrier injection into a portion of the strain-relaxed material formed on the second epitaxial crystalline layer (108) through the additional layer (212), which is formed at least partially on the sidewall of the n-type crystalline template layer (104), such as the sidewall of the enlarged V-grooves (302), thereby advantageously.

[0054] Photolithography and etching techniques are used to form trenches (304) within the crystalline template layer (104), but in other examples, different patterning techniques are used. Additionally, the relative cross-sectional areas of the V-pits (202) and V-grooves (302) are shown in FIGS. 3a through 3d such that the V-grooves (302) are much deeper than the V-pits (202), but in other examples, the V-pits (202) and V-grooves (302) have different relative sizes. The V-pits (202) and V-grooves (302) advantageously provide effective channels for electrical connection between the layers formed on the insulating second epitaxial crystalline layer (108) and the crystalline template layer (104). Advantageously, the V-pits (202) facilitate uniform electron injection into the subsequently grown layers.

[0055] Advantageously, the V-grooves (302) help relax the second epitaxial crystalline layer (108), and the V-pits (202) provide channels for electrical connection to the crystalline template layer (104). If subsequently formed devices, such as LED devices providing pixels with defined light-emitting surfaces, have a light-emitting surface area greater than the density of the V-grooves (302), sufficient current diffusion can be made possible through the V-grooves (302), so the structure can be provided without the V-pits (202). If the light-emitting surface area of ​​the pixel is, for example, smaller than the density of the V-grooves (302), the V-pits (202) are particularly beneficial for providing sufficient current diffusion within the LED device associated with the pixel.

[0056] FIG. 4a illustrates a cross-sectional view of an epitaxial structure (400A) which is a processed form of the epitaxial structure (100B) of FIG. 1b. Channels are formed through the epitaxial structure (400A) to enable lateral relaxation of the second epitaxial crystalline layer (108) after porousing of the first epitaxial crystalline layer (106) to provide a porous first epitaxial crystalline layer (106').

[0057] An epitaxial structure (400A) is patterned on the surface of a second epitaxial crystalline layer (108) using a self-assembling hard mask. A nickel (Ni) thin film is evaporated on the surface of the second epitaxial crystalline layer (108). The nickel thin film is subsequently annealed to form random droplets. Then, dry etching is used to form channels (402) through the epitaxial structure (400A) to provide channels for the conductive n-type crystalline template layer (104). Afterward, the nickel mask is removed using a wet cleaning technique. Porosification of the first epitaxial crystalline layer (106) occurs before the formation of the channels (402), but in other examples, alternatively or additionally, the channels (402) are formed before the porosification of the first epitaxial crystalline layer (106). Advantageously, channels (402) formed through the first epitaxial crystalline layer (106) (or porous first epitaxial crystalline layer (106')) and the second epitaxial crystalline layer (108) at least partially define the outer periphery of two-dimensional domains or islands within the second epitaxial crystalline layer (108).

[0058] When the channels (402) are formed, the process proceeds to FIG. 4b. FIG. 4b shows a cross-sectional view of an epitaxial structure (400B), which is the epitaxial structure (400A) of FIG. 4a, further processed to form a flattened material layer (404) within the channels (402). The conductive material (404) formed within one or more channels is an n-type material (404), such as n-type GaN, which is shown as flattening the structure, but in other examples, alternatively or additionally, the conductive n-type material (404) partially flattens the second epitaxial crystalline layer (108) or does not flatten the second epitaxial crystalline layer (108), while still partially filling one or more channels provided by the channels (402) with the conductive material (404), thereby providing conductivity to relatively strain-relaxed regions formed after the relaxation of the second epitaxial crystalline layer (108).

[0059] Subsequently, an additional layer (412), which is an exemplary InGaN red light-emitting active region, is formed on the material (404) in a manner similar to the additional layer (212) described with reference to FIGS. 2 and 3. In other examples, this additional layer (412) forms one or more LED structures. In other examples, these LED structures form part of an array of LED devices, such as a high-resolution array of micro LED devices. Although the additional layer (412) is shown as being provided on the n-type material (404), in other examples, the additional layer (412) is provided on both the n-type material (404) and the second epitaxial crystalline layer (108). In other examples, the additional layer (412) includes one or more LED devices, which form an array of devices, such as a high-resolution array of micro LED devices in another example. In another example, the additional layer (412) alternatively and / or additionally forms a part of the n-type material (404) and / or replaces the n-type material, thereby enabling direct carrier injection into a part of the strain-relaxed material formed on the second epitaxial crystalline layer (108) through the additional layer (412), which is formed at least partially on the sidewall of the crystalline template layer (104), such as the sidewall of the channel (402) formed through the n-type crystalline template layer (104).

[0060] Advantageously, self-assembled nickel droplets are small and dense, and very narrow gaps can be formed to facilitate not only planarization but also strain relief. Planarization can be achieved over short distances for the narrow gaps. Further filling these densely distributed gaps with n-type material (210) provides good current flow through the epitaxial structure (400B).

[0061] Advantageously, the use of a hard mask, such as the self-assembled nickel hard mask described in connection with FIGS. 4a and 4b, enables the formation of densely packed two-dimensional islands within a second epitaxial crystalline layer (108) having lateral dimensions of approximately 250 nm to 1000 nm. Advantageously, islands formed at such a scale not only facilitate planarization but also provide a uniform strain-relaxed layer, wherein the lateral dimensions of the islands are smaller than the lateral dimensions of the devices formed layered on the relaxed islands, such as micro-LED devices with pixel sizes typically larger than 1000 nm. This effectively means that a size-independent strain-relaxed layer can be provided when the scale of the relaxed islands is smaller than the scale of the functional devices formed on the relaxed islands.

[0062] FIGS. 5A and 5B illustrate the formation of a porous first epitaxial crystalline layer (106') and a second epitaxial crystalline layer (108) on a crystalline template layer (104) having a morphology provided by patterning the crystalline template layer (104).

[0063] FIG. 5a illustrates a cross-sectional view of an epitaxial structure (500A) formed on a patterned substrate. A crystalline template layer (104) as described with reference to FIGS. 1 through 4 is illustrated. The crystalline template layer (104) is patterned using a known technique for depositing a mask (502). Although a cross-sectional view of the mask (502) is illustrated, those skilled in the art understand that the mask (502) may be formed in two dimensions to provide an array of openings on the crystalline template layer. The mask (502) is formed using silicon dioxide. In other examples, the mask (502) is formed using alternatively and / or additionally other materials. Overgrowth (504) of n-type GaN on the masked crystalline template layer results in the formation of a structure of GaN in which the overgrowth (504) electrically communicates with the n-type GaN crystalline template layer (104). Overgrowth (504) is illustrated in FIG. 5a as forming trapezoidal cross-sectional structures, but those skilled in the art understand that the morphology of such overgrowth (504) extends to three dimensions and is related to the underlying crystalline structure of the material used for the overgrowth (504) structures. When grown, the overgrowth (504) structures form part of the crystalline template layer (104).

[0064] The dimensions of the trapezoidal overgrowth (504) structures described in relation to FIGS. 5a and 5b vary as a function of the height of the trapezoidal pyramid. For a height of about 1 μm, the lateral dimensions of the trapezoidal features are about 4 μm at the base of the trapezoidal features and about 3 μm at the top of the trapezoidal features. In other examples, the lateral dimensions of the trapezoidal features are controlled to provide alternative or additional features of different sizes. In other examples, the dimensions of the overgrowth (504) features are controlled to provide islands of lateral size suitable for forming micro LED devices having pixel dimensions of about 1 μm to 10 μm within the second epitaxial crystalline layer (108). Alternatively or additionally, island domains having lateral dimensions smaller than 1 μm are provided within the second epitaxial crystalline layer (108). Advantageously, the formation of two-dimensional islands within the second epitaxial crystalline layer (108) based on such lithographic patterning and overgrowth provides strain-relaxed islands having lateral dimensions of about 1 μm to 10 μm or less. This island formation is highly controllable and provides relaxed island domains comparable in size to devices that can be formed on the relaxed island domains, such as micro LED devices having pixel sizes of about 1 μm to 10 μm.

[0065] When the overgrowth (504) structures are formed, an initial highly doped first epitaxial crystalline layer (106) is formed as described with reference to FIGS. 1 through 4. The first epitaxial crystalline layer (106) is formed on the top and sidewalls of the overgrowth (504) formed within the openings of the mask (502). The thickness of the first epitaxial crystalline layer (106) on the overgrowth (504) features is about 30 nm. The growth rate of the crystalline material on different crystalline planes, such as those provided by the top and sidewalls of the overgrowth (504) structures, may differ and can be controlled by changing the growth rate of the crystalline material as well as, for example, the composition of the crystalline material. Accordingly, the thickness of the crystalline layer deposited on different planes of the overgrowth (504) structures may differ. The thicknesses of the first epitaxial crystalline layer (106) and the second epitaxial crystalline layer (108) are described above in relation to the thicknesses of the layers that are approximately perpendicular to the underlying planar substrate (and thus parallel to the main growth direction). When the thickness of the first epitaxial crystalline layer (106) over the overgrowth (504) features is about 30 nm, the thickness of the first epitaxial crystalline layer (106) on the sidewalls of the overgrowth (504) features is about 1 to 3 nm. In other examples, the thickness of the first epitaxial crystalline layer (106) on the sidewalls is a different thickness. Inferiorly, the fact that the first epitaxial crystalline layer (106) on the sidewalls of the overgrowth (504) features is relatively thin means that, as described below, the first epitaxial crystalline layer (106) on the sidewalls of the overgrowth (504) features can be simply etched to provide a channel for the underlying n-GaN.

[0066] Subsequently, a second epitaxial crystalline layer (108) as described with reference to FIGS. 1 through 4 is formed on the first epitaxial crystalline layer (106). As described above with reference to FIGS. 1 through 4, the second epitaxial crystalline layer (108) is initially deformed by the underlying material of the crystalline template layer (104) and the first epitaxial crystalline layer (106), and accordingly, the different intrinsic natural in-plane lattice parameters of the second epitaxial crystalline layer (108) are non-normalized with the intrinsic natural in-plane lattice parameters of the first epitaxial crystalline layer (106). The second epitaxial crystalline layer (108) has a thickness of 100 nm to 150 nm over the overgrowth (504) features. As described above with respect to the first epitaxial crystalline layer (106) in FIG. 5a, the growth rate of crystalline materials on different crystalline planes, such as those provided by the top and sidewalls of the overgrowth (504) structures, may differ. When the thickness of the second epitaxial crystalline layer (108) on the overgrowth (504) features is about 100 to 150 nm, the thickness of the second epitaxial crystalline layer (108) on the sidewalls of the overgrowth (504) features is about 5 to 20 nm. In other examples, the thickness of the second epitaxial crystalline layer (108) on the sidewalls is different.

[0067] Electrochemical etching of the epitaxial structure (500A) causes porosity of the first epitaxial crystalline layer (106) through penetrating dislocations or other openings in the undoped InGaN of the second epitaxial crystalline layer (108), thereby enabling such electrochemical processing of the subsurface first epitaxial crystalline layer (106). This is facilitated by the high-doping contrast between the n-type crystalline template layer (104) and the first epitaxial crystalline layer (106), which means that only the first epitaxial crystalline layer (106) becomes porous during the electrochemical etching of this layer. Advantageously, the doping contrast enables control of the porosity process as pores are formed in the first epitaxial crystalline layer (106), the porous first epitaxial crystalline layer (106') becomes highly resistant, and accordingly, the electrochemical process used to porous the first epitaxial crystalline layer (106) stops the formation of pores. The porous first epitaxial crystalline layer (106') is illustrated in FIG. 5b.

[0068] FIG. 5b illustrates an epitaxial structure (500B) which is the structure (500A) of FIG. 5a further processed to provide an array of light-emitting structures. A porous first epitaxial crystalline layer (106') formed over the overgrowth (504) structures and a second epitaxial crystalline layer (108) formed on the porous first epitaxial crystalline layer (106') are illustrated. The porosity of the first epitaxial crystalline layer (106) results in the removal of material within the channels between the overgrowth (504) structures from the sidewalls of the overgrowth (504) structures. In another example, the material of the sidewalls of the overgrowth (504) structures is removed by different means to form channels through the porous first epitaxial crystalline layer (106') and the second epitaxial crystalline layer (108) to form a path for n-type GaN of the overgrowth (504) structures formed on the crystalline template layer (104) through the layers (106', 108). Inferiorly, in GaN-based structures such as the epitaxial structures (500A, 500B) described with reference to FIG. 5A and 5B, the growth direction is typically perpendicular to the c-plane, and the etching rate of the inclined surfaces, such as the sidewalls of the overgrowth (504) structures, is faster than the etching rate of the c-plane material formed on the overgrowth (504) structures. This means that the porous first epitaxial crystalline layer (106') and the second first epitaxial crystalline layer (108) can be etched from the sidewalls of the overgrowth (504) structures at a faster rate than the etching rate of the material formed on the overgrowth (504) structures. Thus, the removal of material to form channels for n-GaN through the porous first epitaxial crystalline layer (106') and the second epitaxial crystalline layer (108) is facilitated.

[0069] The removal of the porous first epitaxial crystalline layer (106') and the second epitaxial crystalline layer (108) effectively forms two-dimensional domains or islands within the second epitaxial crystalline layer (108). The porousness of the first epitaxial crystalline layer (106) enables strain relief within the second epitaxial crystalline layer (108) of undoped InGaN. Such strain relief requires the expansion of the second epitaxial crystalline layer (108). As described herein, the lateral expansion of the second epitaxial crystalline layer (108) is controlled to provide advantageous structures. The apparent density, porosity, and degree of porosity of the porous first epitaxial crystalline layer (106') depend on the electrochemical etching process. The electrochemical process advantageously provides a conforming material within the subsurface layer, while resulting in the porous first epitaxial crystalline layer (106') having reduced electrical conductivity compared to the high-dipdency conductivity of the first epitaxial crystalline layer (106) at the time of initial formation. Advantageously, the removal of the porous first epitaxial crystalline layer (106') and the second epitaxial crystalline layer (108) to effectively form two-dimensional domains or islands within the second epitaxial crystalline layer (108) also forms channels for electrical connection between the layers subsequently grown on the second epitaxial crystalline layer (108) and the crystalline template layer (104).

[0070] In relation to FIGS. 2 to 4, an additional layer (506) similar to the additional layers (212, 414) described above is conformally deposited and formed on the relaxed second epitaxial crystalline layer (108). The additional layer (506) is an active region. The additional layer (506) includes one or more quantum wells, such as InGaN-based quantum wells, designed to emit light having a major wavelength of light corresponding to red light during carrier injection and recombination. In other examples, the additional layer (506) includes additional and / or alternative layers that have the advantage of being formed on the relatively relaxed second epitaxial crystalline layer (108). The additional layer (506) is a third epitaxial crystalline layer that provides a channel for electrical conductivity from the n-GaN overgrowth (504) forming part of the crystalline template layer (104) to a part of the active region formed on the relaxed second epitaxial crystalline layer (108).

[0071] On the additional layer (506), a p-type region (508) is formed. The p-type region (508) is conformally deposited and formed on the sidewalls of the overgrowth (504) structures and on the additional layer (506) on top of the overgrowth (504) structures. The p-type region (508) is formed of p-type doped GaN. In other examples, additional and / or alternative layers are used to form the p-type region (508).

[0072] Advantageously, the structure (500B) of FIG. 5b provides an array of light-emitting diode structures having an active region formed on relatively strain-relaxed layers having a lattice constant closer to the lattice constant of the material forming the active region, thereby providing high-quality light-emitting regions with improved efficiency. The formation of these active regions on the overgrowth (504) structures improves light extraction from devices and improves collimation based on these high-quality light-emitting regions.

[0073] Advantageously, when a third epitaxial layer forming an electrical connection through a porous first epitaxial crystalline layer (106') and a second epitaxial crystalline layer (108) forms part of an active region on one or more sidewalls of one or more overgrowth (504) structures, a direct current path for electrons between the active region of an additional layer (506) on an island of the second epitaxial crystalline layer (108) and the crystalline template layer (104) is provided. Advantageously, such injection is controlled, and sidewall injection enables a reduced forward voltage for multiple quantum well (MQW) structures forming part of the additional layer (506) when there is a high operating current.

[0074] FIG. 5b illustrates a mask (502), but in other examples, the mask (502) is removed after the overgrowth (504) step. Furthermore, additional layers (506) and p-type regions (508) are formed conformally on the overgrowth (504) structures, but individual structures are selectively separated, thereby enabling the formation of a plurality of individually addressable light-emitting diode structures having a common n-type electrode formed by the crystalline template layer (104).

[0075] Advantageously, the techniques and structures described herein provide a method for forming a relatively strain-relaxed layer on a conductive template layer, but enabling electrical connection between layers subsequently grown on the relatively strain-relaxed layer and the conductive template layer. Advantageously, when an epitaxial crystalline layer having an intrinsic in-plane lattice parameter different from the intrinsic in-plane lattice parameter of the crystalline template layer is formed on an interlayer such that it is formed irregularly with respect to the interlayer, the porosity of the interlayer enables strain relaxation within the epitaxial crystalline layer as well as current injection routes in devices formed on the relaxed epitaxial crystalline layer, along with the formation of channels through the porous interlayer and the epitaxial crystalline layer.

[0076] Advantageously, channels formed and filled with a material that enables electrical connection overcome the difficulties associated with the use of high-resistance layers utilized for strain relaxation and the provision of functional devices therefrom. Advantageously, the use of channels having faces angled with respect to a direction perpendicular to the flat growth direction of the epitaxial layers provides inclined surfaces to which connection to the underlying crystalline template layer can be made, while simultaneously providing strain-relaxed luminescent structures on isolated islands of a relatively strain-relaxed material having intrinsic in-plane lattice parameters different from the intrinsic in-plane lattice parameters of the crystalline template layer on which the relatively strain-relaxed material is formed.

[0077] Advantageously, light-emitting diode (LED) devices can be formed on the structures described with reference to FIGS. 1 through 5. Advantageously, an array of LEDs having related pixels can be formed on strain-relaxed layers, while allowing n-type contacts through n-type regions even though a high-resistance porous layer is used for strain relaxation. This eliminates the need to form a conductive material layer and the need to form contacts for both p-type and n-type layers within the devices from the same side of the LED device. This is particularly advantageous for longer wavelength InGaN-based light-emitting devices, such as LEDs formed from nitride materials configured to emit light having a major peak wavelength corresponding to red light, where strain-relaxed islands of undoped InGaN can be used instead of thicker conductive layers of InGaN, which typically have poor quality. Furthermore, enabling conduction to create an n-type contact on the opposite side of the device from a p-type contact means that the pixels associated with the LED devices within the array are packed more tightly, thereby improving the resolution of display devices based on such an array.

[0078] Although the processes described herein are given in a specific order, those skilled in the art understand that in other examples, alternative and / or additional steps and process sequences are implemented to enable the provided functions.

Claims

Claim 1 A method for forming a strain-relaxing layer within an epitaxial crystalline structure, comprising: providing a crystalline template layer comprising a material having a first lattice parameter; forming a first epitaxial crystalline layer on the crystalline template layer, wherein the first epitaxial crystalline layer has an initial electrical conductivity higher than the electrical conductivity of the crystalline template layer; forming a second epitaxial crystalline layer on the first epitaxial crystalline layer, wherein the second epitaxial crystalline layer has an electrical conductivity lower than the initial electrical conductivity of the first epitaxial crystalline layer and comprises a material having a second lattice parameter different from the first lattice parameter of the crystalline template layer; and at the interface between the first epitaxial crystalline layer and the second epitaxial crystalline layer or within the first epitaxial crystalline layer, or at the interface between the first epitaxial crystalline layer and the second epitaxial crystalline layer and the first A method comprising: forming pores in the first epitaxial crystalline layer by electrochemical etching of the first epitaxial crystalline layer to enable strain relief in the second epitaxial crystalline layer by plastic deformation of bonds in the epitaxial crystalline layer; and forming one or more channels comprising a conductive material through at least the first epitaxial crystalline layer and the second epitaxial crystalline layer to enable electrical connection to the crystalline template layer through the first epitaxial crystalline layer and the second epitaxial crystalline layer. Claim 2 A method according to claim 1, wherein the pores are formed in a state in which the volume density of the first epitaxial layer between the crystalline template layer and the second epitaxial crystalline layer is greater than 50%, or greater than 60%, or greater than 70%. Claim 3 A method according to claim 1, wherein the second epitaxial crystalline layer comprises at least one V-pit, and optionally the depth of the at least one V-pit is substantially the combined thickness of the first epitaxial crystalline layer and the second epitaxial crystalline layer. Claim 4 In paragraph 3, the method comprises the step of enlarging the at least one V-pit, and optionally the step of enlarging the at least one V-pit comprises the step of etching material from at least one sidewall of the at least one V-pit to expose at least a portion of the crystalline template layer. Claim 5 The method of claim 1, wherein the method comprises the step of etching through at least the second epitaxial crystalline layer to form one or more islands within the second epitaxial crystalline layer, optionally comprising the step of patterning the second epitaxial crystalline layer, wherein the patterning step comprises at least one of a lithography technique and a self-assembled Ni hard mask. Claim 6 A method according to claim 1, comprising the step of forming the crystalline template layer on the patterned template layer. Claim 7 In claim 6, the patterned template layer is patterned to provide trenches, and optionally, the step of forming the crystalline template layer comprises the step of forming an overgrowth material in the trenches to provide V-grooves to enable the formation of two-dimensional domains that are at least partially defined by valleys within the second epitaxial crystalline layer. Claim 8 In claim 6, the crystalline template layer is patterned to provide one or more overgrowth structures, and optionally, the step of forming the patterned crystalline template layer comprises at least partially masking the crystalline template layer to provide one or more openings, and forming an overgrowth material within the one or more openings to provide one or more overgrowth structures, and optionally, the step of forming one or more channels comprising the conductive material through at least the first epitaxial crystalline layer and the second epitaxial crystalline layer comprises removing material from one or more sidewalls of the one or more overgrowth structures. Claim 9 The method of claim 1, wherein the method comprises the step of flattening at least a portion of the second epitaxial crystalline layer to form a third epitaxial crystalline layer that is pseudomorphic to the second epitaxial crystalline layer, and optionally the conductive material forms a portion of the third epitaxial crystalline layer. Claim 10 A method according to claim 9, wherein the third epitaxial crystalline layer is an electrically conductive layer, and optionally the third epitaxial crystalline layer forms at least a portion of an active region configured to electrically communicate with the crystalline template layer or to emit light in response to carrier recombination. Claim 11 A method according to claim 1, comprising a third epitaxial crystalline layer, wherein at least one of the crystalline template layer, the first epitaxial crystalline layer, the second epitaxial crystalline layer, and the third epitaxial crystalline layer comprises a semiconductor material, optionally the semiconductor material is a III-V material, and optionally the III-V material is a nitride material. Claim 12 As an epitaxial crystalline structure, a crystalline template layer comprising a material having a first lattice parameter; a first epitaxial crystalline layer formed on the crystalline template layer; a second epitaxial crystalline layer formed on the first epitaxial crystalline layer comprising a material having a second lattice parameter different from the first lattice parameter of the crystalline template layer; and one or more pores formed in the first epitaxial crystalline layer such that any deformation within the second epitaxial crystalline layer is relieved by plastic deformation of bonds located at the interface between the first epitaxial crystalline layer and the second epitaxial crystalline layer or within the first epitaxial crystalline layer, or at the interface between the first epitaxial crystalline layer and the second epitaxial crystalline layer and within the first epitaxial crystalline layer. An epitaxial crystalline structure comprising: one or more channels comprising a conductive material formed through at least the first epitaxial crystalline layer and the second epitaxial crystalline layer to enable electrical connection to the crystalline template layer through the first epitaxial crystalline layer and the second epitaxial crystalline layer. Claim 13 In claim 12, the epitaxial crystalline structure comprises the second epitaxial crystalline layer and a third epitaxial crystalline layer that is atypical. Claim 14 In claim 12, the one or more pores are formed in an epitaxial crystalline structure such that the volume density of the first epitaxial layer between the crystalline template layer and the second epitaxial crystalline layer is greater than 50%, or greater than 60%, or greater than 70%. Claim 15 An epitaxial crystalline structure according to claim 12, wherein the second epitaxial crystalline layer comprises at least one V-pit, and optionally the depth of the at least one V-pit is substantially the combined thickness of the first epitaxial crystalline layer and the second epitaxial crystalline layer. Claim 16 In claim 15, the at least one V-pit is an epitaxial crystalline structure that exposes at least a portion of the crystalline template layer. Claim 17 In claim 12, the epitaxial crystalline structure comprises one or more islands formed within the second epitaxial crystalline layer. Claim 18 In claim 17, the epitaxial crystalline structure comprises one or more valleys that at least partially surround one or more islands within the second epitaxial crystalline layer to enable the formation of one or more two-dimensional domains. Claim 19 In claim 13, the conductive material is an epitaxial crystalline structure forming part of the third epitaxial crystalline layer. Claim 20 In claim 13, the third epitaxial crystalline layer is an electrically conductive layer, and optionally the third epitaxial crystalline layer forms part of an active region configured to electrically communicate with the crystalline template layer or to emit light in response to carrier recombination, an epitaxial crystalline structure. Claim 21 An epitaxial crystalline structure according to claim 12, comprising a third epitaxial crystalline layer, wherein at least one of the crystalline template layer, the first epitaxial crystalline layer, the second epitaxial crystalline layer, and the third epitaxial crystalline layer comprises a semiconductor material, optionally the semiconductor material is a III-V material, and optionally the III-V material is a nitride material. Claim 22 A light-emitting device comprising an epitaxial crystalline structure as described in any one of claims 12 to 21. Claim 23 An array of light-emitting pixels comprising at least one light-emitting device including an epitaxial crystalline structure described in any one of claims 12 to 21. Claim 24 A method for forming a light-emitting device comprising a method described in any one of claims 1 to 11. Claim 25 A method for forming an array of light-emitting pixels comprising a method for forming a light-emitting device comprising a method described in any one of claims 1 to 11.

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