Strained reduced-nitride gallium indium light emitting diode

Abstract

A method of forming an LED emitter includes providing a Group III nitride layer on a substrate (310), the Group III nitride layer having a planar top surface; providing discrete lateral growth regions on the top surface; selectively epitaxially growing a base region (1210) including In(x)Ga(1-x)N material on each discrete lateral growth region, each base region extending perpendicular to the top surface; providing a surface of the In(x)Ga(1-x)N material on portions of the base region (1210), the surface having a relaxed strain, and characterized by a base lattice constant within 0.1% of its bulk relaxed value; and epitaxially growing an LED region on the surface, the LED region including an In(y)Ga(1-y)N material light emitting layer pseudomorphically on the surface of the In(x)Ga(1-x)N material, and characterized by an active region (1240) lattice constant within 0.1% of the base lattice constant, where 0.05 < x < 0.2 and y > 0.3.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 001,221, filed March 27, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to strain-reduced indium gallium nitride (InGaN) light-emitting diodes (LEDs) and devices incorporating such LEDs. Background Technology

[0004] LEDs (such as micro-LEDs) are candidates for display applications. In some cases, a combination of group III nitride NE LEDs that emit blue, green, and red radiation is desirable. Summary of the Invention

[0005] Growing long-wavelength group III nitride emitting layers can be challenging for several reasons, including a large number of defects (point defects, extended defects) that reduce internal quantum efficiency (IQE) and the difficulty in incorporating large amounts of indium (typically required for long-wavelength emission). These effects are often exacerbated by strain. For example, strain caused by lattice differences between the GaN matrix and the InGaN emitting layer can lead to defect incorporation / creation and reduce In incorporation due to lattice traction.

[0006] There is a need for a microLED with reduced strain effect for long-wavelength emission.

[0007] Various aspects of the present invention are summarized below.

[0008] Typically, in a first aspect, the invention is characterized by a display transmitter comprising:

[0009] Three sub-regions, each corresponding to a sub-pixel of the display, emit blue, green, and red light respectively during operation of the display emitter. Each sub-region includes a light-emitting region (e.g., multiple nanowires (NWs)). Each light-emitting region (e.g., each NW) comprises: a base region having an InGaN composition of at least 5% In and a relaxed regrown surface, its base lattice constant being within 0.1% of its bulk value; and an LED region regrown on the regrown surface, comprising at least one light-emitting layer having an InGaN composition of at least 10% In. The light-emitting layer and the regrown surface are pseudocrystalline, their active region lattice constant being within 0.1% of the base lattice constant.

[0010] An embodiment may include one or more of the following features and / or other features.

[0011] The base region can be formed by hydride vapor phase epitaxy (HVPE).

[0012] The LED region can be regrown by metalorganic chemical vapor deposition (MOCVD).

[0013] The lattice constants of the base and active regions can be in-plane lattice constants.

[0014] The base region can have a uniform composition equal to that of InGaN.

[0015] The NWs can be grown on a planar group-III nitride layer.

[0016] The base region can include a lateral structure with a lateral dimension less than 300 nm, and relaxation of the base region material occurs within the lateral structure.

[0017] Generally, in another aspect, the present invention features a method of forming a nanowire LED emitter, comprising: providing a substrate; growing a planar GaN layer on the substrate; forming a mask having an opening on the substrate; growing an In(x)Ga(1-x)N base region in the opening (e.g., by HVPE) using InCl3 as a precursor, the base region extending vertically above the opening; providing a regrowth surface on a portion of the base region, the regrowth surface being relaxed and characterized in that the base lattice constant is within 0.1% of its bulk relaxed value; and growing an LED region on the regrowth surface, the LED region having a luminescent layer that is pseudomorphic to the regrowth surface and has a composition of In(y)Ga(1-y)N, and characterized in that the active region lattice constant is within 0.1% of the base lattice constant. 0.05 < x < 0.15 and y > 0.2.

[0018] Embodiments can include one or more of the following features and / or features of other aspects.

[0019] Generally, in another aspect, the present invention features a method of forming a nanowire LED emitter, the method comprising: providing a substrate; forming a mask having an opening on the substrate, the mask having a top surface; growing an In(x)Ga(1-x)N base material in the opening by a first growth method having a first growth parameter that substantially promotes lateral growth, the base material extending above the top surface and laterally extending beyond the opening above the top surface; providing at least one regrowth surface on a portion of the base material, the at least one regrowth surface being at least partially relaxed; and growing an LED region on the regrowth surface by a second growth method having a second growth parameter that substantially does not promote lateral growth, the LED region having a light-emitting layer composed of In(y)Ga(1-y)N that is pseudomorphic with the at least one regrowth surface. 0.05 < x < 0.2 and y > 0.3, and the mismatch strain between the light-emitting layer and the regrowth surface is less than half of the mismatch strain between the light-emitting layer and relaxed GaN.

[0020] Embodiments may include one or more of the following features and / or features of other aspects.

[0021] The at least one regrowth surface can be characterized in that the in-plane lattice constant of the base plane is within 0.5% of its bulk relaxed value. The first growth parameter can promote growth with a ratio of lateral to vertical growth rate of 1 or greater (e.g., 2 or greater, 5 or greater, 10 or greater, 100 or greater). The second growth parameter promotes growth with a ratio of vertical to lateral growth rate of 2 or greater (e.g., 10 or greater, 100 or greater). The first method can be HVPE, and the second method can be MOCVD.

[0022] Generally, in yet another aspect, the present invention features a method of forming a light-emitting diode (LED), comprising: growing a buffer layer containing gallium nitride (GaN) on a surface of a substrate; forming a mask having an opening on a surface of the buffer layer; forming a base layer in the opening on the surface of the buffer layer, wherein forming the base layer includes epitaxial growth of In(x)Ga(1-x)N (e.g., using hydride vapor phase epitaxy (HVPE) with a mono-halide or tri-halide precursor); providing a regrowth surface on the base layer, the regrowth surface having a relaxed crystal structure, the in-plane lattice constant of which is within 0.1% of the bulk value of the in-plane lattice constant of In(x)Ga(1-x)N; epitaxially growing one or more additional layers on the regrowth surface to provide an active region of the LED, the one or more additional layers including at least one layer of In(y)Ga(1-y)N that is pseudomorphic with the regrowth surface, the in-plane lattice constant of the active region being within 0.1% of the in-plane lattice constant of the base plane of the regrowth surface; and forming one or more additional layers on the active region and processing the layers to provide an LED. 0.05 < x < 0.15 and y > 0.2.

[0023] The implementation may include one or more of the following features and / or other features. For example, the mask may include a plurality of spaced-apart openings, and the method includes simultaneously forming LEDs in each of the openings to provide a plurality of LEDs. The LEDs may be nanowire LEDs (NW LEDs). Each of the plurality of NW LEDs may be configured to emit light at a first peak wavelength λ1 in the visible spectrum. The plurality of NW LEDs may include a first plurality of NW LEDs grouped in a first area of ​​the substrate, and the method may further include: forming a second plurality of NW LEDs grouped in a second area of ​​the substrate, each of the second plurality of NW LEDs being configured to emit light at a second peak wavelength λ2 in the visible spectrum; and forming a third plurality of NW LEDs grouped in a third area of ​​the substrate, each of the third plurality of NW LEDs being configured to emit light at a third peak wavelength λ3 in the visible spectrum, wherein λ1, λ2, and λ3 are different from each other.

[0024] The opening in the mask can have a first dimension d1 in a first direction in the plane of the surface of the buffer layer, and the regenerated surface can have a second dimension d2 in the first direction, where d2 > d1.

[0025] The precursor can be a chloride precursor. The chloride precursor can be selected from the group consisting of GaCl, GaCl3, InCl, and InCl3.

[0026] GaN layers can be planar layers.

[0027] LEDs can extend perpendicularly to the substrate surface above the opening.

[0028] The substrate can include substrate materials selected from the group consisting of sapphire, silicon, and GaN.

[0029] One or more additional layers can include one or more quantum well (QW) layers configured to emit light with a peak wavelength λ in the visible portion of the electromagnetic spectrum.

[0030] One or more additional layers can be formed using metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

[0031] Generally, in another aspect, the present invention features a light-emitting device including: a GaN buffer layer on a surface of a substrate; a light-emitting diode (LED) extending from the GaN buffer layer, the LED including: an LED region having at least one layer of In(y)Ga(1-y)N; and a base region between the LED region and the GaN buffer layer. The base region includes an In(x)Ga(1-x)N layer having a regrowth surface with a relaxed crystal structure, the base lattice constant of which is within 0.1% of the bulk value of the base lattice constant of In(x)Ga(1-x)N. The In(y)Ga(1-y)N layer in the LED region is pseudomorphic to the regrowth surface, and the active region lattice constant is within 0.1% of the base lattice constant of the regrowth surface, and 0.05 < x < 0.15 and y > 0.2.

[0032] Embodiments may include one or more of the following features and / or features of other aspects. For example, the LED region can include an active region having one or more quantum well (QW) layers supported by an In(y)Ga(1-y)N layer. The LED region can also include a second InGaN layer supported by the active region.

[0033] At the surface of the buffer layer, the base region can have a first dimension d1 in a first direction in a plane of the surface of the buffer layer, and the regrowth surface can have a second dimension d2 in the first direction, where d2 > d1.

[0034] The light-emitting device can include a mask on the surface of the buffer layer, where the NW LED is formed in an aperture in the mask.

[0035] The In(x)Ga(1-x)N layer in the base region can be formed using hydride vapor phase epitaxy (HVPE) with a mono-halide or tri-halide precursor.

[0036] The In(y)Ga(1-y)N layer in the LED region can be formed using metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

[0037] In another aspect, the invention features a display device including a plurality of NW LEDs, each of the NW LEDs extending from a GaN buffer layer and spaced apart from one another. Each of the plurality of NW LEDs can be configured to emit light at a first peak wavelength λ1 in the visible spectrum. The plurality of NW LEDs includes a first plurality of NW LEDs grouped in a first area of a substrate. The display device further includes: a second plurality of NW LEDs grouped in a second area of the substrate, each of the second plurality of NW LEDs being configured to emit light at a second peak wavelength λ2 in the visible spectrum; and a third plurality of NW LEDs grouped in a third area of the substrate, each of the third plurality of NW LEDs being configured to emit light at a third peak wavelength λ3 in the visible spectrum. λ1, λ2, and λ3 are different from one another, and the first area, the second area, and the third area constitute a single pixel of the display device.

[0038] Generally, in yet another aspect, the invention features a method of forming a light-emitting diode (LED). The method includes: providing a growth substrate having a textured top surface; selectively growing a first base material on an area of the top surface using a first growth technique to form a feature having at least one lateral dimension less than 500 nm, the first base material including a relaxed In(x)Ga(1 - x)N layer; growing a second base material above the first base material using a second growth technique, the growth of the second base material extending at least one lateral dimension of the feature to greater than 1 micron, the second base material including a relaxed In(x)Ga(1 - x)N layer, the second growth technique favoring lateral growth over vertical growth; and growing an LED structure above the feature using a third growth technique, the LED structure including at least one In(y)Ga(1 - y)N light-emitting layer that is pseudomorphic with the second base material, the third growth technique favoring vertical growth over lateral growth. 0.05 < x < 0.2 and y > 0.3, and the mismatch strain between the light-emitting layer and the second base material is less than half of the mismatch strain between the light-emitting layer and relaxed GaN.

[0039] Embodiments can include one or more of the following features and / or features of other aspects. For example, the textured top surface of the growth substrate includes a planar surface covered with a mask having an opening with a lateral dimension less than 500 nm, and the selective growth occurs in the opening.

[0040] The feature can be a mesa.

[0041] The first and second base materials can have in-plane lattice constants within 0.5% of their respective unstrained equilibrium values.

[0042] The luminescent layer can be planar and can have a wurtzite crystal structure, and the planarity of the luminescent layer can be along the c-plane of the wurtzite structure.

[0043] These features can have a size of less than 1E7 cm. -1 The average dislocation density.

[0044] The first and second growth techniques can be hydride vapor phase epitaxy (HVPE), and the third growth technique can be metal-organic chemical vapor deposition (MOCVD).

[0045] The first growth technique can be HVPE, and the second and third growth techniques can be MOCVD.

[0046] This method can include preparing characteristic surfaces to facilitate the growth of the LED structure after the growth of the second base material and before the growth of the LED structure.

[0047] One or more advantages will be apparent from this disclosure, the accompanying drawings, and the claims. Attached Figure Description

[0048] Figure 1A and Figure 1B This is a cross-sectional view of an example LED emitter.

[0049] Figure 2A and 2B This is a cross-sectional view of an example LED emitter with different layers.

[0050] Figures 3A to 3D The steps in an example process flow for manufacturing a base region with a transverse structure are shown.

[0051] Figures 4A to 4C The steps in another example process flow for manufacturing a base region with a transverse structure are shown.

[0052] Figure 5A This is a cross-sectional view of an example LED emitter structure.

[0053] Figures 5B to 5D It shows the use of Figure 5A The diagram shows an example compositional cross-sectional view of an LED emitter structure.

[0054] Figure 6A and Figure 6B This is a cross-sectional view showing an example LED emitter with edge material.

[0055] Figure 7A This shows a cross-sectional view of an example LED emitter.

[0056] Figures 7B to 7D It shows the method for growth Figure 7AThe diagram shows a plan view of the mask opening of an example LED emitter.

[0057] Figures 8A to 8I The steps in an example process flow for manufacturing an LED emitter are shown.

[0058] Figure 9 This is a graph illustrating the example relationship between wavelength and internal quantum efficiency in example embodiments and prior art.

[0059] Figures 10A to 10E This is a cross-sectional view showing an example process of LED region regrowth.

[0060] Figures 11A to 11F This is a cross-sectional view showing a step in an example process flow that covers the sidewall of an LED emitter.

[0061] Figure 12A and Figure 12B This is a cross-sectional view showing the geometry and strain state of an example LED emitter.

[0062] Figures 13A to 13C This shows when the NW LED emitter is based on Figures 12A to 12B The evolution of various quantities during growth.

[0063] Figure 14 This is a flowchart illustrating the steps in an example process for forming an LED device.

[0064] Figures 15A to 15D This is a cross-sectional view showing yet another example embodiment of an LED emitter.

[0065] Figures 16A to 16C This is a cross-sectional view showing the steps in an example manufacturing process for a small-board LED.

[0066] Figure 17A This shows a cross-sectional view of an example LED emitter.

[0067] Figures 17B to 17D It is illustrated in Figure 17A The graph shown illustrates the lateral variation of the active region characteristics from the center structure to the edge structure in the example LED emitter.

[0068] Figures 18A to 18H This is a cross-sectional view showing the steps in an example process for forming an LED emitter.

[0069] Figures 19A to 19G This is a cross-sectional view showing the steps in another example process for forming an LED emitter. Detailed Implementation

[0070] LED structure

[0071] Some embodiments disclosed herein are nanowire (NW) LEDs, wherein each LED comprises one or more NWs. The NW has a base region comprising an InGaN layer, an LED region comprising an n-doped layer, an active region (light-emitting region) having at least one light-emitting InGaN layer, and a p-doped layer. The base region can be grown using a first technique, such as HVPE. The LED region can be regrown on the base region using a second technique, such as MOCVD or MBE.

[0072] Figures 1A to 1B Examples of such LEDs, 100' and 100', are shown respectively. Figure 1A In this process, the active region 110 is planar and grows perpendicular to the corresponding NW axis 101. Figure 1B In this configuration, the active region 111 and the p-GaN layer 121 are conformally fitted to the base NW (this is referred to as a core-shell structure). In both examples, NWs 100 and 101 include an n-InGaN layer 130 grown on a GaN layer 140 on a substrate 150. A mask layer 160 is supported on the GaN layer 140 and includes apertures formed therein by the NWs. The shape of the NWs does not have to be vertical—it may have sloping sidewalls; the core-shell structure can have active regions along various facets (including horizontal, vertical, and sloping).

[0073] The base region can have a suitable strain state; it may be fully or partially relaxed. The base region serves as the base for the epitaxial layer growth of the LED region. Some embodiments, compared to conventional LEDs, contain a higher concentration of In in the various layers surrounding the light-emitting layer to reduce the strain of the light-emitting layer.

[0074] Figures 2A to 2B A comparison was made between the conventional LED epitaxial stack 200 and Example 201. Figure 2A In the LED 200, most of the layers are GaN. Specifically, the layers forming the LED 200 are stacked from base to top as follows: GaN buffer 210, n-GaN layer 220, GaN / InGaN bottom layer 230, and GaN spacer 240 supporting the active region 250. The active region 250 consists of In0.2GaN quantum well layers separated by GaN barrier layers. Above the active region 250, the stack includes GaN spacer 260, AlGaN EBL 270, pGaN layer 280, and finally, p++GaN layer 290. These layers are grown on the relaxed GaN buffer 210 and are associated with GaN pseudomorphic crystals. The In0.2GaN QW in the active region 250 is able to undergo high strain due to its large lattice mismatch with GaN.

[0075] exist Figure 2B In this process, the stack forming LED 201 is grown on a relaxed In0.05GaN base layer 211 with a lattice constant greater than that of GaN (in the fully relaxed case, the lattice constant is the same as that of bulk In0.05GaN). The LED layers may contain InGaN instead of GaN. They may have the same content as the base region, resulting in low strain (although other compositions are also possible, including GaN and AlGaN layers). Figure 2B In the example shown, the stack grown on base 211 includes the following layers from bottom to top below active region 251: In0.05GaN layer 221, InGaN / InGaN bottom layer 231, and In0.05GaN spacer 241. Above active region 251, the stack includes In0.05GaN spacer 261, AlGaN EBL 271, pIn0.05GaN layer 281, and p++In0.05GaN layer 291. The same In0.2GaN QW maintenance ratio in active region 251 is maintained. Figure 2A Lower strain in the medium. This can promote higher material quality and higher performance.

[0076] In some embodiments, the LED emitter includes pixels, each pixel having three sub-pixels (e.g., emitting blue, green, and red light). Each sub-pixel includes a nanowire (NW) emitter. The nanowire is characterized by an InGaN base region grown by HVPE and an InGaN LED region having quantum wells grown by MOCVD. The red nanowire is characterized by a relaxed surface region in which 5% < [In] < 15% of the InGaN base region has [In] > 20% of the InGaN quantum wells are pseudomorphic grown on the surface region.

[0077] At least one layer in the InGaN base region may be substantially relaxed and have 50% or less (e.g., 40% or less, 30% or less, 25% or less, 20% or less, 15% or less) of [In] composition. In some embodiments, at least one layer in the InGaN base region is substantially relaxed and has 5% or more (e.g., 7.5% or more, 10% or more, 12.5% ​​or more, 15% or more) of [In] composition.

[0078] growth

[0079] Growth includes the growth of the base region and the growth of the LED region on the base region. These will be discussed now.

[0080] Base region growth

[0081] In some embodiments, the base region of the LED includes a group III nitride region having an In composition.

[0082] Typically, growing thick InGaN layers is challenging. High-quality InGaN layers have been shown to be grown via hydride vapor phase epitaxy (HVPE). For example, trihalide HVPE (THVPE) using InCl3 and / or GaCl3 precursors can effectively incorporate a large amount of In into the crystal, resulting in InGaN compositions ranging from 0% to 100%. THVPE InGaN growth has been illustrated in both planar and non-planar geometries.

[0083] Therefore, the embodiments are able to employ suitable growth techniques to grow the InGaN base region. The base region may have an In content of at least 3% (e.g., 5% or more, 8% or more, 10% or more, 12% or more, e.g., up to 15%), such as in the range of 5% to 15% (e.g., 5% to 10%, 10% to 15%, 5% to 12%).

[0084] The characteristics of InGaN materials may lie in their strain states. In some embodiments, regions of the InGaN material are fully relaxed, where the lattice constant (e.g., in-plane and / or vertical) is equal to the lattice constant of the InGaN material in its bulk state. Although this disclosure focuses on InGaN, other materials that provide suitable lattice constants (e.g., AlInN, AlInGaN) can be employed according to the techniques disclosed herein.

[0085] The base region can be formed on a substrate such as sapphire, Si, or GaN (including GaN templates or quasi-bulk or bulk GaN). The substrate can be configured to reduce strain in the base region (e.g., it can comprise multiple group III nitride layers with various compositions to provide strain engineering). The substrate surface can be functionalized with some other material to promote nucleation and growth. The substrate can have edge material, including edge material ranging from 0° to 3° (e.g., 0° to 1°, 0.1° to 1°) in the +m direction (or -m, +a, -a, +c, -c).

[0086] The base region can be grown as a planar layer; this planar layer can then be used as is or etched to form lateral structures (such as mesas or NWs). In some embodiments, these lateral structures have typical lateral dimensions of 5 micrometers or less (e.g., 3 micrometers or less, 1 micrometer or less, 500 nm or less, 300 nm or less, 150 nm or less, such as as small as 100 nm).

[0087] Figures 3A to 3D The process flow for manufacturing a base region with a lateral structure is shown. Figure 3AIn this process, a substrate 310 (e.g., having a buffer layer 320) is provided. Figure 3B In this process, a planar base layer 330 is grown (e.g., via HVPE); the base layer can be InGaN. Figure 3C In this process, the base layer 330 is patterned and etched (e.g., by dry etching) to form a lateral structure 340 (e.g., NW). Etching may stop at the interface of the base layer (e.g., ...). Figure 3C (as shown), or it may leave part of the base layer unetched, or it may extend below the base layer (e.g., in the buffer and / or substrate). Figure 3C The structure can be used as the base region for LED region regeneration. Alternatively, it can also be regrown (e.g., by HVPE or another technique, such as MOCVD) to grow additional material in the base region; regrowing may occur on all surfaces of the transverse structure, or selectively. Figure 3D The resulting structure is shown, including a regenerated long transverse structure 341, which can be used for the regeneration of LED regions.

[0088] exist Figures 3A to 3C In the illustrated method, strain relaxation may occur due to etching of the transverse structure and / or due to regrowth.

[0089] In some embodiments, the base region is grown as a structured layer, for example, having a non-planar shape facilitated by lateral structures. These lateral structures can have typical lateral dimensions of 5 micrometers or less (e.g., 3 micrometers or less, 1 micrometer or less, 500 nm or less, 300 nm or less, 150 nm or less, such as as small as 100 nm). Structured growth can be achieved by forming a mask (such as a patterned hard mask and etching clear openings into the growth substrate) on a substrate; and growing the base region within the openings of the mask. These openings can have typical lateral dimensions of 5 micrometers or less (e.g., 3 micrometers or less, 1 micrometer or less, 500 nm or less, 300 nm or less, 150 nm or less, such as as small as 100 nm). In some embodiments, growth is substantially vertical above the openings, while in some embodiments, growth extends laterally outside the openings, and in some embodiments, growth is performed inwards above the openings. The characteristic of inward growth is a negative growth rate in the lateral direction, thus the lateral-to-vertical growth ratio is negative. The ratio can be 0 or less (e.g., -0.1 or less, -0.3 or less, -1 or less).

[0090] Figures 4A to 4C The process flow for manufacturing a base region with a lateral structure is shown. Figure 4A In this structure, the growth structure includes a substrate 310, a buffer zone 320, and a growth mask 410 with an opening 411 (the buffer zone is optional). Figure 4B In this process, the base layer is grown in opening 411, forming a lateral structure 420, such as InGaN. Depending on the size of the mask opening 411, the lateral structure can be a mesa, a micromesa (with typical lateral dimensions of one or several micrometers, e.g., 10 micrometers or smaller, 5 micrometers or smaller, 3 micrometers or smaller, 1 micrometer or smaller), or an NW. Figure 4C In this process, growth occurs not only vertically but also laterally, thus providing a lateral structure 430 that extends beyond the opening 411 above the mask 410.

[0091] Lateral growth can result in a significant increase in the size of the lateral structure. In some embodiments, the openings in the growth mask are relatively small (as taught herein) and the lateral size of the lateral structure is relatively large. The lateral structure can have a lateral size at least twice the size of the mask openings (e.g., 5x or greater, 10x or greater, 20x or greater, 30x or greater). As taught herein, the openings can have lateral dimensions selected to facilitate strain relaxation. The final size of the lateral structure can be selected to obtain a device of a desired size—e.g., large enough to facilitate the fabrication process of a planar LED. As an example, the openings have lateral dimensions below 500 nm and the lateral structure has lateral dimensions above 1 micrometer.

[0092] Growth parameters can be selected to drive lateral growth. In some embodiments, a portion of the base layer grows at a lateral-to-vertical growth rate ratio greater than 2 (e.g., 5 or greater, 10 or greater, 50 or greater, 100 or greater). In some embodiments, the base material is initially grown within the opening at a first growth parameter, and lateral growth is driven at a second growth parameter once the base material protrudes above the mask.

[0093] In some embodiments, other growth parameters that do not promote (or even inhibit) lateral growth are used. For example, once the base structure is obtained, the LED can be regrowed under these growth conditions. In some embodiments, the layer grows at a vertical-to-lateral growth ratio greater than 2 (e.g., 5 or greater, 10 or greater, 50 or greater, 100 or greater). For clarity, the lateral growth rate characterizes which non-vertical plane has the fastest growth. This can be the m-plane, the a-plane, or the semi-polar plane.

[0094] In some embodiments, the base region has multiple sub-regions. Each sub-region has a lateral structure, and the characteristics of the structure differ between the sub-regions. For example, the dimensions of the lateral structure may vary (e.g., the NW may have varying diameters or lateral dimensions or heights), and / or the composition of the lateral structure may vary (e.g., some NWs have 5% In, while others have 10% In).

[0095] Lateral structures can be mesa or NW. They can have a height of 10 nm or greater (e.g., 50 nm or greater, 100 nm or greater, e.g., 10 micrometers or less, 3 micrometers or less, 2 micrometers or less, 1 micrometer or less), such as within the range of 50 nm to 10 micrometers, 10 nm to 1 micrometer, 100 nm to 2 micrometers, 500 nm to 3 micrometers, and typical lateral dimensions are 500 nm or greater (e.g., 1 micrometer or greater, such as 20 micrometers or less, 10 micrometers or less, 5 micrometers or less, 3 micrometers or less), such as within the range of 500 nm to 20 micrometers, 1 to 3 micrometers, 1 to 5 micrometers, 1 to 10 micrometers.

[0096] A portion of the base region may be characterized by its strain state and / or its lattice constant. Specifically, the base region has a regrowth surface on which the LED region will be formed. These regrowth surfaces may be the top and / or sidewalls of a lateral structure (NW or mesa). The regrowth surface may be fully relaxed, with its lattice constant (in-plane and / or vertical) equal to the lattice constant of the bulk material of the same composition. In some embodiments, relaxation is partial, wherein the lattice constant is within 1% of the bulk material of the same composition (e.g., within 0.5%, within 0.3%, within 0.1%, within 0.05%, within 0.03%, within 0.01%). The lattice constant of the bulk relaxed material is also referred to as the equilibrium lattice constant. Equivalently, relaxation can be expressed in absolute units rather than relative units. Relaxation layers (including base region layers, active region layers, quantum wells, and superlattices) can have lattice constants within 5E-3 nm (e.g., within 3E-3 nm, 1E-3 nm, 0.5E-3 nm, or 0.1E-3 nm) of their equilibrium lattice constant. The lattice constant of the pseudocrystalline layer grown on the first layer can be within 5E-3 nm (e.g., within 3E-3 nm, 1E-3 nm, 0.5E-3 nm, or 0.1E-3 nm) of the lattice constant of the first layer.

[0097] The cross-section of the transverse structure can have various shapes; this can affect strain relaxation. In some embodiments, the transverse structure is elongated (e.g., a strip whose length is much greater than its width). This can facilitate relaxation along a narrower direction. In some embodiments, the transverse structure has a length L and a width w, where L / W > 3 (e.g., 5 or greater, 10 or greater, 50 or greater, 100 or greater). In some embodiments, w < 300 nm (e.g., < 200 nm, < 150 nm, < 100 nm, < 75 nm, such as as low as 50 nm). In some embodiments, the strain relaxes uniaxially along the width direction. In some embodiments, the two equivalent crystal directions in the plane of the transverse structure (e.g., two so-called a-direction or m-direction) are characterized by different relaxations, where the lattice constant changes by more than 0.1% between the two directions. Conversely, in other embodiments, the shape is substantially regular (e.g., circular, square, triangular, or hexagonal); this can facilitate biaxial strain relaxation. In some embodiments, the two equivalent crystal directions (e.g., two a-directions or m-directions) in the plane of the transverse structure are characterized by equal or similar relaxations, wherein the lattice constant changes by less than 0.1% between the two directions.

[0098] In some embodiments, the strain in the base region varies spatially. For example, the base region is InGaN grown on GaN. Initially, InGaN is pseudomorphic with GaN; as growth proceeds, the InGaN relaxes strain (by forming defects and / or by lateral extension); after sufficient growth, the InGaN acquires partial or complete relaxation. Laterally extended relaxation may occur once the base material can grow freely laterally, for example, when growth reaches the top of the patterned mask. In the case of relaxation formed by defects, the extended defects may terminate at the sidewalls of the lateral structure (e.g., they may bend towards the sidewalls) rather than propagate in the growth direction.

[0099] Some embodiments are characterized by the small thickness required to achieve relaxation: relaxation can occur within a growth of less than 1 micrometer (e.g., 500 nm or less, 200 nm or less, such as as small as 100 nm). This can be facilitated by the presence of lateral structures that provide relaxation mechanisms beyond those available in the quasi-bulk layer. In some embodiments, the base region comprises an InGaN composition characterized by a bulk critical thickness t for relaxation, and relaxation occurs within a thickness less than 80% of t (e.g., 50% or less, 20% or less, 10% or less, such as as small as 1%).

[0100] In some embodiments, relaxation remains elastic, and plastic relaxation is avoided. In some embodiments, plastic relaxation occurs and is associated with the formation of extension defects such as dislocations; the structure is configured such that these extension defects remain away from the light-emitting layer (e.g., at least 100 nm) (this can be achieved by growing a sufficiently thick material over the plastic relaxation region).

[0101] In some embodiments, the regrown surface has a low defect density. It can have a density of less than 5E8 cm⁻¹. -2 Thread dislocation density (TDD) (e.g., 1E8 cm) -2 Or smaller, 5E7 cm -2 Or smaller, 1E8 cm -2 Or smaller, 5E6 cm -2 Or even smaller, down to 1E6 cm -2 This low TDD can be achieved by growing base regions on a low TDD substrate. It can be achieved by allowing TDDs to migrate to the lateral regions or by annihilating each other when grown sufficiently. The density of defects (including TDDs, stacking faults, and v-pits) can be configured to be less than 1 per lateral structure (e.g., less than 1 per NW, less than 1 or less per ten lateral structures, or less than 1 or less per hundred lateral structures).

[0102] In some embodiments, the base region includes an NW with a non-uniform composition. For example, the base region NW may include a first composition (e.g., 5%) of InGaN and a second composition (e.g., 8%) of InGaN.

[0103] Figures 5A to 5D The base regions with different In contents are shown. Figure 5A In the base region, there is an NW 500. The NW500 has multiple regions 510, 520, and 530 with different compositions (e.g., 1, 2, 3). Regions 510, 520, and 530 can be planar or have another shape. Figure 5A In the example, the first component has the same thickness as mask 410, but this is not always the case. Strain and strain relaxation can vary between regions. Figure 5B As shown, the In composition may increase during growth (e.g., 3%, then 5%, then 10%); this may contribute to gradual strain relaxation. Therefore, the variation of In% along the principal epitaxial direction can be at least 2%. These regions can be discrete, or the composition can be consistent with... Figure 5C The same continuous change. For example... Figure 5DAs shown, a high In region may be followed by a low In region (e.g., 5% versus 8%); in this case, the high In region may be partially relaxed and defective, and the low In region may have higher relaxation and fewer defects (e.g., because it grows in pseudomorphic form or has low strain / no strain on the high In region).

[0104] In some embodiments, the regenerated surface has a uniform composition, wherein the composition of each element varies by 2% or less across the regenerated surface (e.g., 1% or less, 0.5% or less).

[0105] In some embodiments, the base region or a portion thereof is doped (e.g., n-doped or p-doped). For example, the base region may have an n-doped InGaN region due to the presence of one or more dopants (such as O, Si), or a p-doped InGaN region due to the presence of dopants (such as Mg, Ge). The doping level may be sufficient to provide good carrier conductivity: it can be at least 1E16 (e.g., 5E16 or greater, 1E17 or greater, 5E17 or greater, 1E18 or greater, 5E18 or greater, 1E19 or greater, 5E19 or greater). The doping level may be low enough to avoid free carrier absorption: it can be less than 1E20 (e.g., 5E19 or less, 1E19 or less, 5E18 or less, 1E18 or less). Suitable lower and upper doping limits may depend on the dopant material (due to variations in activation levels and optical cross-sections between materials). In some embodiments, the dopant material is O, and the doping level is in the range of 1E17 to 1E19 cm⁻¹. -3 Within the crystal, dopants can form various states, including complexes and interstitials. The base region opens up the possibility of an inverse polarity structure for p-doped embodiments (i.e., a junction with n above p in an LED stack). In this case, LED growth can begin with undoped InGaN, including the growth of an undoped layer in the active region, and finally the growth of n-GaN. If desired, the base region can be activated prior to regrowth. The inverse polarity structure can be reversed during processing to expose the p-layer of the base region; p-regrowth steps can be performed on these exposed p-layers to create contact layers for forming p-contacts.

[0106] The base region can be grown in an HVPE reactor. The reactor can use various precursors, including monohalides (e.g., GaCl, InCl) and / or trihalides (e.g., GaCl3, InCl3). MCl and MCl3 (where M is a Group III metal, including Ga, In, Al) can be obtained by pre-reacting M with HCl or a gaseous Cl substance (including Cl2) or from solid form (e.g., sublimation of MCl or MCl3 solid / powder in a suitable carrier gas such as N2 or H2). The precursors can be formed in the reactor, for example, in a region separate from the growth region. NH3 can be used as the N source in the reactor. In some embodiments, InCl3 promotes the incorporation of a high indium composition in the base region, for example, exceeding 3% (e.g., 5% or more, 8% or more, 10% or more). The carrier gas (including H2 / N2 / Ar / He and combinations thereof) can be mixed with these precursor gases. Growth can be achieved using one of the following precursor combinations: GaCl / InCl, GaCl / InCl3, GaCl3 / InCl, or GaCl3 / InCl3. Some precursor combinations may be suitable for certain growth directions. In some embodiments, the precursor is GaCl3 / InCl3 and growth occurs along the -c plane. In some embodiments, the precursor is GaCl / InCl3 and growth occurs along the +c plane. The InCl3 precursor can facilitate the incorporation of high In content; in some embodiments, InCl3 is used and the base region has an In(x)Ga(1-x)N material where x > 0.05. More generally, possible precursors include MX and MX3, where M is a group III metal (In, Ga, Al) and X is one of Cl, Br, or I.

[0107] The composition of the base region can be selected to provide a sufficiently small lattice constant mismatch with the light-emitting layer of the LED region. In some cases, this requires the InGaN material to have a composition within the miscibility gap. Embodiments of the present invention facilitate this by using growth techniques (e.g., HVPE) and growth parameters that favor dynamic growth, thereby eliminating the miscibility gap. The pressure (or partial pressure of the material) can be maintained at a predetermined value to ensure dynamic growth. A predetermined oversaturation of the material can be achieved.

[0108] Dopant elements can be further introduced into the HVPE reactor. The dopant source can be gaseous, including O-containing gases (including O2) or Si-containing gases (including silanes and dichlorosilanes); it can be solid (e.g., Si in oxide or solid form, including high-purity crystalline Si). The dopant material and concentration can be selected to limit doping-induced strain.

[0109] In some embodiments, base region growth conditions are selected to reduce defect formation. Specifically, low-density vacancies (including N, Ga, or In) can be sought, where the vacancy density is less than 1E18 cm⁻¹. -3 (For example, 1E17 cm) -3 Or smaller, 1E16 cm -3 Or smaller, 1E15 cm -3 Or smaller, 1E14 cm -3 Or smaller, 1E13 cm -3 Or smaller, 1E12 cm -3 Or smaller, 1E11cm -3 Or smaller, such as 1E10 cm -3 Low density can be achieved by using relatively low growth temperatures, such as 900°C or lower (e.g., 850°C or lower, 800°C or lower, 750°C or lower, 700°C or lower, 650°C or lower, 600°C or lower, 550°C or lower, 500°C or lower). Low density can also be achieved by using high partial pressures of the corresponding material.

[0110] The composition of the base region can be controlled to limit the optical absorption of light emitted by the LED region. In some embodiments, the LED region has sub-regions that emit at various wavelengths (e.g., blue / green / red); therefore, reabsorption at the shortest wavelength is most likely. The composition of the base region is selected to limit the optical absorption at the shortest wavelength. In some embodiments, the sub-regions of the LED region emit short-wavelength light (e.g., blue light) with a peak wavelength; and the bulk absorption coefficient of the base layer at the peak wavelength (i.e., the absorption it has in bulk) is less than 10 cm⁻¹. -1 (For example, 5cm) -1 Or smaller, 2cm -1 or smaller, 1cm -1 (or less). In some embodiments, after the complete device is formed, the net power absorption of the base region to short-wavelength light is less than 10% (e.g., 5% or less, 2% or less, 1% or less). This net power absorption quantifies how much total light the base layer absorbs and directly competes with the net extraction efficiency of the device. In other words, the extraction efficiency (for a sub-pixel of a given color) can be written as Cex = 1 - Abase - Aother, where Abase is the net base layer absorption and Aother is the absorption from all other sources (metal, active region, free carrier absorption, etc.). In some embodiments, for a blue sub-pixel, Abase < 10% (e.g., < 5%, < 2%, < 1%).

[0111] As taught above, absorption can be reduced by selecting the composition and thickness of the absorbing material. Absorption can be limited in other ways, either alone or in conjunction with the material composition. This includes forming LED devices in which the light path between sub-pixels (e.g., from blue LED to red LED) is reduced or blocked, for example by forming optical isolation layers (e.g., reflectors, mirrors) between sub-pixels. This includes selecting an appropriate physical layout for the sub-pixels. This includes removing the absorbing material (e.g., by etching, polishing, and other techniques disclosed herein). In some embodiments, the absorbing material (e.g., a portion of the substrate, epitaxial layer, or base material) is present during some epitaxial steps and is removed or partially removed when the device is processed (e.g., at least 25%, at least 50%, or at least 90% of the material is removed).

[0112] Therefore, the In composition of the base region can be high enough to reduce strain in the active region, but low enough to reduce optical absorption. In some embodiments, the In composition of the base region is in the range of 2% to 20% (e.g., 5% to 10%, 2% to 5%, 3% to 10%, 5% to 8%, 5% to 12%, 5% to 15%, 10% to 20%).

[0113] In some embodiments, a regrowth region is prepared for regrowth. Surface treatments may be performed to ensure the regrowth region is ready for epitaxy. Surface treatments may include one or more wet etching processes (including acids, alkalis, and solvents). Some wet etching processes may selectively etch certain crystal faces. Wet etching may include KOH or H3PO4 etching. In some embodiments, a polishing step is performed to obtain a smooth surface with an RMS roughness of less than 5 nm (e.g., 3 nm or less, 1 nm or less, 5 Å or less, 3 Å or less). Polishing may be mechanical, chemical, chemimechanical, abrasive, and other techniques known in the art. In some embodiments, a dry etching step (such as ICP, RIE) is used to etch the material. Multiple techniques may be combined to achieve a desired thickness and desired surface state. In some embodiments, a first step (e.g., dry etching) removes material, and a second step (e.g., polishing or wet etching) promotes low roughness. In some embodiments, the regrowth region has a surface with desired edge material from the crystal direction. For example, the regrown surface may be slightly offset from the c-plane, having an edge angle in a specific direction (including the a-plane or the m-plane) ranging from 0.1° to 5° (e.g., 0.1° to 1° or 1° to 5°). The edge can be obtained through a polishing step.

[0114] Figures 6A to 6B An example of the base region of an NW with edge material is shown. Figure 6A In this design, the top surface of the base region is tilted across a macroscopic distance (e.g., the entire wafer), thus providing NW 610 with shared edge material. Figure 6BIn this context, edge material appears individually for each NW 620.

[0115] The growth reactor can be operated at pressures selected for high material quality and desired material properties. High pressures may be required to reduce the presence of some defects, including vacancies. In some embodiments, the pressure is atmospheric pressure or above 1 atm (e.g., at least 1.2 atm, at least 1.5 atm, at least 2 atm, at least 5 atm, at least 10 atm). In some embodiments, the partial pressure of the nitrogen-containing material is high to reduce the presence of N vacancies in the crystal. In some embodiments, the pressure is selected to facilitate the strain relaxation disclosed herein.

[0116] Growth parameters can be selected to ensure a sufficient growth rate. In some embodiments, the growth rate is at least 1 micrometer / hour (e.g., 5 micrometers / hour), which may be sufficient to grow a base region with a thickness ranging from 100 nm to 10 micrometers. In some embodiments, the growth rate is at least 20 micrometers / hour (e.g., 50 micrometers / hour, 100 micrometers / hour), which is beneficial for the growth of thick base layers and / or quasi-bulk base layers.

[0117] HVPE reactors can employ a variety of geometries, including those more commonly encountered in other growth techniques that can provide advantages for the embodiments. It may have a longitudinal / horizontal shape. It may have vertical flow. The reactor can be a two-flow reactor with a carrier gas flow in a given direction and an auxiliary gas flow in a second direction that helps control the carrier gas flow. It may have a shower nozzle design. Geometries can be selected to improve growth uniformity. Growth can occur on at least one wafer with a radius of at least 4”, and the In composition of the base layer material can vary by less than 3% (e.g., 2% or less, 1% or less, 0.5% or less) across at least 60% (e.g., 80% or more, 90% or more) of the wafer area. The reactor can include quartz material. It may be a cold-wall reactor. It can be a hot-wall reactor, wherein the temperature of the reactor inner wall is maintained above a desired temperature, including at least 400°C (e.g., 500°C or higher, 600°C or higher, 650°C or higher, 700°C or higher). The reactor can be designed to restrict the presence of specific atomic substances in the crystal. This includes substances containing Fe, Cu, Sn, C, B, and Mn. The concentration of the selected substances can be below 1E15 cm⁻¹. -3 (For example, 1E14cm) -3 Or lower, 1E13cm -3 Or lower, 1E12cm -3 Or lower, 1E11cm -3 Or lower, 1E10cm -3(or lower). In some embodiments, the reactor portion where growth occurs is set to a higher temperature than other portions of the reactor to reduce defect incorporation and / or parasitic nucleation. The temperature difference can be at least 50°C (e.g., 100°C or higher, 150°C or higher). In some embodiments, the wafer temperature can be kept below a maximum temperature to limit the formation of some defects with high formation energies (e.g., N vacancies and / or group III vacancies) in the base material. Therefore, the wafer temperature can be in the range of 400°C to 1000°C (e.g., 500°C to 600°C, 400°C to 800°C, 450°C to 750°C, 550°C to 650°C).

[0118] In some embodiments, the base region initially has a lateral structure and is coalesced to form a continuous layer. Figure 7A This geometry, in which the lateral structures 710 coalesce, provides a continuous surface 711. Growth conditions can be selected to promote lateral growth (including promoting growth along planes such as semi-polar or non-polar planes); in some cases, growth occurs along the six equivalent crystal planes of the wurtzite structure. Material from individual lateral structures may coalesce at the growth front. The coalescence front can be a plane, a point (i.e., a vertex), or other region. In some cases, defects such as dislocations, stacking faults, and other crystal registration errors may form at the coalescence front. Alternatively, the coalescence front can be defect-free. The geometry of the lateral structures and the growth conditions can be controlled to reduce coalescence defects. The base region can be grown on a patterned mask whose geometry is selected to match the lateral growth behavior and reduce defects. For example, the mask has a triangular lattice and the growth front propagates along the six equivalent directions of the wurtzite structure. Figure 7B and 7C As shown, the mask opening 720 can be aligned so that the growth front 730 is parallel or perpendicular to the triangular lattice of the mask, producing a planar ( Figure 7C ) or dotted ( Figure 7B The coalescence front of the mask. This can correspond to the alignment of the mask lattice with the m-plane or the a-plane, respectively. The alignment can also be intentionally tilted from the a-plane or m-plane by a preselected angle, such as 1 degree, 2 degrees, 5 degrees, or 10 degrees. In some embodiments, the lattice alignment of the mask with the crystal is within + / - 5 degrees (e.g., + / - 1 degree, + / - 0.1 degrees). In some embodiments, no more than one dislocation (or dislocation bundle) is created at the point-like coalescence growth front. This is in Figure 7D The diagram shows a mask opening 720 relative to dislocation 750. The continuous layer surface of the base region can be planar after growth, or it can be planarized through a process.

[0119] The aggregation can be achieved using only one growth technique (e.g., HVPE, MOCVD) or through successive growth steps utilizing different techniques. In some embodiments, the base layer with a lateral structure is grown via HVPE; MOCVD regrowth is used to aggregate the lateral structure. The LED region is then grown in the same MOCVD reactor as the aggregation step or in a third growth step (i.e., separate MOCVD growth for aggregation and the LED region).

[0120] The base region can be processed before the LED region is grown. The base region can be transferred to the substrate before the LED region is grown. In some cases, the base region has a planar top surface. The top surface may have a group III polarity (i.e., along the +c direction). It is transferred once, with the top surface attached to the substrate. The growth substrate and buffer (if any) can be removed using the techniques disclosed herein, including grinding and polishing and / or laser lift-off. A portion of the exposed base region can be removed / thinned; this may include non-aggregated portions (i.e., portions with lateral structures). This can be achieved using the techniques disclosed herein, including grinding and polishing. The base region after this step can be planar. The base region can be transferred a second time to a second substrate. Thereafter, the base region can be a planar layer continuously attached to the second substrate, with its top surface exposed again. The transferred base region can be used as a growth substrate / template for LED growth. The transferred base region can be further patterned (e.g., having a mesa shape): mesas with small dimensions can be formed, such as micron-scale mesas suitable as subpixels. Such a mesa can be formed at various stages of the process, such as once the base region is thinned on the first substrate, or after the base region has been transferred to the second substrate.

[0121] Figures 8A to 8I The process flow is illustrated. (A) For example, a coalesced base region 710 is provided grown on a substrate 310 having a buffer 320 and a mask 410. (B) The base region is attached to a substrate 810. (C) The substrate / mask / buffer is removed by laser lift-off 820. (D) The base region is thinned to obtain a thinned base region 820 planar surface 821. (E) The base region is attached to a second substrate 830. (F) The first substrate 810 is removed. Alternatively, after step (D), in (G), the base region is patterned into mesa 825. (H) The base region having mesa 825 contacts the second substrate 835. (I) Some mesa 825 are transferred. This selective transfer can be achieved by various techniques (e.g., by a patterned material on the second substrate that facilitates selective bonding of some mesa; or by applying mechanical forces to the selective mesa, such as forces applied through the first and / or second substrates to push some mesa).

[0122] The base region transfer method disclosed herein can be used to combine various base regions on the same substrate. For example, multiple aggregated base regions are combined; they have different compositions and / or strain states. This can be achieved through repeated... Figure 8I This is achieved through a process. Base regions can be spatially combined on the substrate, such that each base region corresponds to a type of sub-pixel. For example, three base regions with an increased In composition form three sub-pixel sets on the substrate and are used to regrow LED regions. The repair process can be used to replace defective mesas before or after regrowth.

[0123] LED regional growth

[0124] The LED region is grown on the regrowth surface of the base region.

[0125] The LED region may have an InGaN layer (doped and / or undoped) for carrier transport, similar to the common GaN n-layer, p-layer, and upper and lower barriers found in conventional group III nitride LEDs. It can have AlGaN, AlInGaN, or AlInN layers as electron blocking layers. It can have an active region with a luminescent quantum well (QW) / barrier made of InGaN / GaN or InGaN / InGaN. It can have defect-reducing layers (such as uniform InGaN or AlInN layers, or superlattices of other variants of InGaN / InGaN, InGaN / GaN, InGaN / AlInN, and group III nitride layers). These various layers can have compositions selected to reduce strain in the luminescent layer.

[0126] In some embodiments, the regrowth surface is the top surface of the NW, and... Figure 1A Similarly. In some embodiments, the regrowth surface includes multiple surfaces of the NW, such as Figure 1B The top surface and sidewalls of the structure.

[0127] In some embodiments, the LED region is pseudomorphic to the regenerated surface, or is close to pseudomorphic (where each layer in the LED region has an in-plane lattice constant that differs from the lattice constant of the regenerated surface by less than 0.1% or 0.01%). Therefore, the lattice constant of the regenerated surface is important because it determines the strain state of the active region.

[0128] In some embodiments, the active region includes one or more QWs having a composition. This composition may include at least 10% (e.g., 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more) of In.

[0129] The base region and layers of the LED region can be configured to reduce strain in the QW. For example, the base region has a base composition (e.g., In0.1GaN), and some n-layers and p-layers of the LED region have the same base composition, thus they are strain-free. The barriers between the QWs can also have the same base composition or a similar composition. The composition of the barriers can be configured to compensate for stress in the QWs. For example, the In of the barriers is smaller than that of the base region, and they are under tensile strain that compensates for compressive strain in the QWs.

[0130] The following is an example of the composition in the stack (all layers, but the first layer is regrown as part of the LED region):

[0131]

[0132] The strain state can be quantified by various quantities. A convenient quantity is the mismatch strain (or fundamental strain field) between the in-plane lattice parameters of the two layers:

[0133] e = (a_b - a_l) / a_l

[0134] Where a_b is the in-plane lattice constant of the base layer (i.e., the layer in which pseudomorphic growth occurs), and a_l is the in-plane equilibrium lattice constant of the layer that is growing.

[0135] In some embodiments, if the QW is pseudomorphically grown on a relaxed GaN surface, the mismatch strain in the QW is reduced to less than 80% of the mismatch strain (e.g., 50% or less, 30% or less, 20% or less, 10% or less). For example, the mismatch strain value of a c-plane In20GaN QW pseudomorphically grown on c-plane GaN is -2.2%. In some embodiments, the same In20GaN QW pseudomorphically grows on a relaxed In10GaN layer, and its mismatch strain is approximately -1.1%, which is approximately half the strain grown on GaN.

[0136] The table below illustrates possible embodiments. Embodiments can be configured according to the minimum and maximum limits taught in the table. For example, an embodiment may have a base layer (where the in-plane lattice constant has a value higher than a selected value (e.g., 3.22 Å)) and at least InGaN comprising an active region higher than a selected value (e.g., 30%), and be configured to have a mismatch strain ratio lower than a selected value (e.g., 67%).

[0137]

[0138]

[0139] This table assumes the base layer is relaxed InGaN. However, other materials with similar in-plane lattice constants (including In-containing group III nitride compounds and other materials) are also suitable. The mismatch strain ratio is the ratio of the actual mismatch strain (between the base layer and the active layer) to the mismatch strain value if the active layer were to grow pseudomorphs on GaN.

[0140] In some embodiments, the strain component epsilon_3 is approximately proportional to the mismatch strain, and therefore the strain-induced polarization field is approximately proportional to the mismatch strain. Thus, the mismatch strain ratio used herein can also correspond to a polarization field ratio, which is defined as the actual polarization field in the active layer divided by the polarization field of the structure and the GaN pseudomorphic crystal.

[0141] In some embodiments, at least 50% (e.g., 80% or more, 90% or more) of the light emitted by the LED is emitted by one or more active layers, and the active layers are further characterized by the properties taught herein (such as composition, mismatch strain, mismatch strain ratio, polarization field ratio).

[0142] In some embodiments, the composition and thickness of the active region are at least 1.5 times (e.g., 2 times or more, 3 times or more) the critical thickness for pseudomorphic growth on relaxor GaN at that composition. This is facilitated by a reduction in strain in the active region. In some embodiments, the QW has a thickness ranging from 2 to 4 nm and a composition ranging from 30% to 60%.

[0143] In some embodiments, the active region has an emitting layer with an In content of at least 30% (e.g., 35% or more, 40% or more, 50% or more, for example, within the range of 30% to 60%) and a thickness of at least 2 nm (e.g., 2.5 nm or more, for example, within the range of 2 to 5 nm).

[0144] In some embodiments, the active region undergoes lateral relaxation during its growth. For example, the active region is planar (perpendicular to the axis of the base NW / small plate / mesa), and... Figure 1A Similarly, during growth, the active region is subjected to compressive strain because it has a high In composition and therefore a larger in-plane lattice constant than the underlying layer (including the base region). The typical lateral dimensions of the NW are small enough that the strain relaxes through the lateral expansion of the active region. This relaxation may be partial. The active region may include a quantum well with an in-plane lattice constant that is at least 0.01% (e.g., 0.03% or more, 0.05% or more, 0.1% or more) larger than the lattice constant of the regrown surface of the base region.

[0145] Existing technologies have demonstrated structures with InGaN relaxation (e.g., plastic relaxation by forming defects in a very thick InGaN layer). However, such structures are considered to have very poor IQE. In contrast, some embodiments of the present invention maintain low defect rates and / or high IQE while reducing strain in the active region. This is facilitated by growth on the relaxed base region.

[0146] Therefore, some embodiments are characterized by a low defect level in the active region. The active region can have a defect level of less than 5E8cm. -2 (For example, 1E8cm) -2 Or smaller, 5E7cm -2 Or smaller, 1E8cm -2 Or smaller, 5E6cm -2 Or smaller, 1E6cm -2 TDD (or smaller). It can have a size of less than 1E5cm. -1 The density of stacking faults or mismatched dislocations (e.g., 1E4cm) -1 Or smaller, 1E3cm -1 Or smaller, 1E2cm -1 Or smaller, 1E1cm -1 (or smaller). In embodiments with lateral structures (e.g., NWs or micromesa), the density of defects (including TDD, stacking faults, v-pits) can be configured to be less than one per lateral structure (e.g., one per NW), less than one per ten lateral structures, or less than one per hundred lateral structures.

[0147] Some embodiments are characterized by high internal quantum efficiency (IQE). This high IQE can be significantly higher than that achievable through conventional strain growth on GaN. This can be facilitated by reducing strain in the active region.

[0148] Figure 9The relationship between wavelength and IQE is illustrated, and prior art is compared with embodiments. The prior art curves are based on publicly available data from planar LEDs with various emission wavelengths grown via MOCVD: IQE decreases significantly at longer wavelengths, a well-known characteristic of the green gap. Strain is believed to contribute (at least partially) to this reduction. Therefore, the effect of strain on IQE can be modeled, and the improvement in IQE after strain reduction can be predicted. The embodiment curves illustrate the results of this procedure and show the expected performance of some embodiments. Here, a fully relaxed base layer with In0.05GaN is considered. The best prior art device reported in the red range (620 to 630 nm) has an EQE of approximately 2% to 2.5%, corresponding to an IQE of approximately 3%. In contrast, some embodiments have an IQE of at least 5% (e.g., 10% or more, 15% or more, 20% or more, 30% or more) at a peak emission wavelength of at least 610 nm (e.g., 620 nm or more, 625 nm or more, 630 nm or more). Figure 9 This is an illustration, and other values ​​for In composition and strain relaxation may be required to achieve the desired IQE. Embodiments include selecting a desired peak emission wavelength and at least one criterion for the quality factor of an optoelectronic device (including a minimum desired value for IQE, external quantum efficiency (EQE), or socket efficiency (WPE), and configuring the emitter taught herein (including selecting the composition and strain state of the base region) to achieve at least one criterion. In one embodiment, the emission wavelength is at least 615 nm, the IQE is at least 15%, and the base region has at least 5% In composition and is substantially fully relaxed.

[0149] In some embodiments, the base region has multiple sub-regions. The sub-regions have base layers with different In compositions. This can be achieved as disclosed herein (e.g., according to...). Figures 8A to 8I (The process). For example, there are sub-regions with GaN NW, In0.05GaN NW, and In0.1GaN NW. Regions with more In are more suitable for growing long-wavelength LEDs. Due to lattice pulling effects, under the same growth conditions, regions with more In will naturally incorporate more In during LED growth. In some embodiments, the growth of LED regions occurs simultaneously on each sub-region; due to lattice pulling, each sub-region has a different active region composition and a different emission wavelength. In some embodiments, there are three sets of sub-regions and LEDs are grown simultaneously on these sub-regions, emitting blue, green, and red light respectively. The base region can have three sets of sub-regions with different compositions. LED regions emitting blue, green, and red light are regrown on the three sets of sub-regions respectively.

[0150] In some embodiments, the sub-regions have NWs with different diameters. For example, there are sub-regions with diameters of 80 nm, 120 nm, and 150 nm. This facilitates variations in In incorporation during LED region growth. For example, smaller diameter regions contribute to higher In incorporation because In atoms are consumed by a smaller growth volume. In some embodiments, there are three sets of sub-regions and LEDs are grown simultaneously on these sub-regions, emitting blue, green, and red light, respectively.

[0151] The two concepts presented above can be combined. Subregions can have different compositions and varying NW sizes, and size and composition traction effects can be combined to achieve various emission wavelengths (including the simultaneous growth of LEDs with desired wavelengths, such as blue / green / red).

[0152] In some embodiments, the regrowth of LED regions on multiple sub-regions is performed using the same regrowth steps. In other embodiments, multiple regrowth steps are performed. For example, the base region has three sets of sub-regions. A first set is exposed, while two other sets are covered by a growth mask. The mask may include oxide materials (including SiOx, AlOx); nitride materials (SiNx, AlNx); a dielectric layer; or a metal (including Mo). Growth steps are performed (e.g., by MOCVD), and LED regions with a first wavelength are formed on the first set of sub-regions—these regions may form, for example, blue sub-pixels. The process is repeated using the other two sets of sub-regions to form other LED regions that emit at other wavelengths (e.g., green and red).

[0153] Figures 10A to 10E The diagram illustrates the process of LED region regrowth. (A) Component 1000 provides three base sub-region sets 1020, 1030, and 1040 on substrate 1010. These sets have InGaN compositions 1, 2, and 3. (b) A first growth mask 1050 is formed over sub-regions 1030 and 1040. (C) Growth of LED sub-region 1060 is performed over base sub-region 1020. (D) The first growth mask 1050 is removed, and a second growth mask 1070 is formed over sub-regions 1020 and 1030. (E) After repeated masking and epitaxial steps, LED sub-regions 1060, 1080, and 1090 are grown over all base sub-regions 1020, 1030, and 1040.

[0154] In some embodiments, successive regrowth steps are performed for different wavelengths, with the steps for longer wavelengths being performed last. For example, red LEDs are grown last. This can promote good material quality because the long-wavelength active region requires a high In content to achieve a low thermal budget. In some embodiments, a regrowth step produces a red LED; this regrowth step is performed under low thermal budget conditions. The low thermal budget can be defined by a maximum temperature Tm, with each sub-step in the step performed below Tm. Tm can be 900°C or less (e.g., 850°C or less, 800°C or less, 750°C or less, 700°C or less, 650°C or less, 600°C or less, 550°C or less, 500°C or less). The low thermal budget can be defined by a maximum temperature Tm and a maximum time tm, with each sub-step in the step performed below Tm, and steps performed at or near Tm consistently less than tm.

[0155] In some embodiments, the LED region (or its layer) is grown using pulsed growth techniques—for example, by flowing different group III precursors (such as TMG and TMI) at different times. This can facilitate the growth of layers with high In content.

[0156] In some embodiments, LED regrowth occurs across the entire free surface of the base layer. For example, it appears on the top and sidewalls of the base NW, exhibiting a core-shell geometry, such as... Figure 1B As already shown.

[0157] In contrast, in some embodiments, LED growth occurs only on certain portions of the base layer—for example, only on the top facet of the base layer NWS, such as... Figure 1A As already shown. This can result in a planar active region along the NW axis. The active region can be disk-shaped, or more generally have the same cross-section as the NW.

[0158] Various techniques can be employed to achieve this top-only growth. Growth parameters can be selected to promote nucleation on the top surface. For example, the top surface is a c-plane, and growth conditions promote nucleation of the c-plane over other planes (e.g., m-plane, c-plane, semi-polar plane). Suitable growth conditions may include temperature, pressure, partial pressure of various precursors, III / V ratio, growth rate, and the use of pulsed growth. In some embodiments, cryogenic temperatures are employed to promote top surface growth. The temperature used to grow the luminescent layer can be below 700°C (e.g., 675°C or lower, 650°C or lower, 625°C or lower, 600°C or lower, 550°C or lower, 500°C or lower, 450°C or lower, 400°C or lower). Growth techniques suitable for cryogenic growth can be employed (including MBE, sputtering, plasma-assisted CVD, and other CVD techniques suitable for cryogenic conditions).

[0159] The sidewalls can be covered to prevent epitaxial growth on the sidewalls. In some embodiments, a dielectric material (e.g., SiOx, AlOx, SiNx, AlNx, TiOx, TaOx, ZrOx) is deposited on the sidewalls. It can cover all or almost all of the sidewalls, allowing the top region of the NW to grow freely.

[0160] Figures 11A to 11F The process flow for covering the NW sidewalls is shown. Figure 11A The base region NW 1110 after base region 1100 growth is shown. Figure 11B In this process, NW 1110 is coated with a dielectric material 1120; in this case, the deposition is conformal (which can be obtained using atomic layer deposition and other known processes). Figure 11C In this process, the top of the dielectric material 1120 is removed, exposing the top surface 1130 of the NW 1110. This can be achieved using techniques including: mechanical processes (e.g., grinding, polishing), including selective mechanical processes with a faster etching rate than that used for semiconductor dielectrics; dry etching (e.g., RIE, ICP), including directional dry etching processes (which etch the top surface of the dielectric material faster than its sidewalls and can be achieved by selecting etching parameters [pressure, composition, power]) and selective dry etching processes with a faster dielectric etching rate than that used for semiconductors. The final geometry before regrowth may differ. Figure 11D This illustrates the case where dielectric 1121 is etched below the top surface 1130. Figure 11E The dielectric 1122 is shown extending above the top surface 1130. Figure 11F The case where dielectric 1123 is not conformal and extends around NW 1110 is shown.

[0161] exist Figure 11D In such cases, some lateral growth may occur on their exposed sidewalls (or sloping walls, if present). In some embodiments, it is desirable to limit the amount of lateral growth. Therefore, the grooves of the filler material can be small enough to make the protrusions of the NW small, for example, less than 100 nm (e.g., 50 nm or less, 25 nm or less, 10 nm or less, 5 nm or less).

[0162] In some embodiments, lateral growth occurs and the growth conditions are selected to reduce In incorporation and / or growth rate for lateral growth such that lateral growth occurs but the In-containing layer (i.e., QW) has less In or is thinner on the sides of the NW than on top of the NW. For example, the QW on the top surface has a thickness t and an In composition x, and the corresponding layer on the sidewall has a thickness less than t*0.8 (or 0.5) and / or a composition less than x*0.8 (or 0.5). This can exclude light emission and / or absorption of the lateral material.

[0163] As already disclosed, the regrowth surface can be prepared for regrowth (i.e., epitaxy-ready). This preparation step can occur before or after the dielectric coating step described herein.

[0164] Other materials than dielectrics (e.g., metals) can be used to cover the NW. Various parts of the NW can be coated to prevent them from regrowth nucleation: sidewalls, top portions, inclined walls, semi-polar facets. In some embodiments, some crystal facets are coated while other crystal facets are not, thus promoting regrowth. In some embodiments, the uncoated facet is the c-plane (or m-plane, a-plane, semi-polar). Depending on the crystal orientation of the structure, different planes can correspond to the top facet.

[0165] In some embodiments, the layers of the LED region are configured to achieve a specific polarization field and control the overlap of electron and hole wave functions (WFs) in the light-emitting layer. For various crystal directions, group-III nitride heterostructures exhibit spontaneous and strain-induced polarization fields. These fields have various effects, including: separating WF overlap (which can be harmful to radiative efficiency), increasing the emission wavelength (which can be beneficial, especially to reach longer wavelengths for a given material composition). Thus, embodiments of the present invention can seek fields with a given intensity or within a given range to mitigate the trade-off between these effects. In some embodiments, due to the reduction of strain, the magnitude of the polarization field in the active region is reduced (e.g., an In0.3GaN QW has a lower polarization field when pseudomorphic to an In0.1GaN base region than when pseudomorphic to a conventional GaN layer). In some embodiments, the layers surrounding the active region are selected to control the strain difference and thus control the field. For example, the active region can include an In(x)Ga(1-x)N light-emitting QW, and at least one layer (e.g., a barrier) including In(y)Ga(1-y)N (where y < x) or GaN or AlGaN or AlInGaN close to the QW. In some embodiments, the barrier between QWs consists of multiple layers - for example, the stack between two QWs can be (where the p-side or n-side can be on the left):

[0166] InGaN QW / InGaN / InGaN / InGaN QW

[0167] InGaN QW / InGaN / GaN / InGaN QW

[0168] InGaN QW / InGaN / AlGaN / InGaN QW

[0169] InGaN QW / GaN / AlGaN / InGaN QW

[0170] In some embodiments, QW has a range of 1 to 4 MV cm. -1 (For example, 1 to 2, 2 to 2.5, 2.5 to 3, 3 to 4 MVcm) -1 The polarization field of the QW is selected along with the thickness (because their product equals the voltage drop across the QW). In some embodiments, the product of the QW thickness and the polarization field across the QW is in the range of 0.1 to 1 V (e.g., 0.1 to 0.3 V, 0.25 to 0.5 V, 0.5 to 0.75 V, 0.75 V to 1 V, less than 1 V, less than 0.5 V, less than 0.3 V). In some embodiments, the above values ​​are still obtained even though the QW has the composition In(x)Ga(1-x)N where x>0.2 (e.g., >0.25, >0.3, >0.4). In the embodiment, the QW has a composition In(x)Ga(1-x)N where x>0.3 and a thickness t>1nm; it grows pseudomorphs on a base layer having a composition In(y)Ga(1-y)N where y>0.05; and due to the correct configuration of parameters (including y, t and the composition of the layers surrounding the QW), the voltage drop across the QW is less than 0.5V.

[0171] Some embodiments include a bottom layer, such as a layer configured to improve the IQE of the active region by incorporating defects. The bottom layer may include In; it may be a continuous InGaN or AlInGaN or AlInN layer; or a superlattice containing an In compound. Alternatively, embodiments may not require a separate bottom layer if the In concentration of other layers (i.e., the base layer, the InGaNn layer, and the barrier) has already effectively trapped point defects.

[0172] Figures 12A to 12B The geometry and strain state of the embodiment are illustrated. Figure 12AThe structure after the growth of the base region 1210 is shown. A GaN buffer 320 with a mask 410 is provided on a substrate 310, and the InGaN base region 1210 is grown in the mask opening. As the growth of the base region 1210 proceeds, its strain relaxes. This is shown here as lateral expansion, although other relaxation mechanisms disclosed herein are possible. The base region 1210 ends with a relaxed regrown surface 1220. At different locations along the growth direction, the lattice constant increases. For example, in the mask opening (location 1211), the growth is pseudocrystalline and the in-plane lattice constant is the lattice constant of the GaN buffer. At the intermediate location 1212, relaxation is partial and the in-plane lattice constant is between that of bulk GaN and bulk InGaN. At location 1213, the material is fully relaxed and the in-plane lattice constant is the in-plane lattice constant of bulk InGaN. Figure 12B The regrowth of an LED region on a regrowth surface 1220 is shown, including an n-InGaN 1230, an active region 1240, and a p-InGaN 1250. The LED region can be pseudomorphic with the regrowth surface 1220, i.e., it can have the same in-plane lattice constant as at location 3 (with some tolerances, such as + / - 0.1% lattice constant value).

[0173] Figures 13A to 13C It shows when NW according to Figures 12A to 12B The evolution of various quantities during growth. Figure 13A The layers shown are: base layer 1210 and LED layers 1230, 1240 and 1250 (including layers with the same composition as the base layer, and QW with a higher In composition). Figure 13B The evolution of the in-plane lattice constant along the axis of NW starting from the base region 1210 is shown. First, the base region is pseudomorphic with GaN buffer (lattice constant a1); then relaxation begins and the lattice constant increases towards its bulk value (lattice constant a2), thus reaching full relaxation. Base region growth ends, followed by pseudomorphic growth in the LED region. Figure 13C A simplified sketch of the corresponding strain is shown. The strain decreases during the relaxation of the base layer. The strain in the QW increases due to its higher In content.

[0174] The size of the NW (or other lateral structures) can be selected to facilitate relaxation. In some embodiments, the NW has a diameter (or typical lateral dimension) of less than 200 nm (e.g., 150 nm or less, 120 nm or less, 100 nm or less, 80 nm or less, 50 nm or less). Small diameters can facilitate lateral relaxation. In some embodiments, multiple sets of lateral structures are present on the base surface, characterized by different relaxation levels; this can be facilitated by their different sizes. In some embodiments, three sets of NWs are present, with three different typical lateral dimensions; the larger NWs exhibit less relaxation; in this embodiment, these three sets may correspond to blue, green, and red pixels; it may be advantageous to have greater relaxation for red pixels and lower relaxation for blue pixels.

[0175] In some cases, relaxation in the base region is not due to lateral expansion, but rather to other effects such as the formation of defects (including stacking faults, dislocations, vacancies, interstitial fillers, and other defects) and / or voids. Relaxation can begin immediately, where little or no InGaN material is grown on the GaN buffer. Sometimes relaxation is incomplete, and the lattice constant of the regrowth surface is less than that of bulk InGaN with the same composition. The difference in lattice constant between a regrowth surface and bulk material of the same composition may be less than half the difference in lattice constant between bulk GaN and bulk material of the same composition.

[0176] Figure 14 An example process flow 1400 for obtaining an LED according to an embodiment is shown. In step 1410, a substrate is provided. In step 1420, a GaN buffer is grown on the substrate. In step 1430, the surface of the GaN buffer layer is patterned. In step 1440, an InGaN base region is grown in the openings of the pattern by HVPE. In step 1450, an InGaN LED is grown on the base region by MOCVD. In step 1460, the sample is further processed to form an LED device. Some steps are optional, and some steps can be omitted or reordered.

[0177] In some embodiments, an etching step is performed to remove epitaxial material from the LED region after growth. The etching step can be selective chemical etching, including KOH, H3PO4, and other etchants, and can etch some facets faster than others; it can be dry etching (including ICP, RIE); it can be photochemical, electrochemical, or photoelectrochemical etching. Etching can rapidly etch nonpolar facets (including m and / or a) and can slowly etch c-plane facets (including +c). This can be used to remove sidewall material from the NW or mesa without removing the top material.

[0178] In some embodiments, LED region growth occurs conformally, with material grown on the top and sides of the NW (or mesa). An etching step is then performed to remove sidewall material, leaving the top material intact. The etching step can be performed until the p-type material of the sidewalls and the active region material have been removed. It can expose the n-type material of the LED region or the material of the base region. The top surface can be covered or otherwise protected prior to the etching step, such that only the sidewall material is removed. The etched structure can have substantially vertical sidewalls. Etching can be selected to produce high crystal quality with low defects (e.g., dangling bonds) to reduce sidewall recombination. The sidewalls can be further passivated after growth (e.g., through a dielectric layer) to reduce recombination. Etching can be used to control the lateral dimensions of the transverse structure. In some embodiments, etching removes defective material from the sidewalls. The sidewall material may have defects (including threaded dislocations, mismatched dislocations, dangling bonds), and etching can remove material until the NW is free of defects.

[0179] In some embodiments, etching removes material that emits at unwanted wavelengths. In one example, the NW has a light-emitting region perpendicular to its axis (e.g., a disk-shaped active region in the case of a circular NW), and the emission wavelength of the active region is radially non-uniform (i.e., it varies from the center to the edge), producing a first FWHM of emission; etching removes material near the periphery, resulting in a second FWHM that is narrower than the first FWHM. In another example, the LED region growth is conformal and the top and sidewalls of the active region emit at different wavelengths; etching removes sidewall material so that emission comes only from the top portion of the active region. Etching can form nanoporous materials. In some embodiments, etching promotes strain relaxation. For example, etching removes lateral material, which reduces the NW diameter and promotes lateral lattice expansion of the active region, as well as strain reduction.

[0180] Epitaxial layers can have tensile or compressive strain. In some embodiments, an In(x)Ga(1-x)N layer grown on GaN or on an In(y)Ga(1-y)N layer in which x > y has compressive strain. A layer with tensile strain can be grown near a layer with compressive strain to balance the strain. Tensile strain can be achieved, for example, by adding Al to a group III nitride compound (e.g., using an AlGaN layer, an AlInN layer, or an AlInGaN layer with a suitable composition). For example, an AlGaN barrier can be grown near an InGaN quantum well. In some embodiments, a layer with compressive mismatch strain e1 is grown near a layer with tensile strain e2, and 0.25 < |e1 / e2| < 4 (e.g., 0.5 < |e1 / e2| < 2). The vicinity can be 10 nm or less (e.g., 5 nm or less, 2 nm or less, 1 nm or less).

[0181] Geometric shapes

[0182] Some embodiments include a NW or a countertop or board. One or another of these configurations may be selected hereafter as examples, but the teachings are generally applicable.

[0183] The top surface of the line can be substantially flat. For example, the transition from the sidewall to the top surface occurs when there are no sloping sidewalls or sloping sidewalls are limited (such as less than 20 nm, less than 10 nm, less than 5 nm, less than 3 nm).

[0184] Figures 15A to 15D A cross-section of the NW (or small plate) along its axis 1501 is shown according to some embodiments. Figure 15A In the middle, NW 1510 has a vertical cross-section, and its sidewall 1511 is parallel to the axis 1501. Figure 15B In the NW, there is a cross-section with inclined sidewalls 1521 and an active region 1522 grown only in a plane perpendicular to the NW axis 1501. Figure 15C In the NW1530, the inclined sidewalls 1531 and the growth of the LED active region 1532 have occurred along all the facets (core-shell structure). Figure 15D In the NW 1540, there is a core-shell structure, but the masking layer 1545 prevents growth along part of the sidewalls. Depending on the size of the masking layer 1545, most of the LED active area 1542 can be grown on the planar facets, while almost no growth occurs along other planes.

[0185] NW can be grown substantially along the 0001 (+c) direction or along the 000-1 (-c) direction. It can be substantially without domain inversion (i.e., domains whose polarity switches between +c and -c). In some embodiments, at least 90% (e.g., 95% or more, 99% or more) of the top surface of the base region has a constant polarity.

[0186] The height of the NW can range from 10 nm to 10 micrometers (e.g., 10 nm to 1 micrometer, 100 nm to 10 micrometers, 100 nm to 3 micrometers). The diameter (or typical lateral dimension) of the NW can range from 10 nm to 1 micrometer (e.g., 10 to 100 nm, or 10 nm to 500 nm, or 30 nm to 1000 nm, or 10 nm to 300 nm).

[0187] Some embodiments include microplates (i.e., they have lateral structures with a lateral dimension of about one micrometer or a few micrometers).

[0188] Figures 16A to 16C An example manufacturing process for a small-panel LED is shown according to an embodiment. Figure 16AIn this embodiment, a substrate 1610 with selective growth openings in a mask 1620 is provided, and a relaxed base layer 1630 is grown thereon. The substrate can be, for example, GaN or Si, or Si with an AlN nucleation layer or sapphire. The base layer 1630 growth begins in the openings of the mask 1620. The base layer 1630 undergoes relaxation, as taught herein. Growth along the lateral direction is driven, for example, by selecting appropriate growth conditions. Figure 16A At the end of the structure shown, the base lateral structure can have a lateral dimension of approximately one or several micrometers, or in the range of 500 nm to 10 micrometers (e.g., 1 micrometer to 5 micrometers, 500 nm to 10 micrometers, 1 micrometer to 3 micrometers). Due to the growth pattern, it may not be planar. Therefore, it can be as follows: Figure 16B The diagram illustrates the use of a planarization step to produce a planar layer 1632 with the desired shape as taught herein. Figure 16C In this illustration, the micro-LED structure 1640 is grown on the base region 1632 as taught herein. The LED has a planar active region 1642 extending to the edge of the micro-LED.

[0189] The microLED can have vertical or sloping sidewalls (e.g., corresponding to a semi-polar plane). In some embodiments, the active region extends substantially to the edge of the microLED, but the configuration of the active region varies laterally. The thickness of the active layer can decrease near the edge of the board. The thickness of the active layer at the edge of the board can be less than 90% (e.g., 80% or less, 50% or less) of the same active layer thickness at the center of the board. The composition of the active layer can decrease near the edge of the board. The In composition of the active layer at the edge of the board can be at least 1% (e.g., 2% or more, 5% or more) smaller than the In composition of the same active layer at the center of the board.

[0190] This change can facilitate reduced carrier injection near the edge of the small plate. In some embodiments, an exclusion region exists around the edge of the small plate LED. The area of ​​the exclusion region can be between 5% and 50% of the total area of ​​the active region; it can be at least 5% (e.g., 10% or more, 20% or more, 30% or more) and less than 50% (e.g., 30% or less, 20% or less). Less than 20% (e.g., 10% or less, 5% or less, 1% or less) of the total emitted light may originate from the exclusion region.

[0191] Figures 17A to 17D The diagram illustrates the lateral variation of active region characteristics from the central structure to the edge structure. Figure 17A The diagram illustrates the central and peripheral structures. Figures 17B to 17DThe diagram illustrates how the properties change from the center to the edge as a function of relative lateral distance (0 for the center and 1 for the edge). From the center to the distance (0.8 in this example, but other values ​​are possible, such as approximately 0.7, approximately 0.9), the properties can be substantially constant, and then change from the distance to the edge. The thickness of the active layer 1642 can be reduced by at least 5% (e.g., 10% or more, 20% or more, 30% or more, 40% or more, 50% or more). The In composition of the active layer 1642 can be reduced by at least 1% (e.g., 2% or more, 5% or more, 10% or more). The luminous intensity can be reduced by at least 50% (e.g., 80% or more, 90% or more, 95% or more).

[0192] In addition to thinning the base lateral structure before LED growth, processing steps can be employed to influence the lateral dimensions of the base lateral structure. The lateral dimensions can be reduced, for example, by photolithography and etching, by dry or chemical etching, or by other methods known in the art.

[0193] Different sized plates can be formed on the same substrate. In some embodiments, three sizes exist, corresponding to red / green / blue emission. In some embodiments, different sizes are obtained by varying the size of the mask openings, resulting in plates of different sizes after growth in the base region. In some embodiments, different sizes are obtained by selectively reducing the size of some plates (e.g., by masking some plates and etching others).

[0194] Small plates of base materials with different strain states can be formed on the same substrate. In some embodiments, openings of different sizes are formed in a growth mask before the base material is grown. Smaller openings facilitate a higher degree of relaxation. Larger openings facilitate a lower degree of relaxation.

[0195] As taught herein, altering the lateral dimensions or strain state can facilitate differences in In incorporation during LED growth and may result in the simultaneous growth of LEDs with different emission wavelengths (e.g., red / green / blue), as taught herein. Differences in strain state can lead to different lattice-pulling effects, where more In is incorporated over the base material with lower strain. In some embodiments, the active layer is grown and the In% difference across different plates is at least 5% (e.g., 10% or more, 15% or more). This can facilitate a difference in emission wavelength of at least 50 nm (e.g., 100 nm or greater).

[0196] deal with

[0197] After the base region and LED region are grown, the semiconductor material is processed into an LED device. Various known device architectures can be employed, including lateral, vertical, and flip-chip designs.

[0198] Figures 18A to 18H An example process flow is shown. (A) An NW 1830 is provided grown on a substrate 1810 / buffer layer 1820. The NW 1830 has an n-doped region and a p-doped region (with an active region between the n and p regions). (B) The buffer layer 1820 is etched (e.g., by dry etching) to separate sub-pixels. (C) An n-contact 1840 is formed as an n-doped material (this material may be formed as part of the buffer layer shown or elsewhere: base region, LED region). (D) A planarizer material 1850 is formed to create a planar surface along the top surface of the NW 1830. The planarizer material 1850 may be a dielectric or curing fluid or spin-coated material (e.g., spin-coated glass) deposited by various known techniques (electron beam, CVD, PEVCD, ALD). It may be thinned to expose the p side of the NW. (E) A p-contact 1860 is formed on top of the NW 1830. The n-contact and p-contact may be transparent (e.g., TCO contact) or reflective (e.g., including a metal layer). (F) The p-contact 1860 and planarizer 1850 are removed to open access to the n-contact 1840. The device in (F) can be used as is, making contact with the n-contact 1860 and p-contact 1840. It can be a top or bottom emitting device (depending on whether the substrate and contacts are opaque or transparent). (G) Alternatively, the device is flip-chipped onto a substrate 1880 having metal interconnects 1870 and 1875. The interconnects can have various geometries (here they are shown as surface layers / columns, but they can be vias, interconnects embedded in the substrate (such as redistributed interconnects), and other geometries known in the art). The interconnects 1870 and 1875 can then be connected to electrical drivers to drive various sub-pixels. (H) If desired, the substrate 1810 is removed. This is useful, for example, if the substrate is opaque or if its presence would interfere with the optics of the system. Substrate removal can be achieved through various techniques: wet etching; dry etching; mechanical etching (e.g., grinding, polishing); laser ablation; photochemical, electrochemical, or photoelectrochemical etching; and combinations thereof. This is merely an exemplary process, and variations and substitutions are possible. For example, an n-contact can be formed on top of the sub-pixel after step H, thereby forming a vertical LED geometry; in this case, after the n-contact is formed, a component can be attached to the top of the assembly to provide a current path. Various materials in the assembly can be transparent, including the substrate, substrate, contacts, and the aforementioned components—therefore, light emission can occur from either side of the assembly.

[0199] Figures 19A to 19GAnother example process flow is shown. (A) An NW 1930 is provided grown on substrate layer 1910 / buffer layer 1920. (B) Planarizer material 1940 is formed between NW 1930. (C) p-contacts 1950 are formed over NW 1930. (D) A wafer is flip-chipped onto a substrate 1970 having metal interconnects 1960. (E) Substrate 1910 is removed. (F) Buffer layer 1920 is removed (e.g., by laser lift-off). (G) n-contacts 1980 and pads 1990 are formed on the n-side of NW 1930. This is merely an exemplary process, and variations and substitutions are possible. For example, substrate 1910 may be transparent, and it may be removed in the same step as the buffer layer (e.g., by laser lift-off). n-pads 1990 may be formed to connect n-contacts 1980 to metal traces on the substrate (e.g., by deposition in the direction of n-contacts formed to the sidewalls of the passivated NW).

[0200] Various techniques can be employed to remove the buffer and expose the n-side of the NW, such as: selective chemical etching; grinding and polishing processes; dry etching processes; laser ablation (LLO) processes; mechanical fracture / cutting; ion implantation and fracture / cutting (similar to smart shearing processes); laser ablation or micro-ablation processes (e.g., stealth processes), possibly followed by mechanical fracture.

[0201] In some embodiments, the buffer has a larger bandgap than the NW—for example, the buffer is GaN and the NW has an InGaN region. This facilitates selective LLO using a radiation source (such as a pulsed laser) that is not absorbed by the buffer but is absorbed by the NW. For example, a wavelength of 390 nm is not significantly absorbed by GaN but is significantly absorbed by In0.1GaN. In some embodiments, a specific layer of the NW has a high In composition and is absorptive, while other InGaN layers of the NW are not absorptive. For example, the core region of the NW has In0.1GaN, and the sacrificial layer has In0.2GaN. LLO is performed using a laser that is absorbed by In0.2GaN but not by In0.1GaN. The sacrificial layer can be grown during the growth of the LED region.

[0202] Photochemical etching (or photoelectrochemical etching) can also be used, where a layer with a specific composition that has high absorption for photons and is easily etched is used. Transparency / absorption refers to the wavelength used in the etching step. For example, an embodiment has a transparent substrate, a transparent layer (e.g., GaN), a base InGaN layer with high absorption, and an LED layer. This structure is illuminated through the substrate (which may be polished and / or have an optical finish). The illumination passes through the transparent layer and is absorbed by the base layer, causing the base layer to be etched.

[0203] Wet etching can be used to remove the buffer or substrate (including if the substrate is Si).

[0204] In some embodiments, multiple techniques are used sequentially. For example, an LLO process is used to remove the buffer, thereby exposing a portion of the NW. Then, a material removal step (e.g., mechanical polishing, dry etching, etc.) is used to thin the exposed NW to the desired thickness before contact with the polished NW. The NW can be thinned to obtain a planar surface. The NW can be thinned to reach a doped layer. In some embodiments, a portion of the NW is undoped and a portion is doped; the material removal process is used to remove the undoped material and reach the doped material.

[0205] In some embodiments, the base region may include voids (e.g., the base of the NW may have voids). This weakens the connection between the NW and the underlying layer, and makes the NW prone to breakage near the voids.

[0206] In some embodiments, a surface preparation step is performed on the doped surface of the NW prior to the formation of contacts with the doped surface. This treatment may include cleaning (including by solvents, acids, bases), wet etching, or dry etching. The surface may be n-doped; the treatment may be dry etching containing O or Si with higher doping levels favorable to the surface, resulting in lower contact resistance when contacts with the surface are formed. In some embodiments, the surface-prepared region has a higher doping level than the semiconductor prior to surface preparation. In some embodiments, the surface of the InGaN base region is exposed; the base region has a doping level D after epitaxy (e.g., about 1E16, 5E16, 1E17, 5E17, 1E18, 5E19, 1E19); the surface treatment increases the doping to at least 10 times D. This can still provide good contact resistance, even with moderate doping during growth. Moderate doping may be desirable, for example, to limit strain caused by doping. The base region doping level can be selected to ensure that the NW sub-pixel has a sufficiently low resistivity at the desired current density. In some embodiments, the maximum operating current density is moderate (e.g., less than 50 A.cm). -2 Or 10A.cm -2 Or 1A.cm -2 Or 0.1A.cm -2 Therefore, a moderate level of doping is acceptable.

[0207] other

[0208] Although NW LEDs are discussed in various parts of this disclosure, some of the teachings apply to LEDs that are not characterized by NW. For example, mesa LEDs (also known as small plates, as disclosed herein) can be used instead of NW arrays. Mesa can have small dimensions (e.g., 10 micrometers or less, 5 micrometers or less, 3 micrometers or less) and are subpixels. Mesa can be formed by growing a base region with patterned mesa and regrowth of the LED region. As disclosed herein, strain relaxation can be achieved in small mesa.

[0209] Although InGaN layers are mentioned, it should be understood that other compounds may be suitable (e.g., AlInGaN, AlInN), provided they provide appropriate strain. For example, the base region of an NW could be AlInN with an in-plane lattice constant equal to that of InGaN with the desired content; such a base region reduces lattice mismatch with the InGaN emitting layer, just as the InGaN base region does. This teaching can also be applied to other material systems besides group III nitride systems, including group III-V and II-VI compound semiconductors.

[0210] For example, other crystals (including semiconductors and insulating crystals) with suitable lattice constants can be used as base materials to achieve the reduced active region strain disclosed herein. In some embodiments, the substrate material has crystal symmetry and lattice constants that facilitate InGaN growth and have reduced strain. The symmetry can be hexagonal (including wurtzite symmetry). The lattice constant can promote a mismatch strain less than half that required for pseudomorphic growth on GaN. In some embodiments, an InGaN base layer is grown on the substrate material and an InGaN active region is grown on the InGaN base layer. The InGaN base layer can be substantially relaxed or pseudomorphic with respect to the substrate material. The base layer can have a base layer In composition, and the active region can have an active region In composition, wherein the active region In composition is at least 3% higher than the base layer In composition (e.g., 5% or more, 8% or more, 10% or more, 12% or more, 15% or more, 20% or more, 25% or more, 30% or more).

[0211] The in-plane lattice constant usually refers to the lattice constant perpendicular to the growth direction. For example, in the common case where wurtzite materials are grown along the c-axis (or in a direction close to the c-axis), the in-plane lattice constant refers to the lattice constant perpendicular to the c-axis.

[0212] When elemental compositions are disclosed herein, they should be understood as fractional compositions of the elements in a given group (e.g., column III or column V), as is commonly practiced. For example, In0.2GaN represents In0.2Ga0.8N, where the sum of the number of In and Ga atoms equals the number of N atoms.

[0213] Some embodiments have transverse structures (e.g., countertops or NWs) with cross-sections that are not circular (e.g., squares, rectangles, hexagons, ellipses, etc.). However, such structures can be characterized by typical transverse dimensions: if the cross-section has an area A, then the typical transverse dimension is defined herein as 2*sqrt(A / pi). This definition is consistent with the diameter of a circular cross-section.

[0214] The LED emitters described herein can be used in displays, including microdisplays. Microdisplays typically have multiple pixels, each with red, green, and blue subpixels. The distance between two pixels can be less than 20 μm (e.g., 15 μm, 10 μm, 7 μm, 5 μm, 3 μm). The distance between two subpixels can be less than 10 μm (e.g., 7.5 μm, 5 μm, 3.5 μm, 2.5 μm, 1.5 μm). Microdisplays can be integrated into display systems, such as augmented or virtual reality headsets. The individual subpixels of the display can be electrically operated to emit light and form an image.

[0215] Strain, strain relaxation, and lattice constant can be measured using techniques known in the art. These include X-ray diffraction, X-ray reciprocal space mapping (RSM), grazing incidence X-rays, lateral electron microscopy, Raman spectroscopy, and other techniques known in the art. For example, RSM measurements along appropriate directions (such as the (10-15) direction in group III nitrides) can indicate whether a layer is pseudomorphic, partially or fully relaxed, and can measure the in-plane lattice constant.

[0216] As is known in the art, this measurement also defines the degree of relaxation of the second material grown on the first material. A pseudocrystalline layer is 0% relaxed; a layer with an in-plane lattice constant equal to its bulk equilibrium value is 100% relaxed; a layer grown on the first material with a lattice constant between that of the first material (e.g., GaN) and its equilibrium value is 50% relaxed. In other words, relaxation degree = (a2 - a1) / (a2_relaxed - a1).

[0217] Therefore, embodiments provide InGaN material (e.g., the base layer taught herein) having sufficient In composition (e.g., at least 5%, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more) and sufficient relaxation relative to GaN (e.g., at least 30%, 50% or more, 60% or more, 70% or more, 80% or more). The surface of the InGaN material / base layer can provide this relaxation. An additional layer, such as a light-emitting layer / quantum well, can be grown on top of the relaxed surface. This active layer can have sufficient In composition (e.g., at least 20%, 30% or more, 35% or more, 40% or more, 50% or more, 60% or more) and limited relaxation relative to the InGaN material (e.g., 50% or less, 40% or less, 30% or less, 20% or less, 10% or less). In some embodiments, the device has a buffer layer (e.g., GaN), a base layer grown on the buffer layer, the base layer having an InGaN surface with In > 10% and a relaxation degree of at least 50% (relative to the buffer layer), an LED structure having an active region on the base layer, the active region having an In% > 35% and a relaxation degree of less than 20% (relative to the lattice constant of the first material).

[0218] Several embodiments have been described. Other embodiments are described in the following claims.

Claims

1. A method of forming an LED emitter, the method comprising: Providing a group III nitride layer on a substrate and having a planar top surface; Selectively epitaxially growing a base region including In(x)Ga(1-x)N material on each of a plurality of discrete lateral growth regions on the planar top surface, the base region extending in a direction perpendicular to the planar top surface; Providing a surface of the In(x)Ga(1-x)N material on portions of the base region, the surface of the In(x)Ga(1-x)N material having relaxed strain and having a base lattice constant within 0.1% of the bulk relaxed value; And Epitaxially growing an LED region on the surface, the LED region including a light-emitting layer of In(y1)Ga(1-y1)N material pseudomorphic to the surface of the In(x)Ga(1-x)N material and having an active region lattice constant within 0.1% of the base lattice constant, Where 0.05 < x < 0.15 and y1 > 0.2, and Where the base region and the LED region form a mesa, and a lateral dimension of a surface of each mesa opposite the planar top surface is less than a lateral dimension of the lateral growth region.

2. The method according to claim 1, wherein, The In(x)Ga(1-x)N material relaxes during the growth of the base region.

3. The method according to claim 2, wherein, The relaxation is promoted by lateral expansion of the In(x)Ga(1-x)N material in a direction parallel to the planar top surface.

4. The method according to claim 2, wherein, The relaxation is promoted by forming defects in the base region.

5. The method according to claim 4, wherein, The defects are suppressed during subsequent growth on the base region.

6. The method according to claim 2, wherein, The relaxation is promoted by changing the In composition of the base region along a direction normal to the planar top surface.

7. The method according to claim 1, wherein, Relaxation begins before 1 μm of the base region material is grown.

8. The method according to claim 1, wherein, The epitaxial growth of the LED region drives a reduction in the lateral dimension of the LED region above the lateral growth region.

9. The method according to claim 1, wherein, The mesa includes inclined sidewalls.

10. The method according to claim 9, wherein, The inclined sidewalls correspond to semi-polar facets.

11. The method according to claim 1, further comprising depositing a material on sidewalls of the mesa to passivate the mesa after the epitaxial step.

12. The method according to claim 1, wherein, The total area of the light-emitting region includes a central area corresponding to a central region and a peripheral area corresponding to a peripheral region, where the peripheral area is 10% or more of the total area, and during operation of the LED emitter, 5% or less of the light emitted by the active region originates from the peripheral region.

13. The method according to claim 12, wherein, The active region has an In composition that is at least 1% higher in the central region than in the peripheral region.

14. The method according to claim 1, wherein, The lateral growth region is a first lateral growth region, the LED region is a first LED region, and the base region is a first base region, and the method further comprises: Forming discrete second lateral growth regions on the planar top surface; Epitaxially growing a second base region on the second lateral growth regions; A second LED region comprising an In(y2)Ga(1-y2)N material light-emitting layer is epitaxially grown on the corresponding surface of the second base region; A discrete third lateral growth region is formed on the top surface of the plane; A third base region is epitaxially grown on the third lateral growth region; A third LED region comprising an In(y3)Ga(1-y3)N material light-emitting layer is epitaxially grown on the corresponding surface of the third base region. Wherein, y1>y2>y3, and the first LED region, the second LED region, and the third LED region emit red light, green light, and blue light respectively during operation.

15. The method according to claim 14, wherein, At least one red, green, and blue emitting LED forms a pixel of the display.

16. The method of claim 14, wherein, The corresponding surfaces of the first base region, the second base region, and the third base region have in-plane lattice constants a1, a2, and a3, respectively, where a1>a2>a3.

17. The method according to claim 16, wherein, The first LED region, the second LED region, and the third LED region are grown in the same epitaxial step.

18. The method according to claim 14, wherein, The base region is configured such that during operation of the LED emitter, 10% or less of the blue light emitted by the third LED region is absorbed by the base region.

19. The method according to claim 1, wherein, The relaxation strain is the relaxation mismatch strain, which is less than 50% of the mismatch strain of In(x)Ga(1-x)N grown on GaN pseudomorphs.

20. The method according to claim 1, wherein, The epitaxial growth of the base region and the epitaxial growth of the LED region are performed in separate epitaxial steps, wherein the surface of the In(x)Ga(1-x)N material is a regrowth interface.

21. The method according to claim 1, wherein, The base region includes separate base regions.

22. The method according to claim 1, wherein, The base region includes discrete base regions.

23. A method for forming an LED emitter, the method comprising: A group III nitride layer is provided on a substrate, the group III nitride layer having a planar top surface; Multiple discrete lateral growth regions are provided on the top surface of the plane; A base region comprising In(x)Ga(1-x)N material is selectively epitaxially grown on each discrete lateral growth region, wherein x is sufficient to induce strain relaxation in the base region during the epitaxial growth, resulting in a relaxed surface having a composition of In(y)Ga(1-y)N > 5% and an in-plane lattice constant within 1% of its bulk relaxation value; and An LED structure is selectively epitaxially grown on the relaxation surface, the LED structure having pseudomorphic properties on the relaxation surface and including at least one In(z)Ga(1-z) quantum well with z>30%.

24. The method according to claim 23, wherein, The quantum well has a thickness of 2 nm or greater and emits light with a peak intra-quantum efficiency of at least 20% and an emission wavelength of 620 nm during operation of the LED emitter.

25. The method according to claim 23, wherein, The thickness of the quantum well is greater than the critical relaxation thickness of In(z)Ga(1-z) grown on GaN.

26. The method according to claim 23, wherein, A change of 5% or more in the In% composition of the base region in the growth direction is sufficient to promote strain relaxation.

27. The method according to claim 23, wherein, The lateral growth region has a lateral dimension of 5 μm or less.

28. The method according to claim 23, wherein, Strain relaxation is promoted by lateral expansion of the base region material during growth.

29. The method according to claim 23, wherein, Strain relaxation is promoted by defect formation during growth, the defects being one of the following: screw dislocations, misfit dislocations, and v-pits.

30. A method of forming an LED emitter, the method comprising: Providing a group-III nitride layer on a substrate, the group-III nitride layer having a planar top surface; Growing at least one blue LED structure on the planar top surface; Growing at least one green LED structure on the planar top surface; Providing a plurality of discrete lateral growth regions on the planar top surface; Selectively epitaxially growing a base layer on each lateral growth region, wherein strain relaxes in the base layer and the base layer has a relaxed surface, the relaxed surface having a composition In(y)Ga(1-y)N with y>5% and an in-plane lattice constant within 1% of its bulk relaxed value; and Growing a red LED structure on each relaxed surface.

31. The method according to claim 30, wherein, The blue LED structure and the green LED structure are selectively grown on discrete lateral regions provided on the planar top surface.

32. The method according to claim 30, wherein, The red LED structure is grown after the blue LED structure and the green LED structure.

33. The method according to claim 32, wherein, During the growth of the red LED structure, at least one of the blue LED structure or the green LED structure is covered by a dielectric mask.

34. An LED emitter, comprising: A group-III nitride layer on a substrate, the group-III nitride layer having a planar top surface; A plurality of base regions epitaxially grown on the planar top surface in corresponding discrete lateral growth regions, each base region comprising In(x)Ga(1-x)N material, each base region extending in a direction perpendicular to the planar top surface, the base regions respectively having a surface of the In(x)Ga(1-x)N material, the surface having relaxed strain with respect to the In(x)Ga(1-x)N material of the base region at the planar top surface, the surface of the In(x)Ga(1-x)N material being characterized by a base lattice constant within 0.1% of its bulk relaxed value; and A plurality of LED regions respectively supported by a corresponding one of the base regions, the LED regions respectively comprising a light-emitting layer of In(y1)Ga(1-y1)N material pseudomorphic to the surface of the In(x)Ga(1-x)N material, and being characterized by an active region lattice constant within 0.1% of the base lattice constant, where 0.05<x<0.15 and y1>0.2, and where the base regions and the LED regions form mesa structures, and a lateral dimension of a surface of each mesa structure opposite to the planar top surface is smaller than a lateral dimension of the lateral growth region.

35. The LED emitter according to claim 34, wherein, The In composition of the base region changes by at least 5% along a direction normal to the planar top surface.

36. The LED emitter according to claim 35, wherein, The In composition changes by at least 5% along a direction normal to the planar top surface.

37. The LED emitter according to claim 34, wherein, The mesa structure includes inclined sidewalls.

38. The LED emitter according to claim 37, wherein, The inclined sidewalls correspond to semi-polar facets.

39. The LED emitter according to claim 37, wherein, The base region includes a passivation layer on the inclined sidewall.

40. The LED emitter according to claim 34, wherein, The total area of ​​the light-emitting region of the LED emitter includes a central area corresponding to the central region and a peripheral area corresponding to the peripheral region, wherein the peripheral area is 10% or more of the total area, and during operation of the LED emitter, 5% or less of the light emitted by the active region originates from the peripheral region.

41. The LED emitter according to claim 40, wherein, The active region has an In composition in the central region that is at least 1% higher than that in the peripheral region.

42. The LED emitter according to claim 40, wherein, The active region is thinner in the central region than in the peripheral region.

43. The LED emitter according to claim 34, wherein, The plurality of base regions are first plurality of base regions and the LED region is a first LED region. The LED emitter further includes a second LED region and a third LED region. The second LED region includes a light-emitting layer of In(y2)Ga(1-y2)N material supported by the second plurality of base regions. The third LED region includes a light-emitting layer of In(y3)Ga(1-y3)N material supported by the third plurality of base regions. Wherein, y1>y2>y3, and the first LED region, the second LED region, and the third LED region emit red light, green light, and blue light respectively during operation.

44. The LED emitter according to claim 43, wherein, The corresponding surfaces of the first plurality of base regions, the second plurality of base regions, and the third plurality of base regions have in-plane lattice constants a1, a2, and a3, respectively, where a1>a2>a3.

45. The LED emitter according to claim 34, wherein, The LED emitter has an emission wavelength of 620 nm or greater and an internal quantum efficiency of 20% or greater during operation.

46. ​​The LED emitter according to claim 34, wherein, The base lattice constant is an in-plane lattice constant and is 0.5% or less of its volume equilibrium value.

47. The LED emitter according to claim 34, wherein, The LED region has one of the following geometries: micro-mesa and nanowire.

48. The LED emitter according to claim 34, wherein, The LED area has a lateral dimension of 5 μm or less.

49. The LED emitter according to claim 34, wherein, The LED region has a hexagonal in-plane cross-section.

50. The LED emitter according to claim 34, wherein, The substrate is one of the following: sapphire, silicon, and GaN.

51. The LED emitter according to claim 34, wherein, The substrate has a c-plane orientation.

52. The LED emitter according to claim 34, wherein, The surface is characterized by 1E8 / cm 2 Or even smaller thread dislocation density.

53. The LED emitter according to claim 34, wherein, The group III nitride layer and the base region are n-doped.

54. A display comprising pixels, the pixels comprising the LED emitter of claim 43.

55. An LED emitter, comprising: A group III nitride layer on a substrate, the group III nitride layer having a planar top surface; Multiple discrete lateral growth regions on the top surface of the plane; Multiple base regions are epitaxially grown on the top surface of the plane in the corresponding discrete lateral growth regions, each base region comprising In(x)Ga(1-x)N material, wherein x is sufficient to cause strain relaxation in the base region, resulting in a relaxed surface having a composition of In(y)Ga(1-y)N with y>5% and an in-plane lattice constant within 1% of its bulk relaxation value. as well as The plurality of LED structures on the relaxation surface and the pseudomorphic surface of the relaxation surface each include at least one In(z)Ga(1-z) quantum well with z>30%.

56. The LED emitter according to claim 55, wherein, The quantum well has a thickness of 2 nm or greater and emits light with a peak intra-quantum efficiency of at least 20% and an emission wavelength of 620 nm during operation of the LED emitter.

57. The LED emitter according to claim 55, wherein, The thickness of the quantum well is greater than the critical relaxation thickness of In(z)Ga(1-z) grown on GaN.

58. The LED emitter according to claim 55, wherein, A change of 5% or more in the In% composition of the base region in the growth direction is sufficient to promote the strain relaxation.

59. An LED emitter, comprising: A group III nitride layer on a substrate, the group III nitride layer having a planar top surface; At least one blue LED structure on the top surface of the plane; At least one green LED structure on the top surface of the plane; At least one red LED structure on the top surface of the plane, the red LED structure comprising a base layer epitaxially grown on the top surface of the plane in a corresponding discrete lateral growth region. Wherein, strain relaxes in the base layer and the base layer has a relaxation surface having a composition In(y)Ga(1-y)N with y>5% and an in-plane lattice constant within 1% of its bulk relaxation value.

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