A high-quality LED epitaxial structure and its preparation method

Abstract

The present invention relates to the technical field of light-emitting diodes, and specifically to a high-quality LED epitaxial structure and a preparation method thereof. Through the design of a new nucleation layer, a low-density, high-quality crystal nucleus can be formed, and the density of the grains formed in the subsequent high-pressure roughening layer will be lower, and the size of the grains will be relatively large. The time for subsequent healing between grains will be longer, and the dislocation density at the grain healing boundary will be reduced. In the initial stage of 3D oscillation, the addition of Al can inhibit the growth of GaN on the non-C surface of PSS to a certain extent and improve the lattice quality; in the nucleation layer and roughening layer stages, it tends to a 3D growth mode, reducing the V / III ratio and increasing the pressure, which is conducive to the growth of crystal nuclei and grains, reducing the density of crystal nuclei, and reducing the dislocation density at the interface healing. In the recovery layer growth stage, it tends to a 2D / 3D mixed growth mode, increasing the temperature, increasing the V / III ratio and reducing the pressure are conducive to the healing of the grains, so that the lateral growth rate is greater than the vertical growth rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of light emitting diodes, and in particular relates to a high-quality LED epitaxial structure and a preparation method thereof. Background Art

[0002] Direct growth of GaN on sapphire substrates has long been hampered by limitations such as high dislocation density, high n-type background concentration, and difficulty in achieving p-type doping. Some have proposed and studied the possibility that a low-temperature GaN buffer layer could more effectively improve the quality of GaN epitaxial layers. Although numerous researchers have conducted extensive research on buffer layer growth conditions and significantly improved GaN quality through the use of buffer layer growth processes, the following issues remain:

[0003] 1. The existing buffer layer structure has too high a density of nucleated grains and low grain quality, which results in a high dislocation density at the grain boundaries during healing, leading to low final crystal quality.

[0004] 2. In the early stage of crystal nucleus healing, the growth rate is too fast, which reduces the probability of impurities such as C overflowing due to the decomposition of metal organic matter during the growth process. These impurities will be incorporated into the epitaxial layer and become point defects. At the same time, the threading dislocations in the late stage of healing have no time to heal and continue to grow upward, which eventually leads to the decline of crystal quality.

[0005] With the development of the industry and application needs, higher quality and more efficient epitaxial layer growth is imperative. Summary of the Invention

[0006] In response to the problems in the background technology, the present invention develops a high-quality LED epitaxial structure and a preparation method thereof that further improves the quality of the buffer layer and the nucleation layer.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing a high-quality LED epitaxial structure comprises the following steps:

[0009] S01: Provide a substrate;

[0010] S02: depositing a nucleation layer on the substrate, wherein the nucleation layer structure comprises a low-temperature buffer layer and a high-temperature pause layer;

[0011] The low temperature buffer layer is a non-doped GaN layer with a thickness of 20 Å ~ 25 Å in a single cycle.

[0012] The atmosphere is N2, set at 200~400sccm, and the low temperature is set at 800~850℃;

[0013] The high-temperature pause layer is not an actual growth layer, and the high temperature is set at 880~950℃; the growth atmosphere is N2 and H2, with N2 set at 200~400sccm and H2 set at 200~400sccm;

[0014] The number of high and low temperature cycles is set between 5 and 15 times;

[0015] S03: depositing a roughening layer on the nucleation layer, wherein the roughening layer structure comprises a high-pressure roughening layer and an Al-doped roughening layer;

[0016] The high-pressure roughening layer is not an actual growth layer. The high pressure is set to 300~400torr, and the growth atmosphere is N2, H2, and NH3. N2 is set to 150~300sccm, H2 is set to 100~200sccm, and NH3 is set to 0~20sccm.

[0017] The Al-doped roughening layer is a low-pressure Al-doped GaN layer with a thickness of 300~500nm, an Al content of 5~20slm, a low pressure setting of 150~250torr, and a growth atmosphere of N2, H2, and NH3. The N2 setting is 150~300sccm, the H2 setting is 100~200sccm, and the NH3 setting is 150~300sccm.

[0018] S04: depositing a recovery layer on the roughened layer, with a total thickness of 1500-2100 nm, which is a non-doped GaN layer, in the same growth atmosphere as the Al-doped roughened layer; the recovery layer structure comprises recovery layer 1, recovery layer 2, and recovery layer 3; thickness: recovery layer 2 < recovery layer 1 < recovery layer 3; temperature: recovery layer 1 < recovery layer 2 < recovery layer 3; growth rate: recovery layer 1 < recovery layer 2 < recovery layer 3;

[0019] S05: depositing an unintentionally doped GaN layer on the recovery layer;

[0020] S06: depositing a Si-doped N-GaN layer on the unintentionally doped GaN layer;

[0021] S07: depositing an MQW layer on the N-GaN layer;

[0022] S08: depositing an Al-doped P-GaN EBL layer on the MQW layer;

[0023] S09: depositing a high Mg-doped P-GaN layer on the Al-doped P-GaN EBL layer.

[0024] Furthermore, in step S04, the thickness of the recovery layer 1 is 300-500 nm, the temperature is 1030-1060° C., and the growth rate is 4.5-6 μm / h;

[0025] The thickness of the recovery layer 2 is 100-300 nm, the temperature is 1070-1085°C, and the growth rate is 6-7.5 μm / h;

[0026] The thickness of the recovery layer 3 is 1000-1300 nm, the temperature is 1090-1100° C., and the growth rate is 8-9 μm / h.

[0027] A high-quality LED epitaxial structure comprises, from bottom to top, a substrate, a nucleation layer, a roughening layer, a recovery layer, an unintentionally doped layer, an N-GaN layer, an MQW layer, and a P-GaN layer. The nucleation layer is an alternating cycle layer of a low-temperature buffer layer / a high-temperature pause layer. The roughening layer comprises a high-pressure roughening layer and an Al-doped roughening layer.

[0028] Furthermore, the substrate is a sapphire substrate.

[0029] Furthermore, an Al-doped P-GaN EBL layer is provided between the MQW layer and the P-GaN layer.

[0030] Furthermore, the low-temperature buffer layer is a non-doped GaN layer, and the high-temperature pause layer is a non-actual growth layer.

[0031] Furthermore, the high-pressure roughening layer is a non-actual growth layer, and the Al-doped roughening layer is a low-pressure Al-doped GaN layer.

[0032] Furthermore, the recovery layer is a non-doped GaN layer.

[0033] Furthermore, the recovery layer includes recovery layer 1, recovery layer 2 and recovery layer 3, and the thickness is: recovery layer 2 < recovery layer 1 < recovery layer 3.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The LED epitaxial structure provided by the present invention includes a novel nucleation layer and a novel roughening layer. The design of the novel nucleation layer enables the formation of low-density, high-quality crystal nuclei. The grain density formed in the subsequent high-pressure roughening layer is lower, and the grain size is also larger. The subsequent healing time between grains is prolonged, and the dislocation density at the grain healing boundary is reduced. The incorporation of Al in the initial stage of 3D oscillation can, to a certain extent, inhibit GaN growth on the non-C face of the PSS and improve the lattice quality. In the nucleation layer and roughening layer stages, a 3D growth mode is favored, and lowering the V / III ratio and increasing the pressure are conducive to the growth of crystal nuclei, reducing the density of crystal nuclei, and reducing the dislocation density at the interface healing. In the recovery layer growth stage, a 2D / 3D mixed growth mode is favored. Increasing the temperature, increasing the V / III ratio, and reducing the pressure are conducive to grain healing, making the lateral growth rate greater than the vertical growth rate. The quality of the underlying lattice has been improved, laying a solid foundation for the subsequent growth of the N-type GaN layer. It also expands the growth window of the subsequent V Pits growth layer, thereby increasing the recombination probability of electrons and holes and improving luminous efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is an LED epitaxial structure in the prior art.

[0037] Figure 2 This is the LED epitaxial structure of the present invention.

[0038] Figure 3 This is a comparison chart of the experiment of the present invention. DETAILED DESCRIPTION

[0039] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0040] like Figure 1 As shown, the existing LED epitaxial structure includes, from bottom to top, a substrate, a buffer layer, a GaN layer, an N-GaN layer, an MQW layer, a P-type electron blocking layer, and P-GaN.

[0041] like Figure 2 As shown, the present invention presents a high-quality LED epitaxial structure comprising, from bottom to top, a substrate, a nucleation layer, a roughening layer, a recovery layer, a GaN layer, an N-GaN layer, an MQW layer, a P-type electron blocking layer, and a P-GaN layer. The nucleation layer comprises an alternating cycle of a low-temperature buffer layer and a high-temperature pause layer. The roughening layer comprises a high-voltage roughening layer and an Al-doped roughening layer. The recovery layer comprises recovery layer 1, recovery layer 2, and recovery layer 3, with thicknesses of recovery layer 2 < recovery layer 1 < recovery layer 3.

[0042] A method for preparing a high-quality LED epitaxial structure comprises the following steps:

[0043] S01: Provide a substrate.

[0044] S02: depositing a nucleation layer on the substrate, wherein the nucleation layer structure comprises a low-temperature buffer layer and a high-temperature pause layer;

[0045] The low-temperature buffer layer is an undoped GaN layer, with a single cycle growth thickness of 20-25 Å. The growth atmosphere is N2, set at 200-400 sccm, and the low temperature is set at 800-850°C.

[0046] The high-temperature pause layer is not an actual growth layer, and the high temperature is set at 880~950℃; the growth atmosphere is N2 and H2, N2 is set at 200~400sccm, and H2 is set at 200~400sccm. High-temperature baking allows the nucleation layer to recrystallize; the number of high and low temperature cycles is set at 5~15 times, and repeated crystallization of the buffer layer is achieved through multiple high and low temperature cycle settings.

[0047] S03: depositing a roughening layer on the nucleation layer, wherein the roughening layer structure comprises a high-pressure roughening layer and an Al-doped roughening layer;

[0048] The high-pressure roughening layer is not an actual growth layer. The initial high pressure is set at 300-400 torr. The growth atmosphere is N2, H2, and NH3. The N2 is set at 150-300 sccm, the H2 is set at 100-200 sccm, and the NH3 is set at 0-20 sccm. The high pressure setting can reduce the molecular free path, reduce the density of grain islands in the roughening layer, and increase the size of grain islands. Large and sparse islands can prolong the healing time of the recovery layer film and reduce edge dislocations at the grain boundaries.

[0049] The Al-doped roughening layer is a low-pressure Al-doped GaN layer, the actual growth layer, in the initial stage of recovery layer oscillation. It has a thickness of 300-500nm, an Al content of 5-20 slm, and a low pressure setting of 150-250 Torr. The growth atmosphere is N2, H2, and NH3, with N2 set at 150-300 sccm, H2 at 100-200 sccm, and NH3 at 150-300 sccm. Al doping can somewhat inhibit GaN growth on the non-C-face of the PSS substrate, reducing starting dislocations and improving lattice quality. During the nucleation and roughening layer stages, a 3D growth pattern is favored. Lowering the V / III ratio and increasing the pressure promotes grain growth, reduces nucleus density, and reduces dislocation density at the healing site.

[0050] S04: depositing a recovery layer on the roughened layer: the total thickness is 1500-2100 nm, and the layer is a non-doped GaN layer, and the growth atmosphere is the same as that of the Al-doped roughened layer; the recovery layer structure comprises:

[0051] Recovery layer 1, recovery layer 2, recovery layer 3; thickness: recovery layer 2 < recovery layer 1 < recovery layer 3; temperature: recovery layer 1 < recovery layer 2 < recovery layer 3; growth rate: recovery layer 1 < recovery layer 2 < recovery layer 3;

[0052] Recovery layer 1: thickness 300-500 nm, temperature 1030-1060°C, growth rate 4.5-6 μm / h;

[0053] Recovery layer 2: thickness 100-300 nm, temperature 1070-1085°C, growth rate 6-7.5 μm / h;

[0054] Recovery layer 3: thickness 1000-1300nm, temperature around 1090-1100℃, growth rate 8-9μm / h;

[0055] During the recovery layer growth phase, a mixed 2D / 3D growth mode is preferred. Increasing the temperature, increasing the V / III ratio, and reducing the pressure are beneficial to the healing of the grains, making the lateral growth rate greater than the vertical growth rate.

[0056] S05: depositing an unintentionally doped GaN layer on the recovery layer;

[0057] S06: depositing a Si-doped N-GaN layer on the unintentionally doped GaN layer;

[0058] S07: depositing an MQW layer on the N-GaN layer;

[0059] S08: depositing an Al-doped P-GaN EBL layer on the MQW layer;

[0060] S09: depositing a high Mg-doped P-GaN layer on the Al-doped P-GaN EBL layer.

[0061] like Figure 3 Shown is the use of Figure 1 Structure and Figure 2 Comparison diagram of LED epitaxial structure samples grown on a PSS substrate. It can be seen from the figure that Al doping can inhibit the growth of GaN on the non-C surface of the PSS substrate to a certain extent, reduce the starting dislocation and improve the lattice quality.

[0062] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a high-quality LED epitaxial structure, characterized by: The following steps are involved: S01: Provide a substrate; S02: depositing a nucleation layer on the substrate, wherein the nucleation layer structure comprises a low-temperature buffer layer and a high-temperature pause layer; The low-temperature buffer layer is a non-doped GaN layer, with a single cycle growth thickness of 20Å~25Å, a growth atmosphere of N2, set at 200~400sccm, and a low temperature set at 800~850℃; The high-temperature pause layer is not an actual growth layer. The high temperature is set at 880-950°C. The growth atmosphere is N2 and H2. The N2 is set at 200-400 sccm and the H2 is set at 200-400 sccm. The number of high and low temperature cycles is set at 5-15 times. S03: depositing a roughening layer on the nucleation layer, wherein the roughening layer structure comprises a high-pressure roughening layer and an Al-doped roughening layer; The high-pressure roughening layer is not an actual growth layer, the high pressure is set to 300-400 torr, the growth atmosphere is N2, H2, NH3, N2 is set to 150-300 sccm, H2 is set to 100-200 sccm, and NH3 is set to 0-20 sccm; The Al-doped roughening layer is a low-pressure Al-doped GaN layer with a thickness of 300-500 nm, an Al content of 5-20 slm, a low pressure setting of 150-250 torr, and a growth atmosphere of N2, H2, and NH3, with N2 set at 150-300 sccm, H2 set at 100-200 sccm, and NH3 set at 150-300 sccm; S04: depositing a recovery layer on the roughened layer, with a total thickness of 1500-2100 nm, which is a non-doped GaN layer, in the same growth atmosphere as the Al-doped roughened layer; The recovery layer structure comprises recovery layer 1, recovery layer 2, and recovery layer 3; Thickness: recovery layer 2 < recovery layer 1 < recovery layer 3; Temperature: recovery layer 1 < recovery layer 2 < recovery layer 3; growth rate: recovery layer 1 < recovery layer 2 < recovery layer 3; S05: depositing an unintentionally doped GaN layer on the recovery layer; S06: depositing a Si-doped N-GaN layer on the unintentionally doped GaN layer; S07: depositing an MQW layer on the N-GaN layer; S08: depositing an Al-doped P-GaN EBL layer on the MQW layer; S09: depositing a high Mg-doped P-GaN layer on the Al-doped P_GaN EBL layer.

2. The method for preparing a high-quality LED epitaxial structure according to claim 1, wherein: In step S04, the thickness of the recovery layer 1 is 300~500nm, the temperature is 1030~1060℃, and the growth rate is 4.5~6μm / h; the thickness of the recovery layer 2 is 100~300nm, the temperature is 1070~1085℃, and the growth rate is 6~7.5μm / h; the thickness of the recovery layer 3 is 1000-1300nm, the temperature is 1090~1100℃, and the growth rate is 8~9μm / h.

3. A high-quality LED epitaxial structure prepared by the method for preparing a high-quality LED epitaxial structure according to claim 1 or 2, characterized in that: From bottom to top, it includes a substrate, a nucleation layer, a roughening layer, a recovery layer, an unintentionally doped layer, an N-GaN layer, an MQW layer, and a P-GaN layer. The nucleation layer is an alternating cycle layer of a low-temperature buffer layer / a high-temperature pause layer. The roughening layer includes a high-pressure roughening layer and an Al-doped roughening layer.

4. A high-quality LED epitaxial structure according to claim 3, characterized in that: The substrate is a sapphire substrate.

5. The high-quality LED epitaxial structure according to claim 3, wherein: An Al-doped P-GaN EBL layer is provided between the MQW layer and the P-GaN layer.

6. The high-quality LED epitaxial structure according to claim 3, wherein: The low-temperature buffer layer is a non-doped GaN layer, and the high-temperature pause layer is a non-actual growth layer.

7. The high-quality LED epitaxial structure according to claim 3, wherein: The high-pressure roughening layer is a non-actual growth layer, and the Al-doped roughening layer is a low-pressure Al-doped GaN layer.

8. The high-quality LED epitaxial structure according to claim 3, wherein: The recovery layer is a non-doped GaN layer.

9. The high-quality LED epitaxial structure according to claim 3, wherein: The recovery layer includes recovery layer 1, recovery layer 2 and recovery layer 3, and the thickness is: recovery layer 2 < recovery layer 1 < recovery layer 3.

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