High-luminous-efficiency violet LED epitaxial structure and preparation method thereof

Abstract

This invention relates to the field of LED technology, and particularly to a high-efficiency violet LED epitaxial structure and its growth method. The epitaxial structure, from bottom to top, includes: a patterned AlGaN template substrate and a GaN-based epitaxial layer. The patterned AlGaN template substrate sequentially includes a growth substrate, a buffer layer, an AlGaN layer, and a mask layer, wherein the mask layer is a periodically patterned mask. The GaN-based epitaxial layer sequentially includes: an AlGaN capping layer, an n-type semiconductor layer, a stress relief layer, a multi-quantum-well active region, an electron blocking layer, and a p-type semiconductor layer. The n-type semiconductor includes an Alx3Ga1-x3N layer with an Al composition of 0.01 ≤ x3 ≤ 0.05 and x3 ≥ x2. This invention effectively blocks dislocation propagation and reduces defect density through the synergistic design of the patterned AlGaN template substrate and the laterally epitaxially grown AlGaN capping layer; and achieves progressive stress relief and light absorption suppression through the gradient increase of Al composition in each layer of the all-AlGaN-based structure.

Description

Technical Field

[0001] This invention relates to the field of LED technology, and in particular to a high-efficiency violet LED epitaxial structure and its preparation method. Background Technology

[0002] Ultraviolet (UV) semiconductor light sources are primarily used in biomedicine, anti-counterfeiting, purification (water, air, etc.), computer data storage, and military applications. With advancements in UV technology, new applications are constantly emerging to replace existing technologies and products, leading to applications in general lighting, optical tweezers, plant growth, oil pipeline leak detection, archaeological applications, and authentication. As another major industrial direction for semiconductor lighting, semiconductor UV light sources have attracted widespread attention in the semiconductor optoelectronics industry. The primary challenge facing UV LED technology is its low luminous efficacy; the shorter the wavelength, the lower the luminous efficacy. A 365nm UV LED's output power is only 5%-8% of its input power. How to effectively improve the luminous efficacy of UV LEDs has become a key focus.

[0003] In the prior art, various epitaxial structure improvement schemes have been proposed to improve the luminous efficiency of violet LEDs. For example, Chinese invention patent application CN110970533A discloses a violet epitaxial structure for a flip-chip LED, which uses a patterned sapphire substrate (PSS) with an AlN layer deposited on it, and then sequentially grows a high-temperature AlGaN buffer layer, a superlattice N-type AlGaN layer, an AlInGaN-based multi-quantum well active region, and a P-type layer. This structure reduces light absorption through the all-AlGaN N-type layer and reduces the influence of stress and polarization electric field through the Al composition gradient quantum well / barrier.

[0004] However, this approach still has the following shortcomings: its substrate is still patterned sapphire + AlN, and there is still a lattice mismatch between it and the subsequent AlGaN epitaxial layer, resulting in limited reduction of defect density. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an epitaxial structure for a high-efficiency violet LED that can achieve low stress, high crystal quality, and low light absorption loss, and a method for growing the same.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a high luminous efficiency purple LED epitaxial structure is provided, comprising, from bottom to top: a patterned AlGaN template substrate, and a GaN-based epitaxial layer grown thereon; The patterned AlGaN template substrate sequentially comprises a growth substrate, a buffer layer, an AlGaN layer, and a mask layer; the mask layer is a periodically patterned mask. The GaN-based epitaxial layer comprises, in sequence: an AlGaN capping layer, an n-type semiconductor layer, a stress relief layer, a multi-quantum-well active region, an electron blocking layer, and a p-type semiconductor layer; The AlGaN comprises Alx1Ga1-x1N, where x1 satisfies 0.01≤x1≤0.05, and the AlGaN overlay comprises Alx2Ga1-x2N, where x2 satisfies 0.01≤x2≤0.05 and x2≥x1.

[0007] Another technical solution of the present invention is: providing a method for preparing the above-mentioned high-luminous-efficiency violet LED epitaxial structure, comprising the following steps: (1) A buffer layer and an AlGaN layer are grown sequentially on the growth substrate; (2) A periodic pattern is fabricated on the AlGaN layer and a mask layer is deposited to obtain a patterned AlGaN template substrate; (3) The patterned AlGaN template substrate is placed in the MOCVD reaction chamber, and a group III source and NH3 are introduced under the conditions of temperature 900-1100℃ and pressure 500-1000 mbar to carry out the lateral epitaxial growth of the AlGaN capping layer. (4) An n-type semiconductor layer, a stress relief layer, a multi-quantum well active region, an electron blocking layer and a p-type semiconductor layer are grown sequentially.

[0008] The beneficial effects of this invention are as follows: First, an AlGaN layer is epitaxially obtained on a conventional substrate, and periodic patterns and masks are fabricated within this homogeneous material system. This allows the subsequently grown AlGaN capping layer to preferentially nucleate at the pattern window and be forced to undergo lateral epitaxy.

[0009] During this process, dislocations below the mask region are effectively blocked, while dislocations in the window region bend during lateral growth and cannot extend vertically to the multi-quantum-well active region, thereby reducing the epitaxial defect density by one to two orders of magnitude and significantly improving crystal quality.

[0010] Meanwhile, the AlGaN template and capping layer constitute the bottom structure of the all-AlGaN-based system. Combined with the Al composition gradient design of the n-type layer, stress-relieving layer, quantum barrier layer, and p-type layer, this reduces absorption in the target 370-380nm violet light band and achieves progressive stress release. Specifically, by setting 0.01≤x1≤0.05 and x2≥x1, the bandgap of the capping layer is not lower than that of the template layer. This achieves a smooth transition of the lattice constant, avoiding the formation of new mismatch dislocations due to abrupt composition changes. Furthermore, the moderate increase in Al composition further reduces the absorption coefficient of the capping layer for 370-380nm light, forming a first-level optically transparent window from bottom to top.

[0011] Therefore, this invention achieves synergistic effects in three aspects: defect control, stress management, and light absorption suppression through the homogenization and patterning of the substrate structure, the lateralization of the epitaxial growth mode, and the optimized integration of the overall material system, ultimately realizing a breakthrough improvement in the luminous efficiency of violet LEDs. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the high-efficiency violet LED epitaxial structure of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the patterned AlGaN template substrate for the high-efficiency violet LED epitaxial structure of Embodiment 1 of the present invention. Figure 3 The image shows the EL test results of the epitaxial wafers prepared in Example 1 and Example 2, which are based on traditional violet LED epitaxial structures. 1. Patterned AlGaN template substrate; 11. Growth substrate; 12. Buffer layer; 13. AlGaN layer; 14. Mask layer; 2. AlGaN capping layer; 3. n-type semiconductor layer; 4. Stress relief layer; 5. Multiple quantum well active region; 6. Electron blocking layer; 7. p-type semiconductor layer. Detailed Implementation

[0013] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0014] This invention fundamentally solves the fundamental problems of high dislocation density and defect extension into the active region caused by severe lattice mismatch in heterogeneous substrates in existing technologies (such as the vertical epitaxy based on a patterned sapphire substrate in CN110970533A) through a synergistic structural design of a "patterned AlGaN template substrate" and "selective lateral epitaxial growth of an AlGaN capping layer based on this template." The epitaxial structure of this invention can also effectively reduce the absorption loss of GaN material for violet light in the emission wavelength range of 370-380nm, thereby improving luminous efficiency.

[0015] Please see Figure 1 and Figure 2 The present invention provides a high luminous efficiency purple LED epitaxial structure, comprising, from bottom to top: a patterned AlGaN template substrate 1, and a GaN-based epitaxial layer grown thereon; The patterned AlGaN template substrate 1 sequentially includes a growth substrate 11, a buffer layer 12, an AlGaN layer 13, and a mask layer 14; the mask layer 14 is a periodically patterned mask; it is used to achieve selective lateral epitaxial growth when growing the AlGaN capping layer.

[0016] The GaN-based epitaxial layer comprises, in sequence: an AlGaN capping layer 2, an n-type semiconductor layer 3, a stress relief layer 4, a multi-quantum-well active region 5, an electron blocking layer 6, and a p-type semiconductor layer 7. The AlGaN comprises Alx1Ga1-x1N, where x1 satisfies 0.01≤x1≤0.05, and the AlGaN overlay comprises Alx2Ga1-x2N, where x2 satisfies 0.01≤x2≤0.05 and x2≥x1.

[0017] The beneficial effects of this invention are as follows: First, an AlGaN layer is epitaxially obtained on a conventional substrate. Periodic patterns and masks are then fabricated within this homogeneous material system. This allows the subsequently grown AlGaN capping layer to preferentially nucleate at the patterned windows and undergo forced lateral epitaxy. During this process, dislocations below the mask region are effectively blocked, while dislocations in the window region bend during lateral growth, preventing them from extending vertically to the multi-quantum-well active region. This reduces the epitaxial defect density by one to two orders of magnitude, significantly improving crystal quality. Simultaneously, this AlGaN template and capping layer constitute the bottom structure of an all-AlGaN-based substrate. Combined with the Al composition gradient design of the n-type layer, stress-relieving layer, quantum barrier layer, and p-type layer, this reduces absorption in the target 370-380nm violet light band and achieves progressive stress release. Therefore, the technical solution of the present invention achieves synergistic effects in three aspects: defect control, stress management and light absorption suppression through the homogenization and patterning of the substrate structure, the lateralization of the epitaxial growth mode and the optimization and integration of the overall material system. Ultimately, it achieves a breakthrough improvement in the luminous efficiency of purple LEDs and produces unexpected technical effects.

[0018] The above defines the "composition matching + gradient increase" between the template layer and the capping layer. For example, while the prior art CN110970533A uses a gradient Al composition, it is only implemented in the active region well-barrier layer and does not establish a clear compositional connection between the substrate template and the capping layer. This invention, by setting 0.01≤x1≤0.05 and x2≥x1, ensures that the bandgap of the capping layer is not lower than that of the template layer. This achieves a smooth transition of the lattice constant, avoiding the formation of new mismatched dislocations due to abrupt compositional changes. Furthermore, the moderate increase in Al composition further reduces the absorption coefficient of the capping layer for light in the 370-380nm wavelength range, forming a first-order optically transparent window from bottom to top.

[0019] Furthermore, in the aforementioned high-efficiency violet LED epitaxial structure, the n-type semiconductor layer 3 includes Al x3 Ga 1- x3 The N layer has an Al composition of 0.01 ≤ x3 ≤ 0.05 and x3 ≥ x2.

[0020] As described above, by limiting x3≥x2, it is ensured that dislocations will not generate new stress concentration points due to sudden lattice expansion when crossing heterogeneous interfaces. At the same time, the bandgap of the entire bottom optical path channel is gradually increased, forming a layer-by-layer filtering absorption suppression of the target emission wavelength.

[0021] Furthermore, in the aforementioned high-efficiency violet LED epitaxial structure, the stress relief layer 4 includes Al x4 Ga 1- x4 N, x4 satisfies 0.01≤x4≤0.1, x4≥x3.

[0022] As described above, by limiting x4 to x3, the bandgap of the stress relief layer is not less than that of the n-type layer, thus maintaining the low absorption characteristics of the optical path channel and providing a transition platform with a gradually narrowing lattice constant for the subsequent multi-quantum well active region.

[0023] Furthermore, in the aforementioned high-efficiency violet LED epitaxial structure, the barrier layer of the multi-quantum-well active region 5 includes Al. x5 Ga 1-x5 N, x5 satisfy 0.01≤x5≤0.1.

[0024] As described above, by limiting the barrier material of the active region of the well to AlGaN (instead of quaternary AlInGaN), the growth control difficulty is simplified while ensuring sufficient barrier height, and the low aluminum range of x5≤0.1 is clearly defined to ensure that the barrier layer remains transparent to 370-380nm light waves.

[0025] Furthermore, in the aforementioned high-efficiency violet LED epitaxial structure, the electron blocking layer 6 includes Al x6 Ga 1- x6 N, x6 satisfies 0.01≤x6≤0.2, x6≥x5.

[0026] As described above, by limiting x6 to x5, the potential barrier height of the electron blocking layer is ensured to be at least as high as the quantum barrier, effectively preventing high-energy electrons from escaping from the active region. Simultaneously, setting the upper limit of x6 to 0.2 avoids excessively high Al composition leading to a surge in material defects and difficulties in hole injection. More importantly, this composition constraint results in a complete waveform of Al composition variation throughout the epitaxial structure, "from low to high and then back down"—continuously increasing from the substrate to the electron blocking layer to suppress light absorption and enhance electron confinement, and then moderately decreasing upon entering the p-type layer to improve hole injection.

[0027] Furthermore, in the aforementioned high-efficiency violet LED epitaxial structure, the p-type semiconductor layer 7 includes Al. x7 Ga 1- x7N and x7 satisfy 0.01 ≤ x7 ≤ 0.05 As described above, by limiting x7 to a low aluminum range of 0.01 to 0.05, the lattice continuity with the underlying AlGaN material is maintained, avoiding the generation of reverse dislocations due to abrupt changes in the p-type layer material. On the other hand, the activation energy of the Mg acceptor is significantly reduced, enabling the p-type layer to achieve a high hole concentration under conventional annealing conditions, thereby improving the hole injection efficiency into the active region.

[0028] Furthermore, in the aforementioned high-efficiency violet LED epitaxial structure, the stress relief layer comprises an InGaN / AlGaN superlattice structure with a period of 3. 6.

[0029] As described above, the stress relief layer is defined as an InGaN / AlGaN superlattice with a period number limited to 3-6. This range is the optimal balance point obtained through extensive experimental screening—too low a period number results in insufficient stress relaxation and poor V-pits suppression, while too high a period number introduces too many heterostructures, thus deteriorating crystal quality. A superlattice with 3-6 periods can precisely induce a V-pits array with uniform size and moderate density, providing stress relief points for subsequent quantum well growth while avoiding excessively large pits piercing the active region.

[0030] Furthermore, in the above-mentioned high-efficiency violet LED epitaxial structure, the growth substrate 11 is selected from sapphire, sapphire and SiO2 composite substrate, silicon carbide, silicon, gallium oxide or zinc oxide.

[0031] Furthermore, in the above-mentioned high-efficiency violet LED epitaxial structure, the material of the mask layer 14 is selected from a single-layer film or a stacked film containing at least two of SiOx, TiN, SiNx, SiON or high-melting-point metal films.

[0032] As described above, by limiting the mask material to SiOx, TiN, SiNx, SiON, or high-melting-point metal films, the problems of "nucleation inhibition," "high-temperature stability," and "lifting process compatibility" in selective epitaxy are solved. The above materials have high interface energy, which effectively prevents Ga atoms from nucleating in the mask area; TiN and high-melting-point metal films can withstand high-temperature growth above 1000℃ without decomposition; these materials can all be patterned by wet or dry lift-off methods.

[0033] Another technical solution of the present invention is: providing a method for preparing the above-mentioned high-luminous-efficiency violet LED epitaxial structure, comprising the following steps: (1) A buffer layer and an AlGaN layer are grown sequentially on the growth substrate; (2) A periodic pattern is fabricated on the AlGaN layer and a mask layer is deposited to obtain a patterned AlGaN template substrate; (3) The patterned AlGaN template substrate is placed in the MOCVD reaction chamber, and a group III source and NH3 are introduced under the conditions of temperature 900-1100℃ and pressure 500-1000 mbar to carry out the lateral epitaxial growth of the AlGaN capping layer. (4) An n-type semiconductor layer, a stress relief layer, a multi-quantum well active region, an electron blocking layer and a p-type semiconductor layer are grown sequentially.

[0034] Example 1 Please see Figure 1 and Figure 2 ,like Figure 1 As shown, this embodiment provides a high-efficiency violet LED epitaxial structure, which, from bottom to top, comprises: a patterned AlGaN template substrate 1 and a GaN-based epitaxial layer. The GaN-based epitaxial layer includes: an AlGaN capping layer 2, an n-type semiconductor layer 3, a stress-relieving layer 4, a multi-quantum-well active region 5, an electron-blocking layer 6, and a p-type semiconductor layer 7. The patterned AlGaN template substrate 1 is as follows... Figure 2 As shown, it includes a growth substrate 11, a buffer layer 12, an AlGaN layer 13, and a mask layer 14.

[0035] The method for fabricating the high-efficiency violet LED epitaxial structure includes the following steps: (1) Using magnetron sputtering, the growth substrate 11 (a conventional sapphire PSS substrate or a sapphire + SiO2 composite PSS substrate) is placed into the magnetron sputtering reaction chamber, and an AlN thin film layer with a thickness of 0.01μm-0.2μm is grown on its front side at a temperature of 500-600℃.

[0036] (2) Using metal-organic chemical vapor deposition (MOCVD), the growth substrate 11 coated with AlN layer is placed into the reaction chamber of the metal-organic chemical vapor deposition equipment. The reaction chamber pressure is 100-500 mbar and the temperature is 800-900℃. Hydrogen and ammonia are used as carriers, and a TMGa source of 60-80 sccm is introduced at the same time to grow a buffer layer 12 with a thickness of 0.01-0.02 μm on the substrate.

[0037] (3) Raise the temperature to 900-1200℃, increase the pressure in the reaction chamber to 500-1000mbar, introduce a TMGa source of 300-1000sccm and a TMAl source of 100-1000sccm, and grow an AlGaN layer with a thickness of 2μm-3μm 13, specifically Al x1 Ga 1-x1The N layer has an Al composition of 0.01 ≤ x1 ≤ 0.05.

[0038] (4) Spin-coat the AlGaN layer with negative photoresist at a low speed of 500-700 rpm and a high speed of 3500-4500 rpm; then bake at 100-110℃ for 2-3 min, and then expose the sample with a photolithography machine. After exposure, place the sample into the negative photoresist developer for development. The epitaxial wafer with periodic photoresist pattern was successfully prepared.

[0039] (5) A SiN mask is deposited on the epitaxial wafer using PECVD. A mixed gas of SiH4 and NH3 is introduced into the reaction chamber. The flow rate of NH3 is 100-400 sccm, the flow rate of SiH4 is 20-50 sccm, the chamber pressure is 100-1000 mTorr, the temperature is 250-400℃, the power is 5-150 W, the growth time is 0.5-20 min, and the deposition thickness is 10-300 nm. The material of the mask layer 14 can be silicon oxide (SiO2). x Titanium nitride films (TiN, etc.), silicon nitride films (SiN) x A single layer of either a silicon nitride oxide (SiON) metal film or a laminate containing at least two of these.

[0040] (6) Remove SiN: Immerse the sample in acetone, alcohol and deionized water in sequence until the photoresist and SiN on it are completely removed, and finally obtain a patterned AlGaN template substrate.

[0041] (7) Place the patterned AlGaN template substrate into the MOCVD reaction chamber, raise the temperature to 900-1100℃, raise the reaction chamber pressure to 500-1000mbar, and introduce a TMGa source at 1000-2000sccm and a TMAl source at 100-1000sccm to laterally grow an AlGaN capping layer 2 with a thickness of 1μm-2μm on the patterned AlGaN template substrate. Specifically, Al x2 Ga 1-x2 The N layer has an Al composition of 0.01 ≤ x2 ≤ 0.05 and x2 ≥ x1.

[0042] The specific growth conditions for AlGaN capping layer 2 are as follows: On a patterned AlGaN template substrate, a TMGa source, a TMAl source, and NH3 are introduced. Under set temperature and pressure, an AlGaN layer is first grown on the patterned AlGaN, while SiN growth is suppressed on the mask surface. Once the patterned AlGaN is fully grown, lateral epitaxy is performed at a sufficiently high lateral-to-longitudinal growth rate ratio until the entire epitaxial layer is connected to form a capping layer. The principle is that the difference in bond energy between Si-N and Ga-N bonds results in a much higher viscosity coefficient on GaN than on SiN. On the SiN mask, neither Ga nor N atoms easily form GaN nuclei; they are scattered or re-vaporized, leading to selective lateral growth.

[0043] Since the main defects in GaN materials are line dislocations, and these line dislocations tend to extend upwards, suppressing or reducing their upward extension can lower the defect density of the epitaxial layer. Using lateral epitaxial growth technology, line dislocations in the mask region are truncated and disappear in the lateral growth region. Some line dislocations in the patterned AlGaN bend 90° towards the lateral growth region, preventing them from reaching the multi-quantum-well active region, thus significantly reducing the defect density.

[0044] (8) Maintaining the conditions of the previous step, introduce SiH4 as the doping source to grow an n-type semiconductor layer 3. The doping concentration of Si is 1E+19-2E+19 atom / cm. 3 Specifically, Al x3 Ga 1-x3 The N layer has an Al composition of 0.01 ≤ x3 ≤ 0.05 and x3 ≥ x2.

[0045] (9) Reduce the temperature to 700-800℃, maintain the reaction chamber pressure at 100-500 mbar, and introduce a TMIn source at 1200-1500 sccm and a TEGa source at 25-1000 sccm to periodically grow an InGaN / AlGaN superlattice stress relief layer 4 with a thickness of 0.1 μm-0.2 μm. The number of InGaN / AlGaN cycles is 3-6, specifically Al x4 Ga 1-x4 The N layer has an Al composition of 0.01 ≤ x4 ≤ 0.1 and x4 ≥ x3.

[0046] (10) Reduce the temperature to 700-900℃, the pressure in the reaction chamber to 100-500mbar, and introduce a TMIn source of 1200-1500sccm and a TEGa source of 100-1000sccm to grow a multi-quantum well active region 5 with a thickness of 0.15μm-0.2μm. Specifically, multi-quantum well active region well layer and multi-quantum well active region barrier layer are grown sequentially on the stress relief layer, with the well and barrier alternating for one cycle. The number of cycles of the multi-quantum well active region is 8-14.

[0047] During the growth of the multi-quantum-well active region layer, the reaction chamber temperature was set to 750-800 degrees Celsius. 1200-1500 sccm of TMIn and 100-200 sccm of TEGa were introduced into the reaction chamber. Nitrogen and ammonia were used as carrier gases to grow the multi-quantum-well active region layer. The In doping concentration was 1E+20-2E+20 atom / cm². 3 .

[0048] During barrier layer growth, the reaction chamber temperature is set to 870-900 degrees Celsius, and 300-1000 sccm of TEGa and 100-1000 sccm of TMAl are introduced into the reaction chamber. Using nitrogen and ammonia as carriers, a multi-quantum-well active region barrier layer is grown, with SiH4 as the dopant, and the Si doping concentration is 1E+19-2E+17 atom / cm³. 3 Specifically, Al x5 Ga 1-x5 The N layer has an Al composition of 0.01 ≤ x5 ≤ 0.1.

[0049] (11) In a reaction chamber with a temperature of 700-950℃ and a pressure of 100-500mbar, introduce 55000-65000 sccm of NH3, 25-50 sccm of TMGa source, and 25-50 sccm of TMAL source to grow an AlGaN electron blocking layer 6, specifically Al x6 Ga 1-x6 The N-layer has an Al composition of 0.01≤x6≤0.2, which is higher than the quantum barrier of the multi-quantum-well active region. It can be grown using a multi-segment pulse method with gradually varying Al composition.

[0050] (12) In a reaction chamber with a temperature of 700-950℃ and a pressure of 300-800mbar, introduce 55000-65000sccm of NH3 and 25-50sccm of TMGa source. The Mg source is Cp2Mg, and the Mg doping concentration is 1-5E+20 atom / cm. 3 7. Grow a p-type semiconductor layer. Specifically, Al x7 Ga 1-x7 The N layer has an Al composition of 0.01 ≤ x7 ≤ 0.05.

[0051] After epitaxy is completed, chip fabrication is performed on the epitaxial wafer.

[0052] Example 2 Please see Figure 1 and Figure 2 ,like Figure 1 As shown, this embodiment provides a high-efficiency violet LED epitaxial structure, which, from bottom to top, comprises: a patterned AlGaN template substrate 1 and a GaN-based epitaxial layer. The GaN-based epitaxial layer includes: an AlGaN capping layer 2, an n-type semiconductor layer 3, a stress-relieving layer 4, a multi-quantum-well active region 5, an electron-blocking layer 6, and a p-type semiconductor layer 7. The patterned AlGaN template substrate 1 is as follows... Figure 2 As shown, it includes a growth substrate 11, a buffer layer 12, an AlGaN layer 13, and a mask layer 14.

[0053] The method for fabricating the high-efficiency violet LED epitaxial structure includes the following steps: (1) Using magnetron sputtering, a conventional sapphire PSS substrate is placed into a magnetron sputtering reaction chamber, and an AlN thin film with a thickness of 0.01 μm is grown on its front side at a temperature of 550 °C.

[0054] (2) Using metal-organic chemical vapor deposition (MOCVD), the substrate 1-1 coated with AlN layer was placed into the reaction chamber of the metal-organic chemical vapor deposition equipment. The reaction chamber pressure was 133 mbar and the temperature was 880℃. Hydrogen and ammonia were used as carriers, and an 80 sccm TMGa source was introduced at the same time to grow a buffer layer with a thickness of 0.02 μm on the substrate.

[0055] (3) Raise the temperature to 1050℃, increase the pressure in the reaction chamber to 665mbar, and introduce a 400sccm TMGa source and a 100sccm TMAl source to grow an AlGaN layer with a thickness of 2.5μm. Specifically, Al x1 Ga 1-x1 The N layer has an Al composition x1 = 0.01.

[0056] (4) Spin-coat the AlGaN layer with negative photoresist at a low speed of 600 rpm and a high speed of 4000 rpm; then bake at 110°C for 2 min, and then expose the sample with a photolithography machine. After exposure, the sample is placed in the negative photoresist developer for development, and an epitaxial wafer with periodic photoresist pattern is successfully prepared.

[0057] (5) A SiN mask is deposited on an epitaxial wafer using PECVD. A mixture of SiH4 and NH3 gas is introduced into the reaction chamber. The flow rate of NH3 is 400 sccm, the flow rate of SiH4 gas is 50 sccm, the chamber pressure is 200 mTorr, the temperature is 300℃, the power is 60 W, the growth time is 10 min, and the deposition thickness is 50 nm. The mask layer material can be silicon oxide (SiO2). x A single layer of any one of titanium nitride (TiN, etc.), silicon nitride (SiNx), silicon oxide nitride (SiON) metal films, or a laminated film containing at least two of these.

[0058] (6) Remove SiN: Immerse the sample in acetone, alcohol and deionized water in sequence until the photoresist and SiN on it are completely removed, and finally obtain a patterned AlGaN template substrate.

[0059] (7) The patterned AlGaN template substrate is placed into the MOCVD reaction chamber, the temperature is raised to 1120℃, the reaction chamber pressure is raised to 650mbar, and a 1200sccm TMGa source and a 200sccm TMAl source are introduced to laterally grow an AlGaN capping layer 2 with a thickness of 1.5μm on the patterned AlGaN template substrate. Specifically, Al x2 Ga 1-x2 The N layer has an Al composition of x2 = 0.02.

[0060] (8) Maintaining the above conditions, introduce SiH4 as the doping source to grow an n-type semiconductor layer. The doping concentration of Si is 1E+19-2E+19 atom / cm. 3 Specifically, Al x3 Ga 1-x3 The N layer has an Al composition of x3 = 0.03.

[0061] (9) The temperature was lowered to 800℃, the pressure in the reaction chamber was 250mbar, and a 1000sccm TMIn source and an 800sccm TEGa source were introduced to periodically grow an InGaN / AlGaN superlattice stress-relieving layer 4 with a thickness of 0.2μm. The number of InGaN / AlGaN periods was 4, specifically Al x4 Ga 1-x4 The N layer has an Al composition of x4 = 0.05.

[0062] (10) Reduce the temperature to 700-900℃, the pressure in the reaction chamber to 100-500mbar, and introduce a TMIn source of 1200-1500sccm and a TEGa source of 100-1000sccm to grow a multi-quantum well active region with a thickness of 0.15μm. Specifically, multi-quantum well active region well layer and multi-quantum well active region barrier layer are grown sequentially on the stress relief layer. The well and barrier alternate for one cycle, and the number of cycles of the multi-quantum well active region is 11.

[0063] When growing the multi-quantum well active region layer, the reaction chamber temperature is set to 780 degrees, and 1500 sccm of TMIn and 200 sccm of TEGa are introduced into the reaction chamber. Nitrogen and ammonia are used as carriers to grow the multi-quantum well active region layer, specifically an ln0.05Ga0.95N layer.

[0064] During barrier layer growth, the reaction chamber temperature was set to 890 degrees Celsius, and 1000 sccm of TEGa and 400 sccm of TMAl were introduced into the reaction chamber. Using nitrogen and ammonia as carriers, a multi-quantum-well active region barrier layer was grown, with SiH4 as the dopant, and the Si doping concentration was 1E+19-2E+17 atom / cm³. Specifically, Al... x5 Ga 1-x5 The N layer has an Al composition of x5 = 0.22.

[0065] (11) In a reaction chamber with a temperature of 900℃ and a pressure of 133mbar, 55000sccm of NH3, 50sccm of TMGa source, and 50sccm of TMAL source are introduced to grow an AlGaN electron blocking layer, specifically Al x6 Ga 1-x6 The N-layer has an Al composition of x6=0.25, which is higher than the quantum barrier of the multi-quantum-well active region. It can be grown using a multi-segment pulse method with gradually varying Al composition.

[0066] (12) In a reaction chamber with a temperature of 950℃ and a pressure of 650mbar, NH3 at 65000sccm and a TMGa source at 50sccm are introduced. The Mg source is Cp2Mg, and the Mg doping concentration is 1-5E+20 atom / cm. 3 A p-type semiconductor layer 6 is grown. Specifically, it is Al. x7 Ga 1-x7 The N layer has an Al composition of x7 = 0.05.

[0067] After epitaxy is completed, chip fabrication is performed on the epitaxial wafer.

[0068] Comparative Example 1 This comparative example uses a traditional violet LED epitaxial structure. The difference from Example 2 is that an AlGaN capping layer is grown directly after the buffer is grown. The other steps are the same as in Example 2.

[0069] By performing EL / XRD tests on the epitaxial wafers prepared in Example 2 and Comparative Example 1 of the traditional purple LED epitaxial structure, as shown in Table 1, it can be seen that the epitaxial wafer prepared by the method in Example 2 has a smaller half-width and higher luminous efficiency, and the half-width of the XRD 002 / 102 plane is smaller, indicating that the preparation method in Example 2 can significantly improve the quality of the active region and increase the luminous efficiency of the epitaxial wafer.

[0070] Table 1

[0071] In summary, this invention, by designing a patterned AlGaN template substrate and an AlGaN capping layer laterally grown thereon, can release stress caused by lattice mismatch and differences in thermal expansion coefficients, improve the crystal quality of the active region epitaxial layer, and increase luminous efficiency. The design of the stress-relieving layer can effectively reduce the size of V-pits introduced during InGaN layer growth, promote the uniform distribution of V-pits, improve the crystal quality of the active region epitaxial layer, and further enhance the luminous efficiency of the LED chip.

[0072] This invention fundamentally solves the technical problem of high dislocation density and defect extension to the active region caused by lattice mismatch in existing heteroepitaxial growth of purple LEDs by using a synergistic design of a patterned AlGaN template substrate and a laterally epitaxially grown AlGaN capping layer.

[0073] This invention creates a periodic patterned mask within the AlGaN homogeneous material system, which forces the subsequent AlGaN capping layer to selectively epitaxially grow laterally. Dislocations below the mask region are effectively blocked, and dislocations in the window region bend 90° during lateral growth and cannot extend vertically, thereby reducing the dislocation density by one to two orders of magnitude and achieving a breakthrough improvement in crystal quality. Based on this, the present invention systematically constructs a full AlGaN-based epitaxial architecture from AlGaN template layer, capping layer, n-type layer, stress relief layer, quantum barrier layer, electron blocking layer to p-type layer. Through the seven-layer composition gradient increasing constraint (x2≥x1, x3≥x2, x4≥x3, x6≥x5) and the low Al composition fallback design of the p-type layer, the bandgap width is gradually increased from bottom to top and the lattice constant is smoothly transitioned. This not only significantly reduces the absorption loss of GaN material in the 370-380nm target emission band, but also avoids the formation of new mismatch dislocations induced by compositional abrupt changes. Meanwhile, a "rigid-flexible" bilayer stress-relieving structure is formed by AlGaN continuous layers and InGaN / AlGaN superlattices (3-6 periods). The former is responsible for macroscopic lattice adaptation, while the latter achieves microscopic strain relaxation by precisely controlling the size and distribution of V-pits, which significantly improves the interface quality of multiple quantum wells and the carrier radiative recombination efficiency. Ultimately, this invention achieves a complete technological closed loop across four dimensions—defect control, light absorption suppression, stress management, and bandgap engineering—through the organic integration and synergistic effect of four major technical means: substrate homogeneous patterning, epitaxial lateralization, compositional gradient, and stress-relieving multilayering. This results in a significant improvement in the external quantum efficiency of violet LEDs compared to existing mainstream technologies, a two-order-of-magnitude reduction in dislocation density, a narrower half-width, and higher luminous efficacy. It realizes a breakthrough in luminous efficiency that has long been desired but unattainable in the field.

[0074] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A high-luminous-efficiency violet LED epitaxial structure, characterized in that, From bottom to top, this includes: Patterned AlGaN template substrate, and GaN-based epitaxial layer grown on it; The patterned AlGaN template substrate sequentially comprises a growth substrate, a buffer layer, an AlGaN layer, and a mask layer; The mask layer is a periodic patterned mask; The GaN-based epitaxial layer comprises, in sequence: an AlGaN capping layer, an n-type semiconductor layer, a stress relief layer, a multi-quantum-well active region, an electron blocking layer, and a p-type semiconductor layer; The AlGaN includes Al x1 Ga 1-x1 N, x1 satisfy 0.01≤x1≤0.05, and the AlGaN cover includes Al x2 Ga 1-x2 N, x2 satisfies 0.01≤x2≤0.05 and x2≥x1.

2. The high-efficiency violet LED epitaxial structure according to claim 1, characterized in that, The n-type semiconductor includes Al x3 Ga 1-x3 The N layer has an Al composition of 0.01 ≤ x3 ≤ 0.05 and x3 ≥ x2.

3. The high-efficiency violet LED epitaxial structure according to claim 2, characterized in that, The stress relief includes Al x4 Ga 1-x4 N, x4 satisfies 0.01≤x4≤0.1, x4≥x3.

4. The high-efficiency violet LED epitaxial structure according to claim 3, characterized in that, The barrier of the multi-quantum-well active region includes Al. x5 Ga 1-x5 N, x5 satisfy 0.01≤x5≤0.

1.

5. The high-efficiency violet LED epitaxial structure according to claim 4, characterized in that, The electron barrier includes Al x6 Ga 1-x6 N, x6 satisfies 0.01≤x6≤0.2, x6≥x5.

6. The high-efficiency violet LED epitaxial structure according to claim 5, characterized in that, The p-type semiconductor includes Al. x7 Ga 1-x7 N, x7 satisfy 0.01≤x7≤0.

05.

7. The high-efficiency violet LED epitaxial structure according to claim 1, characterized in that, The stress relief includes an InGaN / AlGaN superlattice structure with a period number of 3.

6.

8. The high-efficiency violet LED epitaxial structure according to claim 1, characterized in that, The material of the mask layer is selected from a single-layer film or a laminated film containing at least two of SiOx, TiN, SiNx, SiON or high-melting-point metal films.

9. A method as claimed in claim 1 The method for preparing the high-luminous-efficiency violet LED epitaxial structure according to any one of the claims is characterized in that, Includes the following steps: (1) A buffer layer and an AlGaN layer are grown sequentially on the growth substrate; (2) A periodic pattern is fabricated on the AlGaN layer and a mask layer is deposited to obtain a patterned AlGaN template substrate; (3) The patterned AlGaN template substrate is placed in the MOCVD reaction chamber and heated to 900°C. 1100℃, 500℃ Lateral epitaxial growth of the AlGaN capping layer was carried out under conditions of 1000 mbar by introducing a group III source and NH3. (4) An n-type semiconductor layer, a stress relief layer, a multi-quantum well active region, an electron blocking layer and a p-type semiconductor layer are grown sequentially.

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