Epitaxial structure of gallium nitride-based LED and preparation method thereof
By introducing a morphological adjustment layer and a layered inclined structure into the gallium nitride-based LED epitaxial structure, the problem of difficulty in controlling dislocation distribution is solved, and the recombination efficiency and reliability of the device are improved.
Patent Information
- Application Number
- CN202510610818.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-13
- Publication Date
- 2025-07-04
AI Technical Summary
The existing gallium nitride-based LED epitaxial growth technology is difficult to effectively control the dislocation distribution, resulting in deterioration of device performance and reduced reliability, and may even cause device failure.
By introducing a morphological adjustment layer, a nuclear unit and a layered inclined structure are designed to concentrate the dislocations in local areas, forming current diffusion channels and stress dispersion channels, slowing down the stress distribution of the epitaxial structure film, and forming leakage channels in the N-type layer to improve carrier recombination efficiency.
The controllable distribution of dislocations is achieved, the stress distribution of epitaxial structure films is slowed down, the recombination efficiency and reliability of the device are improved, and the failure of the device is avoided.
Smart Images
Figure CN120264959A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of LED epitaxial technology, and particularly relates to an epitaxial structure of a gallium nitride-based LED and a preparation method thereof. Background Art
[0002] At present, the mainstream gallium nitride (GaN) LED epitaxial growth technologies are all dedicated to reducing the surface roughness and decreasing the dislocation density. This is because high surface roughness and large dislocation density will cause serious interface effects. Moreover, as the dislocation content increases, not only will leakage current channels be formed, resulting in the deterioration of device performance and the reduction of reliability, but it may even cause device failure.
[0003] On different crystal planes, the growth rate of GaN is different. On the inclined non-polar a-plane and m-plane, the growth rate of GaN exceeds that of the vertical polar c-plane. Since the deposition rate on the inclined plane is faster, some interfaces will protrude, resulting in an increase in roughness. Moreover, in the structure formed by rapid growth, there are a large number of dislocations concentrated, and these dislocations are extremely easy to gather together to form leakage current channels.
[0004] Currently, the mainstream design concept focuses on improving the double crystal quality, and the main approach is to eliminate various defects as much as possible. If a high dislocation density is widely distributed throughout the thin film, the overall crystal quality will be significantly reduced. Carriers are easily trapped by dislocation traps in a large number of dislocation defects, thereby increasing the non-radiative recombination ratio. However, in fact, reducing the overall dislocation density faces great challenges. Due to the complexity in the growth process of GaN materials, such as problems like atomic diffusion and lattice matching, it is almost impossible to avoid the generation of dislocations. The mainstream design concept only focuses on reducing the overall dislocation density, but fails to effectively control the distribution pattern of these unavoidable dislocations. Summary of the Invention
[0005] Based on this, the purpose of the present invention is to provide an epitaxial structure of a gallium nitride-based LED and a preparation method thereof, which can effectively regulate the dislocation distribution without reducing the dislocation density, thereby improving the device performance.
[0006] In the first aspect, the present invention provides an epitaxial structure of a gallium nitride-based LED, including a substrate, and further including a buffer layer, a morphology adjustment layer, an N-type layer, a multi-quantum well layer, and a P-type layer sequentially disposed on the substrate; The side of the morphology adjustment layer close to the substrate includes a plurality of nucleation units, and the surfaces of the nucleation units on the side away from the substrate are separated from each other; the side of the morphology adjustment layer away from the substrate further includes a layered inclined structure, and dislocations merge with the growth of the nucleation units and are incorporated into the N-type layer along the inclined direction of the layered inclined structure; The dislocations in the N-type layer are concentrated in the area above the layered inclined structure to form a current diffusion channel and a stress dispersion channel.
[0007] The basic concept of the present invention is to regulate the lateral distribution of dislocations, concentrating the dislocations in local regions of the epitaxial structure to replace the random dispersion of dislocations throughout the entire epitaxial structure. The technical solution adopted by the present invention is to introduce a morphology adjustment layer and perform special design on the structure of the morphology adjustment layer, including the design of a nucleation structure and a layered inclined structure, so that dislocations are locally concentrated in the layered inclined structure, thereby realizing the concentrated distribution of dislocations in the N-type layer, forming a current diffusion channel and a stress dispersion channel in the N-type layer, slowing down the stress distribution of the entire epitaxial structure thin film, and at the same time, the formed leakage channel enables carriers to more easily enter the active region of the multi-quantum well layer for recombination, slowing down the quantum Stark effect, improving the efficiency of carriers entering the active region of the multi-quantum well layer through dislocations, and further improving the recombination efficiency of the device.
[0008] Optionally, the morphology of the nucleation unit is island-shaped or corrugated, and the vertical height of the nucleation unit is 1 nm - 50 nm.
[0009] Optionally, the material of the morphology adjustment layer is one of GaN, InGaN, and AlGaN, and the thickness of the morphology adjustment layer is 20 nm - 800 nm.
[0010] Preferably, the material of the morphology adjustment layer is GaN, and the thickness of the morphology adjustment layer is 100 nm - 500 nm.
[0011] Optionally, the material of the N-type layer is one of GaN, InGaN, and AlGaN, the characteristic thickness of the N-type layer is 500 nm - 5000 nm; the total dislocation density in the N-type layer is 1.0E9 cm -2 -3.0E9 cm -2 , and the surface of the N-type layer on the side far from the substrate is flat.
[0012] Optionally, the distribution density of the layered inclined structure in the morphology adjustment layer is 1.0E5 cm -2 -1.0E7 cm -2 , and 200 - 1000 dislocations are concentratedly distributed in each layered inclined structure; the inclination direction of the layered inclined structure forms an angle of 0.1° - 15° with the horizontal plane Optionally, the substrate material is one of silicon, sapphire, silicon carbide, and gallium oxide, and the substrate crystal plane has a crystal orientation deviation angle of 0.4° - 6°; the material of the buffer layer is Al x Ga 1-x N (0 ≤ x ≤ 1) monolayer or multilayer, and the characteristic thickness of the buffer layer is 50 nm - 500 nm.
[0013] Optionally, the multi-quantum well layer is GaN, In x Ga 1-x N (0 < x < 1), Al y Ga1-y A superlattice structure composed of two materials in N(0 < y < 1); the P-type layer is made of Al x Ga 1-x A composite layer of one or more materials in N(0 ≤ x ≤ 1).
[0014] Second, the present invention also provides a method for preparing the epitaxial structure of the above-mentioned gallium nitride-based LED, including the following steps: Provide a substrate, and the crystal plane of the substrate has a crystal orientation deviation angle of 0.4° - 6°; Grow a buffer layer with a thickness of 50 nm - 500 nm on the substrate; Grow a morphology adjustment layer with a thickness of 20 nm - 800 nm on the buffer layer: grow nucleation units under the condition of 900°C - 1200°C; after the growth of the nucleation units is completed, adjust the molar ratio of group V / III gases and the gas volume ratio of hydrogen to ammonia under the condition of 800°C - 1180°C to continue growing the morphology adjustment layer to make the nucleation units grow together, realizing the growth of a layered inclined structure, and the dislocations are combined with the growth of the nucleation units and are fused along the inclined direction of the layered inclined structure; Grow an N-type layer on the morphology adjustment layer, and the growth temperature of the N-type layer is 1000°C - 1200°C; the initial growth direction and growth morphology of the N-type layer are consistent with the layered inclined structure in the morphology adjustment layer, and the dislocations in the morphology adjustment layer are fused and enter the N-type layer to form a current diffusion channel and a stress dispersion channel in the N-type layer; the N-type layer gradually becomes flat after changing the gas volume ratio of hydrogen to ammonia in the later stage of growth; Grow a multi-quantum well layer on the N-type layer, and the growth temperature of the multi-quantum well layer is 600°C - 950°C; Grow a P-type layer on the multi-quantum well layer, and the growth temperature of the P-type layer is 800°C - 1090°C.
[0015] Optionally, the molar ratio of group V / III during the growth of the nucleation units is 40000:1 - 5000:1, and the gas volume ratio of hydrogen to ammonia is 0.01:1 - 1:1; the molar ratio of group V / III gases during the growth and combination of the nucleation units is 5000:1 - 500:1, and the gas volume ratio of hydrogen to ammonia is 1:1 - 1:10; the molar ratio of group V / III gases during the initial growth of the N-type layer is 20000:1 - 500:1, and the gas volume ratio of hydrogen to ammonia is 1:1 - 1:10, and the molar ratio of group V / III gases in the later stage of the growth of the N-type layer is 20000:1 - 500:1, and the gas volume ratio of hydrogen to ammonia is 1:1 - 1:5.
[0016] The beneficial effects of the present invention are: This special structure is achieved by introducing a morphology regulation layer with a special structure and selecting an appropriate growth mode, realizing a controllable dislocation distribution, localizing dislocations, slowing down the stress distribution of the entire epitaxial structure thin film, and at the same time, the concentrated dislocations form a leakage channel, making it easier for carriers to enter the active region of the multi-quantum well layer for recombination, thereby improving the recombination efficiency of the device. Brief Description of the Drawings
[0017] Figure 1 . Schematic diagram of the deviation of the substrate angle in the present invention.
[0018] Figure 2 . Schematic diagram of the gallium nitride-based LED epitaxial structure in Embodiment 1 of the present invention.
[0019] Figure 3 . Schematic diagram of the gallium nitride-based LED epitaxial structure in Comparative Example 1 of the present invention.
[0020] Figure 4 . Atomic force microscope photograph of the layered inclined structure in Embodiment 1 of the present invention.
[0021] Figure 5 . Raman spectrum stress distribution diagram of the epitaxial structure in Embodiment 1 of the present invention.
[0022] Figure 6 . Simulated current distribution diagram of the epitaxial structure in Embodiment 1 of the present invention.
[0023] Figure 7 . Simulated current distribution diagram of the epitaxial structure in Comparative Example 1 of the present invention.
[0024] Figure 8 . Schematic diagram of the gallium nitride-based LED epitaxial structure in Embodiment 2 of the present invention.
[0025] Figure 9 . Schematic diagram of the gallium nitride-based LED epitaxial structure in Embodiment 3 of the present invention. Detailed Description of the Embodiments
[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
[0027] The terms used in the embodiments of this application are only for explaining the specific embodiments of this application, and are not intended to limit this application.
[0028] Before describing the embodiments of this application, the related technologies and their technical problems will be described first.
[0029] The gallium nitride-based material system is an important type of compound semiconductor material, mainly including materials such as gallium nitride (GaN), aluminum nitride (AlN), indium gallium nitride (InGaN), aluminum gallium nitride (AlGaN), and indium aluminum gallium nitride (InAlGaN). The quantum Stark effect refers to the phenomenon that the polarization electric field in the active region of the quantum well causes the spatial separation of carriers, resulting in a decrease in the wave function overlap rate and a decrease in the recombination efficiency. In the gallium nitride-based system, due to the composition of group III-V compounds, which are polar materials, the charge transfer between atoms causes the non-coincidence of the positive and negative charge centers, generating a spontaneous polarization effect. In addition, there is a piezoelectric polarization effect, which is caused by the lattice matching of different heterostructure materials. Among them, the spontaneous polarization is caused by polarity, and the piezoelectric polarization depends on whether the stress on the material is tensile stress or compressive stress. The substrate surface and the substrate crystal plane are two different concepts, and their relationship is shown in Figure 1. In the figure, the substrate surface is marked as 101, and the substrate crystal plane is marked as 102. It should be clear that the substrate mentioned in the present invention specifically refers to the substrate crystal plane marked as 102 in the figure.
[0030] The basic concept of the present invention is to regulate the lateral distribution of dislocations, concentrating the dislocations in a local area of the epitaxial structure to replace the random dispersion of dislocations throughout the epitaxial structure.
[0031] Based on this, in the first aspect, the embodiments of the present application provide an epitaxial structure of a gallium nitride-based LED, as Figure 2 shown, including a substrate 102, and further including a buffer layer 103, a morphology adjustment layer 104, an N-type layer 105, a multi-quantum well layer 106, and a P-type layer 107 sequentially disposed on the substrate 102; The side of the morphology adjustment layer 104 close to the substrate includes a plurality of nucleation units 1041, and the surfaces of the nucleation units 1041 on the side away from the substrate 102 are separated from each other; the side of the morphology adjustment layer 104 away from the substrate 102 further includes a layered inclined structure 1042, and the dislocations 100 merge along with the growth of the nucleation units 1041 and enter the N-type layer 105 along the inclined direction of the layered inclined structure 1042; The dislocations 100 in the N-type layer 105 are concentratedly distributed in the area above the layered inclined structure 1042 to form a current diffusion channel and a stress dispersion channel.
[0032] In the embodiments of the present application, by introducing a morphology adjustment layer and specially designing the structure of the morphology adjustment layer, including the design of a nucleation structure and a layered inclined structure, dislocations are locally concentrated in the layered inclined structure, thereby realizing the concentrated distribution of dislocations in the N-type layer. As a result, current diffusion channels and stress dispersion channels are formed in the N-type layer, slowing down the stress distribution of the entire epitaxial structure thin film. At the same time, the formed leakage channels enable carriers to more easily enter the active region of the multi-quantum well layer for recombination, slowing down the quantum Stark effect, improving the efficiency of carriers entering the active region of the multi-quantum well layer through dislocations, and thus enhancing the recombination efficiency of the device.
[0033] In a possible implementation manner, the morphology of the nucleation unit 1041 is island-shaped or corrugated, and the vertical height of the nucleation unit 1041 is 1 nm - 50 nm, for example, 1 nm, 2 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, but not limited thereto. The island-shaped or corrugated nucleation morphology is beneficial to the formation of its growth direction. An overly thin nucleation unit may lead to discontinuous coverage and form holes; an overly thick one will cause excessive stress accumulation.
[0034] In a possible implementation manner, the material of the morphology adjustment layer 104 is one of GaN, InGaN, and AlGaN, and the thickness of the morphology adjustment layer 104 is 20 nm - 800 nm, for example, 20 nm, 30 nm, 100 nm, 200 nm, 300 nm, 500 nm, 800 nm, but not limited thereto. The morphology adjustment layer realizes the transformation of morphology in this process. If it is too thin, the merging transformation cannot be achieved; if it is too thick, the original angular characteristics will be lost.
[0035] In a possible implementation manner, the material of the morphology adjustment layer 104 is GaN, and the thickness of the morphology adjustment layer 104 is 100 nm - 500 nm, for example, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, but not limited thereto. The morphology adjustment layer is preferably gallium nitride. The N-type layer usually needs to have a high carrier concentration and good conductivity. GaN itself, as an N-type material, is more likely to obtain a high electron concentration through doping (such as Si doping).
[0036] In a possible implementation manner, the material of the N-type layer 105 is one of GaN, InGaN, and AlGaN, and the characteristic thickness of the N-type layer 105 is 500 nm - 5000 nm, for example, 500 nm, 1000 nm, 2000 nm, 3000 nm, 5000 nm, but not limited thereto; the total dislocation density in the N-type layer 105 is 1.0E9 cm -2 -3.0E9 cm -2, the surface of the N-type layer 105 on the side away from the substrate 102 is flat. If the N-type layer is too thick, the accumulated stress is too large, and the dislocations will further grow out of control, resulting in through-cracks. If the N-type layer is too thin, its surface is uneven.
[0037] In a possible implementation, the distribution density of the layered inclined structure 1042 in the morphology adjustment layer 104 is 1.0E5 cm -2 -1.0E7 cm -2 , and 200 - 1000 dislocations 100 are concentratedly distributed in each layered inclined structure 1042; the included angle between the inclined direction of the layered inclined structure 1042 and the horizontal plane is 0.1° - 15°. If the density of the layered inclined structure is too large, the dislocations will not be concentrated enough. If the density of the layered inclined structure is too low, the dislocations cannot be concentrated, and the effect of facilitating dislocations cannot be achieved. If the included angle of its inclined direction is too small, it will affect the transport of carriers. If it is too large, they cannot be normally combined, easily leading to dislocation penetration and poor surface combination.
[0038] In a possible implementation, the material of the substrate 102 is one of silicon, sapphire, silicon carbide, and gallium oxide, and the crystal plane of the substrate 102 has a crystal orientation deviation angle of 0.4° - 6°; the material of the buffer layer 103 is a single layer or multiple layers of Al x Ga 1-x N (0 ≤ x ≤ 1), and the characteristic thickness of the buffer layer 103 is 50 nm - 500 nm. The buffer layer can inhibit the thermal mismatch stress between the substrate and GaN and achieve crack-free epitaxial growth.
[0039] In a possible implementation, the multi-quantum well layer 106 is a superlattice structure composed of two materials among GaN, In x Ga 1-x N (0 < x < 1), Al y Ga 1-y N (0 < y < 1); the P-type layer 107 is composed of a composite layer of one or more materials among Al x Ga 1-x N (0 < x < 1). The P-type layer of the composite structure provides holes while changing the energy band structure to limit the transport path of carriers and reduce the non-radiative recombination probability.
[0040] Second, the embodiments of the present application also provide a method for preparing the epitaxial structure of the above-mentioned gallium nitride-based LED, including the following steps: Provide a substrate 102, and the crystal plane of the substrate 102 has a crystal orientation deviation angle of 0.4° - 6°; Grow a buffer layer 103 with a thickness of 50 nm - 500 nm on the substrate 102; A morphology adjustment layer 104 with a thickness of 20 nm - 800 nm is grown on the buffer layer 103: nucleation units 1041 are grown under the condition of 900 °C - 1200 °C; after the growth of the nucleation units 1041 is completed, the molar ratio of group V / III gases and the volume ratio of hydrogen gas to ammonia gas are adjusted to continue growing the morphology adjustment layer to make the nucleation units grow and merge with each other, realizing the growth of a layered inclined structure 1042, and dislocations 100 are fused along the inclined direction of the layered inclined structure 1042 as the nucleation units 1041 grow and merge; An N-type layer 105 is grown on the morphology adjustment layer 104, and the growth temperature of the N-type layer 105 is 1000 °C - 1200 °C; the initial growth direction and growth morphology of the N-type layer 105 are consistent with the layered inclined structure 1042 in the morphology adjustment layer 104, and the dislocations 100 in the morphology adjustment layer 104 are fused and then enter the N-type layer 105, forming a current diffusion channel and a stress dispersion channel in the N-type layer 105; the N-type layer 105 gradually becomes flat in the later stage of growth; A multi-quantum well layer 106 is grown on the N-type layer 105, and the growth temperature of the multi-quantum well layer 106 is 600 °C - 950 °C; A P-type layer 107 is grown on the multi-quantum well layer 106, and the growth temperature of the P-type layer 107 is 800 °C - 1090 °C.
[0041] In the embodiment of the present application, by selecting a suitable growth mode for the morphology adjustment layer, a special structure of the morphology adjustment layer is realized. First, nucleation units are grown. After the growth of the nucleation units is completed, the molar ratio of group V / III gases and the volume ratio of hydrogen gas to ammonia gas are adjusted to realize the merger between the nucleation units. During the merger process of the nucleation units, a large number of dislocations start to proliferate due to the interface contact between the nucleation units. The change in the volume ratio of hydrogen gas to ammonia gas makes the growth rates of the non-polar a-plane and m-plane of the morphology adjustment layer both greater than that of the c-plane. The speed difference between different planes leads to a layered inclination, and the layered inclination changes the speed of the growth direction, forming a layered inclined structure. The dislocations extend along the direction with a faster growth rate, so that the dislocations are fused along the inclined direction of the layered inclined structure as the nucleation units grow and merge and enter the N-type layer, thereby realizing the concentrated distribution of dislocations in the N-type layer, and thus forming a current diffusion channel and a stress dispersion channel in the N-type layer.
[0042] In a possible implementation, the V / III group gas molar ratio during the growth of the nucleation units is 40000:1 - 5000:1, and the volume ratio of hydrogen to ammonia gas is 0.01:1 - 1:1; the V / III group gas molar ratio during the growth and merging of the nucleation units is 5000:1 - 500:1, and the volume ratio of hydrogen to ammonia gas is 1:1 - 1:10; the V / III group gas molar ratio during the initial growth of the N-type layer is 20000:1 - 500:1, and the volume ratio of hydrogen to ammonia gas is 1:1 - 1:10, and the V / III group gas molar ratio during the later growth of the N-type layer is 20000:1 - 500:1, and the volume ratio of hydrogen to ammonia gas is 1:1 - 1:5. By adjusting multiple groups of gas ratios, the density and angle of the layered inclined structure are achieved. Example 1
[0043] This example provides a method for preparing an epitaxial structure of a gallium nitride-based LED, including the following steps: Using an MOCVD device, the substrate 102 is selected as single-crystal Si(111), and there is an angular deviation between the normal direction and the surface crystal orientation of the Si(111) substrate, deviating 2° towards the nearest
[110] .
[0044] A buffer layer 103 is grown on the substrate 102. The buffer layer 103 is a single-layer AlN, and the thickness of the buffer layer 103 is 140 nm.
[0045] A morphology adjustment layer 104 is grown on the buffer layer 103. The material of the morphology adjustment layer 104 is GaN. First, nucleation units 1041 are grown. During the growth of the nucleation units 1041, the ratio of V / III group gases (the V group gas is ammonia, and the III group gas is trimethylgallium) is 10000:1, the growth temperature is 1150 °C, the volume ratio of hydrogen to ammonia gas introduced is 0.1:1, the growth time is 1000 s, the morphology of the nucleation units 1041 is island-shaped, and the vertical height of the nucleation islands is 20 nm - 30 nm. After the growth of the nucleation units 1041 is completed, the V / III molar ratio is reduced to 600:1, the growth temperature is adjusted to 1120 °C, and the volume ratio of hydrogen to ammonia gas introduced is 1:3 to achieve the layered inclined merging of the nucleation units 1041 and realize the growth of the layered inclined structure 1042. Dislocations 100 are fused along the inclined direction of the layered inclined structure 1042 as the nucleation units 1041 grow and merge. The density of the layered inclined structure 1042 is 5.0E6 per cm -2 ², and each layered inclined structure 1042 contains 300 - 500 dislocations. The angle α between the inclined direction of the layered inclined structure 1042 and the horizontal plane is 6° - 7°, and the vertical thickness of the layered inclined structure 1042 is 470 nm - 480 nm.
[0046] The N-type layer 105 is grown on the morphology adjustment layer 104. The material of the N-type layer 105 is GaN with a thickness of 2.5 μm. The initial growth direction and morphology of the N-type layer 105 are consistent with the layered inclined structure 1042. The dislocations 100 in the morphology adjustment layer 104 are fused and enter the N-type layer 105. Each layered inclined structure 1042 contains 300 - 500 dislocations. The total dislocation density in the N-type layer 105 is 1.2E9 cm-2. The dislocation density in the region above the inclined top of the layered inclined structure 1042 in the N-type layer 105 is higher than the overall average level, and a large number of dislocations are concentrated in this region, forming a current diffusion channel and a stress dispersion channel in the N-type layer 105. When the N-type layer 105 is grown, the V / III group gas molar ratio is 2000:1, the gas volume ratio of hydrogen to ammonia introduced is 1:3, and the growth temperature is 1000 °C. The doping donor Si atom concentration is 3.0E18 cm -3 . Dislocations generally have relatively large elastic strain energy and can release part of the residual stress, and finally an N-type layer 105 with a basically flat end surface is obtained.
[0047] The multiple quantum well layer 106 is grown on the N-type layer 105. The multiple quantum well layer 106 is a superlattice multiple quantum well composed of GaN and In 0.29 Ga 0.71 N, and the growth temperature of the multiple quantum well layer 106 is 760 °C.
[0048] The P-type layer 107 is grown on the multiple quantum well layer 106. The P-type layer 107 is a single-layer GaN, the growth temperature of the P-type layer 107 is 950 °C, and the doping atom is Mg with a Mg atom concentration of 1.0E21 cm -3 .
[0049] The epitaxial structure of the gallium nitride-based LED prepared in this embodiment, as Figure 2 shown, sequentially includes a substrate 102, a buffer layer 103, a morphology adjustment layer 104, an N-type layer 105, a multiple quantum well layer 106, and a P-type layer 107.
[0050] The side of the morphology adjustment layer 104 close to the substrate includes a plurality of nucleation units 1041, and the surfaces of the nucleation units 1041 on the side away from the substrate 102 are separated from each other; the side of the morphology adjustment layer 104 away from the substrate 102 also includes a layered inclined structure 1042. The dislocations 100 are merged with the growth of the nucleation units 1041 and are fused into the N-type layer 105 along the inclined direction of the layered inclined structure 1042.
[0051] Figure 4 This is the atomic force microscope photograph of the layered inclined structure 1042 obtained in this embodiment, and its surface obviously shows an inclined shape and there is a height difference.
[0052] Figure 5The stress distribution map of the epitaxial structure of the gallium nitride-based LED prepared in this embodiment, obtained by Raman spectroscopy, shows fluctuations in stress, indicating stress concentration in some regions and stress relaxation in other regions of the epitaxial structure, which is similar to the pattern presented in the atomic force microscopy images in Figure 4 and
[0053] Figure 6 The simulated current distribution map of the epitaxial structure of the gallium nitride-based LED prepared in this embodiment shows that when the same magnitude of current is applied, the current extends significantly along the layered inclined structure, which is beneficial for the current to be dispersed and injected into the active region of the multi-quantum well layer. Example 2
[0054] This embodiment provides a method for preparing an epitaxial structure of a gallium nitride-based LED, including the following steps: Using an MOCVD device, the substrate 102 is selected as sapphire (Al2O3), and there is a 2° deviation from the c-plane crystal orientation towards the m-plane in the surface normal vector of the sapphire substrate.
[0055] A buffer layer 103 is grown on the substrate 102, and the buffer layer 103 is an AlN / Al 0.9 Ga 0.1 N superlattice, and the thickness of the buffer layer 103 is 200 nm.
[0056] A morphology adjustment layer 104 is grown on the buffer layer 103, and the material of the morphology adjustment layer 104 is GaN. First, nucleation units 1041 are grown. During the growth of the nucleation units 1041, the molar ratio of V / III group gases (the V group gas is ammonia, and the III group gases are trimethylgallium and trimethylindium) is 20000:1, the growth temperature is 1150 °C, the gas ratio of hydrogen to ammonia is 0.1:1, and the growth time is 800 s. The morphology of the nucleation units 1041 is island-like, and the vertical height of the nucleation islands is 10 nm - 20 nm. After the growth of the nucleation units 1041 is completed, the V / III molar ratio is reduced to 800:1, the growth temperature is adjusted to 1100 °C, the gas volume ratio of hydrogen to ammonia is adjusted to 1:2, and the growth temperature is adjusted to 1100 °C to achieve the layered inclined merging of the nucleation units 1041 and the growth of the layered inclined structure 1042. The dislocations 100 are combined along with the growth of the nucleation units 1041 and are fused along the inclined direction of the layered inclined structure 1042. The density of the layered inclined structure 1042 is 3.0E6 per cm -2 ², and each layered inclined structure 1042 contains 400 - 600 dislocations. The angle α between the inclined direction of the layered inclined structure 1042 and the horizontal plane is 3° - 5°, and the vertical thickness of the layered inclined structure 1042 is 550 nm - 560 nm.
[0057] The N-type layer 105 is grown on the morphology adjustment layer 104. The material of the N-type layer 105 is GaN with a thickness of 2.5 μm. The initial growth direction and morphology of the N-type layer 105 are consistent with the layered inclined structure 1042. The dislocations 100 in the morphology adjustment layer 104 are fused and enter the N-type layer 105. Each layered inclined structure 1042 contains 400 - 600 dislocations. The total dislocation density in the N-type layer 105 is 1.0E9 cm-2. The dislocation density in the area above the layered inclined structure 1042 in the N-type layer 105 is higher than the overall average level, and the dislocations are concentratedly distributed, forming a current diffusion channel and a stress dispersion channel in the N-type layer 105. When the N-type layer 105 is grown, the V / III group gas ratio is 2500:1, the volume ratio range of hydrogen gas to ammonia gas introduced is 1:2, and the growth temperature is 1050 °C. The doping donor Si atom concentration is 5.0E18 cm -3 . Dislocations generally have a large elastic strain energy and can release part of the residual stress, and finally obtain an N-type layer 105 with a basically flat end surface.
[0058] The multi-quantum well layer 106 is grown on the N-type layer 105. The multi-quantum well layer 106 is a superlattice multi-quantum well composed of GaN and In 0.25 Ga 0.75 N, and the growth temperature of the multi-quantum well layer 106 is 760 °C.
[0059] The P-type layer 107 is grown on the multi-quantum well layer 106. The P-type layer 107 is a single-layer GaN, the growth temperature of the P-type layer 107 is 990 °C, the doping atom is Mg, and the Mg concentration is 1.5E21 cm -3 .
[0060] The epitaxial structure of the gallium nitride-based LED prepared in this embodiment is basically the same as that in Embodiment 1, except that the island-like morphology of the nucleation unit 1041 is different from that in Embodiment 1, as Figure 8 shown. Embodiment 3
[0061] This embodiment provides a method for preparing an epitaxial structure of a gallium nitride-based LED, including the following steps: Using an MOCVD device, the substrate 102 is selected as single-crystal Si(111), and there is an angular deviation between the normal direction and the surface crystal orientation of the Si(111) substrate, deviating 3° towards the nearest
[110] .
[0062] The buffer layer 103 is grown on the substrate 102. The buffer layer 103 is a single-layer AlN, and the thickness of the buffer layer 103 is 280 nm.
[0063] The morphology adjustment layer 104 is grown on the buffer layer 103, and the material of the morphology adjustment layer 104 is GaN. First, the nucleation units 1041 are grown. During the growth process of the nucleation units 1041, the molar ratio of V / III group gases (the V group gas is ammonia gas, and the III group gases are trimethylgallium and trimethylaluminum) is 10000:1, the growth temperature is 1170 °C, the gas ratio of hydrogen to ammonia is 0.1:1, the growth time is 1500 s, the morphology of the nucleation units 1041 is corrugated, and the vertical height of the nucleation units 1041 is 20 nm - 30 nm. After the growth of the nucleation units 1041 is completed, the V / III molar ratio is reduced to 800:1, the growth temperature is adjusted to 1100 °C, and the gas volume ratio of hydrogen to ammonia is 1:3 to achieve the layered inclined merging of the nucleation units 1041 and realize the growth of the layered inclined structure 1042. The dislocations 100 merge with the growth of the nucleation units 1041 and are fused along the inclined direction of the layered inclined structure 1042. The density of the layered inclined structure 1042 is 8.0E6 per cm -2 , and each layered inclined structure 1042 contains 300 - 400 dislocations. The included angle α between the inclined direction of the layered inclined structure 1042 and the horizontal plane is 6° - 7°, and the vertical thickness of the layered inclined structure 1042 is 520 nm - 550 nm.
[0064] The N-type layer 105 is grown on the morphology adjustment layer 104, and the material of the N-type layer 105 is Al 0.01 Ga 0.09 N, with a thickness of 3.1 μm. The initial growth direction and morphology of the N-type layer 105 are consistent with those of the layered inclined structure 1042. The dislocations 100 in the morphology adjustment layer 104 are fused and then enter the N-type layer 105. Each layered inclined structure 1042 contains 300 - 400 dislocations, and the total dislocation density in the N-type layer 105 is 1.1E9 cm-2. The dislocation density in the area above the layered inclined structure 1042 in the N-type layer 105 is higher than the overall average level, and the dislocations are concentratedly distributed, forming current diffusion channels and stress dispersion channels in the N-type layer 105. When the N-type layer 105 is grown, the molar ratio of V / III group gases is 2000:1, the gas volume ratio range of hydrogen to ammonia is 1:3, and the growth temperature is 1000 °C. The doping donor Si atom concentration is 3.0E18 cm -3 . Dislocations generally have relatively large elastic strain energy and can release part of the residual stress, and finally an N-type layer 105 with a basically flat end surface is obtained.
[0065] The multiple quantum well layer 106 is grown on the N-type layer 105. The multiple quantum well layer 106 is a superlattice multiple quantum well composed of GaN and In 0.32 Ga 0.68 N, and the growth temperature of the multiple quantum well layer 106 is 750 °C.
[0066] A P-type layer 107 is grown on the multi-quantum well layer 106. The P-type layer 107 is a single layer of GaN. The growth temperature of the P-type layer 107 is 950 °C, the doping atom is Mg, and the Mg concentration is 1.0E21 atoms / cm -3 .
[0067] The epitaxial structure of the gallium nitride-based LED prepared in this embodiment is basically the same as that in Embodiment 1, except that the morphology of the nucleation unit 1041 is corrugated, as Figure 9 shown. Comparative Example 1
[0068] This comparative example provides an epitaxial structure of a gallium nitride-based LED. The difference in its basic structure from that in Embodiment 1 is that there is no morphology adjustment layer, and the N-type layer is directly prepared on the buffer layer.
[0069] As Figure 3 shown, it sequentially includes a substrate 202, a buffer layer 203, an N-type layer 205, a multi-quantum well layer 206, and a P-type layer 207. Dislocations 200 are randomly distributed in the N-type layer 205. Such microscopic random dislocations are macroscopically uniformly distributed throughout the N-type layer 205. The simulated current distribution diagram of the epitaxial structure prepared in this comparative example is as Figure 7 shown. It can be seen that such microscopically randomly distributed dislocations do not form leakage channels, but instead hinder the internal current expansion. At the same time, due to the disorder of the microscopic distribution, the stress cannot be adjusted.
Claims
1. An epitaxial structure of a gallium nitride-based LED, comprising a substrate, characterized in that: It further includes a buffer layer, a morphology adjustment layer, an N-type layer, a multi-quantum well layer, and a P-type layer sequentially disposed on the substrate; On the side of the morphology adjustment layer close to the substrate, it includes a plurality of nucleation units, and the surfaces of the nucleation units on the side away from the substrate are separated from each other; on the side of the morphology adjustment layer away from the substrate, it further includes a layered inclined structure, and dislocations merge with the growth of the nucleation units and are incorporated into the N-type layer along the inclined direction of the layered inclined structure; The dislocations in the N-type layer are concentratedly distributed in the area above the layered inclined structure to form a current diffusion channel and a stress dispersion channel.
2. The epitaxial structure of the gallium nitride-based LED according to claim 1, characterized in that: The morphology of the nucleation unit is island-shaped or corrugated, and the vertical height of the nucleation unit is 1 nm - 50 nm.
3. The epitaxial structure of the gallium nitride-based LED according to claim 1, characterized in that: The material of the morphology adjustment layer is one of GaN, InGaN, and AlGaN, and the thickness of the morphology adjustment layer is 20 nm - 800 nm.
4. The epitaxial structure of the gallium nitride-based LED according to claim 3, wherein: The material of the morphology adjustment layer is GaN, and the thickness of the morphology adjustment layer is 100 nm - 500 nm.
5. The epitaxial structure of the gallium nitride-based LED according to claim 1, wherein: The material of the N-type layer is one of GaN, InGaN, and AlGaN, and the characteristic thickness of the N-type layer is 500 nm - 5000 nm; the total dislocation density in the N-type layer is 1.0E9 cm -2 -3.0E9 cm -2 , and the surface of the N-type layer on the side far from the substrate is flat.
6. The epitaxial structure of the gallium nitride-based LED according to claim 1, wherein: The distribution density of the layered inclined structure in the topography adjustment layer is 1.0E5 cm -2 -1.0E7 cm -2 , and 200 - 1000 dislocations are concentratedly distributed in each layered inclined structure; the included angle α between the inclination direction of the layered inclined structure and the horizontal plane is 0.1° - 15°.
7. The epitaxial structure of the gallium nitride-based LED according to claim 1, characterized in that: The substrate material is one of silicon, sapphire, silicon carbide, and gallium oxide, and the substrate crystal plane has a crystal orientation deviation angle of 0.4° - 6°; the material of the buffer layer is Al x Ga 1-x N (0 ≤ x ≤ 1) in a single layer or multiple layers, and the characteristic thickness of the buffer layer is 50 nm - 500 nm.
8. The epitaxial structure of the gallium nitride-based LED according to claim 1, characterized in that: The multi-quantum well layer is a superlattice structure composed of two materials among GaN, In x Ga 1-x N (0 < x < 1), Al y Ga 1-y N (0 < y < 1); the P-type layer is composed of a composite layer of one or more materials among Al x Ga 1-x N (0 ≤ x ≤ 1).
9. A method for preparing an epitaxial structure of a gallium nitride-based LED according to any one of claims 1-8, characterized in that, It includes the following steps: Provide a substrate, and the crystal plane of the substrate has a crystal orientation deviation angle of 0.4° - 6°; Grow a buffer layer with a thickness of 50 nm - 500 nm on the substrate; Grow a morphology adjustment layer with a thickness of 20 nm - 800 nm on the buffer layer: grow nucleation units under the condition of 900 °C - 1200 °C; after the growth of the nucleation units is completed, adjust the molar ratio of group V / III gases and the volume ratio of hydrogen to ammonia gas under the condition of 800 °C - 1180 °C to continue growing the morphology adjustment layer to make the nucleation units grow and merge, and realize the growth of the layered inclined structure, and dislocations are incorporated along the inclined direction of the layered inclined structure as the nucleation units grow and merge; Grow an N-type layer on the morphology adjustment layer, and the growth temperature of the N-type layer is 1000 °C - 1200 °C; the initial growth direction and growth morphology of the N-type layer are consistent with the layered inclined structure in the morphology adjustment layer, and the dislocations in the morphology adjustment layer are incorporated into the N-type layer to form a current diffusion channel and a stress dispersion channel in the N-type layer; the N-type layer gradually levels off after changing the gas ratio of hydrogen to ammonia in the later stage of growth; Grow a multi-quantum well layer on the N-type layer, and the growth temperature of the multi-quantum well layer is 600 °C - 950 °C; Grow a P-type layer on the multi-quantum well layer, and the growth temperature of the P-type layer is 800 °C - 1090 °C.
10. The preparation method according to claim 9, wherein: When the nucleation units grow, the molar ratio of group V / III is 40000:1 - 5000:1, and the gas ratio of hydrogen to ammonia is 0.01:1 - 1:1; when the nucleation units grow and merge, the molar ratio of group V / III gases is 5000:1 - 500:1, and the volume ratio of hydrogen to ammonia gas is 1:1 - 1:10; when the N-type layer initially grows, the molar ratio of group V / III gases is 20000:1 - 500:1, and the volume ratio of hydrogen to ammonia gas is 1:1 - 1:10, and in the later stage of the growth of the N-type layer, the molar ratio of group V / III is 20000:1 - 500:1, and the volume ratio of hydrogen to ammonia gas is 1:1 - 1:5.