Epitaxial structure for improving quality of si-based gan thin film crystal and preparation method thereof
By employing MOCVD technology and specific layered growth conditions on Si substrates, the problem of poor crystal quality of GaN thin films on silicon substrates was solved, and high-quality GaN thin films were prepared, suitable for high-frequency and high-power electronic devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTH CHINA UNIV OF TECH
- Filing Date
- 2023-04-18
- Publication Date
- 2026-06-26
AI Technical Summary
Existing techniques for growing GaN thin films on silicon substrates result in poor crystal quality, with issues such as cracks and the inability to effectively control crystal quality.
Metal-organic chemical vapor deposition (MOCVD) is used to optimize growth conditions to improve crystal quality by sequentially stacking a Si substrate, an AlN nucleation layer, an AlGaN stress-modulated layer, and periodically alternating layers of three-dimensional and two-dimensional GaN layers on a Si substrate.
It effectively improves the crystal quality of GaN thin films and reduces dislocation density, making them suitable for high-frequency and high-power electronic device applications.
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Figure CN116344327B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor technology, specifically to epitaxial structures for improving the quality of Si-based GaN thin film crystals and their preparation methods. Background Technology
[0002] GaN, a group III nitride, possesses excellent properties such as wide bandgap, high electron drift velocity, high thermal conductivity, high voltage resistance, high temperature resistance, and radiation resistance, making it suitable for developing high-frequency, high-temperature, and high-power electronic devices. As a third-generation semiconductor material, it has received widespread attention and development. Common substrates for GaN include sapphire, silicon, and silicon carbide. Compared to silicon carbide, silicon-based GaN offers lower costs. However, for sapphire substrates, heat dissipation in high-power devices remains a significant obstacle to its development. Silicon-based GaN offers better cost advantages and performance, showing broad application prospects in automotive electronics, 5G network infrastructure construction, and other fields. The crystal quality of silicon-based GaN significantly affects the performance of electronic devices; however, the crystal quality of silicon-based GaN still presents challenges at present.
[0003] Currently, the traditional GaN growth structure on silicon substrates typically involves three stages. Due to a 17% lattice mismatch between GaN and Si, directly growing GaN on a silicon substrate can result in significant cracks and poor crystal quality. Therefore, a buffer layer structure is introduced. First, an AlN nucleation layer is grown on the silicon substrate after high-temperature baking. Then, one or more AlGaN stress control layers are grown to introduce pre-stress. By adjusting the stress, GaN cracking during growth can be avoided. Next, a two-dimensional GaN crystal film is grown at 1030 degrees Celsius under 500 Tor pressure. While this growth method can obtain crack-free GaN films, the crystal quality is poor. As can be seen from the full width at half maximum (FWHM) of the 002 and 102 planes in X-rays, the quality of high-quality GaN crystals remains unadjustable; the FWHM of the 002 plane is limited to above 400, and the FWHM of the 102 plane is limited to above 500. Based on the above, how to obtain better GaN crystal quality has become an urgent problem to be solved (a method for epitaxial growth of gallium nitride thin films with controllable crystal quality (application number 201310339724.4)). Summary of the Invention
[0004] The purpose of this invention is to overcome the existing technical problems and provide a better growth process method for improving the quality of GaN thin film crystals. This invention utilizes metal-organic chemical vapor deposition (MOCVD). Through the in-situ detection function of the MOCVD machine, reflectivity curves, growth temperature curves, and epitaxial wafer curvature curves are simultaneously monitored. The average value of the reflectivity oscillation curve can reflect the surface flatness of the thin film, thereby determining changes in the growth mode.
[0005] The objective of this invention is achieved by at least one of the following technical solutions.
[0006] An epitaxial structure for improving the crystal quality of Si-based GaN thin films includes a Si substrate, a first AlN nucleation layer, a second AlN nucleation layer, a first AlGaN stress-controlled layer, a second AlGaN stress-controlled layer, a third AlGaN stress-controlled layer, and a periodically alternating three-dimensional GaN layer and a two-dimensional GaN layer stacked sequentially from bottom to top.
[0007] Among them, the three-dimensional GaN layer is a GaN layer with a molar ratio of Ⅲ under high pressure, low temperature, and low V, and the two-dimensional GaN layer is a GaN layer with a molar ratio of Ⅲ under low pressure, high temperature, and high V; the three-dimensional GaN layer and the two-dimensional GaN layer are periodically stacked alternately 2-3 times.
[0008] Furthermore, the diameter of the Si substrate is 6 inches to 8 inches;
[0009] The thickness of the Si substrate is 800-1200 μm;
[0010] The combined thickness of the first AlN nucleation layer and the second AlN nucleation layer is 100-150 nm.
[0011] The total thickness of the first AlGaN stress control layer, the second AlGaN stress control layer, and the third AlGaN stress control layer is 500-800 nm.
[0012] The combined thickness of the periodically alternating three-dimensional GaN layers and two-dimensional GaN layers is 3500-5000 nm.
[0013] The growth thickness of the three-dimensional GaN layer is controlled between 500nm and 700nm; the growth thickness of the two-dimensional GaN layer is controlled between 850nm and 900nm.
[0014] Furthermore, the first AlN nucleation layer is low-temperature AlN, with a growth temperature of 840-870℃, a growth pressure of 70-90 Torr, and a thickness of 10nm-30nm;
[0015] The second AlN nucleation layer is high-temperature AlN, with the growth temperature controlled at 1030-1045℃, the growth pressure at 70-90 Torr, and the thickness at 80-120 nm.
[0016] Furthermore, the percentage of Al molar content in the first AlGaN stress-regulating layer, the second AlGaN stress-regulating layer, and the third AlGaN stress-regulating layer is 50-60%, 40-50%, and 20-30%, respectively. The thickness of the first AlGaN stress-regulating layer, the second AlGaN stress-regulating layer, and the third AlGaN stress-regulating layer increases sequentially, and the thickness of the first AlGaN stress-regulating layer, the second AlGaN stress-regulating layer, and the third AlGaN stress-regulating layer are all in the range of 100nm to 500nm.
[0017] The thicknesses of the first AlGaN stress-controlled layer, the second AlGaN stress-controlled layer, and the third AlGaN stress-controlled layer are 50-150, 150-250, and 300-400 nm, respectively.
[0018] A method for preparing epitaxial structures with improved crystal quality of Si-based GaN thin films includes the following steps:
[0019] S1. High-temperature annealing treatment of the Si substrate surface is performed in the reaction chamber of the MOCVD equipment.
[0020] S2. Epitaxial growth of an AlN nucleation layer on a Si substrate;
[0021] S3. Grow an AlGaN stress-controlled layer on the basis of the AlN nucleation layer after the growth is completed;
[0022] S4. Grow a three-dimensional GaN layer on the AlGaN stress-controlled layer;
[0023] S5. Grow a two-dimensional GaN layer on the grown three-dimensional GaN layer;
[0024] S6. Following steps S4 and S5, grow three-dimensional GaN layers and two-dimensional GaN layers sequentially from bottom to top to obtain periodically alternating three-dimensional GaN layers and two-dimensional GaN layers.
[0025] Further, step S2 includes the following steps:
[0026] S2.1, the first AlN nucleation layer with a growth temperature of 840-870℃, a growth pressure of 70-90 Torr, and a thickness of 10nm-30nm;
[0027] S2.2. A second AlN nucleation layer with a growth temperature of 1030-1045℃, a growth pressure of 70-90 Torr, and a thickness of 80-120 nm.
[0028] Further, step S3 includes the following steps:
[0029] S3.1. Control the growth temperature at 1040-1070℃ and the growth pressure at 70-90mbar. Introduce trimethylgallium, trimethylaluminum and ammonia, with a flow rate of 40-50 sccm for trimethylgallium, a flow rate of 600-750 sccm for trimethylaluminum, and a total flow rate of 5000 sccm for ammonia to grow the first AlGaN stress-controlled layer.
[0030] S3.2. Control the growth temperature at 1040-1070℃ and the growth pressure at 70-90mbar. Introduce trimethylgallium, trimethylaluminum and ammonia, with a flow rate of 70-80sccm for trimethylgallium, a flow rate of 600-750sccm for trimethylaluminum, and a total flow rate of 5000sccm for ammonia, to grow the second AlGaN stress-controlled layer.
[0031] S3.3. Control the growth temperature at 1040-1070℃ and the growth pressure at 70-90mbar. Introduce trimethylgallium, trimethylaluminum and ammonia, with a flow rate of 130-140 sccm for trimethylgallium, 600-750 sccm for trimethylaluminum, and a total flow rate of 5000 sccm for ammonia, to grow the third AlGaN stress-controlled layer.
[0032] Further, in step S4, the growth temperature is controlled at 1020-1040℃, the growth pressure at 350-450mbar, the flow rate of trimethylgallium is 350-450sccm, the total flow rate of ammonia is 5000sccm, the growth thickness is 600-800nm, and the V / III molar ratio during the growth process is 650-800.
[0033] Further, in step S5, the growth temperature is controlled at 1020-1040℃, the growth pressure at 150-250 Torr, the flow rate of trimethylgallium is 250-350 sccm, the total flow rate of ammonia is 3500 sccm, the growth thickness is 800-950 nm, and the V / III molar ratio during the growth process is 1200-1450.
[0034] Further, in step S6, the three-dimensional GaN layer and the two-dimensional GaN layer are repeatedly stacked and grown 1-2 times to obtain a three-dimensional GaN layer and a two-dimensional GaN layer that are periodically and alternately stacked 2-3 times.
[0035] Compared with the prior art, the present invention has the following advantages and technical effects:
[0036] This epitaxy is based on a GaN epitaxial structure on a Si substrate. By optimizing the growth conditions, the quality of the GaN thin film can be effectively improved. High-quality GaN can be fabricated on large-size Si substrates. The silicon substrate GaN fabrication process of this invention is simple, has good repeatability, and is suitable for high-frequency, high-power power supplies, switches, communications, and other applications. Attached image description:
[0037] Figure 1 This is a schematic diagram of the epitaxial structure for improving the crystal quality of Si-based GaN thin films in Embodiment 1 of the present invention;
[0038] Figure 2 This is a schematic diagram of the epitaxial structure for improving the crystal quality of Si-based GaN thin films in Embodiment 1 of the present invention;
[0039] Figure 3 This is the XRD (002) surface rocking curve of the GaN thin film prepared in Example 1 of this invention;
[0040] Figure 4 The XRD (102) rocking curve of the GaN thin film prepared in Example 1 of this invention;
[0041] Figure 5 This is the XRD (002) surface rocking curve of the GaN thin film prepared in Example 2 of this invention;
[0042] Figure 6 This is the rocking curve of the XRD (102) plane of the GaN thin film prepared in Example 2 of the present invention. Detailed implementation method:
[0043] The specific implementation of the present invention will be further described below with reference to the accompanying drawings and examples. It should be noted that any processes or process parameters not specifically described below are those that can be implemented by those skilled in the art with reference to the prior art.
[0044] This invention provides a method for growing GaN thin films on silicon substrates. By introducing periodic growth of three-dimensional GaN and two-dimensional GaN, the dislocation density in GaN is effectively reduced, thereby improving the quality of GaN thin films.
[0045] The growth equipment of this invention is entirely carried out in a metal-organic chemical vapor deposition (MOCVD) apparatus. Trimethylaluminum (TMAl), trimethylgallium (TMGa) and ammonia (NH3) are used as aluminum (Al) source, gallium (Ga) source and nitrogen (N) source, respectively, and hydrogen (H2) and nitrogen (N2) are used as carrier gases.
[0046] Example 1:
[0047] In this embodiment, the diameter of Si substrate 1 is 6 inches; in another embodiment, the diameter of Si substrate 1 is 8 inches.
[0048] The thickness of Si substrate 1 is 1 mm;
[0049] The combined thickness of the first AlN nucleation layer 2 and the second AlN nucleation layer 3 is 120 nm.
[0050] The total thickness of the first AlGaN stress control layer 4, the second AlGaN stress control layer 5, and the third AlGaN stress control layer 6 is 700 nm.
[0051] The combined thickness of the periodically alternating three-dimensional GaN layer and the two-dimensional GaN layer is 4050 nm.
[0052] A first AlN nucleation layer 2 and a second AlN nucleation layer 3 are epitaxially grown on a Si substrate 1, including:
[0053] In the first stage, low-temperature AlN was grown at a temperature of 865℃, a growth pressure of 75 Torr, and a thickness of 20 nm.
[0054] In the second stage, the growth temperature was controlled at 1045℃, the growth pressure at 75mbar, and the thickness at 100nm for high-temperature AlN.
[0055] In the first AlGaN stress-regulating layer 4, the second AlGaN stress-regulating layer 5, and the third AlGaN stress-regulating layer 6, the molar content of Al element in each layer decreases sequentially from bottom to top, namely 0.6, 0.4, and 0.2, respectively, and the thickness increases sequentially, namely 100nm, 200nm, and 400nm, respectively.
[0056] The periodically alternating three-dimensional and two-dimensional GaN layers are composed of a periodically alternating high-pressure, low-temperature, low-V GaN layer with a 3 molar ratio and a low-pressure, high-temperature, high-V GaN layer with a 3 molar ratio. The thickness of the high-pressure, low-temperature, low-V GaN layer with a 3 molar ratio is 550 nm and the thickness of the low-pressure, high-temperature, high-V GaN layer with a 3 molar ratio is 800 nm, with a period of 2 cycles.
[0057] like Figure 1 As shown, the method for manufacturing an epitaxial structure to improve the crystal quality of Si-based GaN thin films includes the following steps:
[0058] Step 1: Place the Si substrate 1 into a metal-organic chemical vapor deposition apparatus and anneal the surface of the Si substrate 1 at a temperature of 1050 degrees Celsius for 5 minutes.
[0059] Step 2: Introduce an aluminum source, trimethylaluminum, into the reaction chamber at a flow rate of 100 sccm for 20 seconds.
[0060] Step 3: Grow a first AlN nucleation layer 2 and a second AlN nucleation layer 3 on the Si substrate 1. When growing the first AlN nucleation layer 2, the reaction chamber temperature is lowered to 865℃, the chamber pressure is adjusted to 75 Torr, the growth time is 1 min, and the thickness is 10 nm. When growing the second AlN nucleation layer 3, the growth temperature is increased to 1045℃, the chamber pressure remains unchanged, the growth time is 30 min, and the thickness is 110 nm.
[0061] Step 4: Grow the first AlGaN stress-controlled layer 4 on the second AlN nucleation layer 3. Raise the cavity temperature to 1065℃, maintain the cavity pressure at 75 Torr, control the inlet flow rate of trimethylaluminum to 700 sccm, the inlet flow rate of trimethylgallium to 46 sccm, the total flow rate of ammonia to 5000 sccm, the growth time to 20 min, the growth thickness to 100 nm, and the molar content of Al to 0.6%.
[0062] Step 5: Grow a second AlGaN stress-controlled layer 5 on the first AlGaN stress-controlled layer 4. Maintain the chamber temperature at 1065℃, the chamber pressure at 75 Torr, control the inlet flow rate of trimethylaluminum to 700 sccm, the inlet flow rate of trimethylgallium to 70 sccm, the total flow rate of ammonia to 5000 sccm, the growth time to 30 min, the growth thickness to 200 nm, and the molar content of Al to 0.4%.
[0063] Step 6: Grow a third AlGaN stress-controlled layer 6 on the second AlGaN stress-controlled layer 5. Maintain the chamber temperature at 1065℃, the chamber pressure at 75 Torr, control the inlet flow rate of trimethylaluminum to 700 sccm, the inlet flow rate of trimethylgallium to 140 sccm, the total flow rate of ammonia to 5000 sccm, the growth time to 50 min, the growth thickness to 400 nm, and the molar content of Al to 0.2%.
[0064] Step seven: A first three-dimensional GaN layer 7 is grown on the third AlGaN stress-controlled layer 6. In one embodiment, the three-dimensional GaN is grown by adjusting parameters such as growth temperature, chamber pressure, and NH3 flow rate. In the three-dimensional growth mode, GaN exhibits an island-island structure, which can be effectively absorbed by the subsequent two-dimensional GaN growth. The chamber pressure is adjusted to 400 Torr, the trimethylgallium gas inlet flow rate is adjusted to 400 sccm, the growth temperature is reduced to 900℃, the growth time is 12 min, the growth thickness is 550 nm, and the total ammonia flow rate is 5000 sccm.
[0065] Step 8: Grow the first two-dimensional GaN layer 8 on the first three-dimensional GaN layer 7. Adjust the cavity pressure to 200 Torr, maintain the trimethylgallium gas inlet flow rate at 400 sccm, increase the growth temperature to 1030℃, grow for 20 min, grow to a thickness of 800 nm, and maintain the total ammonia flow rate at 3500 sccm.
[0066] Step nine: Repeat step seven to grow a second three-dimensional GaN layer 9 on the first two-dimensional GaN layer 8.
[0067] Step 10: Repeat the process in Step 8 to grow a second two-dimensional GaN layer 10 on the second three-dimensional GaN layer 9.
[0068] XRD analysis showed that the full width at half maximum (FWHM) of the rocking curve on plane 002 was 395 arcsec. Figure 3 The half-width of the 102-plane rocking curve is 568.7 arcsec. Figure 4
[0069] Example 2:
[0070] In this embodiment, the diameter of the Si substrate 1 is 6 inches.
[0071] The thickness of Si substrate 1 is 1 mm;
[0072] The combined thickness of the first AlN nucleation layer 2 and the second AlN nucleation layer 3 is 120 nm.
[0073] The total thickness of the first AlGaN stress control layer 4, the second AlGaN stress control layer 5, and the third AlGaN stress control layer 6 is 700 nm.
[0074] The combined thickness of the periodically alternating three-dimensional GaN layer and the two-dimensional GaN layer is 4050 nm.
[0075] A first AlN nucleation layer 2 and a second AlN nucleation layer 3 are epitaxially grown on a Si substrate 1, including:
[0076] In the first stage, low-temperature AlN was grown at a temperature of 865℃, a growth pressure of 75 Torr, and a thickness of 20 nm.
[0077] In the second stage, the growth temperature was controlled at 1045℃, the growth pressure at 75mbar, and the thickness at 100nm for high-temperature AlN.
[0078] In the first AlGaN stress-regulating layer 4, the second AlGaN stress-regulating layer 5, and the third AlGaN stress-regulating layer 6, the molar content of Al element in each layer decreases sequentially from bottom to top, namely 0.6, 0.4, and 0.2, respectively, and the thickness increases sequentially, namely 100nm, 200nm, and 400nm, respectively.
[0079] The periodically alternating three-dimensional and two-dimensional GaN layers are composed of a periodically alternating high-pressure, low-temperature, low-V GaN layer with a 3 molar ratio and a low-pressure, high-temperature, high-V GaN layer with a 3 molar ratio. The thickness of the high-pressure, low-temperature, low-V GaN layer with a 3 molar ratio is 550 nm and the thickness of the low-pressure, high-temperature, high-V GaN layer with a 3 molar ratio is 800 nm, with a period of 3 cycles.
[0080] like Figure 2 As shown, the method for manufacturing an epitaxial structure to improve the crystal quality of Si-based GaN thin films includes the following steps:
[0081] Step 1: Place the Si substrate in a metal-organic chemical vapor deposition apparatus and anneal the substrate surface at a temperature of 1050 degrees Celsius for 5 minutes.
[0082] Step 2: Introduce an aluminum source, trimethylaluminum, into the reaction chamber at a flow rate of 100 sccm for 20 seconds.
[0083] Step 3: Grow a first AlN nucleation layer 2 and a second AlN nucleation layer 3 on the Si substrate 1. When growing the first AlN nucleation layer 2, the reaction chamber temperature is lowered to 865℃, the chamber pressure is adjusted to 75 Torr, the growth time is 1 min, and the thickness is 10 nm. When growing the second AlN nucleation layer 3, the growth temperature is increased to 1045℃, the chamber pressure remains unchanged, the growth time is 30 min, and the thickness is 110 nm.
[0084] Step 4: Grow the first AlGaN stress-controlled layer 4 on the second AlN nucleation layer 3. Raise the cavity temperature to 1065℃, maintain the cavity pressure at 75 Torr, control the inlet flow rate of trimethylaluminum to 700 sccm, the inlet flow rate of trimethylgallium to 46 sccm, the total flow rate of ammonia to 5000 sccm, the growth time to 20 min, the growth thickness to 100 nm, and the molar content of Al to 0.6%.
[0085] Step 5: Grow a second AlGaN stress-controlled layer 5 on the first AlGaN stress-controlled layer 4. Maintain the chamber temperature at 1065℃, the chamber pressure at 75 Torr, control the inlet flow rate of trimethylaluminum to 700 sccm, the inlet flow rate of trimethylgallium to 70 sccm, the total flow rate of ammonia to 5000 sccm, the growth time to 30 min, the growth thickness to 200 nm, and the molar content of Al to 0.4%.
[0086] Step 6: Grow a third AlGaN stress-controlled layer 6 on the second AlGaN stress-controlled layer 5. Maintain the chamber temperature at 1065℃, the chamber pressure at 75 Torr, control the inlet flow rate of trimethylaluminum to 700 sccm, the inlet flow rate of trimethylgallium to 140 sccm, the total flow rate of ammonia to 5000 sccm, the growth time to 50 min, the growth thickness to 400 nm, and the molar content of Al to 0.2%.
[0087] Step seven: A first three-dimensional GaN layer 7 is grown on the third AlGaN stress-controlled layer 6. In one embodiment, the three-dimensional GaN is grown by adjusting parameters such as growth temperature, chamber pressure, and NH3 flow rate. In the three-dimensional growth mode, GaN exhibits an island-island structure, which can be effectively absorbed by the subsequent two-dimensional GaN growth. The chamber pressure is adjusted to 400 Torr, the trimethylgallium gas inlet flow rate is adjusted to 400 sccm, the growth temperature is reduced to 900℃, the growth time is 12 min, the growth thickness is 550 nm, and the total ammonia flow rate is 5000 sccm.
[0088] Step 8: Grow the first two-dimensional GaN layer 8 on the first three-dimensional GaN layer 7. Adjust the cavity pressure to 200 Torr, maintain the trimethylgallium gas inlet flow rate at 400 sccm, increase the growth temperature to 1030℃, grow for 20 min, grow to a thickness of 800 nm, and maintain the total ammonia flow rate at 3500 sccm.
[0089] Step nine: Repeat step seven to grow a second three-dimensional GaN layer 9 on the first two-dimensional GaN layer 8.
[0090] Step 10: Repeat the process in Step 8 to grow a second two-dimensional GaN layer 10 on the second three-dimensional GaN layer 9.
[0091] Step 11: Repeat step 7 to grow a third three-dimensional GaN layer 11 on the second two-dimensional GaN layer 8.
[0092] Step 12: Repeat step 8 to grow a third 2D GaN layer 12 on top of the third 3D GaN layer 9. XRD analysis shows that the full width at half maximum (FWHM) of the rocking curve on the 002 plane is 316 arcsec. Figure 5 The half-peak width of the 102-surface rocking curve is 496.6 arcsec. Figure 6
[0093] Compared with Example 1, Example 2 shows a larger GaN thickness and a significantly improved crystal quality. The half-width at half maximum (WHM) of the XRD 002 plane rocking curve is 316 arcsec, and the half-width at half maximum (WHM) of the 102 plane rocking curve is 496.6 arcsec.
[0094] This invention relates to a GaN epitaxial structure based on a Si substrate. By optimizing growth conditions, the quality of the GaN thin film can be effectively improved. High-quality GaN can be fabricated on large-size Si substrates. The silicon substrate GaN fabrication process of this invention is simple, has good repeatability, and is suitable for high-frequency, high-power applications such as power supplies, switches, and communications.
[0095] The epitaxial structure of this invention, through a periodic growth structure of GaN three-dimensional and GaN two-dimensional growth layers, possesses the advantages of high GaN crystal quality and excellent surface morphology. Compared with existing epitaxial structures, the GaN thin film exhibits higher crystal quality and can be widely used in high-frequency, high-power electronic devices.
[0096] It should be noted that the above-described embodiments do not constitute any limitation on the present invention. Any modifications and changes in form and detail made by those skilled in the art without departing from the principles and scope of the present invention should be included within the protection scope of the present invention.
Claims
1. An epitaxial structure for improving the crystal quality of Si-based GaN thin films, characterized in that, It includes a Si substrate (1), a first AlN nucleation layer (2), a second AlN nucleation layer (3), a first AlGaN stress control layer (4), a second AlGaN stress control layer (5), a third AlGaN stress control layer (6) stacked sequentially from bottom to top, and a three-dimensional GaN layer and a two-dimensional GaN layer stacked periodically and alternately. The Si substrate (1) has a diameter of 6-8 inches and a thickness of 800-1200 μm. The first AlN nucleation layer (2) is low-temperature AlN with a growth temperature of 840-870℃, a growth pressure of 70-90 Torr, and a thickness of 10nm-30nm; The second AlN nucleation layer (3) is high-temperature AlN with a growth temperature of 1030-1045℃, a growth pressure of 70-90 Torr, and a thickness of 80-120nm; The percentage of Al element molar content in the first AlGaN stress control layer (4), the second AlGaN stress control layer (5) and the third AlGaN stress control layer (6) are 50-60%, 40-50% and 20-30% respectively, and the thicknesses are 50-150nm, 150-250nm and 300-400nm respectively. The three-dimensional GaN layer is a GaN layer with a growth pressure of 350-450 mbar, a growth temperature of 1020-1040℃, a V / III molar ratio of 650-800, and a thickness of 500-700 nm. The two-dimensional GaN layer is a GaN layer with a growth pressure of 150-250 Torr, a growth temperature of 1020-1040℃, a V / III molar ratio of 1200-1450, and a thickness of 850-900 nm. The three-dimensional GaN layer and the two-dimensional GaN layer are periodically stacked alternately 2-3 times.
2. A method for preparing an epitaxial structure to improve the crystal quality of Si-based GaN thin films, characterized in that, Includes the following steps: S1. In the reaction chamber of the MOCVD equipment, the surface of the Si substrate is subjected to high-temperature annealing treatment at a temperature of 1050℃ for 5 minutes. S2. Epitaxial growth of an AlN nucleation layer on a Si substrate, including: S2.1, The first AlN nucleation layer with a growth temperature of 840-870℃, a growth pressure of 70-90 Torr, and a thickness of 10nm-30nm (2); S2.2, The second AlN nucleation layer with a growth temperature of 1030-1045℃, a growth pressure of 70-90 Torr, and a thickness of 80-120nm (3); S3. An AlGaN stress-controlled layer is grown on the basis of the completed AlN nucleation layer, including: S3.
1. Control the growth temperature to 1040-1070℃, the growth pressure to 70-90mbar, the flow rate of trimethylgallium to 40-50sccm, the flow rate of trimethylaluminum to 600-750sccm, and the total flow rate of ammonia to 5000sccm to grow the first AlGaN stress control layer (4). S3.2, control the growth temperature to 1040-1070℃, the growth pressure to 70-90mbar, the flow rate of trimethylgallium to 70-80sccm, the flow rate of trimethylaluminum to 600-750sccm, and the total flow rate of ammonia to 5000sccm, and grow the second AlGaN stress control layer (5). S3.3, control the growth temperature to 1040-1070℃, the growth pressure to 70-90mbar, the flow rate of trimethylgallium to 130-140sccm, the flow rate of trimethylaluminum to 600-750sccm, and the total flow rate of ammonia to 5000sccm, and grow the third AlGaN stress control layer (6). S4. A three-dimensional GaN layer is grown on the AlGaN stress-controlled layer, with the growth temperature controlled at 1020-1040℃, the growth pressure at 350-450mbar, the trimethylgallium flow rate at 350-450sccm, the total ammonia flow rate at 5000sccm, the growth thickness at 600-800nm, and the V / III molar ratio at 650-800 during the growth process. S5. Grow a two-dimensional GaN layer on the grown three-dimensional GaN layer, controlling the growth temperature at 1020-1040℃, the growth pressure at 150-250 Torr, the trimethylgallium flow rate at 250-350 sccm, the total ammonia flow rate at 3500 sccm, the growth thickness at 800-950 nm, and the V / III molar ratio at 1200-1450 during the growth process. S6. Following steps S4 and S5, grow three-dimensional GaN layers and two-dimensional GaN layers sequentially from bottom to top, repeating 1-2 times to obtain three-dimensional GaN layers and two-dimensional GaN layers that are periodically and alternately stacked 2-3 times.
3. The preparation method according to claim 2, characterized in that, The high-temperature annealing described in step S1 is carried out in a hydrogen atmosphere.
4. The preparation method according to claim 2, characterized in that, The growth temperature described in steps S4 and S5 is 1020-1040℃.