A silicon-based AlGaN / GaN HEMT epitaxial structure and preparation method

Abstract

The invention discloses a silicon-based AlGaN / GaN HEMT epitaxial structure and a preparation method. The epitaxial structure comprises a silicon substrate, an AlN buffer layer, a stepped AlGaN stress release layer, a GaN seed padding roughening layer, a GaN epitaxial layer, a first AlN insertion layer, a first C-doped GaN layer, a second AlN insertion layer, a second C-doped GaN layer, a third AlN insertion layer, an undoped GaN channel layer, a fourth AlN insertion layer, an AlGaN barrier layer, and a GaN capacitor layer, which are sequentially stacked from bottom to top; the stepped AlGaN stress release layer comprises a plurality of AlGaN layers with a molar content of Al component of 70%-20%, the molar content of Al component of each AlGaN layer decreases layer by layer from bottom to top, and the thickness of each AlGaN layer increases layer by layer from bottom to top.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing, and in particular to a silicon-based AlGaN / GaN HEMT epitaxial structure and a preparation method thereof. Background Art

[0002] To date, silicon (Si) materials account for a large proportion of the semiconductor market and play a major role in the development of semiconductor technology. However, due to the low theoretical limit of Si materials themselves, they cannot meet the current demand for low energy consumption. People have gradually turned their attention to the third-generation wide bandgap semiconductor materials with high thermal conductivity, high electron saturation velocity and high breakdown field strength.

[0003] As a typical third-generation semiconductor power device, GaN-HEMT benefits from the excellent properties of GaN materials such as wide bandgap, high electron saturation drift rate, and high critical breakdown electric field. It has a high-concentration, high-mobility two-dimensional electron gas at the AlGaN / GaN heterojunction, thus having the advantages of high power density, high breakdown voltage, and low on-resistance. Therefore, it is widely used in aerospace, 5G base stations, and new energy vehicles.

[0004] Si-based GaN has a higher cost advantage than SiC substrates and GaN self-supporting substrates. However, due to the large lattice mismatch and thermal mismatch coefficient between Si substrates and GaN, stress mismatch is gradually generated during epitaxy, forming a large number of dislocation groups in epitaxial growth, causing surface anomalies such as cracking of the epitaxial layer, which seriously hinders the electrical performance and reliability of GaN-HEMT under high power density working conditions.

[0005] Therefore, how to effectively reduce the lattice and stress mismatch through the design of the epitaxial structure, thereby reducing the crystal defects of Si-based GaN epitaxial materials, is the key to the application of Si-based GaN-HEMT in the RF and power fields. Summary of the invention

[0006] Purpose of the invention: In view of the above shortcomings, the present invention provides a silicon-based AlGaN / GaN HEMT epitaxial structure and a preparation method to reduce the lattice and stress mismatch during epitaxy and reduce the crystal defects of Si-based GaN epitaxial materials.

[0007] Technical solution: To solve the above problems, the present invention adopts a silicon-based AlGaN / GaN HEMT epitaxial structure, including a silicon substrate, an AlN buffer layer, a stepped AlGaN stress release layer, a GaN seed pad roughening layer, a GaN epitaxial layer, a first AlN insertion layer, a first C-doped GaN layer, a second AlN insertion layer, a second C-doped GaN layer, a third AlN insertion layer, an undoped GaN channel layer, a fourth AlN insertion layer, an AlGaN barrier layer, and a GaN capacitor layer stacked in sequence from bottom to top;

[0008] The stepped AlGaN stress release layer includes a plurality of AlGaN layers with an Al component molar content of 70%-20%, the Al component molar content of each AlGaN layer decreases layer by layer from bottom to top, and the thickness of each AlGaN layer increases layer by layer from bottom to top.

[0009] Furthermore, the stepped AlGaN stress release layer includes a high Al component AlGaN epitaxial layer, a medium Al component AlGaN epitaxial layer, and a low Al component AlGaN epitaxial layer, the molar content of Al component in the high Al component AlGaN epitaxial layer is 50%-70%, the molar content of Al component in the medium Al component AlGaN epitaxial layer is 40%-60%, and the molar content of Al component in the medium Al component AlGaN epitaxial layer is less than the molar content of Al component in the high Al component AlGaN epitaxial layer, and the molar content of Al component in the low Al component AlGaN epitaxial layer is 20%-30%.

[0010] Furthermore, the thickness of the high Al component AlGaN epitaxial layer is 50-100 nm, the thickness of the medium Al component AlGaN epitaxial layer is 100-200 nm, and the thickness of the low Al component AlGaN epitaxial layer is 500-600 nm.

[0011] Furthermore, the AlN buffer layer includes a first AlN buffer layer and a second AlN buffer layer, the first AlN buffer layer has an epitaxial thickness of 10-30 nm, and the second AlN buffer layer has an epitaxial thickness of 100-200 nm.

[0012] The present invention also provides a method for preparing the silicon-based AlGaN / GaN HEMT epitaxial structure, comprising the following steps:

[0013] S1, placing a silicon substrate into a reaction chamber, introducing hydrogen gas, and performing high-temperature surface passivation on the silicon substrate;

[0014] S2, stop the introduction of hydrogen, introduce trimethylaluminum into the reaction chamber, and pre-spread Al source on the surface of the silicon substrate;

[0015] S3, introducing ammonia gas into the reaction chamber, and then introducing trimethylaluminum to grow an AlN buffer layer on the silicon substrate;

[0016] S4, introducing ammonia, trimethylgallium, and trimethylaluminum into the reaction chamber, and growing a stepped AlGaN stress release layer on the AlN buffer layer by adjusting the amount of trimethylaluminum introduced;

[0017] S5, introducing ammonia and trimethylgallium into the reaction chamber to grow a GaN seed crystal pad roughening layer on the stepped AlGaN stress release layer;

[0018] S6, continuing to introduce ammonia and trimethylgallium into the reaction chamber to grow a GaN epitaxial layer on the GaN seed crystal roughening layer;

[0019] S7, introducing ammonia and trimethylaluminum into the reaction chamber to grow a first AlN insertion layer on the GaN epitaxial layer;

[0020] S8, introducing ammonia, trimethylgallium and ethylene into the reaction chamber, and setting the growth rate to step growth, and growing a first C-doped GaN layer on the basis of the first AlN insertion layer;

[0021] S9, introducing ammonia and trimethylaluminum into the reaction chamber to grow a second AlN insertion layer on the basis of the first C-doped GaN layer;

[0022] S10, introducing ammonia, trimethylgallium, and ethylene into the reaction chamber, and setting the growth rate to step growth, and growing a second C-doped GaN layer on the basis of the second AlN insertion layer;

[0023] S11, introducing ammonia and trimethylaluminum into the reaction chamber to grow a third AlN insertion layer on the second C-doped GaN layer;

[0024] S12, introducing ammonia and trimethylgallium into the reaction chamber to grow an undoped GaN channel layer on the third AlN insertion layer;

[0025] S13, introducing ammonia gas and trimethylaluminum into the reaction chamber to grow a fourth AlN insertion layer on the undoped GaN channel layer;

[0026] S14, introducing trimethylgallium and trimethylaluminum into the reaction chamber to grow an AlGaN barrier layer on the fourth AlN insertion layer;

[0027] S15, introducing ammonia and trimethylgallium into the reaction chamber to grow a GaN capacitor layer on the AlGaN barrier layer.

[0028] Furthermore, in step S3, the reaction chamber temperature is first set to 600°C-700°C and the reaction chamber pressure is 100 mbar to grow a first AlN buffer layer; then the reaction chamber temperature is set to 1000°C-1200°C and the reaction chamber pressure remains unchanged to grow a second AlN buffer layer, and the growth temperature of the first AlN buffer layer is lower than the growth temperature of the second AlN buffer layer.

[0029] Furthermore, in step S4, the reaction chamber temperature is 1200°C, the reaction chamber pressure is 100 mbar, and the amount of trimethylaluminum introduced is gradually reduced to generate a high Al component AlGaN epitaxial layer with an Al component molar content of 50%-70%, a medium Al component AlGaN epitaxial layer with an Al component molar content of 40%-60%, and a low Al component AlGaN epitaxial layer with an Al component molar content of 20%-30%.

[0030] Furthermore, in steps S8 and S10, the growth rate is divided into three stages, the growth rate in the first stage is 0.8-1.2 μm / h, the growth rate in the second stage is 2-3 μm / h, and the growth rate in the third stage is 3-5 μm / h. The growth thickness of the first C-doped GaN layer and the second C-doped GaN layer is 0.8-1.2 μm.

[0031] Furthermore, in steps S8 and S10, the temperature of the reaction chamber is 1100° C., and the pressure of the reaction chamber is 200 mbar.

[0032] Furthermore, in steps S7, S9, S11 and S13, the temperature of the reaction chamber is 1100°C and the pressure of the reaction chamber is 100 mbar.

[0033] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) the design of growing an AlGaN stress release layer with a gradient Al composition and thickness on a Si substrate effectively releases the stress caused by the lattice mismatch and different thermal expansion coefficients between the Si substrate and the GaN layer, reduces the lattice defects caused by the different lattice constants between the Si substrate and the GaN, reduces the probability of substrate breakage and cracking of the Si-based GaN epitaxial wafer during high-temperature growth, and lays a good foundation for the growth of the GaN layer and the AlGaN two-dimensional electron gas formation layer in the nitride thin film structure layer, and finally achieves the purpose of improving the quality of Si-based GaN epitaxial material and adjusting the surface flatness and morphology of the epitaxial wafer. The obtained GaN-HEMT epitaxial wafer has a high-quality heterostructure and a high-conductivity 2DEG. channel; (2) two AlN buffer layers are set, and the first AlN buffer layer is grown on the substrate at a lower temperature to better release the stress generated by the substrate during the heating process, and at the same time, it can provide nucleation sites for the second AlN buffer layer, which is conducive to the growth of the second AlN buffer layer; the second AlN buffer layer cooperates with the first AlGaN stress release layer structure to better relieve and release the tensile stress formed by the lattice mismatch between the Si substrate and GaN; (3) the growth rate of the first C-doped GaN layer is increased in a step-by-step manner, ensuring quality while improving growth efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the epitaxial structure of the silicon-based AlGaN / GaN HEMT of the present invention;

[0035] Figure 2 The XRD rocking curve diagram of the epitaxial wafer obtained in the embodiment of the present invention;

[0036] Figure 3 This is a diagram of the C doping content of the epitaxial wafer obtained in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The equipment used for the epitaxial structure growth of the present invention is a metal organic chemical vapor deposition (MOCVD) equipment, the carrier gas of the organic metal source is hydrogen and nitrogen, the organic metal source (Group III source) includes a gallium source and an aluminum source, the carbon source is acetylene (C2H4), the nitrogen source (Group V source) is ammonia (NH3), the gallium source is trimethylgallium (TMGa), and the aluminum source is trimethylaluminum (TMAl).

[0038] Example 1

[0039] A silicon-based AlGaN / GaN HEMT epitaxial structure and a preparation method in this embodiment include the following steps:

[0040] 1. Place a (111) lightly doped silicon wafer on a graphite tray and then put it into the reaction chamber of the MOCVD system; raise the temperature of the MOCVD reaction chamber to 1100°C, set the reaction chamber pressure to 100 mbar, and set the plate speed to 1000 r / h. Introduce hydrogen to perform high-temperature surface purification on the surface of the silicon substrate 1 for 300 seconds to remove oxygen impurities, open the surface suspended bonds, and make the surface full of activity.

[0041] 2. Stop the introduction of hydrogen, set the reaction chamber temperature to 900° C., the reaction chamber pressure to 50 mbar, introduce trimethylaluminum into the reaction chamber for 10 s, and pre-spread Al source on the surface of the silicon substrate 1.

[0042] 3. The reaction chamber temperature is set to 600° C., the reaction chamber pressure is set to 100 mbar, ammonia is introduced for pre-nitridation, and then trimethylaluminum is introduced to grow a first AlN buffer layer 2 on the basis of the silicon substrate 1, with an epitaxial thickness of about 10 nm.

[0043] 4. The reaction chamber temperature is set to 1000° C., the reaction chamber pressure is set to 100 mbar, and trimethylaluminum is continuously introduced to grow a second AlN buffer layer 3 on the basis of the first AlN buffer layer 2, with an epitaxial thickness of about 100 nm.

[0044] 5. The temperature of the reaction chamber is raised to 1200°C, the pressure of the reaction chamber is set to 100 mbar, ammonia, trimethylgallium and trimethylaluminum are introduced, and a high Al component AlGaN stress release layer 4 with an Al molar content of about 70% and a thickness of about 50 nm is grown on the basis of the second AlN buffer layer 3.

[0045] 6. Maintaining the temperature and pressure of the reaction chamber unchanged, reducing the amount of trimethylaluminum introduced, and growing a medium Al component AlGaN stress release layer 5 with an Al molar content of about 60% on the basis of the high Al component AlGaN stress release layer 4, with a thickness of about 100 nm.

[0046] 7. Maintaining the temperature and pressure of the reaction chamber unchanged, continue to reduce the amount of trimethylaluminum introduced, and grow a low Al component AlGaN stress release layer 6 with an Al molar content of about 30% on the basis of the medium Al component AlGaN stress release layer 5, with a thickness of about 500 nm.

[0047] 8. The temperature of the reaction chamber is lowered to 1100°C, the pressure of the reaction chamber is increased to 600 mbar, the rotation speed of the large disk is set to 600 r / h, ammonia and trimethylgallium are introduced, and a GaN seed crystal bedding roughening layer 7 with a thickness of about 100 nm is grown on the basis of the low Al component AlGaN stress release layer 6.

[0048] 9. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 200 mbar, set the rotation speed of the large plate to 1200 r / h, continue to introduce ammonia and trimethylgallium, and grow a GaN epitaxial layer 8 on the basis of the GaN seed crystal roughening layer 7, with a thickness of about 1000 nm.

[0049] 10. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a first AlN insertion layer 9 on the basis of the GaN epitaxial layer 8 with a thickness of about 10 nm.

[0050] 11. Keep the temperature of the reaction chamber unchanged, increase the pressure of the reaction chamber to 200 mbar, introduce ammonia, trimethylgallium and ethylene, and set the growth rate in three stages. The growth rate in the first stage is 0.8 μm / h, the growth rate in the second stage is 2 μm / h, and the growth rate in the third stage is 3 μm / h. Grow a first C-doped GaN layer 10 on the basis of the first AlN insertion layer 9 with a thickness of about 0.8 μm.

[0051] 12. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a second AlN insertion layer 11 on the basis of the first C-doped GaN layer 10 with a thickness of about 10 nm.

[0052] 13. Keep the temperature of the reaction chamber unchanged, increase the pressure of the reaction chamber to 200 mbar, introduce ammonia, trimethylgallium and ethylene, and set the growth rate in three stages. The growth rate in the first stage is 0.8 μm / h, the growth rate in the second stage is 2 μm / h, and the growth rate in the third stage is 3 μm / h. Grow a second C-doped GaN layer 12 on the basis of the second AlN insertion layer 11, with a thickness of about 0.8 μm.

[0053] 14. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a third AlN insertion layer 13 on the second C-doped GaN layer 12 with a thickness of about 10 nm.

[0054] 15. Keep the temperature of the reaction chamber unchanged, increase the pressure of the reaction chamber to 200 mbar, stop introducing ethylene, continue to introduce ammonia and trimethylgallium, and grow an undoped GaN channel layer 14 on the third AlN insertion layer 13 with a thickness of about 300 nm.

[0055] 16. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a fourth AlN insertion layer 15 on the undoped GaN channel layer 14 with a thickness of about 10 nm.

[0056] 17. The temperature of the reaction chamber is lowered to 1000° C., the pressure of the reaction chamber is maintained at 100 mbar, trimethylgallium and trimethylaluminum are introduced, and an AlGaN barrier layer 16 with an Al content of about 20% and a thickness of about 20 nm is grown on the fourth AlN insertion layer 15 .

[0057] 18. The temperature of the reaction chamber is raised to 1100° C., the pressure of the reaction chamber is increased to 150 mbar, ammonia and trimethylgallium are introduced, and a GaN capacitor layer 17 is grown on the AlGaN barrier layer 16 with a thickness of about 2 nm.

[0058] The final product is Figure 1 The epitaxial structure shown.

[0059] Example 2

[0060] A silicon-based AlGaN / GaN HEMT epitaxial structure and a preparation method in this embodiment include the following steps:

[0061] 1. Place a (111) lightly doped silicon wafer on a graphite tray and then put it into the reaction chamber of the MOCVD system; raise the temperature of the MOCVD reaction chamber to 1200°C, set the reaction chamber pressure to 150 mbar, and set the plate speed to 1100 r / h. Introduce hydrogen to perform high-temperature surface purification on the surface of the silicon substrate 1 for 400 seconds to remove oxygen impurities, open the surface floating bonds, and make the surface full of activity.

[0062] 2. Stop the introduction of hydrogen, set the reaction chamber temperature to 950° C., the reaction chamber pressure to 75 mbar, introduce trimethylaluminum into the reaction chamber for 20 seconds, and pre-spread Al source on the surface of the silicon substrate 1.

[0063] 3. The reaction chamber temperature is set to 650° C., the reaction chamber pressure is set to 100 mbar, ammonia is introduced for pre-nitridation, and then trimethylaluminum is introduced to grow a first AlN buffer layer 2 on the basis of the silicon substrate 1, with an epitaxial thickness of about 20 nm.

[0064] 4. The reaction chamber temperature is set to 1100° C., the reaction chamber pressure is set to 100 mbar, trimethylaluminum is continuously introduced, and a second AlN buffer layer 3 is grown on the basis of the first AlN buffer layer 2, with an epitaxial thickness of about 150 nm.

[0065] 5. The temperature of the reaction chamber is raised to 1200° C., the pressure of the reaction chamber is set to 100 mbar, ammonia, trimethylgallium and trimethylaluminum are introduced, and a high Al component AlGaN stress release layer 4 with an Al molar content of about 60% and a thickness of about 75 nm is grown on the basis of the second AlN buffer layer 3.

[0066] 6. Maintaining the temperature and pressure of the reaction chamber unchanged, reducing the amount of trimethylaluminum introduced, and growing a medium Al component AlGaN stress release layer 5 with an Al molar content of about 50% on the basis of the high Al component AlGaN stress release layer 4, with a thickness of about 150 nm.

[0067] 7. Maintaining the temperature and pressure of the reaction chamber unchanged, continue to reduce the amount of trimethylaluminum introduced, and grow a low Al component AlGaN stress release layer 6 with an Al molar content of about 25% on the basis of the medium Al component AlGaN stress release layer 5, with a thickness of about 550 nm.

[0068] 8. The temperature of the reaction chamber is lowered to 1100°C, the pressure of the reaction chamber is increased to 600 mbar, the rotation speed of the large disk is set to 600 r / h, ammonia and trimethylgallium are introduced, and a GaN seed crystal bedding roughening layer 7 with a thickness of about 150 nm is grown on the basis of the low Al component AlGaN stress release layer 6.

[0069] 9. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 200 mbar, set the rotation speed of the large plate to 1200 r / h, continue to introduce ammonia and trimethylgallium, and grow a GaN epitaxial layer 8 on the basis of the GaN seed crystal roughening layer 7, with a thickness of about 1300 nm.

[0070] 10. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a first AlN insertion layer 9 on the basis of the GaN epitaxial layer 8 with a thickness of about 10 nm.

[0071] 11. Keep the temperature of the reaction chamber unchanged, increase the pressure of the reaction chamber to 200 mbar, introduce ammonia, trimethylgallium and ethylene, and set the growth rate in three stages. The growth rate in the first stage is 1 μm / h, the growth rate in the second stage is 2.5 μm / h, and the growth rate in the third stage is 4 μm / h. Grow a first C-doped GaN layer 10 on the basis of the first AlN insertion layer 9 with a thickness of about 1 μm.

[0072] 12. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a second AlN insertion layer 11 on the basis of the first C-doped GaN layer 10 with a thickness of about 10 nm.

[0073] 13. Keep the temperature of the reaction chamber unchanged, increase the pressure of the reaction chamber to 200 mbar, introduce ammonia, trimethylgallium and ethylene, and set the growth rate in three stages. The growth rate in the first stage is 1 μm / h, the growth rate in the second stage is 2.5 μm / h, and the growth rate in the third stage is 4 μm / h. Grow a second C-doped GaN layer 12 on the basis of the second AlN insertion layer 11 with a thickness of about 1 μm.

[0074] 14. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a third AlN insertion layer 13 on the second C-doped GaN layer 12 with a thickness of about 15 nm.

[0075] 15. Keep the temperature of the reaction chamber unchanged, increase the pressure of the reaction chamber to 200 mbar, stop introducing ethylene, continue to introduce ammonia and trimethylgallium, and grow an undoped GaN channel layer 14 on the third AlN insertion layer 13 with a thickness of about 350 nm.

[0076] 16. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a fourth AlN insertion layer 15 on the undoped GaN channel layer 14 with a thickness of about 15 nm.

[0077] 17. The temperature of the reaction chamber is lowered to 1000° C., the pressure of the reaction chamber is maintained at 100 mbar, trimethylgallium and trimethylaluminum are introduced, and an AlGaN barrier layer 16 with an Al content of about 20% and a thickness of about 25 nm is grown on the fourth AlN insertion layer 15 .

[0078] 18. The temperature of the reaction chamber is raised to 1100° C., the pressure of the reaction chamber is increased to 200 mbar, ammonia and trimethylgallium are introduced, and a GaN capacitor layer 17 is grown on the AlGaN barrier layer 16 with a thickness of about 2.5 nm.

[0079] Example 3

[0080] A silicon-based AlGaN / GaN HEMT epitaxial structure and a preparation method in this embodiment include the following steps:

[0081] 1. Place a (111) lightly doped silicon wafer on a graphite tray and then put it into the reaction chamber of the MOCVD system; raise the temperature of the MOCVD reaction chamber to 1300°C, set the reaction chamber pressure to 200 mbar, and set the plate speed to 1200r / h. Introduce hydrogen to perform high-temperature surface purification on the surface of the silicon substrate 1 for 500s to remove oxygen impurities, open the surface floating bonds, and make the surface full of activity.

[0082] 2. Stop the introduction of hydrogen, set the reaction chamber temperature to 1000° C., the reaction chamber pressure to 100 mbar, introduce trimethylaluminum into the reaction chamber for 30 seconds, and pre-spread Al source on the surface of the silicon substrate 1.

[0083] 3. The reaction chamber temperature is set to 700° C., the reaction chamber pressure is set to 100 mbar, ammonia is introduced for pre-nitridation, and then trimethylaluminum is introduced to grow a first AlN buffer layer 2 on the basis of the silicon substrate 1, with an epitaxial thickness of about 30 nm.

[0084] 4. The reaction chamber temperature is set to 1200° C., the reaction chamber pressure is set to 100 mbar, and trimethylaluminum is continuously introduced to grow a second AlN buffer layer 3 on the basis of the first AlN buffer layer 2, with an epitaxial thickness of about 200 nm.

[0085] 5. The temperature of the reaction chamber is raised to 1200° C., the pressure of the reaction chamber is set to 100 mbar, ammonia, trimethylgallium and trimethylaluminum are introduced, and a high Al component AlGaN stress release layer 4 with an Al molar content of about 50% and a thickness of about 100 nm is grown on the basis of the second AlN buffer layer 3.

[0086] 6. Maintaining the temperature and pressure of the reaction chamber unchanged, reducing the amount of trimethylaluminum introduced, and growing a medium Al component AlGaN stress release layer 5 with an Al molar content of about 40% on the basis of the high Al component AlGaN stress release layer 4, with a thickness of about 200 nm.

[0087] 7. Maintaining the temperature and pressure of the reaction chamber unchanged, continue to reduce the amount of trimethylaluminum introduced, and grow a low Al component AlGaN stress release layer 6 with an Al molar content of about 20% on the basis of the medium Al component AlGaN stress release layer 5, with a thickness of about 600 nm.

[0088] 8. The temperature of the reaction chamber is lowered to 1100°C, the pressure of the reaction chamber is increased to 600 mbar, the rotation speed of the large plate is set to 600 r / h, ammonia and trimethylgallium are introduced, and a GaN seed crystal bedding roughening layer 7 with a thickness of about 200 nm is grown on the basis of the low Al component AlGaN stress release layer 6.

[0089] 9. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 200 mbar, set the rotation speed of the large plate to 1200 r / h, continue to introduce ammonia and trimethylgallium, and grow a GaN epitaxial layer 8 on the basis of the GaN seed crystal roughening layer 7, with a thickness of about 1500 nm.

[0090] 10. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a first AlN insertion layer 9 on the basis of the GaN epitaxial layer 8 with a thickness of about 10 nm.

[0091] 11. Keep the temperature of the reaction chamber unchanged, increase the pressure of the reaction chamber to 200 mbar, introduce ammonia, trimethylgallium and ethylene, and set the growth rate in three stages. The growth rate in the first stage is 1.2 μm / h, the growth rate in the second stage is 3 μm / h, and the growth rate in the third stage is 5 μm / h. Grow a first C-doped GaN layer 10 on the basis of the first AlN insertion layer 9 with a thickness of about 1.2 μm.

[0092] 12. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a second AlN insertion layer 11 on the basis of the first C-doped GaN layer 10 with a thickness of about 10 nm.

[0093] 13. Keep the temperature of the reaction chamber unchanged, increase the pressure of the reaction chamber to 200 mbar, introduce ammonia, trimethylgallium and ethylene, and set the growth rate in three stages. The growth rate in the first stage is 1.2 μm / h, the growth rate in the second stage is 3 μm / h, and the growth rate in the third stage is 5 μm / h. Grow a second C-doped GaN layer 12 on the basis of the second AlN insertion layer 11, with a thickness of about 1.2 μm.

[0094] 14. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a third AlN insertion layer 13 on the second C-doped GaN layer 12 with a thickness of about 20 nm.

[0095] 15. Keep the temperature of the reaction chamber unchanged, increase the pressure of the reaction chamber to 200 mbar, stop introducing ethylene, continue to introduce ammonia and trimethylgallium, and grow an undoped GaN channel layer 14 on the third AlN insertion layer 13 with a thickness of about 400 nm.

[0096] 16. Keep the temperature of the reaction chamber unchanged, reduce the pressure of the reaction chamber to 100 mbar, introduce ammonia and trimethylaluminum, and grow a fourth AlN insertion layer 15 on the undoped GaN channel layer 14 with a thickness of about 20 nm.

[0097] 17. The temperature of the reaction chamber is lowered to 1000° C., the pressure of the reaction chamber is maintained at 100 mbar, trimethylgallium and trimethylaluminum are introduced, and an AlGaN barrier layer 16 with an Al content of about 20% and a thickness of about 30 nm is grown on the fourth AlN insertion layer 15 .

[0098] 18. The temperature of the reaction chamber is raised to 1100° C., the pressure of the reaction chamber is increased to 300 mbar, ammonia and trimethylgallium are introduced, and a GaN capacitor layer 17 is grown on the AlGaN barrier layer 16 with a thickness of about 3 nm.

[0099] See also Figure 2 As shown, the red, green and blue colors correspond to the XRD rocking curves of the Si-based GaN-HEMT epitaxial wafers obtained in Examples 1, 2 and 3, respectively. It can be seen from the figure that the GaN and AlGaN peaks of the obtained XRD graph are sharp and clear. There is no obvious difference in the test results of the epitaxial structures obtained in the three examples.

[0100] See also Figure 3 As shown, the C doping concentration of the C-GaN epitaxial layer is between 1E18 and 1E19 (at / cm3).

[0101] For the Si-based GaN-HEMT epitaxial wafer obtained in Example 1 of the present invention, the electron mobility, surface density and sheet resistance of the AlGaN / GaN heterointerface two-dimensional electron gas 2DEG (two-dimensional electron gas) were measured by Hall measurement at room temperature, and were 2200 cm2 / V•s, 9×10-12 / cm2, and 400 Ω / □, respectively, with a high-quality heterostructure and a high-conductivity 2DEG channel.

[0102] In summary, the present invention adopts the design of growing an AlGaN stress release layer with a step-by-step gradient of Al composition and thickness on a Si substrate, which effectively releases the stress caused by the lattice mismatch between the Si substrate and the GaN layer and the different thermal expansion coefficients, reduces the lattice defects caused by the different lattice constants between the Si substrate and the GaN, and reduces the probability of substrate breakage and cracking of the Si-based GaN epitaxial wafer during the high-temperature growth process, lays a good foundation for the growth of the GaN layer and the AlGaN two-dimensional electron gas formation layer in the nitride thin film structure layer, and ultimately achieves the purpose of improving the quality of Si-based GaN epitaxial materials and adjusting the surface flatness and morphology of the epitaxial wafer. The resulting GaN-HEMT epitaxial wafer has a high-quality heterostructure and a highly conductive 2DEG channel.

Claims

1. A silicon-based AlGaN / GaN HEMT epitaxial structure, characterized in that: The invention comprises a silicon substrate, an AlN buffer layer, a stepped AlGaN stress release layer, a GaN seed crystal paving roughening layer (7), a GaN epitaxial layer (8), a first AlN insertion layer (9), a first C-doped GaN layer (10), a second AlN insertion layer (11), a second C-doped GaN layer (12), a third AlN insertion layer (13), an undoped GaN channel layer (14), a fourth AlN insertion layer (15), an AlGaN barrier layer (16), and a GaN capacitor layer (17) which are stacked in sequence from bottom to top; the first C-doped GaN layer (10) and the second C-doped GaN layer (12) have a growth thickness of 0.8-1.2 μm; The stepped AlGaN stress release layer comprises a plurality of AlGaN layers with an Al component molar content of 70%-20%, the Al component molar content of each AlGaN layer decreases layer by layer from bottom to top, and the thickness of each AlGaN layer increases layer by layer from bottom to top; the stepped AlGaN stress release layer comprises a high Al component AlGaN epitaxial layer (4), a medium Al component AlGaN epitaxial layer (5), and a low Al component AlGaN epitaxial layer (6), the high Al component AlGaN epitaxial layer (4) has a thickness of 50-100nm, the medium Al component AlGaN epitaxial layer (5) has a thickness of 100-200nm, and the low Al component AlGaN epitaxial layer (6) has a thickness of 500-600nm.

2. The silicon-based AlGaN / GaN HEMT epitaxial structure according to claim 1, characterized in that: The molar content of the Al component in the high Al component AlGaN epitaxial layer (4) is 50%-70%, the molar content of the Al component in the medium Al component AlGaN epitaxial layer (5) is 40%-60%, and the molar content of the Al component in the medium Al component AlGaN epitaxial layer (5) is less than the molar content of the Al component in the high Al component AlGaN epitaxial layer (4), and the molar content of the Al component in the low Al component AlGaN epitaxial layer (6) is 20%-30%.

3. The silicon-based AlGaN / GaN HEMT epitaxial structure according to claim 1, characterized in that: The AlN buffer layer comprises a first AlN buffer layer (2) and a second AlN buffer layer (3); the first AlN buffer layer (2) has an epitaxial thickness of 10-30 nm, and the second AlN buffer layer (3) has an epitaxial thickness of 100-200 nm.

4. A method for preparing a silicon-based AlGaN / GaN HEMT epitaxial structure according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, placing a silicon substrate into a reaction chamber, introducing hydrogen gas, and performing high-temperature surface passivation on the silicon substrate; S2, stop the introduction of hydrogen, introduce trimethylaluminum into the reaction chamber, and pre-spread Al source on the surface of the silicon substrate; S3, introducing ammonia gas into the reaction chamber, and then introducing trimethylaluminum to grow an AlN buffer layer on the silicon substrate; S4, introducing ammonia, trimethylgallium, and trimethylaluminum into the reaction chamber, and growing a stepped AlGaN stress release layer on the AlN buffer layer by adjusting the amount of trimethylaluminum introduced; S5, introducing ammonia and trimethylgallium into the reaction chamber to grow a GaN seed crystal pad roughening layer (7) on the stepped AlGaN stress release layer; S6, continuing to introduce ammonia and trimethylgallium into the reaction chamber to grow a GaN epitaxial layer (8) on the GaN seed crystal roughening layer (7); S7, introducing ammonia gas and trimethylaluminum into the reaction chamber to grow a first AlN insertion layer (9) on the GaN epitaxial layer (8); S8, introducing ammonia, trimethylgallium and ethylene into the reaction chamber, and setting the growth rate to be step growth, and growing a first C-doped GaN layer (10) on the basis of the first AlN insertion layer (9); S9, introducing ammonia gas and trimethylaluminum into the reaction chamber to grow a second AlN insertion layer (11) on the basis of the first C-doped GaN layer (10); S10, introducing ammonia, trimethylgallium and ethylene into the reaction chamber, and setting the growth rate to step growth, and growing a second C-doped GaN layer (12) on the basis of the second AlN insertion layer (11); S11, introducing ammonia gas and trimethylaluminum into the reaction chamber to grow a third AlN insertion layer (13) on the second C-doped GaN layer (12); S12, introducing ammonia gas and trimethylgallium into the reaction chamber to grow an undoped GaN channel layer (14) on the third AlN insertion layer (13); S13, introducing ammonia gas and trimethylaluminum into the reaction chamber to grow a fourth AlN insertion layer (15) on the undoped GaN channel layer (14); S14, introducing trimethylgallium and trimethylaluminum into the reaction chamber to grow an AlGaN barrier layer (16) on the fourth AlN insertion layer (15); S15, introducing ammonia gas and trimethylgallium into the reaction chamber to grow a GaN capacitor layer (17) on the AlGaN barrier layer (16).

5. The preparation method according to claim 4, characterized in that: In step S3, the reaction chamber temperature is first set to 600°C-700°C and the reaction chamber pressure is set to 100 mbar to grow a first AlN buffer layer (2); the reaction chamber temperature is then set to 1000°C-1200°C and the reaction chamber pressure remains unchanged to grow a second AlN buffer layer (3), the growth temperature of the first AlN buffer layer (2) being lower than the growth temperature of the second AlN buffer layer (3).

6. The preparation method according to claim 4, characterized in that: In step S4, the reaction chamber temperature is 1200° C., the reaction chamber pressure is 100 mbar, and the amount of trimethylaluminum introduced is gradually reduced to generate a high Al component AlGaN epitaxial layer (4) with an Al component molar content of 50%-70%, a medium Al component AlGaN epitaxial layer (5) with an Al component molar content of 40%-60%, and a low Al component AlGaN epitaxial layer (6) with an Al component molar content of 20%-30%.

7. The preparation method according to claim 4, characterized in that: In steps S8 and S10, the growth rate is divided into three stages, the growth rate in the first stage is 0.8-1.2 μm / h, the growth rate in the second stage is 2-3 μm / h, and the growth rate in the third stage is 3-5 μm / h.

8. The preparation method according to claim 4, characterized in that: In steps S8 and S10, the temperature of the reaction chamber is 1100° C. and the pressure of the reaction chamber is 200 mbar.

9. The preparation method according to claim 4, characterized in that: In steps S7, S9, S11 and S13, the temperature of the reaction chamber is 1100°C and the pressure of the reaction chamber is 100 mbar.

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