CN108550518B - Method for growing superlattice insertion layer for relieving/eliminating aluminum gallium nitrogen film surface cracks by adopting molecular beam epitaxy technology - Google Patents

Method for growing superlattice insertion layer for relieving/eliminating aluminum gallium nitrogen film surface cracks by adopting molecular beam epitaxy technology Download PDF

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CN108550518B
CN108550518B CN201810440768.9A CN201810440768A CN108550518B CN 108550518 B CN108550518 B CN 108550518B CN 201810440768 A CN201810440768 A CN 201810440768A CN 108550518 B CN108550518 B CN 108550518B
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insertion layer
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CN108550518A (en
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刘斌
李振华
谢自力
吴耀政
陶涛
修向前
施毅
张�荣
郑有炓
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Nanjing University
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Abstract

The invention discloses a method for growing a superlattice insertion layer for relieving/eliminating cracks on the surface of an aluminum gallium nitrogen film by adopting a molecular beam epitaxy technology, wherein a GaN epitaxial layer is homoepitaxially grown on a substrate by using the molecular beam epitaxy technology through controlling growth parameters, and the superlattice insertion layer is epitaxially grown on the GaN epitaxial layer by using the molecular beam epitaxy technology through controlling the growth parameters; using molecular beam epitaxy technique, by controlling growth parameters, a layer of Al is epitaxially grown on the superlattice insertion layerxGa(1‑x)And (6) N thin films. The invention adopts molecular beam epitaxy technology to form GaN epitaxial layer and AlxGa(1‑x)A superlattice insertion layer is grown between the N thin film layers, so that Al can be relieved/eliminatedxGa(1‑x)The surface of the N film is cracked. The invention also can conveniently, quickly and accurately control the opening and closing states of the Ga source and the Al source baffle and the flow of the nitrogen by designing a program, can solve the problems of inconvenience, errors and the like caused by manual control, and further realizes the epitaxial growth of the high-quality superlattice insertion layer.

Description

Method for growing superlattice insertion layer for relieving/eliminating aluminum gallium nitrogen film surface cracks by adopting molecular beam epitaxy technology
Technical Field
The invention relates to a method for growing a superlattice insertion layer for relieving/eliminating cracks on the surface of an aluminum gallium nitrogen film by adopting a molecular beam epitaxy technology, belonging to the technical field of semiconductor materials.
Background
The III group nitride semiconductor material system refers to InN, GaN, AlN and ternary and quaternary alloy materials formed by the InN, GaN and AlN. Group III nitride as a third-generation semiconductor material has excellent properties such as large forbidden band width, high electron drift saturation velocity, small dielectric constant, good thermal conductivity, and chemical corrosion resistance (document 1: Wang Dangyou. group III nitride semiconductor epitaxial layer thin film growth and characterization research [ D)]The university of sienna electronics, 2012). As a ternary alloy in a group III nitride semiconductor, Al changes with Al compositionxGa(1-x)The forbidden bandwidth of N can be continuously changed from 3.4eV of GaN to 6.2eV of AlN, and the corresponding wavelength change is 210nm-365 nm. Thus, AlxGa(1-x)The N material and the heterojunction structure thereof have very wide application in the field of photoelectron and microelectronic devices of ultraviolet wave bands, and can be used for manufacturing devices such as ultraviolet light emitting diodes, ultraviolet laser diodes, ultraviolet photoelectric detectors, high mobility transistors and the like (document 2: Liyao, molecular beam epitaxial growth of high Al component AlGaN thin film and characterization thereof [ D]Chongqing university, 2012). Due to GaN and AlxGa(1-x)Large lattice mismatch exists between N, so that AlxGa(1-x)The N/GaN heterojunction structure material generates strain, and dislocation and cracks are generated by strain release. Thus, AlxGa(1-x)The problems of epitaxial growth quality and stress control of an N material heterojunction structure are difficult technical problems in the current research of III group nitride semiconductor materials.
To address this problem, researchers at home and abroad have developed different methods and techniques. The insertion layer technology is the regulation and control Al which is widely researched at presentxGa(1-x)Method of N heterojunction stress. The mainstream insertion layers mainly include a low-temperature AlN insertion layer, a high-temperature AlN insertion layer, a superlattice insertion layer, and the like. Kamiyam S et Al report that low temperature AlN insertion layer technology regulates Al grown on GaN substratexGa(1-x)Method for stressing N thin film (document 3: Kamiyama S, Iwaya M, Hayashi N, etment of AlGaN/GaNheterostructure[J]Journal of Crystal Growth 2001,223(1-2): 83-91). In-Hwan Lee et Al reported that the technique of preparing high temperature AlN insertion layer by MOVPE method regulates Al grown on GaN substratexGa(1-x)Method for stress of N thin film (document 4: Lee I H, Kim T G, Park Y.growth of crack-free AlGaN film on high-temperature in AlN interlayer [ J ]]Journal of CrystalGrowth,2002, 234 (2-3): 305-. At present, the disclosure relates to AlxGa(1-x)The patented technology for N film growth mainly uses AlN insert layer technology to regulate and control AlxGa(1-x)Stress of N thin film (see Chinese patent: CN101538730A, 106350783A). From the patents published in China at present, the most adopted method is to grow Al by MOCVD or MOVPE technologyxGa(1-x)N thin films are not much related to Molecular Beam Epitaxy (MBE) technology.
The superlattice insertion layer technology is stress relief and Al reductionxGa(1-x)A very efficient method for defects in N thin films. The Molecular Beam Epitaxy (MBE) technology is a highly controllable material growth technology, which improves the thickness control precision of a grown film material from micron level to single atomic layer scale and has great advantages in the preparation of superlattice structures (document 5: slow-formed InAs/GaSb II type superlattice detector structure MBE growth research [ D]Graduate institute of Chinese academy of sciences (Shanghai institute of technology and physics), 2014.). Compared with the traditional Superlattice technology, the Digital Graded Superlattice technology does not need to change the temperature of a source furnace (MBE growth) or the flow of a gas source (MOCVD growth), only needs to change the thickness ratio of a well layer and a barrier layer, can realize the Superlattice structure with a step-shaped Graded component and a good interface, has better stability in a growth mode, can effectively reduce dislocation of the heterojunction structure caused by lattice mismatch, and improves the epitaxial quality. In the literature, 1991, Wei Gao et al reported the use of MBE to epitaxially grow In0.53Ga0.47As/In0.52Al0.48Work on the As digital gradient superlattice structures (document 7: Gao W, Berger P R, Zydzik G J, et. in 0.53 Ga 0.47 As MSM photodiodes with transparent CTO Schottky contactsand digital superlattice grading[J]IEEE Transactions on Electron Devices,1997,44(12): 2174-. Jung-Hee Lee et Al, 1999 and 2001, reported epitaxial GaAs/Al with MBE0.15Ga0.85The related work on As digital gradient superlattice structures (document 8: Lee J H, Li S, Tidrow M Z, et. Quantum-well-induced photodetectors with digital graded superlattice for long-wavelength and broadband detection [ J]Applied Physics letters,1999,75(20): 3207-: lee J H, Li S, Tidrow M Z, et al, investment of Multi-color, broadband and quaternary well-induced photodetectant switch digital graded super barrier and linear-graded barrier for longwave induced applications].Infrared Physics&Technology,2001,42(3): 123-. In 2003, Ming-Kwen Tsai et Al reported epitaxial epitaxy of GaAs/Al using MOCVD0.45Ga0.55Work on As digital gradient superlattice structures (document 10: Tsai M K, Tan S W, Wu Y W, et Al. improvements-current characteristics of Al 0.45 Ga 0.55 As-GaAs digital-graded-upper-estimate HBTs with reduced turn-on voltage by wet oxidation [ J ] of]Electron Devices IEEE Transactions on,2003,50(2): 303-. In 2009, Wangkai et al reported epitaxy of In using MBE0.78Al0.22As/In0.78Ga0.22Work related to As digital gradient superlattice structure (document 11: Wangkai, Zhang Yonggang, consider overflow, etc.. improvement of heterointerface digital gradient superlattice on performance of extended wavelength InGaAs photodetector [ J]Infrared and millimeter wave bulletins, 2009,28(6): 405-. In the published patents, there are patents relating to a digitally-graded superlattice using MBE epitaxial AlInSb structures (see foreign patent: WO2005086868A2), epitaxial InAs/InAsSb and InAs/Ga (in) Sb digitally-graded superlattice structures (see foreign patent: EP2933845A2) and MOCVD epitaxial AlGaN digitally-graded superlattice structures (see foreign patent: US6618413B 2).
In conclusion, in the existing domestic and foreign documents and patents, MBE epitaxial digital gradient Al composition [ GaN/Al ] is rarely usedxGa(1-x)N]mPatterns of superlattice insertion layersExamples are reported. Thus, the use of molecular beam epitaxy techniques to grow superlattice insertion layers, particularly with a numerical gradient of Al composition [ GaN/Al ]xGa(1-x)N]mSuperlattice insertion layer to mitigate/eliminate AlxGa(1-x)The N thin film stress has important technical value.
Disclosure of Invention
The invention aims to provide a method for growing a film by using molecular beam epitaxy technology for relieving/eliminating (Al)xGa(1-x)N) a superlattice insertion layer with cracks on the surface of the film.
The purpose of the invention is realized by the following technical scheme:
a method for growing a superlattice insertion layer for relieving/eliminating cracks on the surface of an AlGaN film by adopting a molecular beam epitaxy technology comprises the following steps:
1) selecting a substrate, and carrying out pretreatment before epitaxial growth on the substrate;
2) a molecular beam epitaxy technology is used, and a GaN epitaxial layer is homoepitaxially grown on the substrate by controlling growth parameters;
3) extending a superlattice insertion layer on the GaN epitaxial layer by using a molecular beam epitaxy technology and controlling growth parameters;
4) using molecular beam epitaxy technique, by controlling growth parameters, a layer of Al is epitaxially grown on the superlattice insertion layerxGa(1-x)Thin film of N, AlxGa(1-x)The Al component x of the N film is 0.2-0.55, and the thickness is 150-180 nm.
Preferably, in step 3), the superlattice insertion layer is [ GaN/AlN ]]nThe structure is characterized in that the thickness of the AlN sublayer is gradually changed, the growth time of the AlN sublayer is changed from 4min to 2min, and n is 15-25; or the AlN sub-layer has non-gradient thickness and n is 10-15.
Preferably, in step 3), the superlattice insertion layer is [ GaN/Al ]xGa(1-x)N]mStructure of wherein AlxGa(1-x)The thickness of the N sublayer is gradually changed, AlxGa(1-x)The growth time of the N sublayer is changed from 4min to 2min, and m is 15-25; or AlxGa(1-x)N sublayers have a thickness ofNon-gradual change thickness, m is 10-15; al (Al)xGa(1-x)The value range of the Al component x of the N sublayer is 0.2-0.55.
Preferably, when Al is presentxGa(1-x)When the thickness of the N sublayer is non-gradient, the thickness of the GaN sublayer is also non-gradient, [ GaN/Al ]xGa(1-x)N]mThe superlattice insertion layer is a digital gradient insertion layer with digital gradient [ GaN/Al ]xGa(1-x)N]mThe number of cycles of the superlattice insertion layer is 10, AlxGa(1-x)The thickness ratio of the N sublayer to the GaN sublayer is 10:1, 9:2 … … 2:9, 1:10 from cycle 1 to cycle 10.
Preferably, in step 3), [ GaN/Al ] is realized by alternately changing the open and closed states of the Ga source and Al source bafflesxGa(1-x)N]mOr [ GaN/AlN]nAnd (3) alternately growing each sublayer of the superlattice insertion layer, wherein the growth parameters of the epitaxial superlattice insertion layer are as follows: epitaxy of [ GaN/AlxGa(1-x)N]mThe growth temperature of the superlattice insertion layer is 820-840 ℃, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, Al source beam flux of 1.3X 10-8-9.2×10-8Torr, nitrogen flow of 0.5-0.9sccm, GaN sub-layer growth time of 1-2 min, AlxGa(1-x)The growth time of the N sublayer is 2min30s-3min30s, and the GaN/AlN is epitaxial]nThe growth temperature of the superlattice insertion layer is 820-840 ℃, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, Al source beam flux of 7.0X 10-8Torr, the flow of nitrogen is 0.5-0.9sccm when growing a GaN sublayer in the superlattice, the flow of nitrogen is 0.2-0.3sccm when growing an AlN sublayer in the superlattice, the flow of nitrogen is reduced from 0.5-0.9sccm to 0.2-0.3sccm, the baffle plates of the Ga source and the Al source are kept in a closed state, the time of the whole process of reducing the flow of nitrogen is 8-12s, the growth time of the GaN sublayer is 1-2 min, the growth time of the AlN layer is 2-4 min, and the radio frequency power of a plasma generator is 400-500W.
Preferably, in step 3), epitaxial digital gradient [ GaN/Al ] is realized by alternately changing the open and closed states of the Ga source and Al source bafflesxGa(1-x)N]mIntersection of sub-layers of superlattice insertion layerAnd growing the epitaxial superlattice insertion layer by the following growing parameters: epitaxial digital gradient [ GaN/Al ]xGa(1-x)N]mThe growth temperature of the superlattice insertion layer is 820-840 ℃, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, Al source beam flux of 1.3X 10-8-9.2×10-8Torr, nitrogen flow of 0.5-0.9sccm, GaN sub-layer growth time of 1-2 min, AlxGa(1-x)The growth time of the N sublayer is 2min30s-3min30s, the radio frequency power of the plasma generator is 400-500W, and the epitaxial digital gradient [ GaN/Al-xGa(1-x)N]mIn the process of growing the superlattice insertion layer, the Ga source baffle is always kept in an open state, and Al with different thicknesses is obtained by controlling the time for keeping the open state of the Al source bafflexGa(1-x)N sublayer, GaN sublayers with different thicknesses are obtained by controlling the time for keeping the closed state of the Al source baffle plate, so that Al is enabled to be in contact with the GaN sublayersxGa(1-x)The thickness ratio of N to GaN sublayers ranges from cycle 1 to cycle 10 to 10, 10:1, 9:2 … … 2:9, 1:10, and two Al sources are used for alternately performing odd-numbered cycles and even-numbered cycles of AlxGa(1-x)And growing an N sublayer, and keeping the Al source beam current consistent.
Preferably, in step 3), the duration required to turn off the Ga source or Al source shutter is set to 3 to 7 s.
Preferably, in step 4), the epitaxial layer of Al is formedxGa(1-x)The growth parameters of the N film are as follows: the growth temperature is 850-870 DEG, the Ga source beam flux is 5.6 multiplied by 10-7Torr, Al source beam flux of 1.3X 10-8-9.2×10-8Torr, the flow rate of nitrogen gas is 0.5-0.9sccm, and the RF power of the plasma generator is 400-500W.
Preferably, in step 1), the substrate is an undoped GaN thick film heteroepitaxial on a sapphire substrate by a hydride vapor phase epitaxy method, and the GaN substrate obtained by stripping has a diameter of 50.8 +/-1 mm, a thickness of about 430 μm and a dislocation density of less than 5 × 106cm-2The surface roughness is less than 0.6 nm; the substrate pretreatment method comprises evaporating 1.3 μm thick metal Ti on the back of GaN substrate by physical vapor deposition at a deposition rate of 12nm/min,after the back surface is plated with titanium, the substrate is sequentially cleaned by acetone, alcohol and deionized water, the substrate is blown dry by nitrogen after cleaning, then the substrate is placed into a degassing chamber of MBE equipment, and surface degassing treatment is carried out on the substrate for at least 30min at the temperature of 450 ℃.
Preferably, in step 2), the growth parameters of the homoepitaxial GaN epitaxial layer are as follows: the growth temperature is 810--7Torr, the flow rate of nitrogen is 0.5-0.9sccm, the RF power of the plasma generator is 400-500W, and the thickness of the GaN epitaxial layer is 400-800 nm.
The invention adopts molecular beam epitaxy technology to form GaN epitaxial layer and AlxGa(1-x)A superlattice insertion layer is grown between the N thin film layers, so that Al can be relieved/eliminatedxGa(1-x)The surface of the N film is cracked. Through designing a program, the opening and closing states of the Ga source baffle and the Al source baffle and the flow of nitrogen can be conveniently, quickly and accurately controlled, the problems of inconvenience, errors and the like caused by manual control can be solved, and the epitaxial growth of a high-quality superlattice insertion layer is further realized. The invention also provides a method for growing a superlattice insertion layer with a gradually changed thickness to relieve/eliminate AlxGa(1-x)The surface of the N film is cracked. The invention also provides a method for growing the [ GaN/Al ] with digital gradient by adopting the molecular beam epitaxy technologyxGa(1-x)N]mThe method of the superlattice insertion layer uses a double-Al source control method, so that the frequency of frequent switching of a single-Al source baffle is greatly reduced, and the stability and the safety of equipment are ensured. The current patents and literature are rarely concerned with mitigating/eliminating Al with respect to the use of superlattice insertion layers with graded Al compositions and graded thicknessesxGa(1-x)And reporting surface cracks of the N thin film.
Drawings
FIG. 1 shows Al with superlattice insertion layer according to the inventionxGa(1-x)And the epitaxial structure of the N/GaN heterojunction structure is shown schematically.
FIG. 2 is a schematic diagram of an inventive method for Al mitigation/elimination using molecular beam epitaxyxGa(1-x)Superlattice insertion layer with N-shaped film surface cracksAccording to the RHEED pattern according to which the nitrogen flow rate is adjusted.
FIG. 3 is a schematic representation of a molecular beam epitaxy technique for Al mitigation/elimination in accordance with the present inventionxGa(1-x)The flow chart of the designed program in the method of the superlattice insertion layer with N-film surface cracks is shown schematically.
FIG. 4 is a graphical representation of the results of X-ray diffractometer ω -2 θ measurements of the samples of example 1.
FIG. 5 is a graphical representation of the results of X-ray diffractometer ω -2 θ measurements of the sample of example 2.
FIG. 6 is a graphical comparison of the statistical results of the surface crack density and crack spacing for the comparative example 1 sample, examples 1-2 samples.
FIG. 7 is a schematic diagram comparing Scanning Electron Microscope (SEM) photographs of the surfaces of a sample of comparative example 1 and samples of examples 1-3.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Example 1
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to 450W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was warmed to 820 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the duration required for the closing of the Ga source shutter was set to 5s, and the time of change (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.7 sccm.
After the nitrogen flow is debugged and determined, a program is designed and operated, and the structure starts to grow. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 820 ℃, the power of the plasma generator was 450W, the Ga source baffle was kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, the Al source shutter was kept in a closed state, the flow rate of nitrogen gas was kept at 0.7sccm, and the thickness of the GaN epitaxial layer was 400 nm. Next, [ GaN/Al ] as shown in FIG. 1 was grownxGa(1-x)N]m(the number of cycles m of the superlattice in this embodiment is 10) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart of fig. 3. Wherein S2 is GaN/Al grown for one periodxGa(1-x)N structure, S3 was grown 10 times for the set cycle. At S2, the substrate temperature is 820 deg.C, and when GaN sub-layer is grown as 31 in FIG. 1, the Ga source baffle is kept open, and the Ga source beam current is 5.6 × 10-7Torr, Al source baffle plate is kept in a closed state, the growth time of GaN sublayer is 2min, and Al growsxGa(1-x)When the N sublayers are 32 in FIG. 1, the Ga source baffle is kept open, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, Al sourceThe baffle is also kept open, and the flow rate of the Al source beam is 9.2 multiplied by 10-8Torr，AlxGa(1-x)The growth time of the N sublayer is 3min, the flow of nitrogen is kept at 0.7sccm, and Al is addedxGa(1-x)The Al component x of the N sublayer is 0.55, and the GaN sublayer and the Al are alternately grownxGa(1-x)The duration required for the Al source shutter to close during the transition of the N sublayer was set to 5 s. Then, as in S4 in the program flowchart shown in fig. 3, the Ga source and Al source shutters were closed, and the duration required for the closing of the Ga source and Al source shutters was set to 5S, and the substrate temperature was increased to 860 ℃ at a rate of 10 ℃/min. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as shown in S5 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was kept at 860 deg.C, the power of the plasma generator was 450W, the Ga source shutter was kept open, the Al source shutter was also kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, Al source beam flux of 7.0X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.7sccm, and Al was addedxGa(1-x)The thickness of the N film is 180nm, and AlxGa(1-x)The Al composition x of the N thin film was 0.40.
Example 2
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to 450W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was warmed to 820 ℃. Holding a Ga source beamFlow 5.6X 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the buffer time required for the closing of the Ga source shutter was set to 5s, and the change time (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.65 sccm.
After the nitrogen flow is debugged and determined, a program is designed and operated, and the structure starts to grow. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 820 ℃, the power of the plasma generator was 450W, the Ga source baffle was kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, the Al source shutter was kept in a closed state, the flow rate of nitrogen gas was kept at 0.65sccm, and the thickness of the GaN epitaxial layer was 400 nm. Next, [ GaN/AlN ] as shown in FIG. 1 was grown]n(the number of cycles n of the superlattice in this embodiment is 10) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart of fig. 3. Where S2 is a GaN/AlN structure grown for one period, and S3 is a set-up cyclic growth 10 times. At S2, the substrate temperature is 820 deg.C, and when GaN sub-layer is grown as 31 in FIG. 1, the Ga source baffle is kept open, and the Ga source beam current is 5.6 × 10-7Keeping the Al source baffle in a closed state, keeping the flow of nitrogen at 0.65sccm, keeping the growth time of the GaN sublayer at 2min, keeping the baffles of the Ga source and the Al source in a closed state before growing the AlN sublayer, reducing the flow of nitrogen from 0.65sccm to 0.2sccm, keeping the duration of the process of reducing the flow of nitrogen at about 8-12s, keeping the Ga source baffle in a closed state when growing the AlN sublayer such as 32 in FIG. 1, keeping the Al source baffle in an open state, and keeping the flow of the Al source beam at 7.0 x 10-8Torr, the growth time of AlN layer is 3min, in the conversion process of alternatively growing GaN layer and AlN layer,the duration required for the Al source shutter to close was set to 5 s. Then, as in S4 in the program flowchart shown in fig. 3, the Ga source and Al source shutters were closed, and the buffer times required for the closing of the Ga source and Al source shutters were each set to 5S, and the substrate temperature was increased to 860 ℃ at a rate of 10 ℃/min. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as shown in S5 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was kept at 860 deg.C, the power of the plasma generator was 450W, the Ga source shutter was kept open, the Al source shutter was also kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, Al source beam flux of 7.0X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.65sccm, and Al was addedxGa(1-x)The thickness of the N thin film is 180 nm.
Example 3
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to 450W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was warmed to 820 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the duration required for the closing of the Ga source shutter was set to 5s, and the time of change (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the variation time is within 6-20sThen, the nitrogen flow rate is maintained and the next step is continued. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.7 sccm.
After the nitrogen flow is debugged and determined, a program is designed and operated, and the structure starts to grow. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 820 ℃, the power of the plasma generator was 450W, the Ga source baffle was kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, the Al source shutter was kept in a closed state, the flow rate of nitrogen gas was kept at 0.7sccm, and the thickness of the GaN epitaxial layer was 400 nm. Next, [ GaN/AlN ] as shown in FIG. 1 was grown]n(the number of cycles n of the superlattice is 14 in this embodiment) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart of fig. 3. Where S2 is a GaN/AlN structure grown for one period, and S3 is a set-cycle growth of 14 times. At S2, the substrate temperature is 820 deg.C, and when GaN sub-layer is grown as 31 in FIG. 1, the Ga source baffle is kept open, and the Ga source beam current is 5.6 × 10-7Keeping the Al source baffle in a closed state, keeping the flow of nitrogen at 0.7sccm, keeping the growth time of the GaN sublayer at 1min30s, keeping the baffles of the Ga source and the Al source in a closed state before growing the AlN sublayer, reducing the flow of nitrogen from 0.7sccm to 0.3sccm, wherein the buffer time of the nitrogen flow reduction process is about 8-12s, keeping the Ga source baffle in a closed state when growing the AlN sublayer, keeping the Al source baffle in an open state when growing the AlN sublayer as shown in 32 in FIG. 1, and keeping the flow of the Al source beam at 7.0 x 10-8Torr, AlN layer growth time was 2min, and the buffer time required for the closing of the Al source shutter during the transition between the alternate growth of the GaN layer and AlN layer was set to 5 s. Then, as in S4 in the flowchart of the routine shown in fig. 3, the Ga source and Al source shutters were closed, and the duration required for the closing of the Ga source and Al source shutters was set to 5S, and the substrate temperature was raised to 860 ℃ at a rate of 10 °/min. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as in S5 of the flowchart of the routine shown in FIG. 3, the substrate temperature is maintained atAt 860 deg.C, the power of the plasma generator is 450W, the Ga source baffle is kept open, the Al source baffle is also kept open, and the flux of Ga source beam is 5.6X 10-7Torr, Al source beam flux of 7.0X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.7sccm, and Al was addedxGa(1-x)The thickness of the N thin film is 180 nm.
Example 4
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to 400W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was warmed to 820 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the duration required for the closing of the Ga source shutter was set to 5s, and the time of change (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.9 sccm.
After the nitrogen flow is debugged and determined, designing and operating a program,the growth of the structure according to the invention is started. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 820 ℃, the power of the plasma generator was 400W, the Ga source baffle was kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, the Al source shutter was kept in a closed state, the flow rate of nitrogen gas was kept at 0.64sccm, and the thickness of the GaN epitaxial layer was 450 nm. Next, [ GaN/Al ] as shown in FIG. 1 was grownxGa(1-x)N]m(the number m of the cycles of the superlattice in this embodiment is 13) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart shown in fig. 3. Wherein S2 is GaN/Al grown for one periodxGa(1-x)N structure, S3 was grown 13 times for the set cycle. At S2, the substrate temperature is 820 deg.C, and when GaN sub-layer is grown as 31 in FIG. 1, the Ga source baffle is kept open, and the Ga source beam current is 5.6 × 10-7Torr, Al source baffle is kept in a closed state, the growth time of GaN sub-layer is 1min, and Al growsxGa(1-x)When the N sublayers are 32 in FIG. 1, the Ga source baffle is kept open, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, the Al source baffle is also kept open, and the flow of the Al source beam is 1.3X 10-8Torr，AlxGa(1-x)The growth time of the N sublayer is 2min and 30s, the flow rate of nitrogen is kept at 0.5sccm, and Al is addedxGa(1-x)The Al component x of the N sublayer is 0.2, and the GaN sublayer and the Al are alternately grownxGa(1-x)The duration required for the Al source shutter to close during the transition of the N sublayer was set to 7 s. Then, as in S4 in the program flowchart shown in fig. 3, the Ga source and Al source shutters were closed, and the duration required for the closing of the Ga source and Al source shutters was set to 5S, and the substrate temperature was increased to 860 ℃ at a rate of 10 ℃/min. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as shown in S5 in the program flowchart of FIG. 3, the substrate temperature was kept at 850 deg.C, the power of the plasma generator was 400W, the Ga source baffle was kept open, the Al source baffle was also kept open, and the flux of Ga source beam was 5.6X 10- 7Torr, Al source beam flux is 8.0X 10-8Torr, nitrogen flow rate was maintained at 0,64sccm, AlxGa(1-x)The thickness of the N film is 180nm, and AlxGa(1-x)The Al composition x of the N thin film was 0.46.
Example 5
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to be 500W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was heated to 850 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 9 min. Then the Ga source shutter was closed, the duration required for the closing of the Ga source shutter was set to 5s, and the time of change (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.5 sccm.
After the nitrogen flow is debugged and determined, a program is designed and operated, and the structure starts to grow. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 850 deg.C, the plasma generator power was 500W, and the Ga source was blockedThe plate is kept in an open state, and the flux of Ga source beam is 5.6 multiplied by 10-7Torr, the Al source shutter was kept in a closed state, the flow rate of nitrogen gas was kept at 0.64sccm, and the thickness of the GaN epitaxial layer was 800 nm. Next, [ GaN/Al ] as shown in FIG. 1 was grownxGa(1-x)N]m(the number m of cycles of the superlattice in this embodiment is 15) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart of fig. 3. Wherein S2 is GaN/Al grown for one periodxGa(1-x)N structure, S3 was grown 15 times for the set cycle. In S2, when the substrate temperature is 840 ℃ and the GaN sub-layer is grown as 31 in FIG. 1, the Ga source baffle is kept open, and the Ga source beam current is 5.6X 10-7Torr, Al source baffle is kept in a closed state, the growth time of GaN sub-layer is 1min30s, and Al is grownxGa(1-x)When the N sublayers are 32 in FIG. 1, the Ga source baffle is kept open, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, the Al source baffle is also kept open, and the flow rate of the Al source beam is 9.2X 10-8Torr，AlxGa(1-x)The growth time of the N sublayer is 3min and 30s, the flow rate of nitrogen is kept at 0.9sccm, and Al is addedxGa(1-x)The Al component x of the N sublayer is 0.43, and the GaN sublayer and the Al are alternately grownxGa(1-x)The duration required for the Al source shutter to close during the transition of the N sublayer was set to 3 s. Then, as in S4 in the program flowchart shown in fig. 3, the Ga source and Al source shutters were closed, and the duration required for the closing of the Ga source and Al source shutters was set to 5S, and the substrate temperature was increased to 860 ℃ at a rate of 10 ℃/min. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as shown in S5 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was maintained at 870 deg.C, the power of the plasma generator was 500W, the Ga source barrier was kept open, the Al source barrier was also kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, Al source beam flux is 8.0X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.64sccm, and Al was addedxGa(1-x)The thickness of the N film is 180nm, and AlxGa(1-x)The Al composition x of the N thin film was 0.55.
Example 6
The selective Hydride Vapor Phase Epitaxy (HVPE) method is inHeteroepitaxial undoped GaN thick film on sapphire substrate, stripping to obtain GaN substrate with diameter of 50.8mm, thickness of 430 μm, and dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ° for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to 450W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was heated to 810 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the duration required for the closing of the Ga source shutter was set to 5s, and the time of change (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.7 sccm.
After the nitrogen flow is debugged and determined, a program is designed and operated, and the structure starts to grow. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 810 deg.C, the power of the plasma generator was 450W, the Ga source baffle was kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, the Al source shutter was kept in a closed state, the flow rate of nitrogen gas was kept at 0.7sccm, and the thickness of the GaN epitaxial layer was 600 nm. Next, [ GaN/AlN ] as shown in FIG. 1 was grown]n(the number of cycles n of the superlattice is 15 in this embodiment) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart of fig. 3. Where S2 is a GaN/AlN structure grown for one period, and S3 is a set-up cyclic growth 15 times. At S2, the substrate temperature was 830 deg.C, and when GaN sub-layers were grown as 31 in FIG. 1, the Ga source shutter was kept open, and the Ga source beam flux was 5.6X 10-7Keeping the Al source baffle in a closed state, keeping the flow of nitrogen at 0.7sccm, keeping the growth time of the GaN sublayer at 1min30s, keeping the baffles of the Ga source and the Al source in a closed state before growing the AlN sublayer, reducing the flow of nitrogen from 0.7sccm to 0.25sccm, wherein the buffer time of the nitrogen flow reduction process is about 8-12s, keeping the Ga source baffle in a closed state when growing the AlN sublayer, keeping the Al source baffle in an open state when growing the AlN sublayer as shown in 32 in FIG. 1, and keeping the flow of the Al source beam at 7.0 x 10- 8Torr, AlN layer growth time was 4min, and the buffer time required for the closing of the Al source shutter during the transition between the alternate growth of the GaN layer and AlN layer was set to 5 s. Then, as in S4 in the flowchart of the routine shown in fig. 3, the Ga source and Al source shutters were closed, and the duration required for the closing of the Ga source and Al source shutters was set to 5S, and the substrate temperature was raised to 850 ℃. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as shown in S5 in the program flowchart of FIG. 3, the substrate temperature was kept at 850 deg.C, the power of the plasma generator was 450W, the Ga source baffle was kept open, the Al source baffle was also kept open, and the flux of Ga source beam was 5.6X 10-7Torr, Al source beam flux of 7.0X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.7sccm, and Al was addedxGa(1-x)The thickness of the N film is 180nm, and AlxGa(1-x)The Al composition x of the N thin film was 0.2.
Example 7
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in FIG. 1, gold was evaporated to a thickness of 1.3 μm on the back surface of a substrate 1 by Physical Vapor Deposition (PVD)Belongs to titanium (Ti), and the deposition rate is 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to be 500W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was warmed to 820 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the duration required for the closing of the Ga source shutter was set to 5s, and the time of change (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.64 sccm.
After the nitrogen flow is debugged and determined, a program is designed and operated, and the structure starts to grow. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 820 ℃, the power of the plasma generator was 500W, the Ga source baffle was kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, the Al source shutter was kept in a closed state, the flow rate of nitrogen gas was kept at 0.64sccm, and the thickness of the GaN epitaxial layer was 400 nm. Next, a numerical gradient [ GaN/Al ] as shown in FIG. 1 was grownxGa(1-x)N]m(the number of cycles m of the superlattice in this embodiment is 10) superlattice insertion layers 31 and 32, in which Al is presentxGa(1-x)The composition x of the N sublayer is 0.4 as in S2 and S3 in the program flowchart shown in FIG. 3. Wherein S2 is GaN/Al grown for one periodxGa(1-x)N structure, S3 for setting 10 times of cyclic growth, Al in each cyclexGa(1-x)The ratio of the thicknesses of the N and GaN sublayers ranged from cycle 1 to cycle 10 (10:1, 9:2 … … 2:9, 1: 10). The substrate temperature is 820 ℃, the Ga source baffle is kept in an open state, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, Al source beam flux of 9.2X 10-8Tor, obtaining Al with different thicknesses by controlling the time for which the open state of the Al source baffle is keptxGa(1-x)A N sublayer, a GaN sublayer with different thickness obtained by controlling the time for keeping the closed state of the Al source baffle platexGa(1-x)The thickness ratio of the N and GaN sublayers ranges from cycle 1 to cycle 10 (10:1, 9:2 … … 2: 2, 9: 1:10), and two Al sources are used to alternately perform odd-numbered cycles and even-numbered cycles of AlxGa(1-x)Growing N sublayers, keeping the Al source beam current consistent, keeping the flow of nitrogen at 0.64scc, and alternately growing GaN sublayers and AlxGa(1-x)The duration required for the Al source shutter to close during the transition of the N sublayer was set to 5 s. Then, as in S4 in the program flowchart shown in fig. 3, the Ga source and Al source shutters were closed, and the duration required for the closing of the Ga source and Al source shutters was set to 5S, and the substrate temperature was increased to 860 ℃ at a rate of 10 ℃/min. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as shown in S5 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was maintained at 860 deg.C, the power of the plasma generator was 500W, the Ga source shutter was kept open, the Al source shutter was also kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, Al source beam flux is 6.6X 10-8Torr, nitrogen flow rate was maintained at 0,64sccm, AlxGa(1-x)The thickness of the N film is 180nm, and AlxGa(1-x)The Al composition x of the N thin film was 0.35.
Example 8
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in FIG. 1, physical therapy is usedThe phase deposition (PVD) method deposits 1.3 μm thick titanium (Ti) metal on the back of the substrate 1 at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to 450W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was warmed to 820 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the duration required for the closing of the Ga source shutter was set to 5s, and the time of change (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.7 sccm.
After the nitrogen flow is debugged and determined, a program is designed and operated, and the structure starts to grow. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 820 ℃, the power of the plasma generator was 450W, the Ga source baffle was kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, the Al source shutter was kept in a closed state, the flow rate of nitrogen gas was kept at 0.7sccm, and the thickness of the GaN epitaxial layer was 400 nm. Next, [ GaN/Al ] as shown in FIG. 1 was grownxGa(1-x)N]m(the number m of cycles of the superlattice in this embodiment is 15) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart of fig. 3. Wherein S2 is GaN/Al grown for one periodxGa(1-x)N structure, S3 isThe set cycle growth was 15 times. At S2, the substrate temperature is 820 deg.C, and when GaN sub-layer is grown as 31 in FIG. 1, the Ga source baffle is kept open, and the Ga source beam current is 5.6 × 10-7Torr, Al source baffle plate is kept in a closed state, the growth time of GaN sublayer is 2min, and Al growsxGa(1-x)When the N sublayers are 32 in FIG. 1, the Ga source baffle is kept open, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, the Al source baffle is also kept open, and the flow rate of the Al source beam is 9.2X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.7sccm, and Al was addedxGa(1-x)The Al composition x of the N sublayer is 0.55, AlxGa(1-x)The growth time of the N sublayer is changed from 3min30s to 2min30s, and the GaN sublayer and the Al are alternately grownxGa(1-x)The duration required for the Al source shutter to close during the transition of the N sublayer was set to 5 s. Then, as in S4 in the program flowchart shown in fig. 3, the Ga source and Al source shutters were closed, and the duration required for the closing of the Ga source and Al source shutters was set to 5S, and the substrate temperature was increased to 860 ℃ at a rate of 10 ℃/min. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as shown in S5 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was kept at 860 deg.C, the power of the plasma generator was 450W, the Ga source shutter was kept open, the Al source shutter was also kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, Al source beam flux of 7.0X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.7sccm, and Al was addedxGa(1-x)The thickness of the N film is 180nm, and AlxGa(1-x)The Al composition x of the N thin film was 0.40.
Example 9
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After cleaning, nitrogen gas is usedThe surface of the substrate 1 is blow-dried. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to 450W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was warmed to 820 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the buffer time required for the closing of the Ga source shutter was set to 5s, and the change time (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.65 sccm.
After the nitrogen flow is debugged and determined, a program is designed and operated, and the structure starts to grow. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 820 °, the power of the plasma generator was 450W, the Ga source shutter was kept open, and the flux of the Ga source beam was 5.6X 10- 7Torr, the Al source shutter was kept in a closed state, and the flow rate of nitrogen gas was kept at 0.65 sccm. Next, [ GaN/AlN ] as shown in FIG. 1 was grown]n(the number of cycles n of the superlattice is 15 in this embodiment) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart of fig. 3. Where S2 is a GaN/AlN structure grown for one period, and S3 is a set-up cyclic growth 15 times. In S2, the substrate temperature is 820 ℃, the Ga source baffle is kept open when growing the GaN sub-layer, and the flux of the Ga source beam is 5.6 multiplied by 10- 7Torr, Al source baffle plate is kept in closed state, nitrogen flow is kept at 0.65sccm, GaN sub-layer growth time is 2min, AlN sub-layer is grownBefore the layer, the baffle plates of the Ga source and the Al source are kept in a closed state, the nitrogen flow is reduced from 0.65sccm to 0.2sccm, the duration of the nitrogen flow reduction process is about 8-12s, when an AlN sublayer is grown as 32 in a graph 1, the baffle plates of the Ga source are kept in the closed state, the baffle plates of the Al source are kept in an open state, and the beam flow of the Al source is 7.0 multiplied by 10-8Torr, AlN sublayer growth time was changed from 4min to 2min, and the duration required for the Al source shutter to be closed during the transition between alternately growing GaN layers and AlN layers was set to 5 s. Then, as in S4 in the program flowchart shown in fig. 3, the Ga source and Al source shutters were closed, and the buffer times required for the closing of the Ga source and Al source shutters were each set to 5S, and the substrate temperature was increased to 860 ℃ at a rate of 10 ℃/min. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as shown in S5 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was kept at 860 deg.C, the power of the plasma generator was 450W, the Ga source shutter was kept open, the Al source shutter was also kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, Al source beam flux of 7.0X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.65sccm, and Al was addedxGa(1-x)The thickness of the N thin film is 180nm, and x is 0.55.
Example 10
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. Introducing nitrogen, setting the power of the plasma generator to 450W to ignite the nitrogen plasma, and opening the baffle of the nitrogen plasma. The substrate 1 was heated to 850 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 8 min. Then the Ga source shutter was closed, the duration required for the closing of the Ga source shutter was set to 5s, and the time of change (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.5 sccm.
After the nitrogen flow is debugged and determined, a program is designed and operated, and the structure starts to grow. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in the program flow chart of FIG. 3, S1, the substrate temperature was 850 deg.C, the power of the plasma generator was 450W, the Ga source shutter was kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, the Al source shutter was kept in a closed state, the flow rate of nitrogen gas was kept at 0.7sccm, and the thickness of the GaN epitaxial layer was 400 nm. Next, [ GaN/Al ] as shown in FIG. 1 was grownxGa(1-x)N]m(the number of cycles m of the superlattice is 20 in this embodiment) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart of fig. 3. Wherein S2 is GaN/Al grown for one periodxGa(1-x)N structure, S3 was grown 15 times for the set cycle. In S2, when the substrate temperature is 840 ℃ and the GaN sub-layer is grown as 31 in FIG. 1, the Ga source baffle is kept open, and the Ga source beam current is 5.6X 10-7Torr, Al source baffle is kept in a closed state, the growth time of GaN sub-layer is 1min, and Al growsxGa(1-x)When the N sublayers are 32 in FIG. 1, the Ga source baffle is kept open, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, the Al source baffle is also kept open, and the flow rate of the Al source beam is 9.2X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.5sccm, and Al was addedxGa(1-x)Al composition x of the N sublayer is 0.40, AlxGa(1-x)The growth time of the N sublayer is changed from 3min30s to 2min, and the GaN sublayer and the Al sublayer are alternately grownxGa(1-x)The duration required for the Al source shutter to close during the transition of the N sublayer was set to 5 s. Then, as in S4 in the program flowchart shown in fig. 3, the shutters of the Ga source and the Al source are closed, the durations required for the closing of the Ga source and the Al source shutters are each set to 5S, and the substrate temperature is raised to 850 ℃. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as shown in S5 in the program flowchart of FIG. 3, the substrate temperature was kept at 850 deg.C, the power of the plasma generator was 450W, the Ga source baffle was kept open, the Al source baffle was also kept open, and the flux of Ga source beam was 5.6X 10-7Torr, Al source beam flux of 9.2X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.5sccm, and Al was addedxGa(1-x)The thickness of the N film is 180nm, and AlxGa(1-x)The Al composition x of the N thin film was 0.35.
Example 11
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to 450W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was heated to 810 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the duration required for the Ga source shutter to close was set to 7s,the time of change (transitiontime) of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) from the pattern in the progress of GaN growth as shown by 001 in fig. 2 to the pattern after the end of growth as shown by 002 in fig. 2 was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.9 sccm.
After the nitrogen flow is debugged and determined, a program is designed and operated, and the structure starts to grow. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 810 deg.C, the power of the plasma generator was 450W, the Ga source baffle was kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, the Al source shutter was kept in a closed state, the flow rate of nitrogen gas was kept at 0.7sccm, and the thickness of the GaN epitaxial layer was 400 nm. Next, [ GaN/Al ] as shown in FIG. 1 was grownxGa(1-x)N]m(the number m of cycles of the superlattice in this embodiment is 25) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart of fig. 3. Wherein S2 is GaN/Al grown for one periodxGa(1-x)N structure, S3 was grown 15 times for the set cycle. At S2, the substrate temperature was 830 deg.C, and when GaN sub-layers were grown as 31 in FIG. 1, the Ga source shutter was kept open, and the Ga source beam flux was 5.6X 10-7Torr, Al source baffle is kept in a closed state, the growth time of GaN sub-layer is 1min30s, and Al is grownxGa(1-x)When the N sublayers are 32 in FIG. 1, the Ga source baffle is kept open, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, the Al source baffle is also kept open, and the flow of the Al source beam is 1.3X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.9sccm, and Al was addedxGa(1-x)Al composition x of the N sublayer is 0.2, AlxGa(1-x)The growth time of the N sublayer is changed from 4min to 2min, and the GaN sublayer and the Al are alternately grownxGa(1-x)The duration of the closing of the Al source baffle during the conversion of the N sublayers is set asAnd 7 s. Then, as in S4 in the program flowchart shown in fig. 3, the shutters of the Ga source and the Al source are closed, the time durations required for the closing of the Ga source and the Al source shutters are each set to 7S, and the substrate temperature is raised to 870 ℃ at a rate of 10 ℃/min. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as shown in S5 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was maintained at 870 deg.C, the power of the plasma generator was 400W, the Ga source baffle plate was kept open, the Al source baffle plate was also kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, Al source beam flux of 1.3X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.9sccm, and Al was addedxGa(1-x)The thickness of the N film is 180nm, and AlxGa(1-x)The Al composition x of the N thin film was 0.3.
Example 12
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to 450W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was warmed to 820 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the buffer time required for the closing of the Ga source shutter was set to 3s, and the change time (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. Time of changeIf the time is within 6-20s, the nitrogen flow rate is kept unchanged, and the next step is continued. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.65 sccm.
After the nitrogen flow is debugged and determined, a program is designed and operated, and the structure starts to grow. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 820 °, the power of the plasma generator was 450W, the Ga source shutter was kept open, and the flux of the Ga source beam was 5.6X 10- 7Torr, the Al source shutter was kept in a closed state, and the flow rate of nitrogen gas was kept at 0.65 sccm. Next, [ GaN/AlN ] as shown in FIG. 1 was grown]n(the number of cycles n of the superlattice is 20 in this embodiment) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart of fig. 3. Where S2 is a GaN/AlN structure grown for one period, and S3 is a set-up cyclic growth 15 times. In S2, the substrate temperature is 820 ℃, the Ga source baffle is kept open when growing the GaN sub-layer, and the flux of the Ga source beam is 5.6 multiplied by 10- 7Keeping the Al source baffle in a closed state, keeping the flow of nitrogen at 0.65sccm, keeping the growth time of the GaN sublayer at 2min, keeping the baffles of the Ga source and the Al source in a closed state before growing the AlN sublayer, reducing the flow of nitrogen from 0.65sccm to 0.2sccm, keeping the duration of the process of reducing the flow of nitrogen at about 8-12s, keeping the Ga source baffle in a closed state when growing the AlN sublayer such as 32 in FIG. 1, keeping the Al source baffle in an open state, and keeping the flow of the Al source beam at 7.0 x 10-8Torr, AlN word layer growth time was changed from 4min to 2min, and the duration required for the Al source shutter to be closed during the transition between the alternate growth of GaN layers and AlN layers was set to 3 s. Then, as in S4 in the program flowchart shown in fig. 3, the baffles of the Ga source and the Al source were closed, and the buffer times required for the closing of the baffles of the Ga source and the Al source were each set to 3S, and the substrate temperature was increased to 860 ℃ at a rate of 10 ℃/min. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, substrate temperature, S5 in the flowchart of the procedure shown in FIG. 3The power of the plasma generator is 450W when the temperature is kept at 860 ℃, the Ga source baffle is kept in an open state, the Al source baffle is also kept in an open state, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, Al source beam flux of 7.0X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.65sccm, and Al was addedxGa(1-x)The thickness of the N thin film is 180nm, and x is 0.2.
Example 13
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ℃ for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to 450W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was warmed to 820 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the buffer time required for the closing of the Ga source shutter was set to 5s, and the change time (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.65 sccm.
After the nitrogen flow is adjusted and determined,the program is designed and run to begin growing the structures described in the present invention. First, a GaN epitaxial layer 2 as shown in FIG. 1 was homoepitaxially grown, as shown in S1 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was 840 °, the plasma generator power was 450W, the Ga source shutter was kept open, and the Ga source beam current was 5.6X 10- 7Torr, the Al source shutter was kept in a closed state, and the flow rate of nitrogen gas was kept at 0.65 sccm. Next, [ GaN/AlN ] as shown in FIG. 1 was grown]n(the number of cycles n of the superlattice in this embodiment is 25) the superlattice insertion layers 31 and 32 are as shown in S2 and S3 in the program flowchart of fig. 3. Where S2 is a GaN/AlN structure grown for one period, and S3 is a set-up cyclic growth 15 times. In S2, the substrate temperature is 840 ℃, and when growing GaN sub-layer, the Ga source baffle is kept open, the Ga source beam flux is 5.6X 10- 7Keeping the Al source baffle in a closed state, keeping the flow of nitrogen at 0.65sccm, keeping the growth time of the GaN sublayer at 2min, keeping the baffles of the Ga source and the Al source in a closed state before growing the AlN sublayer, reducing the flow of nitrogen from 0.65sccm to 0.2sccm, keeping the duration of the process of reducing the flow of nitrogen at about 8-12s, keeping the Ga source baffle in a closed state when growing the AlN sublayer such as 32 in FIG. 1, keeping the Al source baffle in an open state, and keeping the flow of the Al source beam at 5.0 x 10-8Torr, AlN word layer growth time was changed from 3min30s to 2min, and the duration required for the Al source shutter to be closed during the transition between the alternate growth of GaN layers and AlN layers was set to 7 s. Then, as in S4 in the program flowchart shown in fig. 3, the Ga source and Al source shutters were closed, and the buffer times required for the closing of the Ga source and Al source shutters were each set to 5S, and the substrate temperature was increased to 860 ℃ at a rate of 10 ℃/min. Finally, Al as shown in FIG. 1 is grownxGa(1-x)N film 4, as shown in S5 in the flowchart of the procedure shown in FIG. 3, the substrate temperature was kept at 860 deg.C, the power of the plasma generator was 450W, the Ga source shutter was kept open, the Al source shutter was also kept open, and the flux of the Ga source beam was 5.6X 10-7Torr, Al source beam flux of 5.0X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.8sccm, and Al was addedxGa(1-x)The thickness of the N thin film is 180nm, and x is 0.55.
Comparative example 1
Selectively carrying out Hydride Vapor Phase Epitaxy (HVPE) on the undoped GaN thick film heteroepitaxial on the sapphire substrate, and stripping to obtain the GaN substrate with the diameter of about 50.8mm, the thickness of about 430 μm, and the dislocation density of less than 5 × 106cm-2And the surface roughness is less than 0.6 nm. As shown in fig. 1, metal titanium (Ti) was evaporated on the back surface of the substrate 1 to a thickness of 1.3 μm using a Physical Vapor Deposition (PVD) method at a deposition rate of 12 nm/min. Then, the substrate 1 is washed with acetone, ethanol, and deionized water in this order. After the cleaning, the surface of the substrate 1 was blown dry using nitrogen gas. After cleaning the substrate 1, the substrate is placed in a degassing chamber of an MBE apparatus, and the substrate 1 is subjected to surface degassing treatment at a temperature of 450 ° for at least 30 min.
The Ga source barrier is set to maintain a closed state. And introducing nitrogen, setting the power of the plasma generator to 450W, igniting the nitrogen plasma, and opening a baffle of the nitrogen plasma. The substrate 1 was warmed to 820 ℃. Keeping Ga source beam current at 5.6 multiplied by 10-7The Torr was not changed, the shutter of the Ga source was opened, and GaN was grown for 6 min. Then the Ga source shutter was closed, the duration required for the closing of the Ga source shutter was set to 5s, and the time of change (transitiontime) of the pattern transition from the pattern in progress of GaN growth as shown in 001 in fig. 2 to the pattern after the end of growth as shown in 002 in fig. 2 of the pattern of the Reflection High Energy Electron Diffractometer (RHEED) was observed and recorded. If the change time is within 6 to 20 seconds, the next step is continued while maintaining the nitrogen flow rate at that time. If the change time is not about 6-20s, the nitrogen flow rate needs to be changed, the step is repeated until the change time is about 6-20s, then the nitrogen flow rate is kept unchanged, and the next step is continued. The nitrogen flow was finally determined to be 0.7 sccm.
After the nitrogen flow is adjusted and determined, homoepitaxially growing a GaN epitaxial layer 2 as shown in FIG. 1, wherein the substrate temperature is 820 ℃, the power of the plasma generator is 450W, the Ga source baffle is kept in an open state, and the flow of the Ga source beam is 5.6 multiplied by 10- 7Torr, the Al source shutter was kept in a closed state, and the flow rate of nitrogen gas was kept at 0.7 sccm. Then, the baffle of the Ga source is closed, the Al source baffle is kept in a closed state, and the Ga source is used for lining at the speed of 10 DEG/minThe bottom temperature was raised to 860 ℃. Finally, Al as shown in FIG. 1 is grownxGa(1-x)The temperature of the substrate of the N film 4 is kept at 860 ℃, the power of the plasma generator is 450W, the Ga source baffle is kept in an open state, the Al source baffle is also kept in an open state, and the flux of Ga source beams is 5.6 multiplied by 10-7Torr, Al source beam flux of 7.0X 10-8Torr, the flow rate of nitrogen gas was maintained at 0.7sccm, and Al was addedxGa(1-x)The thickness of the N thin film is 180 nm.
The samples obtained by the above method were tested. The results of the X-ray diffractometer ω -2 θ test of the sample were analyzed as shown in fig. 4. It can be seen from the graph shown in FIG. 4 with the abscissa of 31-34 degrees that [ GaN/Al ] is epitaxially grown according to the method of the present inventionxGa(1-x)N]m(the number of cycles m of the superlattice in this embodiment is 10) the interfaces of the respective layers of the superlattice structure are very clear. The interfaces of the individual layers of the superlattice structure according to example 1 are also relatively sharp, as can be seen from the curves shown in fig. 5 with an abscissa of 32-34.5 degrees. As shown in FIG. 6, Al of comparative example 1, example 1 and example 2 was addedxGa(1-x)And carrying out statistical analysis on the surface crack density and the crack spacing of the N/GaN heterojunction sample. Sample No. 1 shown in FIG. 6 is a sample of comparative example 1, and its crack density is about 1485/mm2The crack spacing was about 14.24 μm. Sample No. 2 shown in FIG. 6 is a sample of example 1, and its crack density is about 490/mm2The crack spacing was about 37.52 μm. Sample No. 3 shown in FIG. 6 is a sample of example 2, and its crack density is about 604/mm2The crack spacing was about 30.56 μm. As shown in fig. 7, the surface of the sample was observed using a Scanning Electron Microscope (SEM). Among them, SEM photographs of the surfaces of the samples of comparative example 1 and examples 1 to 3 correspond to 01, 02, 03 and 04 in fig. 7, respectively. The results of fig. 6 and 7 show that the sample with the superlattice insertion layer has a greatly reduced surface crack density and a widened crack spacing compared to the sample without the superlattice insertion layer, indicating that the degree of surface cracking thereof is alleviated. Example 3 [ GaN/AlN ] grown in comparison with example 2]14The number of cycles of the superlattice insertion layer and the growth time of the sub-layerDifferent. As shown in 04 of FIG. 7, the SEM photograph shows the crystal having [ GaN/AlN]14Al of superlattice insertion layerxGa(1-x)Surface cracks of the N/GaN heterojunction structure are eliminated. Numerical gradient [ GaN/Al ] in example 7xGa(1-x)N]m(the number of cycles m of the superlattice in the present embodiment is 10) the superlattice insertion layer can also effectively achieve Al mitigation/eliminationxGa(1-x)The purpose of surface crack of the N film is achieved, and a double-Al source control method is used, so that the frequency of frequent switching of a single-Al source baffle is greatly reduced, and the stability and the safety of equipment are ensured.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (7)

1. A method for growing a superlattice insertion layer for relieving/eliminating cracks on the surface of an AlGaN film by adopting a molecular beam epitaxy technology comprises the following steps:
1) selecting a substrate, and carrying out pretreatment before epitaxial growth on the substrate;
2) a molecular beam epitaxy technology is used, and a GaN epitaxial layer is homoepitaxially grown on the substrate by controlling growth parameters;
3) extending a superlattice insertion layer on the GaN epitaxial layer by using a molecular beam epitaxy technology and controlling growth parameters;
4) using molecular beam epitaxy technique, by controlling growth parameters, a layer of Al is epitaxially grown on the superlattice insertion layerxGa(1-x)Thin film of N, AlxGa(1-x)The Al component x of the N film is 0.2-0.55, and the thickness is 150-180 nm;
wherein in the step 3), the superlattice insertion layer is [ GaN/Al ]xGa(1-x)N]mStructure, x ranges from 0.2 to 0.55;
AlxGa(1-x)the thickness of the N sub-layer is non-gradual change, and m is 10-15;
when Al is presentxGa(1-x)When the thickness of the N sublayer is non-gradient, the thickness of the GaN sublayer is also non-gradient, [ GaN/Al ]xGa(1-x)N]mThe superlattice insertion layer is a digital gradient insertion layer with digital gradient [ GaN/Al ]xGa(1-x)N]mThe number of cycles of the superlattice insertion layer is 10, AlxGa(1-x)The thickness ratio of the N sublayer to the GaN sublayer is 10 from cycle 1 to cycle 10: 1. 9: 2. 8: 3. 7: 4. 6: 5. 5: 6. 4: 7. 3: 8. 2: 9. 1: 10.
2. the method for growing the superlattice insertion layer for alleviating/eliminating the cracks on the surface of the aluminum gallium nitride film by adopting the molecular beam epitaxy technology as claimed in claim 1, wherein the superlattice insertion layer comprises the following steps:
in step 3), the opening and closing states of the Ga source baffle and the Al source baffle are changed alternately to realize the GaN/AlxGa(1-x)N]mAlternately growing each sublayer of the superlattice insertion layer;
the growth parameters of the epitaxial superlattice insertion layer are as follows: epitaxy of [ GaN/AlxGa(1-x)N]mThe growth temperature of the superlattice insertion layer is 820-840 ℃, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, Al source beam flux of 1.3X 10-8-9.2×10-8Torr, nitrogen flow of 0.5-0.9sccm, GaN sub-layer growth time of 1-2 min, AlxGa(1-x)The growth time of the N sublayer is 2min30s-3min30 s;
the RF power of the plasma generator is 400-500W.
3. The method for growing the superlattice insertion layer for alleviating/eliminating the cracks on the surface of the aluminum gallium nitride film by adopting the molecular beam epitaxy technology as claimed in claim 2, wherein the superlattice insertion layer comprises the following steps: in the step 3), epitaxial digital gradient [ GaN/Al ] is realized by alternately changing the opening and closing states of the Ga source baffle and the Al source bafflexGa(1-x)N]mAnd (3) alternately growing each sublayer of the superlattice insertion layer, wherein the growth parameters of the epitaxial superlattice insertion layer are as follows: epitaxial digital gradient [ GaN/Al ]xGa(1-x)N]mThe growth temperature of the superlattice insertion layer is 820-840 ℃, and the flux of the Ga source beam is 5.6 multiplied by 10-7Torr, Al source beam flux of 1.3X 10-8-9.2×10-8Torr, nitrogen flow of 0.5-0.9sccm, GaN sub-layer growth time of 1-2 min, AlxGa(1-x)The growth time of the N sublayer is 2min30s-3min30s, the radio frequency power of the plasma generator is 400-500W, and the epitaxial digital gradient [ GaN/Al-xGa(1-x)N]mIn the process of growing the superlattice insertion layer, the Ga source baffle is always kept in an open state, and Al with different thicknesses is obtained by controlling the time for keeping the open state of the Al source bafflexGa(1-x)N sublayer, GaN sublayers with different thicknesses are obtained by controlling the time for keeping the closed state of the Al source baffle plate, so that Al is enabled to be in contact with the GaN sublayersxGa(1-x)The thickness ratio of the N and GaN sublayers ranges from cycle 1 to cycle 10 to 10: 1. 9: 2. 8: 3. 7: 4. 6: 5. 5: 6. 4: 7. 3: 8. 2: 9. 1: al alternating odd and even cycles with two Al sourcesxGa(1-x)And growing an N sublayer, and keeping the Al source beam current consistent.
4. The method for growing the superlattice insertion layer for alleviating/eliminating the cracks on the surface of the aluminum gallium nitride film by adopting the molecular beam epitaxy technology as claimed in claim 3, wherein the superlattice insertion layer comprises the following steps: in step 3), the duration required to turn off the Ga source or Al source shutter is set to 3 to 7 s.
5. The method for growing the superlattice insertion layer for alleviating/eliminating the cracks on the surface of the aluminum gallium nitride film by adopting the molecular beam epitaxy technology as claimed in claim 1, wherein the superlattice insertion layer comprises the following steps: in step 4), extending a layer of AlxGa(1-x)The growth parameters of the N film are as follows: the growth temperature is 850-870 DEG, the Ga source beam flux is 5.6 multiplied by 10-7Torr, Al source beam flux of 1.3X 10-8-9.2×10-8Torr, the flow rate of nitrogen gas is 0.5-0.9sccm, and the RF power of the plasma generator is 400-500W.
6. The method for growing the superlattice insertion layer for alleviating/eliminating the cracks on the surface of the aluminum gallium nitride film by adopting the molecular beam epitaxy technology as claimed in claim 5, wherein the superlattice insertion layer comprises the following steps:
in the step 1), the substrate is an undoped GaN thick film which is heteroepitaxially formed on a sapphire substrate by a hydride vapor phase epitaxy method, and the GaN substrate obtained by stripping has the diameter of 50.8 +/-1 mm, the thickness of 430 mu m and the dislocation density of less than 5 multiplied by 106cm-2The surface roughness is less than 0.6 nm;
the substrate pretreatment method comprises the following steps: and evaporating 1.3 mu m thick metal Ti on the back surface of the GaN substrate by using a physical vapor deposition method, wherein the deposition rate is 12nm/min, after the back surface is plated with the titanium, sequentially cleaning the substrate by using acetone, alcohol and deionized water, drying the substrate by using nitrogen after cleaning, then placing the substrate into a degassing chamber of MBE equipment, and carrying out surface degassing treatment on the substrate for at least 30min at the temperature of 450 ℃.
7. The method for growing the superlattice insertion layer for alleviating/eliminating the cracks on the surface of the aluminum gallium nitride film by adopting the molecular beam epitaxy technology as claimed in claim 6, wherein the superlattice insertion layer comprises the following steps: in the step 2), the growth parameters of the homoepitaxial GaN epitaxial layer are as follows: the growth temperature is 810--7Torr, the flow rate of nitrogen is 0.5-0.9sccm, the RF power of the plasma generator is 400-500W, and the thickness of the GaN epitaxial layer is 400-800 nm.
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