CN111739791B - Epitaxial structure of gallium nitride material and preparation method - Google Patents
Epitaxial structure of gallium nitride material and preparation method Download PDFInfo
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- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 title claims abstract description 84
- 229910002601 GaN Inorganic materials 0.000 title claims abstract description 82
- 238000002360 preparation method Methods 0.000 title claims abstract description 15
- 239000000463 material Substances 0.000 title abstract description 14
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 claims abstract description 55
- 229910010271 silicon carbide Inorganic materials 0.000 claims abstract description 53
- 239000000758 substrate Substances 0.000 claims abstract description 52
- 239000011248 coating agent Substances 0.000 claims abstract description 27
- 238000000576 coating method Methods 0.000 claims abstract description 27
- 238000000034 method Methods 0.000 claims abstract description 24
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 22
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 22
- 238000004381 surface treatment Methods 0.000 claims abstract description 8
- 239000010410 layer Substances 0.000 claims description 95
- 230000012010 growth Effects 0.000 claims description 55
- XCZXGTMEAKBVPV-UHFFFAOYSA-N trimethylgallium Chemical compound C[Ga](C)C XCZXGTMEAKBVPV-UHFFFAOYSA-N 0.000 claims description 15
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 14
- JLTRXTDYQLMHGR-UHFFFAOYSA-N trimethylaluminium Chemical compound C[Al](C)C JLTRXTDYQLMHGR-UHFFFAOYSA-N 0.000 claims description 13
- 238000000137 annealing Methods 0.000 claims description 9
- 239000012298 atmosphere Substances 0.000 claims description 7
- 229910052757 nitrogen Inorganic materials 0.000 claims description 7
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 6
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 claims description 6
- 229910052733 gallium Inorganic materials 0.000 claims description 6
- 239000001257 hydrogen Substances 0.000 claims description 5
- 229910052739 hydrogen Inorganic materials 0.000 claims description 5
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 4
- 239000011247 coating layer Substances 0.000 claims description 3
- 239000000956 alloy Substances 0.000 claims 1
- 229910002704 AlGaN Inorganic materials 0.000 description 11
- 239000013078 crystal Substances 0.000 description 10
- 238000012360 testing method Methods 0.000 description 7
- 235000012431 wafers Nutrition 0.000 description 6
- 238000001816 cooling Methods 0.000 description 5
- 238000005259 measurement Methods 0.000 description 4
- 230000003287 optical effect Effects 0.000 description 4
- 230000003698 anagen phase Effects 0.000 description 3
- 125000004429 atom Chemical group 0.000 description 3
- 239000010408 film Substances 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 229910052594 sapphire Inorganic materials 0.000 description 3
- 239000010980 sapphire Substances 0.000 description 3
- 239000012159 carrier gas Substances 0.000 description 2
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- PIGFYZPCRLYGLF-UHFFFAOYSA-N Aluminum nitride Chemical compound [Al]#N PIGFYZPCRLYGLF-UHFFFAOYSA-N 0.000 description 1
- 229910007991 Si-N Inorganic materials 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 229910006294 Si—N Inorganic materials 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- NRQNMMBQPIGPTB-UHFFFAOYSA-N methylaluminum Chemical compound [CH3].[Al] NRQNMMBQPIGPTB-UHFFFAOYSA-N 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 1
- 125000004430 oxygen atom Chemical group O* 0.000 description 1
- 238000002161 passivation Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
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- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02367—Substrates
- H01L21/0237—Materials
- H01L21/02373—Group 14 semiconducting materials
- H01L21/02378—Silicon carbide
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- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02436—Intermediate layers between substrates and deposited layers
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Abstract
The invention provides an epitaxial structure of a gallium nitride material and a preparation method thereof, wherein the preparation method at least comprises the following steps: providing a silicon carbide substrate, and carrying out surface treatment on the silicon carbide substrate; growing an aluminum coating on the silicon carbide substrate; growing Al on the aluminum coatingxGa1‑xN buffer layer of AlxGa1‑xIn N, x is 0.2-0.3; in the AlxGa1‑xAnd growing a gallium nitride epitaxial layer on the N buffer layer. The method has simple process, and solves the warping problem of the gallium nitride epitaxial layer grown on the large-size silicon carbide substrate.
Description
Technical Field
The invention relates to the technical field of epitaxial growth of semiconductor materials, in particular to an epitaxial structure of a gallium nitride material and a preparation method thereof.
Background
Gallium nitride (GaN) is used as a third-generation wide-bandgap semiconductor material, has high application value in the field of microwave devices due to the characteristics of high thermal conductivity, high electronic saturation drift velocity, high breakdown electric field, strong radiation resistance, high chemical stability and the like, and is expected to play an important role in the aspects of aviation, high-temperature radiation, radar, communication, automobile electronics and the like. Since the fabrication of GaN single crystal substrates is very difficult, most GaN-based devices are fabricated by a heteroepitaxial method on foreign substrates, which mainly include silicon (Si), silicon carbide (SiC), and sapphire, but grown GaN single crystals have high dislocation density and large stress due to the large lattice mismatch between sapphire and Si substrates and GaN (16.1% lattice mismatch between sapphire and GaN, and about 17% lattice mismatch between Si substrates and GaN). The lattice mismatch degree of the SiC substrate and the GaN is as small as 3.5%, the SiC substrate and the GaN have excellent heat conduction performance, and the heat conductivity reaches 4.9 w/cm.k, so that the SiC is firstly used as a substrate material in the preparation process of the high-frequency high-power GaN device material, for example, a power amplifier in a 5G base station must adopt a GaN material device with the SiC substrate at present. However, because of the thermal mismatch of 24% between SiC and GaN, the problem of large warpage of the GaN thin film grown on the SiC substrate occurs after the GaN thin film is completed, and particularly, as the size of the substrate increases, the warpage problem becomes more prominent.
Disclosure of Invention
Aiming at the defects and shortcomings in the prior art, the invention provides an epitaxial structure of a gallium nitride material and a preparation method thereof, which are used for solving the problems of large warpage and poor uniformity of a GaN epitaxial film grown on a large-size SiC substrate.
In order to achieve the above and other related objects, the present invention provides a method for preparing an epitaxial layer of gallium nitride, comprising at least the following steps:
providing a silicon carbide substrate, and carrying out surface treatment on the silicon carbide substrate;
growing an aluminum coating on the silicon carbide substrate;
growing Al on the aluminum coatingxGa1-xAn N buffer layer, wherein the AlxGa1-xX in N is 0.2-0.3;
in the AlxGa1-xAnd growing a gallium nitride epitaxial layer on the N buffer layer.
In an embodiment of the invention, the surface treatment of the silicon carbide substrate includes annealing the silicon carbide substrate in a hydrogen atmosphere, wherein the annealing temperature is 1020 to 1070 ℃, the pressure is 100 to 200mbar, the hydrogen flow rate is 130 to 160L/min, and the time is 5 to 10 min.
In an embodiment of the invention, the growing of the aluminum coating on the silicon carbide substrate includes providing an aluminum source of trimethylaluminum, wherein a flow rate of the trimethylaluminum is 30sccm, a time is 10 to 30s, a growth temperature is controlled to be 1010 to 1050 ℃, and a growth pressure is 50 to 80 mbar.
Further, the thickness of the formed aluminum coating is 0.5-1.5 nm.
In one embodiment of the present invention, Al is grown on the aluminum coating layerxGa1-xThe N buffer layer comprises providing gallium source trimethyl gallium, aluminum source trimethyl aluminum and nitrogen source ammonia gas, wherein the flow rate of trimethyl gallium is 130sccm, and the flow rate is threeThe flow rate of the methyl aluminum is 350-400 sccm, the V/III molar ratio in the growth process is 200-270, the growth temperature is controlled to be 1010-1050 ℃, and the growth pressure is controlled to be 45-65 mbar.
Further, the Al formedxGa1-xThe thickness of the N buffer layer is 70-100 nm.
In an embodiment of the present invention, the Al isxGa1-xGrowing a gallium nitride epitaxial layer on the N buffer layer comprises providing gallium source trimethyl gallium and nitrogen source ammonia gas, wherein the flow of trimethyl gallium is 200-300 sccm, and the molar ratio of V/III in the growth process is 700-1200.
In an embodiment of the present invention, the Al isxGa1-xGrowing an epitaxial layer of gallium nitride on the N buffer layer further comprises,
in the first growth stage, the growth temperature is controlled to be 1000-1050 ℃, and the growth pressure is 70-150 mbar; and
in the second growth stage, the growth temperature is controlled to be 1020-1070 ℃, and the growth pressure is controlled to be 150-250 mbar.
Furthermore, the thickness of the gallium nitride epitaxial layer formed in the first growth stage is 200-300 nm, and the thickness of the gallium nitride epitaxial layer formed in the second growth stage is 1.5-2 μm.
In one embodiment of the invention, after the growth is finished, the temperature needs to be reduced by a method of reducing the temperature in a nitrogen atmosphere at a rate of 40-45 ℃/min.
A second aspect of the present invention provides an epitaxial structure of gallium nitride material, comprising,
a silicon carbide substrate;
an aluminum coating on the silicon carbide substrate;
AlxGa1-xthe N buffer layer is positioned on the aluminum coating; and
an epitaxial layer of gallium nitride on the AlxGa1-xN buffer layer;
as described above, the present invention provides a method for preparing an epitaxial layer of gallium nitride by introducing Al on a SiC substratexGa1-xBuffer layer of N, AlxGa1-xN bufferThe impact layer can reduce the crystal mismatch of SiC and GaN to a certain extent, provides a certain space for the tensile stress borne by the follow-up GaN epitaxial layer during growth, can offset the tensile stress generated in the epitaxial layer cooling process, and improves the warping problem of large-size epitaxial wafers caused by lattice mismatch and thermal mismatch.
Drawings
The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are illustrative and not to be construed as limiting the invention in any way, and in which:
FIG. 1 is a flow chart of a method for preparing an epitaxial layer of gallium nitride according to the present invention.
Fig. 2 is a schematic view of an epitaxial structure of a gan material according to the present invention.
Fig. 3 is a diagram illustrating warpage in PL testing of gan epitaxial layers according to an embodiment of the present invention.
Fig. 4 is a graph showing warpage of PL test of gallium nitride epitaxial layers of the same thickness prepared by the prior art.
Fig. 5 (a) is an optical microscope photograph of an epitaxial layer of gan prepared in an embodiment of the present invention; fig. 5 (b) shows an optical microscope picture of the gallium nitride epitaxial layer with the same thickness prepared in the prior art.
Reference numerals
1. A SiC substrate; 2. an Al coating; 3. al (Al)xGa1-xN buffer layer; 4. and a GaN epitaxial layer.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict. It is also to be understood that the terminology used in the examples is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. Test methods in which specific conditions are not specified in the following examples are generally carried out under conventional conditions or under conditions recommended by the respective manufacturers.
When numerical ranges are given in the examples, it is understood that both endpoints of each of the numerical ranges and any value therebetween can be selected unless the invention otherwise indicated. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs and the description of the present invention, and any methods, apparatuses, and materials similar or equivalent to those described in the examples of the present invention may be used to practice the present invention.
The invention provides a preparation method of a gallium nitride epitaxial layer, which is characterized in that an AlGaN buffer layer is introduced on a silicon carbide (SiC) substrate, the lattice constant of AlGaN is between that of aluminum nitride (AlN) and gallium nitride (GaN), the AlGaN buffer layer with specific components is added, the crystal mismatch of SiC and GaN can be reduced to a certain extent, meanwhile, the growth rate of the AlGaN layer is accelerated due to the introduction of Ga atoms, the AlGaN buffer layer provides smaller compressive stress for SiC, and a larger space is provided for the subsequent tensile stress borne by GaN.
Referring to fig. 1 to 2, the present invention provides a method for preparing an epitaxial layer of gallium nitride, which is performed in a Metal Organic Chemical Vapor Deposition (MOCVD) apparatus, including trimethylaluminum (TMAl), trimethylgallium (TMGa), and ammonia (NH)3) Hydrogen (H) as Al source, Ga source and N source, respectively2) And nitrogen (N)2) As a carrier gas.
Referring to fig. 1 to 2, a method for preparing an epitaxial layer of gallium nitride at least includes the following steps:
s1, providing a SiC substrate 1, and carrying out surface treatment on the SiC substrate 1;
s2, growing an Al coating 2 on the SiC substrate 1;
s3 growing Al on the Al coating 2xGa1-x N buffer layer 3 of AlxGa1-xX in N is 0.2-0.3;
s4 in AlxGa1-xA GaN epitaxial layer 4 is grown on the N buffer layer 3.
Referring to fig. 1 to 2, in step S1, the surface treatment of the SiC substrate 1 is: placing SiC substrate 1 in H2And carrying out annealing treatment in the atmosphere. Wherein the annealing treatment temperature is 1020-1070 ℃, the pressure is 100-200 mbar, and H2The flow rate is 130-160L/min, and the time is 5-10 min. At H2Annealing the SiC substrate 1 in an atmosphere H2Will react with the oxide layer of the SiC substrate 1 to remove surface O atoms and form Si-H bonds which are favorable for preventing Si atoms from being introduced into NH subsequently3Si-N bonds are formed during the process, and passivation of the surface is avoided. At H2The annealing treatment is not excessive in the atmosphere, and excessive annealing treatment easily causes uneven surface etching of the SiC substrate 1, thereby affecting the surface flatness and the crystal quality of a subsequently grown film.
Referring to fig. 1 to 2, in an embodiment, when performing surface treatment on the SiC substrate 1, the SiC substrate 1 is placed in an MOCVD apparatus, the MOCVD reaction chamber is closed, the temperature of the reaction chamber is raised to 1020 to 1070 ℃, the pressure of the reaction chamber is adjusted to 100 to 200mbar, and H is introduced into the reaction chamber2，H2The gas flow is 130-160L/min, and the time is 5-10 min. The ranges given by the parameters can remove the surface dirt and the oxide layer of the SiC substrate 1 to improve the surface flatness of the SiC substrate 1, and can not influence the growth of subsequent crystals.
Referring to fig. 1 to 2, step S2 is performed to grow an Al coating 2 on the SiC substrate 1. In one embodiment, the temperature of the reaction chamber is adjusted to 1010-1050 ℃, the pressure of the reaction chamber is adjusted to 50-80 mbar, and an aluminum source, such as TMAl, is introduced into the reaction chamber, wherein the flow rate of TMAl is 30sccm, and the time is 10-30 s. Any value of the two endpoints and any value between the two endpoints of the range given by each parameter can be selected, the thickness of the Al coating 2 grown on the SiC substrate 1 according to the range given by the parameters is 0.5-1.5 nm, for example 1nm, and the Al coating 2 can provide a crystal nucleus for the subsequent growth of the AlGaN buffer layer 3. The thickness of the Al coating 2 grown in step S2 is suitable, and too thin an Al coating 2 cannot provide suitable crystal nuclei for the growth of the AlGaN buffer layer 3, which results in poor quality of the subsequently grown low film aggregation, and too thick an Al coating 2 results in the occurrence of crystallites with different subsequent orientations.
Referring to fig. 1 to 2, step S3 is performed to grow Al on the Al coating 2xGa1-xAnd an N buffer layer 3. In one embodiment, the temperature of the reaction chamber is adjusted to 1010-1050 ℃, the pressure is adjusted to 45-65 mbar, and a gallium source, such as TMGa, an aluminum source, such as TMAl, a nitrogen source, such as NH, is introduced3Wherein the flow rate of TMGa is 130sccm, the flow rate of TMAl is 350-400 sccm, and the molar ratio of V/III (V represents an element of a fifth main group, and III represents an element of a third main group) in the growth process is 200-270. In this step, AlxGa1-xThe growth rate of the N buffer layer 3 is 20-25 nm/min, and AlxGa1-xThe thickness of the N buffer layer 3 is 70-100 nm. Any value of the two endpoints and the value between the two endpoints of the range given by each parameter can be selected, and the optimal values such as growth temperature, growth pressure and gas flow can be selected according to the warpage and the performance of the grown GaN epitaxial layer 4. The surface appearance is uneven easily caused by overhigh V/III molar ratio in the growth process, and the crystal quality is not favorable when the V/III molar ratio is overlow. Al mentioned abovexGa1-xX in N is 0.2-0.3, and Al components in the interval can better serve as an intermediate bridge of lattice mismatch between SiC and GaN. The AlGaN lattice constant is between AlN and GaN, the AlGaN buffer layer added with specific components can reduce the crystal mismatch between SiC and GaN to a certain extent, and simultaneously, the growth rate of the AlGaN layer is accelerated due to the introduction of Ga atoms, the AlGaN buffer layer provides smaller compressive stress for SiC, and a larger space is provided for the tensile stress borne by subsequent GaN.
Referring to fig. 1-2, step S4 is executed at AlxGa1-xA GaN epitaxial layer 4 is grown on the N buffer layer 3. In one embodiment, the growth of the GaN epitaxial layer 4 includes at least a first growth stage, in which the temperature of the reaction chamber is adjusted to 1000-1050 ℃, the pressure is adjusted to 70-150 mbar, a gallium source such as TMGa and a nitrogen source such as NH are introduced3Wherein the TMGa flow is 250sccm, the V/III molar ratio in the growth process is 700-1200, the growth rate of the GaN epitaxial layer 4 at the stage is 30-40 nm/min, and the thickness of the GaN epitaxial layer 4 is 200-300 nm; in the second growth stage, the temperature of the reaction chamber is adjusted to 1020-1070 ℃, and the growth pressure is 150-250 mbar, TMGa flow and NH3The flow rate of the GaN epitaxial layer 4 is kept unchanged, the growth rate of the GaN epitaxial layer 4 at the stage is 20-25 nm/min, and the thickness of the GaN epitaxial layer 4 is 1.5-2 mu m. The second growth phase has a higher growth pressure and a slower growth rate than the first growth phase, and this high pressure slow growth phase can provide a high quality, low doped signal (channel) layer. Any value of the two endpoints and the value between the two endpoints of the range given by each parameter can be selected, and the optimal values such as growth temperature, growth pressure, gas flow and the like can be selected according to the warping degree and the performance of the grown GaN epitaxial layer 4.
Referring to fig. 1-2, in one embodiment, Al coating 2, Al, is grownxGa1-xWhen the N buffer layer 3 and the GaN epitaxial layer 4 are both formed, a carrier gas, such as H, is introduced into the reaction chamber2The Al source, the Ga source and the N source can be loaded into the reaction chamber, so that the reaction in the reaction chamber is more uniform.
After the growth of the GaN epitaxial layer 4 is finished, cooling treatment is required, and in some embodiments, N is adopted for cooling2Lowering the temperature of the atmosphere, e.g. by switching the entire atmosphere to N while keeping the pressure at the second growth stage of the GaN layer constant2And the cooling rate is 40-45 ℃/min.
Referring to fig. 2, another aspect of the present invention provides an epitaxial structure of GaN material, including at least:
a SiC substrate 1;
an Al coating 2 on the SiC substrate 1;
AlxGa1-xan N buffer layer 3 on the Al coating layer 2, wherein AlxGa1-xX in N is 0.2-0.3;
The thickness of the Al coating 2 is 0.5-1.5 nm, for example, 1 nm.
Wherein, AlxGa1-xThe thickness of the N buffer layer 3 is 70-100 nm.
Wherein, the thickness of the GaN epitaxial layer 4 is 2-3 μm.
Referring to fig. 3 to 5, the results of the examination of the GaN epitaxial layer grown on the 6-inch SiC substrate by the preparation method of the present invention and the GaN epitaxial layer of the same thickness prepared by the prior art using AlN as the buffer layer are as follows:
FIG. 3 shows the results of warpage test of 6-inch GaN epitaxial wafer grown by the method of the present invention, showing that the average value of surface height measurement is 32.56 μm, the surface height measurement range is 6-56 μm, the corresponding warpage Bowing X is 9.45 μm, Bowing Y is 11.92 μm, FIG. 4 shows the warpage test results of PL test of GaN epitaxial layer with the same thickness prepared by the prior art, showing that the average value of surface height measurement is 215.03 μm, the surface height measurement range is 53-376 μm, the corresponding warpage Bowing X is 96.29 μm, and Bowing Y is 120.32 μm. The conclusion of warping degree in PL test shows that the warping degree of the GaN epitaxial wafer prepared by the method is obviously reduced.
Fig. 5 (a) is an optical microscope picture of a gallium nitride epitaxial layer grown by the preparation method of the present invention, from which it can be seen that the GaN epitaxial layer has a flat appearance without obvious defects, and fig. 5 (b) is an optical microscope picture of the gallium nitride epitaxial layer prepared by the prior art under the same multiple, from which it is seen that the GaN epitaxial layer has a flat appearance, and the test results show that the surface of the GaN epitaxial layer prepared by the preparation method of the present invention has no obvious difference from the appearance of the GaN epitaxial layer prepared by the prior art.
The detection result shows that the preparation method greatly reduces the warping of the GaN epitaxial wafer under the condition of not influencing the appearance quality of the GaN epitaxial wafer.
In conclusion, the preparation process is simple, and Al is introduced into the SiC substratexGa1-xThe N buffer layer provides a certain space for the tensile stress borne by the subsequent GaN epitaxial layer during growth, the tensile stress generated in the epitaxial layer cooling process can be offset, and the warping problem of the large-size epitaxial wafer caused by lattice mismatch and thermal mismatch is solved. Therefore, the invention effectively overcomes some practical problems in the prior art, thereby having high utilization value and use significance.
The foregoing embodiments are merely illustrative of the principles of this invention and its efficacy, rather than limiting it, and various modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the invention, which is defined in the appended claims.
Claims (4)
1. A preparation method of a gallium nitride epitaxial layer is characterized by at least comprising the following steps:
providing a silicon carbide substrate, and carrying out surface treatment on the silicon carbide substrate;
growing an aluminum coating on the silicon carbide substrate;
growing Al on the aluminum coatingxGa1-xN buffer layer of AlxGa1-xIn N, x is 0.2-0.3;
in the AlxGa1-xGrowing a gallium nitride epitaxial layer on the N buffer layer;
growing an aluminum coating on the silicon carbide substrate comprises providing an aluminum source of trimethylaluminum, wherein the flow rate of the trimethylaluminum is 30sccm, the time is 10-30 s, the growth temperature is controlled to be 1010-1050 ℃, and the growth pressure is 50-80 mbar;
the thickness of the formed aluminum coating is 0.5-1.5 nm;
growing Al on the aluminum coatingxGa1-xThe N buffer layer comprises a gallium source trimethyl gallium, an aluminum source trimethyl aluminum and a nitrogen source ammonia gas, wherein the flow rate of trimethyl gallium is 130sccm, the flow rate of trimethyl aluminum is 350-400 sccm, the molar ratio of V/III in the growth process is 200-270, the growth temperature is controlled to be 1010-1050 ℃, and the growth pressure is controlled to be 45-65 mbar;
the Al formedxGa1-xThe thickness of the N buffer layer is 70-100 nm;
in the AlxGa1-xGrowing an epitaxial layer of gallium nitride on the N buffer layer includes,
in the first growth stage, the growth temperature is controlled to be 1000-1050 ℃, and the growth pressure is 70-150 mbar; and
in the second growth stage, the growth temperature is controlled to be 1020-1070 ℃, and the growth pressure is controlled to be 150-250 mbar;
the thickness of the gallium nitride epitaxial layer formed in the first growth stage is 200-300 nm, and the thickness of the gallium nitride epitaxial layer formed in the second growth stage is 1.5-2 mu m.
2. The method according to claim 1, wherein the surface treatment of the silicon carbide substrate comprises annealing the silicon carbide substrate in a hydrogen atmosphere, wherein the annealing is performed at a temperature of 1020 to 1070 ℃, at a pressure of 100 to 200mbar, at a hydrogen flow rate of 130 to 160L/min, and for a time of 5 to 10 min.
3. The method according to claim 1, wherein Al is present in the alloyxGa1-xGrowing a gallium nitride epitaxial layer on the N buffer layer comprises providing gallium source trimethyl gallium and nitrogen source ammonia gas, wherein the flow of trimethyl gallium is 200-300 sccm, and the molar ratio of V/III in the growth process is 700-1200.
4. An epitaxial structure prepared according to the preparation method of any one of claims 1 to 3, comprising:
a silicon carbide substrate;
an aluminum coating on the silicon carbide substrate;
AlxGa1-xan N buffer layer on the aluminum coating layer, wherein AlxGa1-xX in N is 0.2-0.3; and
an epitaxial layer of gallium nitride on the AlxGa1-xAnd an N buffer layer.
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