An epitaxial wafer and its preparation method

Abstract

This invention provides an epitaxial wafer and its preparation method. This invention utilizes C-doped Sc x Ga y Al 1‑x‑y An N-type buffer layer (y = 0 or y ≠ 0) is used as the buffer layer, C-doped ScN is used as the insertion layer, and the second carbon-doped Sc is controlled. x Ga y Al 1‑x‑y The lattice constant of the N-buffer layer is greater than that of the first carbon-doped Sc. x Ga y Al 1‑x‑y The lattice constant of the N-doped buffer layer, and the lattice constant of the carbon-doped buffer layer, is less than that of the GaN thin film. This can improve the crystal stress and crystal quality of GaN epitaxial films, and reduce the dislocation density of heteroepitaxial GaN thin films to 6 × 10⁻⁶. 7 cm ‑2 The following technologies can meet the requirements of high-power GaN-LEDs, Micro-LEDs, GaN-HEMTs, and GaN power devices, thereby promoting the development of the industry chain.

Description

Technical Field

[0001] This invention relates to the field of semiconductor materials, and in particular to an epitaxial wafer and its preparation method. Background Technology

[0002] Gallium nitride (GaN) is a typical third-generation semiconductor material, primarily used in light-emitting devices, optoelectronic devices, radio frequency devices, and power devices. The GaN industry chain has begun to take shape, with the GaN-based LED industry becoming increasingly mature and playing a significant role in lighting, displays, and other fields. The GaN-based radio frequency device industry is also rapidly developing to support applications such as 5G communication and radar, while GaN-based power devices are accelerating their entry into a wide range of application areas, including consumer electronics, industrial electronics, data centers, energy, automotive, and transportation.

[0003] Currently, the global gallium nitride (GaN) industry is experiencing explosive growth. According to analysis by research firm Yole Développement, the market size for GaN radio frequency devices was $891 million in 2020 and is projected to grow to $2.4 billion by 2026, representing a CAGR of 18%. In the GaN power device sector, the market size was $46 million in 2020 and is projected to grow to $1.1 billion by 2026, representing a CAGR of 70%.

[0004] From an industry chain perspective, the industrial structure includes upstream substrates (epitaxy wafers and epitaxial wafers), midstream device modules, and downstream application scenarios. Among these, upstream substrates, due to the high price and difficulty in mass production of wafers, primarily consist of heteroepitaxial wafers. There are three main types of GaN epitaxial wafers: GaN / Sapphire, GaN / SiC, and GaN / Si. Regardless of whether GaN is epitaxially grown on Sapphire, SiC, or Si substrates, lattice mismatch, thermal mismatch, and chemical mismatch issues exist, necessitating the use of heteroepitaxial processes to reduce mismatch stress and dislocation density.

[0005] Epitaxial GaN on Si is typically achieved using AlN and Al x Ga 1-x Nitrogen (N) acts as a buffer layer. GaN has a lower lattice constant than Si, making it prone to cracking due to tensile stress when epitaxially grown on Si; while AlN and Al... x Ga 1-x The lattice constants of nitrogen are all lower than those of GaN. As buffer layers, they can apply appropriate compressive stress to GaN, preventing GaN from cracking. During the fabrication process, Al... x Ga 1-x N-buffer layers can only be grown using epitaxial technology, which has high requirements, high cost, and poor reliability. Furthermore, in terms of blocking dislocations, Al... x Ga 1-xIt is difficult for N to set up individual dislocation blocking layers with very small lattice mismatches, and it cannot effectively control dislocations. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide an epitaxial wafer and a method for preparing the same. The epitaxial wafer prepared by the present invention can improve the stress control and dislocation control problems of GaN heteroepitaxial growth, and improve the crystal stress and crystal quality of GaN epitaxial films.

[0007] This invention provides a method for preparing an epitaxial wafer, comprising the following steps:

[0008] S1. Growing the first carbon-doped Sc on the substrate x Ga y Al 1-x-y N buffer layers; where 0 ≤ y ≤ 0.25, 0 < x < 0.18;

[0009] S2, in the first carbon doped Sc x Ga y Al 1-x-y A second carbon-doped Sc is grown on the N-buffer layer. x Ga y Al 1-x-y N-buffer layer; second carbon-doped Sc x Ga y Al 1-x-y In buffer layer N, 0 ≤ y ≤ 0.25, 0 < x < 0.18;

[0010] S3, the second carbon-doped Sc of the product obtained in step S2 x Ga y Al 1-x-y The first GaN thin film is epitaxially grown on the N-buffer layer;

[0011] S4. A carbon-doped ScN insertion layer is grown on the first GaN thin film;

[0012] S5. Epitaxially grow a second GaN thin film on the carbon-doped ScN insertion layer to obtain an epitaxial wafer;

[0013] in,

[0014] Second carbon doped Sc x Ga y Al 1-x-y The lattice constant of the N-buffer layer is greater than that of the first carbon-doped Sc. x Ga y Al 1-x-y The lattice constant of the N-buffer layer;

[0015] The lattice constants of both the first and second GaN films are greater than those of the second carbon-doped Sc film. x Gay Al 1-x-y The lattice constant of the N-buffer layer.

[0016] Preferably, y = 0, after step S2 and before step S3, the process further includes: annealing the product obtained in step S2.

[0017] Preferably, y≠0, and step S1 specifically includes:

[0018] An AlN nucleation layer is grown on a substrate, and then a first carbon-doped Sc is grown on the AlN nucleation layer. x Ga y Al 1-x-y N buffer layers; where 0 ≤ y ≤ 0.25, 0 < x < 0.18.

[0019] Preferably, in step S1, the first carbon-doped Sc x Ga y Al 1-x-y The carbon doping concentration in the N buffer layer is <1×10⁻⁶. 20 atom / cm 3 ;

[0020] In step S2, the second carbon-doped Sc x Ga y Al 1-x-y The carbon doping concentration in the N buffer layer is <1×10⁻⁶. 20 atom / cm 3 .

[0021] Preferably, in step S4, the carbon doping concentration in the carbon-doped ScN insertion layer is <1×10⁻⁶. 19 atom / cm 3 .

[0022] Preferably, the first carbon-doped Sc is grown. x Ga y Al 1-x-y N-buffer layer, growth of second carbon-doped Sc x Ga y Al 1-x-y The methods for growing the N buffer layer and the carbon-doped ScN insertion layer are independently selected from: PVD process, MOCVD process or MBE process;

[0023] The methods for epitaxially growing the first GaN thin film are: MOCVD process or MBE process;

[0024] The methods for epitaxially growing a second GaN thin film are: MOCVD process or MBE process.

[0025] Preferably, the first carbon-doped Sc x Gay Al 1-x-y The thickness of the N buffer layer is 200–500 nm;

[0026] The second carbon-doped Sc x Ga y Al 1-x-y The thickness of the N buffer layer is 200–600 nm;

[0027] The thickness of the carbon-doped ScN insertion layer is 0.5–5 nm;

[0028] The thickness of the first GaN thin film is 300–500 nm;

[0029] The thickness of the second GaN film is 1.5–10 μm;

[0030] The substrate is a Si substrate, a SiC substrate, or a Sapphire substrate.

[0031] Preferably, the annealing conditions are as follows: for Si substrates, annealing temperature 1000-1200℃, time 5-10h;

[0032] For SiC / Sapphire substrates, the annealing temperature is 1500–1700℃ and the time is 5–10 h.

[0033] Preferably, the method for growing the AlN nucleation layer is: MOCVD process or MBE process; the thickness of the AlN nucleation layer is 5-30 nm.

[0034] The present invention also provides an epitaxial wafer prepared by the preparation method described in the above technical solution.

[0035] The preparation method provided by this invention is a method for improving the crystal stress and crystal quality of GaN epitaxial films. This invention utilizes C-doped Sc x Ga y Al 1-x-y An N-type buffer layer (y = 0 or y ≠ 0) is used as the buffer layer, C-doped ScN is used as the insertion layer, and the second carbon-doped Sc is controlled. x Ga y Al 1-x-y The lattice constant of the N-buffer layer is greater than that of the first carbon-doped Sc. x Ga y Al 1-x-y The lattice constant of the N-doped buffer layer, and the lattice constant of the carbon-doped buffer layer, is less than that of the GaN thin film. This can improve the crystal stress and crystal quality of GaN epitaxial films, and reduce the dislocation density of heteroepitaxial GaN thin films to 10. 7 cm -2The following can meet the requirements of high-power GaN-LED, Micro-LED, GaN-HEMT and GaN power devices, thereby promoting the development of the industry chain.

[0036] Experimental results show that the epitaxial wafer prepared by this invention has a dislocation density of 6 × 10⁻⁶. 7 cm -2 The following methods effectively improve the crystal stress and crystal quality of GaN-based epitaxial films. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the structure of the epitaxial wafer obtained in Example 1;

[0039] Figure 2 This is a schematic diagram of the structure of the epitaxial wafer obtained in Example 2. Detailed Implementation

[0040] This invention provides a method for preparing an epitaxial wafer, comprising the following steps:

[0041] S1. Growing the first carbon-doped Sc on the substrate x Ga y Al 1-x-y N buffer layers; where 0 ≤ y ≤ 0.25, 0 < x < 0.18;

[0042] S2, in the first carbon doped Sc x Ga y Al 1-x-y A second carbon-doped Sc is grown on the N-buffer layer. x Ga y Al 1-x-y N-buffer layer; second carbon-doped Sc x Ga y Al 1-x-y In buffer layer N, 0 ≤ y ≤ 0.25, 0 < x < 0.18;

[0043] S3, the second carbon-doped Sc of the product obtained in step S2 x Ga y Al 1-x-y The first GaN thin film is epitaxially grown on the N-buffer layer;

[0044] S4. A carbon-doped ScN insertion layer is grown on the first GaN thin film;

[0045] S5. Epitaxially grow a second GaN thin film on the carbon-doped ScN insertion layer to obtain an epitaxial wafer;

[0046] in,

[0047] Second carbon doped Sc x Ga y Al 1-x-y The lattice constant of the N-buffer layer is greater than that of the first carbon-doped Sc. x Ga y Al 1-x-y The lattice constant of the N-buffer layer;

[0048] The lattice constants of both the first and second GaN films are greater than those of the second carbon-doped Sc film. x Ga y Al 1-x-y The lattice constant of the N-buffer layer.

[0049] Regarding step S1 :

[0050] S1. Growing the first carbon-doped Sc on the substrate x Ga y Al 1-x-y N-buffer layer.

[0051] In this invention, the substrate is preferably a Si substrate, a SiC substrate, or a Sapphire substrate. In this invention, the surface of the substrate is preferably cleaned before use; the cleaning method is not particularly limited and can be performed according to conventional cleaning methods in the art.

[0052] In this invention, the first carbon-doped Sc is grown. x Ga y Al 1-x-y N-buffer layer (i.e., C-doped Sc) x Ga y Al 1-x-y The preferred method for constructing the N-buffer layer is PVD (physical vapor deposition), MOCVD (metal-organic chemical vapor deposition), or MBE (molecular beam epitaxy). Among these, reactive magnetron sputtering is more preferred for PVD. These processes are respectively carried out in a PVD apparatus, an MOCVD reaction chamber, or an MBE reaction chamber.

[0053] Taking PVD process as an example, the first carbon-doped Sc is grown x Ga y Al 1-x-y The specific process of the N buffer layer is as follows: (1) Provide Scx Ga y Al 1-x-y (2) Fix the target and clean substrate in the corresponding positions in the magnetron sputtering equipment chamber; evacuate to <1×10 -3 After Pa, working gases Ar, N2 and NH3 are introduced; (3) The substrate is heated to 350-650°C, and then magnetron sputtering begins. Among them, Sc in step (1) x Ga y Al 1-x-y There are no special restrictions on the preparation method of nitrogen targets; they can be prepared using conventional alloy preparation methods. For example, high-purity metallic elements Sc, Ga, and Al are mixed in the appropriate molar ratio and then melted in a high-temperature furnace. The furnace cavity can be filled with inert gas and equipped with a magnetic stirring device. If doping is required, a trace amount of carbon (high-purity graphite) is added. Through the above preparation method and parameter control, it is beneficial to obtain carbon-doped Sc with a smooth surface and a certain thickness. x Ga y Al 1-x-y N-buffer layer.

[0054] Taking MOCVD process as an example, the first carbon-doped Sc is grown x Ga y Al 1-x-y The N-buffer layer process is as follows: Sc source, trimethyl Ga and trimethyl Al, and ammonia (NH3) are introduced in a certain molar ratio to grow carbon-doped Sc. x Ga y Al 1-x-y N-buffer layer.

[0055] Taking the MBE process as an example, the growth of first carbon-doped Sc x Ga y Al 1-x-y The N-buffer layer process is as follows: Sc source, Ga source, Al source, and N source are introduced according to a certain molar ratio to grow carbon-doped Sc. x Ga y Al 1-x-y N-buffer layer.

[0056] In this invention, the first carbon-doped Sc x Ga y Al 1-x-y The thickness of the N buffer layer is preferably 200–500 nm, specifically 200 nm, 300 nm, 400 nm, or 500 nm, and more preferably 300–400 nm.

[0057] In this invention, the first carbon-doped Sc x Ga y Al 1-x-yIn the N-buffer layer, the carbon doping concentration is preferably <1×10⁻⁶. 20 atom / cm 3 More preferably 1×10 18 ~1×10 19 atom / cm 3 This invention relates to Sc x Ga y Al 1-x-y Nitrogen (N) is doped with carbon (C) in small amounts. The radius of a C atom is 0.077 nm, slightly larger than the radius of a Ni atom (0.07 nm). The substitution of Ni with C introduces compressive stress into the crystal lattice. Therefore, carbon doping can increase the chromium content of Sc. x Ga y Al 1-x-y The compressive stress of N improves the stress of the crystal.

[0058] In this invention, the first carbon-doped Sc x Ga y Al 1-x-y In the N-buffer layer, 0 ≤ y ≤ 0.25, specifically 0, 0.05, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25. 0 < x < 0.18, specifically 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17. When y = 0, the first carbon doped with Sc... x Ga y Al 1-x-y The N-buffer layer is the first carbon-doped Sc. x Al 1-x N buffer layers; at this time, the value of x is the same as described above, and will not be repeated here.

[0059] In this invention, when y = 0, the first carbon-doped Sc is directly grown on the substrate. x Ga y Al 1-x-y N-buffer layer. When y≠0, the first carbon-doped Sc is grown on the substrate. x Ga y Al 1-x-y Before the N-buffer layer, it is preferable to first grow an AlN nucleation layer; that is, step S1 specifically includes: growing an AlN nucleation layer on the substrate, and then growing a first carbon-doped Sc on the AlN nucleation layer. x Ga y Al 1-x- y N-buffer layer.

[0060] The preferred method for growing the AlN nucleation layer is MOCVD (metal-organic chemical vapor deposition) or MBE (molecular beam epitaxy); the above methods are carried out in the corresponding MOCVD reaction chamber or MBE reaction chamber.

[0061] Taking MOCVD process as an example, the process of growing AlN nucleation layer on Si substrate is as follows: (1) At a substrate temperature of about 1100℃, clean with hydrogen for 10 to 30 minutes; (2) When the substrate temperature drops to 950℃ to 1000℃, pre-pass trimethyl Al for 10 to 15 seconds, and then pass NH3 to start AlN nucleation layer growth.

[0062] Taking the MBE process as an example, the process of growing an AlN nucleation layer on a sapphire substrate is as follows: (1) The substrate is fully nitrided with an N source at a substrate temperature of about 800℃; (2) AlN is deposited on the substrate at 700℃~750℃.

[0063] In this invention, the thickness of the AlN nucleation layer is preferably 5–30 nm, specifically 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, or 30 nm, and more preferably 15–25 nm. After forming the AlN nucleation layer, a first carbon-doped Sc is grown on the AlN nucleation layer. x Ga y Al 1-x-y N-buffer layer. First carbon-doped Sc x Ga y Al 1-x-y The types, specifications, and growth processes of the N-buffer layer are the same as those described above, and will not be repeated here.

[0064] Regarding step S2 :

[0065] S2, in the first carbon doped Sc x Ga y Al 1-x-y A second carbon-doped Sc is grown on the N-buffer layer. x Ga y Al 1-x-y N-buffer layer.

[0066] In this invention, a second carbon-doped Sc is grown. x Ga y Al 1-x-y The preferred methods for creating the N-buffer layer are PVD (physical vapor deposition), MOCVD (metal-organic chemical vapor deposition), or MBE (molecular beam epitaxy). The specific procedures for each method are described above in the section on growing the first carbon-doped Sc. x Ga y Al 1-x-yThe operation process of the N buffer layer is roughly the same, and will not be described in detail here.

[0067] In this invention, the second carbon-doped Sc x Ga y Al 1-x-y The thickness of the N buffer layer is preferably 200–600 nm, specifically 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, or 600 nm, and more preferably 350–450 nm.

[0068] In this invention, the second carbon-doped Sc x Ga y Al 1-x-y In the N-buffer layer, 0 ≤ y ≤ 0.25, specifically 0, 0.05, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25. 0 < x < 0.18, specifically 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17. When y = 0, the second carbon doped Sc... x Ga y Al 1-x-y The N-buffer layer is the second carbon-doped Sc. x Al 1-x N buffer layers; at this time, the value of x is the same as described above, and will not be repeated here.

[0069] In this invention, the first carbon doped Sc x Ga y Al 1-x-y y in the N-buffer layer and the second carbon-doped Sc x Al 1-x In the N-buffer layer, y is either simultaneously 0 or simultaneously non-0. Specifically, the buffer layer includes a first carbon-doped Sc layer. x Al 1-x N-buffer layer and second carbon-doped Sc x Al 1-x N-buffer layer, or, the buffer layer includes a first carbon-doped Sc x Ga y Al 1-x-y N-buffer layer and second carbon-doped Sc x Ga y Al 1-x-y N buffer layer (y≠0). When y≠0, it is equivalent to Sc. x Al 1-x The doping of Ga atoms into N is beneficial for improving Scx Al 1- x The crystal quality of N.

[0070] In this invention, the second carbon-doped Sc x Ga y Al 1-x-y In the N-buffer layer, the carbon doping concentration is preferably <1×10⁻⁶. 20 atom / cm 3 More preferably 5×10 17 ~5×10 18 atom / cm 3 This invention relates to Sc x Ga y Al 1-x-y Nitrogen (N) is doped with carbon (C) in small amounts. The radius of a C atom is 0.077 nm, slightly larger than the radius of a Ni atom (0.07 nm). The substitution of Ni with C introduces compressive stress into the crystal lattice. Therefore, carbon doping can increase the chromium content of Sc. x Ga y Al 1-x-y The compressive stress of N improves the stress of the crystal.

[0071] In this invention, the second carbon doped Sc x Ga y Al 1-x-y The lattice constant of the N-buffer layer is greater than that of the first carbon-doped Sc. x Ga y Al 1-x- y The lattice constant of the N-buffer layer. In this invention, the lattice constant of the first carbon doped Sc is controlled. x Ga y Al 1-x-y N-buffer layer and second carbon-doped Sc x Ga y Al 1-x-y The lattice constants of the two layers are controlled by the different values ​​of x and y in the N-buffer layer; increasing the values ​​of both x and y increases the lattice constant of the buffer layer. The lattice constant of the buffer layer is more sensitive to the value of x; an increase of 0.01 in x is approximately equivalent to an increase of 0.05 in y. The first carbon layer is doped with Sc. x Ga y Al 1-x-y In the N-buffer layer, x and y are denoted as x1 and y1, respectively, and the second carbon doped Sc x Ga y Al 1-x-yIf the x and y in the N buffer layer are denoted as x2 and y2, it is preferably specifically controlled that the relationship between x1 and x2 is 0.02 < x1 < 0.17, 0.02 < x2 < 0.17, and x1 and x2 are specifically independently selected from 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, and moreover, x1 < x2, x2 - x1 > 0.03; when y ≠ 0, the relationship between x1 and x2 is the same as above and will not be elaborated, and the relationship between y1 and y2 is preferably 0.01 < y1 < 0.25, 0.01 < y2 < 0.25, and y1 and y2 are specifically independently selected from x x Ga y Al 1-x in the N buffer layer, x = 0.1, the second carbon-doped Sc x Ga y Al 1-x in the N buffer layer, x = 0.15. In some other embodiments of the present invention, y ≠ 0, the first carbon-doped Sc x Ga y Al 1-x-y in the N buffer layer, x = 0.08, y = 0.11, the second carbon-doped Sc x Ga[[ID=二十一]] y Al 1-x-y in the N buffer layer, x = 0.12, y = 0.17.

[0072] In some embodiments of the present invention, the first carbon-doped Sc x Al<00,00261> The lattice constant a of the N buffer layer = 3.1514, the second carbon-doped Sc x Al 1-x The lattice constant a of the N buffer layer = 3.1740, the lattice constant a of the first GaN film = 3.1888, and the lattice constant a of the second GaN film = 3.1891. In some other embodiments of the present invention, the first carbon-doped Sc x Ga​​​​​​​​​The lattice constant of the N buffer layer is a = 3.1738, the lattice constant of the first GaN thin film is a = 3.1886, and the lattice constant of the second GaN thin film is a = 3.1891.

[0073] Regarding step S3 :

[0074] S3, the second carbon-doped Sc of the product obtained in step S2 x Ga y Al 1-x-y The first GaN thin film is epitaxially grown on the N-buffer layer.

[0075] In this invention, when the first carbon is doped with Sc x Ga y Al 1-x-y N-buffer layer and second carbon-doped Sc x Ga y Al 1-x-y When y = 0 on the N-buffer layer, after step S2 and before step S3, the process further includes: annealing the product obtained in step S2; that is, before epitaxializing the first GaN film, it is preferable to anneal the product obtained in step S2 first. Annealing helps to improve the carbon doping of Sc. x Ga y Al 1-x-y The crystallinity of the N-buffer layer. After annealing, a second carbon-doped Sc layer is then formed. x Ga y Al 1-x-y The first GaN thin film is epitaxially grown on the N-buffer layer.

[0076] Different annealing conditions are used for different substrates. For Si substrates, the annealing temperature is 1000–1200℃, specifically 1000℃, 1100℃, or 1200℃; the annealing time is 5–10 hours, specifically 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours. For SiC / Sapphire substrates, the annealing temperature is 1500–1700℃, specifically 1500℃, 1600℃, or 1700℃; the annealing time is 5–10 hours, specifically 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0077] In this invention, when the first carbon is doped with Sc x Ga y Al 1-x-y N-buffer layer and second carbon-doped Sc x Ga y Al 1-x-y When y≠0 on the N-buffer layer, no annealing is required; the second carbon-doped Sc of the product obtained in step S2 can be directly processed. x Ga y Al 1-x-yThe first GaN thin film can be epitaxially grown on the N-buffer layer.

[0078] In this invention, the method for epitaxially growing GaN thin films is not particularly limited; it can be performed according to conventional GaN thin film epitaxial processes in the art, preferably using MOCVD or MBE processes. The process of growing GaN thin films using MOCVD or MBE processes is not particularly limited; it can be performed according to conventional operating procedures in the art. In this invention, before epitaxially growing the first GaN thin film, it is preferable to first clean the buffer layer with plasma.

[0079] In this invention, the thickness of the first GaN thin film is preferably 300-500 nm, specifically 300 nm, 400 nm, or 500 nm.

[0080] Regarding step S4 :

[0081] S4. A carbon-doped ScN insertion layer is grown on the first GaN thin film.

[0082] In this invention, the preferred method for growing carbon-doped ScN intercalation layers is PVD (physical vapor deposition). The specific process of growing carbon-doped ScN intercalation layers using PVD is as follows: (1) Fix the target material Sc and the clean substrate in the corresponding positions of the magnetron sputtering equipment chamber; evacuate to <1×10 -3 After Pa, the working gases Ar, N2 and NH3 are introduced. If C doping is required, a small amount of CH4 gas is introduced. (2) The substrate is heated to 350-650℃ to deposit and grow a carbon-doped ScN insertion layer.

[0083] In this invention, the carbon doping concentration in the carbon-doped ScN insertion layer is preferably <1×10⁻⁶. 19 atom / cm 3 More preferably 1×10 17 ~1×10 18 atom / cm 3 The lattice constant of ScN is slightly smaller than that of GaN. Adding a small amount of C can slightly increase the lattice constant of ScN, making its lattice mismatch with GaN smaller, which is beneficial to improving the crystal quality of the product.

[0084] In this invention, the thickness of the carbon-doped ScN insertion layer is preferably 0.5 to 5 nm, specifically 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, and more preferably 1 to 3 nm.

[0085] Regarding step S5 :

[0086] S5. Epitaxially grow a second GaN film on the carbon-doped ScN insertion layer to obtain an epitaxial wafer.

[0087] In this invention, the method for epitaxially growing the second GaN thin film is not particularly limited, and can be performed according to conventional GaN thin film epitaxial processes in the art, preferably MOCVD or MBE processes. The process of growing the GaN thin film using MOCVD or MBE processes is not particularly limited, and can be performed according to conventional operating procedures in the art. In this invention, before epitaxially growing the second GaN thin film, it is preferable to first clean the buffer layer with plasma.

[0088] In this invention, the thickness of the second GaN thin film is preferably 1.5–10 μm, specifically 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, and more preferably 2–5 μm. In this invention, the lattice constants of both the first and second GaN thin films are greater than those of the second carbon-doped Sc. x Ga y Al 1-x-y The lattice constant of the N-buffer layer.

[0089] In this invention, "first" and "second" have no special limiting meaning and are not a limitation on the type of buffer layer, but rather indicate that there are two buffer layers for the convenience of describing each buffer layer. Similarly, "first," "second," etc., used elsewhere in this document have no special limiting meaning.

[0090] The present invention also provides an epitaxial wafer prepared by the preparation method described in the above technical solution, namely a GaN-based epitaxial wafer.

[0091] When y = 0, the epitaxial wafer structure includes the following sequentially stacked composite layers: substrate → first carbon-doped Sc x Al 1-x N-buffer layer → Growth of second carbon-doped Sc x Al 1-x N-buffer layer → First GaN thin film → Carbon-doped ScN insertion layer → Second GaN thin film, see Figure 1 , Figure 1 This is a schematic diagram of the epitaxial wafer obtained in Embodiment 1 of the present invention. The specifications, types, and thicknesses of each layer are consistent with those described in the preceding technical solution, and will not be repeated here.

[0092] When y≠0, the epitaxial wafer structure includes the following sequentially stacked composite layers: substrate → AlN nucleation layer → first carbon-doped Sc. x Ga y Al 1-x-y N-buffer layer → Growth of second carbon-doped Sc x Ga y Al 1-x-y N-buffer layer → First GaN thin film → Carbon-doped ScN insertion layer → Second GaN thin film, see Figure 2 , Figure 2This is a schematic diagram of the epitaxial wafer obtained in Embodiment 2 of the present invention. The specifications, types, and thicknesses of each layer are consistent with those described in the preceding technical solution, and will not be repeated here.

[0093] The epitaxial wafer provided by this invention utilizes C-doped Sc x Ga y Al 1-x-y An N-type buffer layer (y = 0 or y ≠ 0) is used as the buffer layer, C-doped ScN is used as the insertion layer, and the second carbon-doped Sc is controlled. x Ga y Al 1-x-y The lattice constant of the N-buffer layer is greater than that of the first carbon-doped Sc. x Ga y Al 1-x-y The lattice constant of the N-doped buffer layer, and the lattice constant of the carbon-doped buffer layer, is less than that of the GaN thin film. This can improve the crystal stress and crystal quality of GaN epitaxial films, and reduce the dislocation density of heteroepitaxial GaN thin films to 10. 7 cm -2 The following can meet the requirements of high-power GaN-LED, Micro-LED, GaN-HEMT and GaN power devices, thereby promoting the development of the industry chain.

[0094] Experimental results show that the epitaxial wafer prepared by this invention has a dislocation density of 6 × 10⁻⁶. 7 cm -2 The following methods effectively improve the crystal stress and crystal quality of GaN-based epitaxial films.

[0095] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0096] Example 1

[0097] S1. After cleaning the surface of the Si substrate (650 μm thick), place it in a PVD apparatus to grow the first carbon-doped Sc. x Al 1-x N-buffer layer (x = 0.1, carbon doping concentration 5 × 10⁻⁶) 18 atom / cm 3 (380nm thick).

[0098] S2, in the first carbon doped Sc x Al 1-x A second carbon-doped Sc continues to grow on the N-buffer layer. x Al 1-x N-buffer layer (x = 0.15, carbon doping concentration 2 × 10⁻⁶) 18atom / cm 3 (Layer thickness 460nm).

[0099] S3. Anneal the sample obtained in step S2 under the following conditions: 1200℃ for 9 hours. After annealing, clean the buffer layer with plasma and then transfer it to the MOCVD reaction chamber for the first GaN thin film epitaxy (thickness 350nm).

[0100] S4. Transfer the sample obtained in step S3 to a PVD device and grow a carbon-doped ScN insertion layer (carbon doping concentration of 2×10⁻⁶) on the first GaN film. 17 atom / cm 3 (Layer thickness 1.5nm).

[0101] S5. Transfer the sample obtained in step S4 to the MOCVD reaction chamber for a second GaN thin film epitaxy (thickness of 5 μm).

[0102] Among them, the first carbon-doped Sc x Al 1-x The lattice constant of the N-buffer layer is a = 3.1514, and the second carbon-doped Sc x Al 1-x The lattice constant of the N buffer layer is a = 3.1740, the lattice constant of the first GaN thin film is a = 3.1888, and the lattice constant of the second GaN thin film is a = 3.1891.

[0103] The cross-sectional structure of the epitaxial wafer obtained in Example 1 is as follows: Figure 1 As shown.

[0104] Example 2

[0105] S1. After cleaning the surface of the Si substrate (1000 μm thick), place it in the MOCVD reaction chamber to grow an AlN nucleation layer (20 nm thick). Then, place it in an MBE device to grow the first carbon-doped Sc. x Ga y Al 1-x-y N-buffer layer (x = 0.08, y = 0.11, carbon doping concentration 6 × 10⁻⁶) 18 atom / cm 3 (300nm thick).

[0106] S2, in the first carbon doped Sc x Ga y Al 1-x-y A second carbon-doped Sc continues to grow on the N-buffer layer. x Ga y Al 1-x-y N-buffer layer (x = 0.12, y = 0.17, carbon doping concentration 3 × 10⁻⁶) 18atom / cm 3 (Layer thickness 400nm).

[0107] S3. Transfer the sample obtained in step S2 to the MOCVD reaction chamber, and then perform second carbon doping on the Sc. x Ga y Al 1-x-y The first GaN thin film epitaxy (thickness 300 nm) was performed on the N buffer layer.

[0108] S4. Transfer the sample obtained in step S3 to a PVD device and grow a carbon-doped ScN insertion layer (carbon doping concentration of 5 × 10⁻⁶) on the first GaN film. 17 atom / cm 3 (Layer thickness 1 nm).

[0109] S5. Transfer the sample obtained in step S4 to the MOCVD reaction chamber for a second GaN thin film epitaxy (thickness 4.5 μm).

[0110] Among them, the first carbon-doped Sc x Ga y Al 1-x-y The lattice constant of the N-buffer layer is a = 3.1513, and the second carbon-doped Sc x Ga y Al 1-x-y The lattice constant of the N buffer layer is a = 3.1738, the lattice constant of the first GaN thin film is a = 3.1886, and the lattice constant of the second GaN thin film is a = 3.1891.

[0111] The cross-sectional structure of the epitaxial wafer obtained in Example 2 is as follows: Figure 2 As shown.

[0112] Comparative Example 1

[0113] Implemented according to Example 1, except that in step S2 only the first carbon-doped Sc is grown. x Al 1-x N-buffer layer, without growing a second carbon-doped Sc x Al 1-x N-buffer layer.

[0114] Comparative Example 2

[0115] The implementation follows Example 1, except that the value of x is changed to make the second carbon doped with Sc. x Al 1-x The lattice constant of the N-buffer layer is < that of the first carbon-doped Sc. x Al 1-x The lattice constant of the N-buffer layer.

[0116] Example 3: Product Testing

[0117] The dislocation densities of the epitaxial wafers obtained in Examples 1-2 and Comparative Examples 1-2 were tested, and the results are shown in Table 1.

[0118] Table 1: Dislocation density of products obtained in Examples 1-2 and Comparative Examples 1-2

[0119] <![CDATA[Dislocation density, cm -2 > Example 1 <![CDATA[6×10 7 ]]> Example 2 <![CDATA[5×10 7 ]]> Comparative Example 1 <![CDATA[2×10 8 ]]> Comparative Example 2 <![CDATA[5×10 9 ]]>

[0120] As can be seen, compared with Comparative Examples 1-2, the dislocation density of the products obtained in Examples 1-2 is significantly reduced. The comparison of the effects of Example 1 and Comparative Examples 1-2 demonstrates that the present invention, by setting two layers of carbon-doped Sc... x Al 1-x With N buffer layers and controlling the lattice constant of the second buffer layer to be greater than that of the first buffer layer, the dislocation density of the material can be significantly reduced and the crystal quality of the material can be improved.

[0121] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing an epitaxial wafer, characterized in that, Includes the following steps: S1. Growing the first carbon-doped Sc on the substrate x Ga y Al 1-x-y N buffer layers; where 0 ≤ y ≤ 0.25, 0 < x < 0.18; S2, in the first carbon doped Sc x Ga y Al 1-x-y A second carbon-doped Sc is grown on the N-buffer layer. x Ga y Al 1-x-y N-buffer layer; second carbon-doped Sc x Ga y Al 1-x-y In buffer layer N, 0 ≤ y ≤ 0.25, 0 < x < 0.18; S3, the second carbon-doped Sc of the product obtained in step S2 x Ga y Al 1-x-y The first GaN thin film is epitaxially grown on the N-buffer layer; S4. A carbon-doped ScN insertion layer is grown on the first GaN thin film; S5. Epitaxially grow a second GaN thin film on the carbon-doped ScN insertion layer to obtain an epitaxial wafer; in, Second carbon doped Sc x Ga y Al 1-x-y The lattice constant of the N-buffer layer is greater than that of the first carbon-doped Sc. x Ga y Al 1-x-y The lattice constant of the N-buffer layer; The lattice constants of both the first and second GaN films are greater than those of the second carbon-doped Sc film. x Ga y Al 1-x-y The lattice constant of the N-buffer layer; in, When y=0, the first carbon-doped Sc is grown directly on the substrate. x Ga y Al 1-x-y The N-buffer layer, and after step S2 and before step S3, also includes: annealing the product obtained in step S2; When y≠0, step S1 specifically includes: growing an AlN nucleation layer on the substrate, and then growing a first carbon-doped Sc on the AlN nucleation layer. x Ga y Al 1-x-y N-buffer layer.

2. The preparation method according to claim 1, characterized in that, In step S1, the first carbon-doped Sc x Ga y Al 1-x-y The carbon doping concentration in the N buffer layer is <1×10⁻⁶. 20 atom / cm 3 ; In step S2, the second carbon-doped Sc x Ga y Al 1-x-y The carbon doping concentration in the N buffer layer is <1×10⁻⁶. 20 atom / cm 3 .

3. The preparation method according to claim 1, characterized in that, In step S4, the carbon doping concentration in the carbon-doped ScN insertion layer is <1×10⁻⁶. 19 atom / cm 3 .

4. The preparation method according to claim 1, characterized in that, Growth of first carbon-doped Sc x Ga y Al 1-x-y N-buffer layer, growth of second carbon-doped Sc x Ga y Al 1-x-y The methods for growing the N buffer layer and the carbon-doped ScN insertion layer are independently selected from: PVD process, MOCVD process or MBE process; The methods for epitaxially growing the first GaN thin film are: MOCVD process or MBE process; The methods for epitaxially growing a second GaN thin film are: MOCVD process or MBE process.

5. The preparation method according to claim 1, characterized in that, The first carbon-doped Sc x Ga y Al 1-x-y The thickness of the N buffer layer is 200~500nm; The second carbon-doped Sc x Ga y Al 1-x-y The thickness of the N buffer layer is 200~600nm; The thickness of the carbon-doped ScN insertion layer is 0.5~5 nm; The thickness of the first GaN thin film is 300~500nm; The thickness of the second GaN film is 1.5~10μm; The substrate is a Si substrate, a SiC substrate, or a Sapphire substrate.

6. The preparation method according to claim 1, characterized in that, The annealing conditions are as follows: for Si substrates, annealing temperature is 1000~1200℃, time is 5~10h; For SiC / Sapphire substrates, the annealing temperature is 1500~1700℃ and the time is 5~10h.

7. The preparation method according to claim 1, characterized in that, The methods for growing AlN nucleation layers are: MOCVD process or MBE process; The thickness of the AlN nucleation layer is 5~30nm.

8. An epitaxial wafer prepared by any one of claims 1 to 7.

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