Method for growing a gaN single crystal thin film on a gallium lanthanum silicate crystal substrate based on mocvd

Abstract

The application discloses a method for growing GaN single crystal thin film on a gallium lanthanum silicate crystal substrate based on a MOCVD method, and is characterized by comprising the following steps: (1) putting the cleaned gallium lanthanum silicate crystal substrate into a metal organic chemical vapor deposition chamber, introducing a mixed gas of H2 and NH3 into a reaction chamber, heating to 1000-1200 DEG C, and keeping the pressure in the reaction chamber at 100-300 mbar to high-temperature treat the substrate for 3-8 min; (2) taking trimethyl gallium and NH3 as a gas source, and growing a low-temperature GaN nucleation layer on the gallium lanthanum silicate crystal substrate at a temperature of 400-600 DEG C; and (3) heating the reaction chamber to 900-1200 DEG C to grow a high-temperature GaN single crystal thin film on the low-temperature GaN nucleation layer, and the method has the advantages that the lattice mismatch and the thermal expansion coefficient mismatch are both low, and the GaN single crystal thin film has high quality.

Description

Technical Field

[0001] This invention relates to a method for growing semiconductor materials, and more particularly to a method for growing GaN single-crystal thin films on lanthanum gallium silicate-based crystal substrates using MOCVD. Background Technology

[0002] In recent years, GaN has attracted much attention as an extremely popular material due to its wide direct bandgap, high thermal conductivity, and good chemical stability, making it a promising candidate for applications in optoelectronics, high-frequency devices, and high-power devices. Despite the widespread use of GaN, producing high-quality GaN epitaxial layers remains a significant challenge.

[0003] Since there is no natural GaN substrate, heteroepitaxial growth is the main growth method for GaN thin films. Considering factors such as substrate price and thermal conductivity, sapphire, Si, and SiC substrates are currently widely used. However, due to the large lattice and thermal mismatches, the grown GaN is prone to cracking and has a high dislocation density, which affects and limits its application. Therefore, finding a suitable substrate material to grow high-quality GaN thin films is a huge challenge. In 2015, Byung-Guon Park et al. from Chungnam National University in South Korea (Journal of Crystal Growth, 425, 2015, 149-153) reported the growth of GaN thin films on sapphire, Si, and LGS substrates using plasma-assisted molecular beam epitaxy (PA-MBE). They found that stress-free GaN thin films were grown on lanthanum gallium silicate crystal substrates, indicating that lanthanum gallium silicate crystal is an ideal GaN epitaxial substrate. However, due to the low growth rate and high cost of the MBE method, it is difficult to meet the growing demand for GaN materials in the current rapid development of semiconductor devices.

[0004] Currently, with the rapid development of semiconductor devices, the demand for high-quality and high-yield GaN thin films is increasing, and problems such as large lattice mismatch and poor thermal expansion matching between current mainstream heteroepitaxial substrates and GaN are becoming more prominent. Metal-organic chemical vapor deposition (MOCVD) is a commonly used method for epitaxial growth of GaN thin films, offering fast growth rates and high-quality epitaxial films, which is of great significance for promoting the rapid development of GaN-based devices. However, compared to the lower growth temperature of the MBE method, the growth temperature of the MOCVD method is usually above 1000˚C. This places high demands on the high-temperature stability of the substrate, and the large difference in thermal expansion coefficients between GaN and the substrate during the cooling process after growth can easily increase the stress of the film and cause cracking. Therefore, the MOCVD method for growing GaN thin films usually places more stringent requirements on the substrate. Currently, there is no published research on growing high-quality GaN single-crystal thin films on gallium lanthanum silicate-based crystal substrates using the MOCVD method, either domestically or internationally. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for growing GaN single crystal thin films on lanthanum gallium silicate-based crystal substrates based on MOCVD with low lattice mismatch and thermal expansion coefficient mismatch.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a method for growing GaN single crystal thin films on lanthanum gallium silicate-based crystal substrates based on MOCVD, comprising the following steps:

[0007] (1) Place the cleaned gallium lanthanum silicate crystal substrate into the metal-organic chemical vapor deposition (MOCVD) chamber, introduce a mixture of H2 and NH3 into the reaction chamber, heat to 1000-1200 ˚C, and perform high-temperature treatment on the substrate for 3-8 min while maintaining the reaction chamber pressure at 100-300 mbar.

[0008] (2) Using trimethylgallium (TMGA) and NH3 as gas sources, a low-temperature GaN nucleation layer is grown on a lanthanum gallium silicate crystal substrate in the temperature range of 400 to 600 °C;

[0009] (3) Heat the reaction chamber to 900-1200 °C and grow a high-temperature GaN single crystal thin film on the low-temperature GaN nucleation layer.

[0010] Furthermore, the general formula of the lanthanum gallium silicate crystal described in step (1) is A3BC3D2O. 14 Where A is La 3+ Nb 3+ Ca 2+ Sr 2+ Ba 2+ Pb2+ Or Na + B is Ga 3+ Al 3+ Zn 3+ Co 3+ In 3+ Fe 3+ Ta 5+ Nb 5+ V 5+ or Sb 5+ C is Ga 3+ Al 3+ or Fe 3+ D is Si 4+ Ge 4+ Ti 4+ or Sn 4+ ,

[0011] Furthermore, the method for preparing gallium lanthanum silicate crystals in step (1) includes the Czochralski method and the drop method, with a size of 1 to 6 inches.

[0012] Further, step (2) specifically involves cooling the reaction chamber to 400-600˚C, introducing trimethylgallium (TMGA) at a flow rate of 40-75 sccm, adjusting the NH3 flow rate to 5-18 slm, and growing for 3-8 min under a pressure of 100-600 mbar to obtain a low-temperature GaN nucleation layer.

[0013] Further, step (3) specifically involves heating the reaction chamber to 1000-1150˚C, adjusting the TMGa flow rate to 220-450 sccm, adjusting the NH3 flow rate to 20-40 slm, and growing for 1-5 hours under a pressure of 150-500 mbar, thereby growing a high-temperature GaN single crystal thin film on the low-temperature GaN nucleation layer.

[0014] Compared with existing technologies, the advantages of this invention are as follows: This invention is based on the MOCVD method for growing GaN single-crystal thin films on lanthanum gallium silicate-based crystal substrates. It selects an ideally lattice-matched lanthanum gallium silicate-based crystal as the substrate and directly grows high-quality GaN single-crystal thin films on the substrate using MOCVD. Because the selected lanthanum gallium silicate crystal has low lattice mismatch and low thermal expansion coefficient mismatch with GaN, the quality of the grown film is significantly improved. In the embodiments of this invention, the single-crystal GaN thin films grown on CTAGS substrates exhibit good continuity, smooth surfaces, and high single-crystal quality, effectively avoiding the generation of defects such as dislocations. These films can be used to fabricate GaN-based high-frequency and high-power devices, as well as GaN-based semiconductor devices. Furthermore, the operation process is simple, which is of great significance for promoting the industrial application of GaN thin films. Attached Figure Description

[0015] Figure 1 This is a rocking curve of the GaN thin film grown on the CTAS crystal substrate by MOCVD in Example 1.

[0016] Figure 2 The images shown are: (a) a transmission electron microscope (TEM) image of the GaN thin film grown on the CTAGS substrate, (b) a high-resolution transmission electron microscope (HRTEM) image of the GaN thin film, (c) a selected area electron diffraction (SAED) pattern of the GaN thin film, and (d) a selected area electron diffraction (SAED) pattern of the CTAGS substrate in Example 2.

[0017] Figure 3 This is a schematic diagram of the lattice arrangement of GaN grown on the CTAGS substrate in Example 2. (a) The GaN lattice and the CTAGS lattice without rotation, (b) and (c) There is a rotation of 19.1˚ between the GaN lattice and the CTAGS lattice after actual growth.

[0018] Figure 4 This is an atomic force microscope (AFM) image of the GaN thin film grown on the CNAS substrate in Example 3. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. I. Specific Implementation Methods

[0021] Example 1

[0022] 1 inch of Ca3TaAl3Si2O 14 (CTAS) Single-crystal substrates were sequentially placed in acetone and isopropanol and sonicated for 10 min, then rinsed with deionized water and dried with N2. The cleaned substrates were placed in a metal-organic chemical vapor deposition (MOCVD) chamber, and a mixture of H2 and NH3 was introduced into the reaction chamber. The temperature was raised to 1200 ˚C, and the substrate was subjected to high-temperature treatment for 3 min while maintaining a reaction chamber pressure of 100 mbar. Then, the temperature was lowered to 400 ˚C, and TMGa was introduced at a flow rate of 40 sccm, while the NH3 flow rate was adjusted to 5 slm. The substrates were grown for 6 min while maintaining a pressure of 300 mbar to obtain a low-temperature GaN nucleation layer. The temperature was then raised to 1000 ˚C, the TMGa flow rate was adjusted to 300 sccm, the NH3 flow rate was adjusted to 20 slm, and the substrates were grown for 1 h while maintaining a pressure of 150 mbar to obtain a high-temperature GaN single-crystal thin film on the low-temperature GaN nucleation layer. Figure 1 The image shows the rocking curve of the GaN thin film grown on the CTAS crystal substrate. The full width at half maximum (FWHM) is 720 arcsec, indicating that a high-quality GaN thin film with low defect density has been grown.

[0023] Example 2

[0024] 2-inch Ca3Ta(Ga 0.5 Al 0.5 )3Si2O 14 The (CTAGS) single-crystal substrate was sequentially placed in acetone and isopropanol and ultrasonically treated for 10 min, then rinsed with deionized water and dried with N2. The cleaned substrate was placed in the MOCVD chamber, and a mixture of H2 and NH3 was introduced into the reaction chamber. The temperature was raised to 1100 ˚C, and the substrate was subjected to high-temperature treatment for 5 min while maintaining a reaction chamber pressure of 200 mbar. Then, the temperature was lowered to 560 ˚C, and TMGa was introduced at a flow rate of 75 sccm. The NH3 flow rate was adjusted to 10 slm, and growth was carried out for 3 min while maintaining a pressure of 600 mbar to obtain a low-temperature GaN nucleation layer. Then, the temperature was raised to 1080 ˚C, the TMGa flow rate was adjusted to 220 sccm, the NH3 flow rate was adjusted to 30 slm, and growth was carried out for 3 h while maintaining a pressure of 300 mbar to grow a high-temperature GaN single-crystal thin film on the low-temperature GaN nucleation layer.

[0025] Reference Figure 2 , Figure 2 (a) is a TEM image of the substrate and the thin film cross section. The interface is flat, indicating that the grown thin film is of good quality and the substrate is not damaged. Figure 2 (b) is the HRTEM image of the thin film. The lattice fringes are consistent, which indicates that the grown GaN thin film is a single crystal thin film. Figure 2 (c) and (d) are selected area electron diffraction (SAED) patterns of GaN thin film and CTAGS substrate under the same test conditions, respectively. By calibrating the diffraction spots, the lattice arrangement relationship between the substrate and the thin film after growing GaN single-crystal thin film on the CTAGS substrate by MOCVD can be determined as: GaN(0001) / / CTAGS(0001), GaN( / / CTAGS( This indicates that the GaN lattice has a certain deflection angle on the substrate, which is CTAGS ( ) and CTAGS The angle between the two points is calculated to be 19.1˚, indicating that the GaN lattice has rotated by 19.1˚ on the CTAGS substrate. This relationship can be used to draw... Figure 3 The diagram shows a schematic of the crystal lattice arrangement.

[0026] After calculating the lattice arrangement relationship between the actually grown GaN and CTAGS, the lattice mismatch between GaN and CTAGS can be calculated, and the results are shown in Table 1. It can be seen that the GaN lattice rotates by 19.1˚ during MOVCVD growth on the CTAGS substrate, resulting in a lattice mismatch of 4.15%. In contrast, when GaN is grown on a sapphire substrate, the lattice rotation is 30˚, and the lattice mismatch is 16.1% (CrystEngComm, 2013, 15, 7965–7969). This demonstrates that the CTAGS substrate we used is of high quality, and its lattice mismatch for epitaxial growth of GaN thin films is significantly lower than that of sapphire.

[0027] Example 3

[0028] 1 inch of Ca3NbAl3Si2O 14 (CNAS) The single-crystal substrate was sequentially placed in acetone and isopropanol and ultrasonically treated for 10 min, then rinsed with deionized water and dried with N2. The cleaned substrate was placed in the MOCVD chamber, and a mixture of H2 and NH3 was introduced into the reaction chamber. The temperature was raised to 1000 ˚C, and the substrate was treated at high temperature for 8 min while maintaining a reaction chamber pressure of 300 mbar. Then, the temperature was lowered to 600 ˚C, and TMGa was introduced at a flow rate of 60 sccm. The NH3 flow rate was adjusted to 18 slm, and the substrate was grown for 8 min while maintaining a pressure of 100 mbar to obtain a low-temperature GaN nucleation layer. Then, the temperature was raised to 1150 ˚C, the TMGa flow rate was adjusted to 450 sccm, the NH3 flow rate was adjusted to 40 slm, and the substrate was grown for 5 h while maintaining a pressure of 500 mbar to obtain a high-temperature GaN single-crystal thin film on the low-temperature GaN nucleation layer. Figure 4 The image shows the AFM pattern of a GaN thin film grown on a CNAS crystal substrate. Obvious step flow can be observed on the surface, indicating that the grown film is of good quality.

[0029] II. Comparison of Experimental Results

[0030] Comparative Example 1

[0031] Compared with the 2013 paper (CrystEngComm, 2013, 15, 7965–7969) on a single-crystal GaN film grown on 2-inch sapphire, the study found that the actual lattice mismatch between GaN and sapphire was 16.1% when single-crystal GaN was epitaxially grown on sapphire.

[0032] Referring to Table 1, the lattice mismatches between the CTAS, CTAGS, and CNAS substrates and the GaN thin film in Examples 1, 2, and 3 of this patent are 4.15%, 5.26%, and 5.39%, respectively, which are much lower than the lattice mismatches between sapphire and the GaN thin film.

[0033] Comparative Example 2

[0034] Comparing the GaN thin film grown on an LGS substrate using the MBE method in the literature (CrystEngComm, 2015, 17, 4455), the half-width at half-maximum (WHM) of the grown GaN film is 828 arcsec, while the WHM of the GaN thin film grown on a CTAS substrate using the MOCVD method in Example 1 of this patent is only 720 arcsec. This demonstrates that the present invention can grow GaN thin films with fewer defects on LGS-type substrates. Table 1 shows the actual lattice matching calculation results of the CTAS, CTAGS, and CNAS substrates and GaN thin films in Examples 1, 2, and 3.

[0035] Table 1. Calculation of lattice mismatch between the grown GaN film and CTAGS, CTAS, and CNAS crystals

[0036] .

[0037] The foregoing description is not intended to limit the invention, nor is the invention limited to the examples given. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the invention should also be considered within the protection scope of the invention.

Claims

1. A method for growing GaN single-crystal thin films on lanthanum gallium silicate-based crystal substrates using MOCVD, characterized in that... Includes the following steps: (1) The cleaned gallium lanthanum silicate crystal substrate is placed in a metal-organic chemical vapor deposition chamber. A mixture of H2 and NH3 is introduced into the reaction chamber, and the temperature is raised to 1000-1200 °C. The substrate is then subjected to high-temperature treatment for 3-8 min while maintaining a reaction chamber pressure of 100-300 mbar. The gallium lanthanum silicate crystal is selected from Ca3Ta(Ga x Al 1-x )3Si2O 14 x = 0 to 1; (2) Using trimethylgallium and NH3 as gas sources, a low-temperature GaN nucleation layer is grown on a lanthanum gallium silicate crystal substrate in the temperature range of 400-600 °C. Specifically, the reaction chamber is cooled to 400-600 °C, trimethylgallium is introduced at a flow rate of 40-75 sccm, the flow rate of NH3 is adjusted to 5-18 slm, and the growth is carried out for 3-8 min under the condition of maintaining a pressure of 100-600 mbar to obtain a low-temperature GaN nucleation layer. (3) The reaction chamber is heated to 900-1200 °C, and a high-temperature GaN single crystal film is grown on the low-temperature GaN nucleation layer. Specifically, the reaction chamber is heated to 1000-1150 °C, the TMGa flow rate is adjusted to 220-450 sccm, the NH3 flow rate is adjusted to 20-40 slm, and the film is grown for 1-5 hours under the condition of maintaining a pressure of 150-500 mbar. A high-temperature GaN single crystal film is then grown on the low-temperature GaN nucleation layer.

2. The method for growing GaN single-crystal thin films on lanthanum gallium silicate-based crystal substrates based on MOCVD according to claim 1, characterized in that: The method for preparing gallium lanthanum silicate crystals described in step (1) includes the Czochralski method and the drop method, with a size of 1 to 6 inches.

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