A method for growing a high carrier concentration heavily doped gallium oxide epitaxial film

Abstract

The application discloses a growth method of a high-carrier-concentration heavily doped gallium oxide epitaxial film, and mainly solves the problems of high cost, high defect density and low carrier concentration of a currently used heavily doped epitaxial film substrate. The implementation scheme is as follows: a sapphire substrate is selected and cleaned; the cleaned substrate is put into a reaction cavity of a MOCVD (Metal Organic Chemical Vapor Deposition) for pretreatment; two layers of buffer layers with different mechanisms are sequentially grown on the substrate by changing the temperature, pressure and ratio of reaction sources of the reaction chamber; a Ge heavily doped beta-Ga2O3 film with an epitaxial concentration of 10 19 cm ‑3 -10 20 cm ‑3 is epitaxially prepared on the second buffer layer by using a pulse MOCVD method with GeH4 as a dopant and a catalyst, and the epitaxial film is annealed, so that the preparation of the epitaxial film is completed. The defect density of the epitaxial film and the substrate use cost are reduced, and the carrier concentration is improved, so that the epitaxial film can be used for the preparation of power devices and switching devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor thin film materials technology, and specifically relates to a method for growing heavily doped gallium oxide thin films, which can be used for the fabrication of power devices and switching devices. Background Technology

[0002] Since the 1950s, the rapid development of integrated circuits has primarily been based on silicon-based semiconductor devices. The disadvantages of silicon-based semiconductors lie in their small bandgap, low electron mobility, and sensitivity to high temperatures and radiation. These drawbacks limit their use in certain applications. Particularly in high-voltage and high-frequency applications, the high density of charged particles and high temperatures have a significant impact on the performance of silicon-based devices, often leading to irreversible permanent damage or failure. Compared to traditional narrow-bandgap semiconductors, wide-bandgap semiconductors offer many advantages, such as higher breakdown field strength, better radiation resistance, and higher operating temperatures. They are widely used in high-power electronic devices, ultraviolet photodetectors, laser diodes, and solar cells. Furthermore, due to their excellent photoelectric conversion properties, wide-bandgap semiconductors also show broad application prospects in solar cells and ultraviolet photodetectors. Research and development of wide-bandgap semiconductors has received widespread attention and continuous progress over the past few decades. The most typical wide-bandgap semiconductor materials include gallium nitride, gallium oxide, and silicon carbide. By achieving high-quality crystal growth and optimizing the electrical properties of these materials, the characteristics of wide-bandgap semiconductors have been further understood and optimized, providing a solid foundation for their application in novel electronic devices and sensors. Compared with silicon carbide and gallium nitride, gallium oxide has a significant cost advantage in preparing gallium oxide single-crystal thin films via the floating zone growth method (FZ) and the edge-fixed film generation (EFG) method. Currently, large-area single crystals of up to 4 inches can be prepared using the EFG method, and 2-inch substrates with a crystal orientation of (-201) have been successfully commercialized.

[0003] Ga₂O₃, with its large bandgap of 4.7–4.9 eV and high breakdown electric field, is attracting increasing attention as a semiconductor material for high-power devices. In particular, β-Ga₂O₃ is considered the optimal choice; compared to α, γ, δ, and ε crystal forms, monoclinic β-Ga₂O₃ exhibits stable physicochemical properties and excellent optical performance. β-Ga₂O₃ has a melting point exceeding 1900℃ and a transmittance of over 80% in the visible light range, while also exhibiting strong absorption in the ultraviolet region at wavelengths of 200–300 nm, making it highly promising for military applications. However, the presence of interatomic gallium, oxygen vacancies, and unintentional dopants causes intrinsic gallium oxide to exhibit N-type semiconductor properties, making it difficult to control its conductivity and thus limiting its application in device development. To obtain materials with controllable carrier concentration, device applications typically improve the conductivity of gallium oxide materials by doping with impurities such as Sn and Si. By properly controlling factors such as reactant concentration, substrate temperature, and reaction chamber pressure, a carrier concentration of 10 can be obtained. 17 -10 20 cm -3 Epitaxial films within the specified range.

[0004] In 2015, Xuejian Du, Zhao Li, and others proposed homoepitaxial gallium oxide films on gallium oxide substrates by tin doping in their paper "Preparation and characterization of Sn-doped β-Ga₂O₃ homoepitaxial films by MOCVD" (J. Mater. Sci, 50, 3252-3257, 2015). This method significantly improved the crystallinity and carrier concentration of the doped films. However, this preparation method has two shortcomings: firstly, the prepared carrier concentration is still relatively low, only 10⁻⁶. 17 cm -3 Furthermore, the resistivity even reaches 10 when the doping ratio is 12%. 4 The Ω·cm is obviously insufficient to meet the requirements for device use; secondly, the homogeneous substrate used is expensive, making it difficult to reduce the manufacturing cost.

[0005] In 2015, M Baldini, M Albrecht, and others proposed homoepitaxial growth of β-Ga2O3 using MOVPE and a catalyst in their paper "Effect of indium as asurfactant in (Ga1-xInx)2O3 epitaxial growth on β-Ga2O3 by metal organic vapor phase epitaxy" (Journal: Semiconductor Science and Technology, 30, 024013, 2015). This method significantly improves the surface morphology and reduces roughness of the film through In catalysis. However, this method has two drawbacks: first, the In doping ratio must be less than 3% to achieve a catalytic effect, making it difficult to apply to heavily doped epitaxial films; second, In catalysis only shows good efficiency at higher temperatures, but heavily doped film growth requires lower growth temperatures, which inevitably weakens the catalytic effect of In.

[0006] Therefore, there is an urgent need for a method to grow large-area heavily doped gallium oxide on inexpensive substrates while maintaining the excellent electrical properties of the thin film. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for growing heavily doped gallium oxide epitaxial films. This method aims to reduce the defect density of the epitaxial film, improve doping efficiency and carrier concentration, and reduce substrate usage costs.

[0008] To achieve the above objectives, the implementation steps of the present invention include the following:

[0009] 1. A method for growing heavily doped gallium oxide epitaxial thin films, characterized by comprising the following steps:

[0010] (1) The sapphire substrate was sequentially placed in acetone solution, acid solution and ultrapure water for ultrasonic cleaning;

[0011] (2) Two gallium oxide buffer layers with different mechanisms were grown on the cleaned sapphire substrate:

[0012] (2a) Place the cleaned sapphire substrate onto the tray inside the reaction chamber, turn on the primary vacuum pump to evacuate the reaction chamber, and when the pressure in the reaction chamber drops to 10... -1 When the pressure reaches the order of magnitude, turn on the secondary vacuum pump until the reaction chamber pressure reaches 10. -4 When the quantity is on the order of magnitude, turn on the variable tray rotation power supply to make the tray rotate;

[0013] (2b) The substrate is preheated at a high temperature of 800℃-900℃. When the temperature rises to 950℃-1000℃, the N2 control terminal is turned on, so that one of the N2 flows into the triethylgallium (TEGa) organic source bottle at a flow rate of 40 sccm-50 sccm, and the other flows into the oxygen (O2) bottle at a flow rate of 900 sccm-1000 sccm. The first buffer layer is grown by MOCVD.

[0014] (2c) The substrate temperature was reduced to 700℃-800℃, the flow rate of the triethylgallium TEGa organic source bottle was set to 40sccm-50sccm, and the flow rate of N2 mixed with O2 was set to 800sccm-900sccm. The second buffer layer was grown by MOCVD.

[0015] (3) Growth of Ge-doped β-Ga2O3 thin films on the buffer layer:

[0016] (3a) Carrier gas N2 is alternately introduced into the triethylgallium (TEGa) organic source bottle and the GeH4 organic source bottle at a flow rate of 40 sccm-50 sccm, while O2 is continuously introduced through a separate gas path at a flow rate of 1700 sccm-1800 sccm during the growth period.

[0017] (3b) Repeat (3a) until the alternating inlet time of TEGa and Ge gas paths reaches the set time, and epitaxially doped β-Ga2O3 thin film of Ge at a low temperature of 600-700℃ on the sapphire substrate, and shut off the organic source gas path.

[0018] (4) The epitaxial β-Ga2O3 film was annealed in an O2 atmosphere, then the heating was stopped, and after cooling to room temperature, the vacuum valve was closed, and high-purity N2 was introduced until the pressure in the reaction chamber was equal to that in the outside environment. The film was then removed to complete the preparation of the gallium oxide epitaxial film.

[0019] Furthermore, the acid solution used in step (1) is a mixed solution prepared from H2SO4, HF and H2O2.

[0020] Furthermore, in step (2b), the first buffer layer is grown using MOCVD, with the following process conditions: the O source flow rate is set to 1800 sccm-2000 sccm; the pressure in the reaction chamber is set to 50 Torr; and the continuous growth time is 20 min-30 min.

[0021] Furthermore, in step (2c), a second buffer layer is grown using MOCVD, with the following process conditions: the O source flow rate is set to 1500 sccm-1700 sccm; the pressure in the reaction chamber is set to 40 Torr; and the continuous growth time is 20 min-30 min.

[0022] Furthermore, the timing of alternating introduction of carrier gas N2 into the triethylgallium (TEGa) organic source bottle and the GeH4 organic source bottle in step (3a) is set as follows:

[0023] (3a1) After introducing N2 into the triethylgallium TEGa organic source bottle for 0.1 min to 0.3 min, the triethylgallium TEGa organic source bottle passage is closed;

[0024] (3a2) After introducing N2 into the GeH4 organic source bottle for 0.1 min to 0.3 min, close the GeH4 organic source bottle passage;

[0025] (3a3) Repeat the above steps (3a1) and (3a2) to reach the set time of 2 hours.

[0026] Furthermore, in step (4), the epitaxial film is annealed in an O2 atmosphere, and the process conditions are as follows: annealing temperature is 700℃-800℃; cooling rate during annealing is 20℃ / min; and natural cooling begins after the temperature drops to 300℃.

[0027] 2. The thin film grown by the above method is characterized in that the bottom layer is a first buffer layer, the middle layer is a second buffer layer, and the top layer is a Ge-doped gallium oxide layer.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] First, this invention first uses a high oxygen source to gallium source ratio to grow a first buffer layer under high temperature and high pressure, and then uses a low oxygen source to gallium source ratio to grow a second buffer layer on the first buffer layer under low temperature and low pressure. Compared with the existing single-layer buffer layer, the two different buffer layers of this invention have a large window for the preparation process parameters, low process requirements, and the addition of the second buffer layer can further reduce the formation of epitaxial thin film twins and defects, and improve the crystal quality of the thin film.

[0030] Secondly, since the present invention uses pulsed MOCVD to grow heavily doped gallium oxide, it can further improve the doping efficiency of germanium, reduce damage to the crystal lattice, and increase the carrier concentration.

[0031] Third, this invention greatly reduces the cost of substrate use by preparing high-quality heavily doped films with high carrier concentration on inexpensive sapphire. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the implementation of the present invention;

[0033] Figure 2 This is a schematic diagram showing the time of alternating introduction of triethylgallium (TEGa) organic source bottles and GeH4 organic source bottles in this invention;

[0034] Figure 3 This is a schematic diagram of the thin film epitaxially grown on the substrate according to the present invention. Detailed Implementation

[0035] To make the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0036] Reference Figure 1 The present invention provides the following three embodiments:

[0037] Example 1: A first buffer layer was grown at a reaction chamber temperature of 950°C, a gallium source flow rate of 40 sccm, and an oxygen source flow rate of 1800 sccm. A second buffer layer was grown at a reaction chamber temperature of 700°C, a gallium source flow rate of 50 sccm, and an oxygen source flow rate of 1500 sccm. A heavily doped β-Ga₂O₃ thin film was epitaxially grown on a sapphire substrate at a temperature of 600°C, an oxygen source flow rate of 1800 sccm, a Ge source flow rate of 50 sccm, and a Ge source pulse introduction time of 0.1 min.

[0038] Step 1: Clean the substrate.

[0039] A sapphire substrate with C-plane was selected, and 50 ml of acid solution was prepared using H2SO4, HF and H2O2.

[0040] The substrate was first ultrasonically cleaned in acetone for 15 minutes, then ultrasonically cleaned in an acid solution for 15 minutes, then ultrasonically cleaned in ultrapure water for 15 minutes, and finally dried with nitrogen.

[0041] Step 2: Grow two gallium oxide buffer layers with different mechanisms on the cleaned sapphire substrate.

[0042] 2a) Place the cleaned sapphire substrate onto the tray inside the reaction chamber, turn on the primary vacuum pump to evacuate the reaction chamber, and when the pressure in the reaction chamber drops to 10... -1 When the pressure reaches the order of magnitude, turn on the secondary vacuum pump until the reaction chamber pressure reaches 10. -4 When the quantity is on the order of magnitude, turn on the variable tray rotation power supply to make the tray rotate;

[0043] 2b) Preheat the substrate to a high temperature of 900°C;

[0044] 2c) Raise the temperature to 950℃, turn on the N2 control terminal, and let N2 flow in two streams. One stream flows into the triethylgallium (TEGa) organic source bottle at a flow rate of 40 sccm, and the other stream mixes with oxygen (O2) at a flow rate of 1000 sccm. Set the O source flow rate to 1800 sccm and the pressure in the reaction chamber to 50 Torr. Use MOCVD to continuously grow the first buffer layer for 20 min.

[0045] 2d) The substrate temperature was lowered to 700°C, the flow rate of the triethylgallium (TEGa) organic source bottle was set to 50 sccm, the flow rate of N2 mixed with O2 was set to 900 sccm, the flow rate of the O source was set to 1500 sccm, the pressure of the reaction chamber was set to 40 Torr, and the second buffer layer was continuously grown by MOCVD for 20 min.

[0046] Step 3: Grow a Ge-doped β-Ga2O3 thin film on the buffer layer.

[0047] Reference Figure 2 The implementation of this step is as follows:

[0048] 3a) After passing N2 into the triethylgallium TEGa organic source bottle at a flow rate of 50 sccm for 0.1 min, close the triethylgallium TEGa organic source bottle passage, and then pass N2 into the GeH4 organic source bottle at the same flow rate of 50 sccm.

[0049] 3b) After N2 is introduced into the GeH4 organic source bottle for 0.1 min, the GeH4 organic source bottle passage is closed, and then the triethylgallium (TEGa) organic source bottle is introduced.

[0050] 3c) Repeat (3a) and (3b) and continuously introduce O2 through a separate gas path at a flow rate of 1800 sccm until the alternating introduction time of the TEGa and Ge gas paths reaches the set time of 2h. Epitaxially doped β-Ga2O3 film of Ge at a low temperature of 600℃ on the sapphire substrate, and then shut off the organic source gas path.

[0051] Step 4: Anneal the β-Ga2O3 film.

[0052] Under an O2 atmosphere, the annealing temperature is set at 800℃, and the temperature is reduced at a rate of 20℃ / min until it drops to 300℃, after which it begins to cool naturally.

[0053] After cooling to room temperature, the vacuum valve is closed, and high-purity N2 is introduced until the pressure in the reaction chamber is equal to that of the external environment. The resulting epitaxial film on a sapphire substrate is then removed. Figure 3 .

[0054] Example 2: A first buffer layer was grown at a reaction chamber temperature of 1000°C, a gallium source flow rate of 50 sccm, and an oxygen source flow rate of 2000 sccm. A second buffer layer was grown at a reaction chamber temperature of 800°C, a gallium source flow rate of 40 sccm, and an oxygen source flow rate of 1700 sccm. A heavily doped β-Ga₂O₃ thin film was epitaxially grown on a sapphire substrate at a temperature of 700°C, an oxygen source flow rate of 1700 sccm, a Ge source flow rate of 40 sccm, and a Ge source pulse duration of 0.2 min.

[0055] Step 1: Clean the substrate.

[0056] The specific implementation of this step is the same as step 1 in Example 1.

[0057] Step 2: Grow two gallium oxide buffer layers with different mechanisms on the cleaned sapphire substrate.

[0058] 2.1) Place the cleaned sapphire substrate onto the tray inside the reaction chamber, turn on the primary vacuum pump to evacuate the reaction chamber, and when the pressure in the reaction chamber drops to 10... -1 When the pressure reaches the order of magnitude, turn on the secondary vacuum pump until the reaction chamber pressure reaches 10. -4 When the quantity is on the order of magnitude, turn on the variable tray rotation power supply to make the tray rotate;

[0059] 2.2) Preheat the substrate to a high temperature of 800℃;

[0060] 2.3) Raise the temperature to 1000℃, turn on the N2 control terminal, and let N2 flow in two streams. One stream flows into the triethylgallium (TEGa) organic source bottle at a flow rate of 50 sccm, and the other stream mixes with oxygen (O2) at a flow rate of 900 sccm. Set the O source flow rate to 2000 sccm and the pressure in the reaction chamber to 50 Torr. Use MOCVD to continuously grow the first buffer layer for 30 min.

[0061] 2.4) The substrate temperature was lowered to 800°C, the flow rate of the triethylgallium (TEGa) organic source bottle was set to 40 sccm, the flow rate of N2 mixed with O2 was set to 800 sccm, the flow rate of the O source was set to 1700 sccm, the pressure of the reaction chamber was set to 40 Torr, and the second buffer layer was continuously grown by MOCVD for 30 min.

[0062] Step 3: Grow a Ge-doped β-Ga2O3 thin film on the buffer layer.

[0063] 3.1) After passing N2 into the triethylgallium (TEGa) organic source bottle at a flow rate of 40 sccm for 0.1 min, close the TEGa organic source bottle passage and then pass N2 into the GeH4 organic source bottle at the same flow rate of 40 sccm.

[0064] 3.2) After N2 has been introduced into the GeH4 organic source bottle for 0.2 min, the GeH4 organic source bottle passage is closed, and then the triethylgallium (TEGa) organic source bottle is introduced.

[0065] 3.3) Repeat steps 3.1) and 3.2), and continuously introduce O2 through a separate gas path at a flow rate of 1700 sccm until the alternating introduction time of the TEGa and Ge gas paths reaches the set time of 2 hours. Epitaxially doped β-Ga2O3 film with Ge at a low temperature of 700℃ on the sapphire substrate, and then shut off the organic source gas path.

[0066] Step 4: Anneal the β-Ga2O3 film.

[0067] Under an O2 atmosphere, the annealing temperature is set at 700℃, and the temperature is reduced at a rate of 20℃ / min until it drops to 300℃, after which it begins to cool naturally.

[0068] After cooling to room temperature, the vacuum valve is closed, and high-purity N2 is introduced until the pressure in the reaction chamber is equal to that in the outside environment. The resulting epitaxial film on the sapphire substrate is then removed.

[0069] Example 3: A first buffer layer was grown at a reaction chamber temperature of 950°C, a gallium source flow rate of 40 sccm, and an oxygen source flow rate of 1900 sccm. A second buffer layer was grown at a reaction chamber temperature of 750°C, a gallium source flow rate of 50 sccm, and an oxygen source flow rate of 1600 sccm. A heavily doped β-Ga₂O₃ thin film was epitaxially grown on a sapphire substrate at a temperature of 650°C, an oxygen source flow rate of 1700 sccm, a Ge source flow rate of 50 sccm, and a Ge source pulse introduction time of 0.3 min.

[0070] Step A: Clean the substrate.

[0071] The specific implementation of this step is the same as step 1 in Example 1.

[0072] Step B: Grow two gallium oxide buffer layers with different mechanisms on the cleaned sapphire substrate.

[0073] B1) Place the cleaned sapphire substrate onto the tray inside the reaction chamber, turn on the primary vacuum pump to evacuate the reaction chamber, and when the pressure in the reaction chamber drops to 10... -1 When the pressure reaches the order of magnitude, turn on the secondary vacuum pump until the reaction chamber pressure reaches 10. -4 When the quantity is on the order of magnitude, turn on the variable tray rotation power supply to make the tray rotate;

[0074] B2) Preheat the substrate to a high temperature of 850°C;

[0075] B3) Raise the temperature to 950℃, turn on the N2 control terminal, and let N2 flow in two streams. One stream flows into the triethylgallium (TEGa) organic source bottle at a flow rate of 50 sccm, and the other stream mixes with oxygen (O2) at a flow rate of 900 sccm. Set the O source flow rate to 1900 sccm and the pressure in the reaction chamber to 50 Torr. Use MOCVD to continuously grow the first buffer layer for 30 min.

[0076] B4) The substrate temperature was lowered to 750°C, the flow rate of the triethylgallium (TEGa) organic source bottle was set to 40 sccm, the flow rate of N2 mixed with O2 was set to 800 sccm, the flow rate of the O source was set to 1600 sccm, the pressure of the reaction chamber was set to 40 Torr, and the second buffer layer was continuously grown by MOCVD for 30 min.

[0077] Step C: Grow a Ge-doped β-Ga2O3 thin film on the buffer layer.

[0078] C1) After passing N2 into the triethylgallium (TEGa) organic source bottle at a flow rate of 40 sccm for 0.1 min, the flow path of the triethylgallium (TEGa) organic source bottle is closed, and then N2 is passed into the GeH4 organic source bottle at the same flow rate of 40 sccm.

[0079] C2) After N2 is introduced into the GeH4 organic source bottle for 0.3 min, the GeH4 organic source bottle passage is closed, and then the triethylgallium (TEGa) organic source bottle is introduced.

[0080] C3) Repeat C1) and C2), and continuously introduce O2 through a separate gas path at a flow rate of 1700 sccm until the alternating introduction time of the TEGa and Ge gas paths reaches the set time of 1 hour. Epitaxially doped β-Ga2O3 film of Ge is formed on the sapphire substrate at a low temperature of 650℃, and then the organic source gas path is turned off.

[0081] Step D: Anneal the β-Ga2O3 film.

[0082] Under an O2 atmosphere, the annealing temperature is set at 700℃, and the temperature is reduced at a rate of 20℃ / min until it drops to 300℃, after which it begins to cool naturally.

[0083] After cooling to room temperature, the vacuum valve is closed, and high-purity N2 is introduced until the pressure in the reaction chamber is equal to that in the outside environment. The resulting epitaxial film on the sapphire substrate is then removed.

[0084] Reference Figure 3 The gallium oxide epitaxial film prepared according to the above method comprises a three-layer structure: the bottom layer is a first buffer layer, the middle layer is a second buffer layer, and the top layer is a Ge-doped gallium oxide epitaxial layer. Wherein:

[0085] The thickness of the first buffer layer is 50nm-100nm;

[0086] The thickness of the second buffer layer is 50nm-100nm;

[0087] The thickness of the Ge-doped gallium oxide epitaxial layer is 300 nm-600 nm, and the carrier concentration is 10. 19 cm -3 -10 20 cm-3 .

[0088] In Example 1, the gallium oxide epitaxial film has a first buffer layer thickness of 50 nm, a second buffer layer thickness of 50 nm, a Ge-doped gallium oxide epitaxial layer thickness of 600 nm, and a carrier concentration of 10. 19 cm -3 .

[0089] In Example 2, the gallium oxide epitaxial film fabricated has a first buffer layer thickness of 100 nm, a second buffer layer thickness of 100 nm, a Ge-doped gallium oxide epitaxial layer thickness of 600 nm, and a carrier concentration of 10. 20 cm -3 .

[0090] In Example 3, the gallium oxide epitaxial film has a first buffer layer thickness of 100 nm, a second buffer layer thickness of 100 nm, a Ge-doped gallium oxide epitaxial layer thickness of 300 nm, and a carrier concentration of 10. 20 cm -3 .

[0091] The above description is only three preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of variations or substitutions within the scope of the technology disclosed in the present invention. For example, in addition to the sapphire used in this example, substrates such as gallium oxide, SiC, and GaN can also be used, but these should all be covered within the scope of protection of the present invention.

Claims

1. A method for growing heavily doped gallium oxide epitaxial thin films with high carrier concentration, characterized in that, Includes the following steps: (1) The sapphire substrate was placed in acetone solution, acid solution and ultrapure water in sequence for ultrasonic cleaning; (2) Two gallium oxide buffer layers with different mechanisms are grown on the cleaned sapphire substrate, including first growing the first buffer layer under high temperature and high pressure using a high oxygen source to gallium source ratio, and then growing the second buffer layer on the first buffer layer under low temperature and low pressure using a low oxygen source to gallium source ratio: (2a) Place the cleaned sapphire substrate onto the tray inside the reaction chamber, turn on the primary vacuum pump to evacuate the reaction chamber, and when the pressure in the reaction chamber drops to 10... -1 When the pressure reaches the order of magnitude, turn on the secondary vacuum pump until the reaction chamber pressure reaches 10. -4 When the quantity is on the order of magnitude, turn on the variable tray rotation power supply to make the tray rotate; (2b) The substrate is preheated at a high temperature of 800℃-900℃. When the temperature rises to 950℃-1000℃, the N2 control terminal is turned on, so that one of the N2 flows into the triethylgallium (TEGa) organic source bottle at a flow rate of 40 sccm-50 sccm, and the other flows into the oxygen (O2) bottle at a flow rate of 900 sccm-1000 sccm. The first buffer layer is grown by MOCVD. (2c) The substrate temperature was reduced to 700℃-800℃, the flow rate of the triethylgallium TEGa organic source bottle was set to 40sccm-50sccm, and the flow rate of N2 mixed with O2 was set to 800sccm-900sccm. The second buffer layer was grown by MOCVD. (3) Growth of heavily Ge-doped β-Ga2O3 thin films on the buffer layer: (3a) Carrier gas N2 is alternately introduced into the triethylgallium (TEGa) organic source bottle and the GeH4 organic source bottle at a flow rate of 40 sccm-50 sccm, while O2 is continuously introduced through a separate gas path at a flow rate of 1700 sccm-1800 sccm during the growth period. (3b) Repeat (3a) until the alternating inlet time of TEGa and Ge gas paths reaches the set time, and epitaxially doped β-Ga2O3 thin film of Ge at a low temperature of 600-700℃ on the sapphire substrate, and shut off the organic source gas path. (4) Anneal the epitaxial β-Ga2O3 film in an O2 atmosphere, then stop heating, cool to room temperature, close the vacuum valve, and then introduce high-purity N2 until the pressure in the reaction chamber is equal to that in the outside environment. The film is then removed to complete the preparation of the gallium oxide epitaxial film.

2. The method as described in claim 1, characterized in that, The acid solution used in step (1) is a mixed solution prepared with H2SO4, HF and H2O2.

3. The method as described in claim 1, characterized in that, In step (2b), the first buffer layer is grown using MOCVD, and the process conditions are as follows: The oxygen flow rate was set to 1800-2000 sccm; The pressure in the reaction chamber is set to 50 Torr; The continuous growth time is 20-30 minutes.

4. The method as described in claim 1, characterized in that, In step (2c), the second buffer layer is grown using MOCVD, and the process conditions are as follows: The oxygen flow rate was set to 1500 sccm-1700 sccm; The pressure in the reaction chamber was set to 40 Torr; The continuous growth time is 20-30 minutes.

5. The method as described in claim 1, characterized in that, In step (3a), the timing of alternating N2 carrier gas flow into the triethylgallium (TEGa) organic source bottle and the GeH4 organic source bottle is set as follows: (3a1) After introducing N2 into the triethylgallium TEGa organic source bottle for 0.1 min to 0.3 min, the triethylgallium TEGa organic source bottle passage is closed; (3a2) After introducing N2 into the GeH4 organic source bottle for 0.1 min to 0.3 min, close the GeH4 organic source bottle passage; (3a3) Repeat the above steps (3a1) and (3a2) to reach the set time of 2 hours.

6. The method as described in claim 1, characterized in that, In step (4), the epitaxial film is annealed in an O2 atmosphere under the following process conditions: The annealing temperature is 700℃-800℃; The cooling rate during the annealing process is 20℃ / min; After the temperature drops to 300℃, it begins to cool down naturally.

7. The thin film grown using the method of claim 1, characterized in that, The bottom layer is the first buffer layer, the middle layer is the second buffer layer, and the top layer is a Ge-doped gallium oxide layer.

8. The thin film according to claim 7, characterized in that: The thickness of the first buffer layer is 50nm-100nm; The thickness of the second buffer layer is 50nm-100nm; The thickness of the Ge-doped gallium oxide layer is 300 nm-600 nm, and the carrier concentration is 10. 19 cm -3 -10 20 cm -3 .

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