A double-doped diamond of ultra-wide bandgap semiconductor and its preparation method

Abstract

The present invention discloses an ultra-wide bandgap semiconductor double-doped diamond and a preparation method thereof. By using microwave plasma chemical vapor deposition method, with methane, hydrogen, carbon tetrafluoride and diethyl beryllium vapor as growth gas sources, a double-doped diamond containing fluorine and beryllium elements is grown on a substrate after pretreatment and diamond nucleation. The present invention increases the diamond nucleation density by implanting nano-diamond seed solution, reducing the roughness of the deposited diamond layer; during the diamond growth process, gas sources containing fluorine and beryllium elements are added, and the fluorine and beryllium doped atoms substitute for the host carbon atoms, without significantly changing the lattice structure of the diamond. The double-doping with fluorine as a donor impurity and beryllium as an acceptor impurity belongs to shallow energy level doping, which improves the carrier concentration and mobility of the diamond; a C-H terminal structure is formed at the end of the deposition, and the stress distribution is adjusted by annealing to stabilize the compositional uniformity, improving the electrical and mechanical properties of the double-doped diamond.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-wide bandgap semiconductors, and particularly relates to an ultra-wide bandgap semiconductor double-doped diamond and a preparation method thereof. Background Art

[0002] As an allotrope of carbon (C), diamond is a typical atomic crystal. In diamond, each carbon atom forms four sp 3 hybrid atomic orbitals, and forms σ-type covalent single bonds with the adjacent four carbon atoms, combining into a regular tetrahedron structure. This carbon atom arrangement and lattice structure characteristics of diamond endow it with excellent physical properties: a large bandgap (5.5 eV), a high carrier mobility (hole: 3800 cm 2 ·V -1 ·s -1 , electron: 4500 cm 2 ·V -1 ·s -1 ), a high breakdown field strength (> 10 MV·cm -1 ), a large thermal conductivity (22 W·K -1 ·cm -1 ), and biocompatibility. However, diamond is an insulator with a resistivity ρ > 1015 Ω·cm, and semiconductorization is the biggest obstacle to its application and development.

[0003] Ultra-wide bandgap semiconductor materials need to be doped to significantly improve their intrinsic conductivity. Selecting suitable doping elements is the key to fabricating high-performance semiconductor diamond. Currently, p-type diamond can be achieved through boron (B) doping, while for n-type diamond, phosphorus (P), nitrogen (N), and sulfur (S) doping are generally used. Diamond doping is restricted by factors such as the solubility of dopants, the ionization energy of dopants, and the compensation of impurities or defects. For conventional single-element doping, it is difficult for doping atoms to be incorporated into the diamond lattice. Even if the doping atoms are incorporated and replace positions other than C atoms, as the concentration of effectively incorporated impurity atoms increases, the carrier concentration increases and the activation energy decreases. However, at the same time, the activation energy of holes decreases, impurity diffusion increases, and the carrier mobility decreases. With the in-depth research, the doping of diamond is no longer limited to single elements. It has been found that by doping two elements with opposite numbers of electrons, impurity atoms can be inserted into the diamond structure more stably, thereby obtaining n-type diamond with low resistance. For example, the patent with the application number CN201910879808.4 discloses a co-doped diamond whose lattice structure includes multiple carbon atoms, one boron atom, multiple sulfur atoms, and multiple vacancies. Donor atoms not exceeding 0.17% provide conduction electrons with an ionization energy of 0.25 - 0.27 eV; the patent with the application number CN201910182374.2 discloses a nitrogen-sulfur co-doped n-type semiconductor diamond material. Using a diamond single crystal as a seed crystal and H2S or SO2 as the S source and N2 or NH3 as the nitrogen source, an N-S co-doped diamond single crystal material is prepared. However, the impurity distribution brought about by co-doping tends to be in a non-uniform state, making the repeatability and stability of dopant elements providing free carriers the biggest problem in diamond doping.

[0004] The doping of diamond is mainly achieved by the high-pressure high-temperature method (HPHT), chemical vapor deposition method (CVD), and ion implantation method. In the first two methods, during the diamond growth process, impurity elements are directly controlled to enter the diamond lattice in the form of substitution atoms, which can well limit the number of lattice defects such as vacancies. However, due to the strong C-C bond energy and compact lattice of diamond, only a small amount of impurity elements can enter the interior of diamond and reach a high concentration; the ion implantation method circumvents the problem of the solubility of impurities in diamond. It can directly inject impurity ions into diamond, but this method cannot achieve the overall doping of diamond and will cause great damage to the diamond lattice, resulting in a large number of hole and self-interstitial atom defects.

[0005] Whether it is the combination of doping elements or the selection of doping methods, the common problem that diamond doping needs to solve is to ensure the mobility while increasing the carrier concentration to obtain stable high electrical conductivity. Based on co-doping means, how to introduce a large number of composite impurities that can become shallow-level donors during the diamond growth process is an urgent problem to be solved in the preparation of high-quality and high-conductivity semiconductor diamond. Summary of the Invention

[0006] Based on the deficiencies of the prior art, the purpose of the present invention is to provide a double-doped diamond of ultra-wide bandgap semiconductor, and a preparation method thereof. By using microwave plasma chemical vapor deposition method and through the synergistic doping of fluorine and beryllium, the conductivity and mechanical properties of the diamond film are improved.

[0007] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A preparation method of a double-doped diamond of ultra-wide bandgap semiconductor, using microwave plasma chemical vapor deposition method, nucleating diamond on the pretreated substrate, and then using methane, hydrogen, carbon tetrafluoride and diethyl beryllium vapor as the growth gas source to grow double-doped diamond containing fluorine and beryllium elements on the substrate.

[0009] The preparation method of the double-doped diamond of ultra-wide bandgap semiconductor includes the following steps:

[0010] S1. Substrate pretreatment: polishing, cleaning, implanting nanodiamond seed solution and drying the substrate;

[0011] S2. Nucleation of undoped diamond: placing the pretreated substrate in a microwave plasma device, evacuating to a pressure less than 10 -5 Pa, turning on the microwave excitation source, and introducing hydrogen, controlling the microwave power to be 1000 - 1200W, the deposition gas pressure to be 4.0 - 4.5kPa, and the substrate temperature to be 850 - 950°C, and then using the mixed gas of hydrogen and methane as the nucleation gas source to deposit undoped diamond for 10 - 20 minutes;

[0012] S3. Growth of double-doped diamond: maintaining the microwave power, deposition gas pressure and substrate temperature, using the mixed gas of methane, hydrogen, carbon tetrafluoride and diethyl beryllium vapor as the growth gas source to epitaxially grow double-doped diamond for 4 - 8 hours; then stopping the introduction of methane, carbon tetrafluoride and diethyl beryllium vapor, and maintaining the hydrogen plasma environment for 5 - 10 minutes;

[0013] S4. Annealing treatment: placing the product obtained in step S3 in a vacuum heating furnace, evacuating to a pressure less than 10 -2 Pa, starting to heat up, and filling the furnace with a mixed gas of methane, hydrogen and nitrogen, maintaining at a temperature of 600 - 800°C and a pressure of 1 - 3MPa for 1 - 2 hours, and taking it out after cooling to below 60°C with the furnace.

[0014] Before growing the double-doped diamond, the substrate is pretreated with a nano-diamond seed solution, which can increase the diamond nucleation density, thereby reducing the roughness of the deposited diamond layer; during the diamond growth process, a gas source containing fluorine and beryllium elements is added. The fluorine and beryllium doping atoms substitute for the main carbon atoms, and the lattice structure of the diamond will not be significantly changed. The double doping with fluorine as a donor impurity and beryllium as an acceptor impurity belongs to shallow-level doping, which improves the carrier concentration and mobility of the diamond; at the end of the deposition, a C-H terminal structure is formed, and the stress distribution is adjusted by annealing to stabilize the compositional uniformity, improving the electrical and mechanical properties of the double-doped diamond.

[0015] When non-doped diamond nucleates, a relatively high C / H ratio is required. In the nucleation gas source described in step S2, the total flow rate of hydrogen and methane is 220 - 300 sccm, and the volume ratio of methane to hydrogen is 2.5 - 4.5%; when growing double-doped diamond, compared with the nucleation stage, the C / H ratio should be reduced. At the same time, to avoid etching of the diamond and obtain a better growth rate and doping effect, the total flow rate of the growth gas source in step S3 is the same as that of the nucleation gas source in step S2. The volume percentage of methane in the growth gas source is 1 - 2%, the volume percentage of diethylberyllium vapor in the growth gas source is 250 - 400 ppm, and the volume percentage of carbon tetrafluoride in the growth gas source is 500 - 750 ppm; hydrogen carrier gas is used when introducing carbon tetrafluoride and diethylberyllium vapor.

[0016] When annealing to stabilize the stress, in order to further compensate for the growth defects of the double-doped diamond, in the mixed gas of methane, hydrogen and nitrogen described in step S4, the volume percentage of methane is 1 - 5%, and the volume percentage of hydrogen is 0.5 - 2.5%.

[0017] To facilitate the growth of double-doped diamond, the substrate is single-crystalline silicon or single-crystalline diamond with a (100) crystal orientation; and in step S1, the cleaning is performed by ultrasonic cleaning with acetone, absolute ethanol and pure water to remove impurities on the substrate surface; in step S1, the nano-diamond seed solution seeding is to place the cleaned substrate in the nano-diamond seed solution and ultrasonicate for 20 - 40 min. The nano-diamond seed solution is an aqueous solution containing 2 - 3 wt% nano-diamond, and the grain size of the nano-diamond is 3 - 5 nm.

[0018] The ultra-wide bandgap semiconductor double-doped diamond prepared by the above method has a substrate thickness of 0.5 - 2 mm, a double-doped diamond thickness of 1.0 - 3.5 μm, and an average roughness of 6.5 - 8.5 nm; the carrier concentration of the double-doped diamond is not less than 6.06×10 18 cm -3 , and the electron mobility is not less than 331 cm 2 / (V·s). Detailed implementation manners

[0019] In order to make the technical objectives, technical solutions and beneficial effects of the present invention clearer, the following further describes the technical solutions of the present invention in conjunction with specific embodiments. However, the embodiments are intended to explain the present invention and should not be construed as limiting the present invention. For those not specifying specific technologies or conditions in the embodiments, the technologies or conditions described in the literature in the art or the product specifications are followed.

[0020] Embodiment 1

[0021] A preparation method of a double-doped diamond with an ultra-wide bandgap semiconductor includes the following steps:

[0022] S1. Substrate pretreatment: Select single-crystalline silicon with a (100) crystal orientation as the substrate, polish the substrate to a roughness Ra < 1 nm, ultrasonically clean the substrate successively with acetone, absolute ethanol and pure water for 10 min each using an ultrasonic cleaner, and then place the cleaned substrate in a nano-diamond seed solution (an aqueous solution containing 2.5 wt% nano-diamonds with a nano-diamond grain size of 3 nm) at room temperature for ultrasonic seeding for 30 min, and take it out for drying treatment (blow dry);

[0023] S2. Nucleation of undoped diamond: Place the pretreated substrate in a microwave plasma device, evacuate to a pressure less than 10 -5 Pa, turn on the microwave excitation source, and introduce hydrogen. Control the microwave power to be 1200 W, the deposition pressure to be 4.0 kPa, and the substrate temperature to be 900 °C. Then, use a mixed gas of hydrogen and methane as the nucleation gas source to deposit undoped diamond for 15 min;

[0024] Among them, the flow rate of hydrogen is 250 sccm, and the flow rate of methane is 10 sccm;

[0025] S3. Growth of double-doped diamond: Keep the microwave power, deposition pressure and substrate temperature, and use a mixed gas of methane, hydrogen, carbon tetrafluoride and diethyl beryllium vapor as the growth gas source to epitaxially grow double-doped diamond for 4 h; then stop introducing methane, carbon tetrafluoride and diethyl beryllium vapor, and maintain the hydrogen plasma environment for 10 min;

[0026] Among them, the flow rate of hydrogen is 234 sccm; the flow rate of methane is 2.6 sccm; carbon tetrafluoride uses a hydrogen carrier gas (hydrogen carrying 1 vt% carbon tetrafluoride) with a flow rate of 15.6 sccm; diethyl beryllium vapor uses a hydrogen carrier gas (hydrogen carrying 1 vt% diethyl beryllium vapor) with a flow rate of 7.8 sccm;

[0027] S4. Annealing treatment: Place the product obtained in step S3 in a vacuum heating furnace, evacuate to a pressure less than 10-2 Pa, heat it to 600 °C at a heating rate of 5 °C / min, and introduce a mixed gas of methane, hydrogen and nitrogen (containing 2 vt% methane and 1 vt% hydrogen) into the furnace. Keep the pressure at 2 MPa and hold it isothermally for 0.5 h. Then heat it to 700 °C at a heating rate of 10 °C / min, hold it isothermally for 0.5 h, then heat it to 800 °C at a heating rate of 10 °C / min, hold it isothermally for 0.5 h, and take it out after cooling in the furnace to below 60 °C.

[0028] Example 2

[0029] A preparation method of a super-wide bandgap semiconductor double-doped diamond, comprising the following steps:

[0030] S1. Substrate pretreatment: Select single-crystalline silicon with a (100) crystal orientation as the substrate, polish the substrate to a roughness Ra < 1 nm, and use an ultrasonic cleaner to ultrasonically clean the substrate with acetone, absolute ethanol and pure water for 10 min each in turn. Then, at room temperature, place the cleaned substrate in a nano-diamond seed solution (an aqueous solution containing 2.5 wt% nano-diamond, and the nano-diamond grain size is 3 nm) and ultrasonically implant seeds for 30 min, and take it out for drying treatment (blow dry);

[0031] S2. Nucleation of undoped diamond: Place the pretreated substrate in a microwave plasma device, evacuate to a pressure less than 10 -5 Pa, turn on the microwave excitation source, and introduce hydrogen. Control the microwave power to be 1200 W, the deposition gas pressure to be 4.0 kPa, and the substrate temperature to be 900 °C. Then use a mixed gas of hydrogen and methane as the nucleation gas source to deposit undoped diamond for 15 min;

[0032] Among them, the flow rate of hydrogen is 250 sccm, and the flow rate of methane is 10 sccm;

[0033] S3. Growth of double-doped diamond: Keep the microwave power, deposition gas pressure and substrate temperature, and use a mixed gas of methane, hydrogen, carbon tetrafluoride and diethyl beryllium vapor as the growth gas source to epitaxially grow double-doped diamond for 4 h; then stop introducing methane, carbon tetrafluoride and diethyl beryllium vapor, and maintain the hydrogen plasma environment for 10 min;

[0034] Among them, the flow rate of hydrogen is 237.9 sccm; the flow rate of methane is 2.6 sccm; carbon tetrafluoride uses a hydrogen carrier gas (hydrogen containing 1 vt% carbon tetrafluoride), and the flow rate is 13 sccm; diethyl beryllium vapor uses a hydrogen carrier gas (hydrogen containing 1 vt% diethyl beryllium vapor), and the flow rate is 6.5 sccm;

[0035] S4. Annealing treatment: Place the product obtained in step S3 in a vacuum heating furnace, evacuate to a pressure less than 10 -2Pa, heat it to 600 °C at a heating rate of 5 °C / min, and fill the furnace with a mixed gas of methane, hydrogen and nitrogen (containing 2 vt% methane and 1 vt% hydrogen), keep the pressure at 2 MPa, hold it at a constant temperature for 0.5 h, then heat it to 700 °C at a heating rate of 10 °C / min, hold it at a constant temperature for 0.5 h, then heat it to 800 °C at a heating rate of 10 °C / min, hold it at a constant temperature for 0.5 h, and take it out after cooling in the furnace to below 60 °C.

[0036] Example 3

[0037] A preparation method of ultra-wide bandgap semiconductor double-doped diamond, comprising the following steps:

[0038] S1. Substrate pretreatment: Select single-crystalline silicon with a (100) crystal orientation as the substrate, polish the substrate to a roughness Ra < 1 nm, ultrasonically clean the substrate with acetone, absolute ethanol and pure water for 10 min each using an ultrasonic cleaner, and then place the cleaned substrate in a nano-diamond seed solution (an aqueous solution containing 2.5 wt% nano-diamond, with a nano-diamond grain size of 3 nm) at room temperature for ultrasonic seeding for 30 min, and take it out for drying treatment (blow dry);

[0039] S2. Nucleation of undoped diamond: Place the pretreated substrate in a microwave plasma device, evacuate to a pressure less than 10 -5 Pa, turn on the microwave excitation source, and introduce hydrogen, control the microwave power to 1200 W, the deposition gas pressure to 4.0 kPa, and the substrate temperature to 900 °C, and then use a mixed gas of hydrogen and methane as the nucleation gas source to deposit undoped diamond for 15 min;

[0040] Among them, the flow rate of hydrogen is 250 sccm, and the flow rate of methane is 10 sccm;

[0041] S3. Growth of double-doped diamond: Keep the microwave power, deposition gas pressure and substrate temperature, use a mixed gas of methane, hydrogen, carbon tetrafluoride and diethylberyllium vapor as the growth gas source to epitaxially grow double-doped diamond for 4 h; then stop introducing methane, carbon tetrafluoride and diethylberyllium vapor, and maintain the hydrogen plasma environment for 10 min;

[0042] Among them, the flow rate of hydrogen is 230.1 sccm; the flow rate of methane is 2.6 sccm; carbon tetrafluoride uses a hydrogen carrier gas (hydrogen carrying 1 vt% carbon tetrafluoride), and the flow rate is 18.2 sccm; diethylberyllium vapor uses a hydrogen carrier gas (hydrogen carrying 1 vt% diethylberyllium vapor), and the flow rate is 9.1 sccm;

[0043] S4. Annealing treatment: Place the product obtained in step S3 in a vacuum heating furnace, evacuate to a pressure less than 10 -2Pa, heat it to 600 °C at a heating rate of 5 °C / min, and fill the furnace with a mixed gas of methane, hydrogen and nitrogen (containing 2 vt% methane and 1 vt% hydrogen), keep the pressure at 2 MPa, keep the temperature constant for 0.5 h, then heat it to 700 °C at a heating rate of 10 °C / min, keep the temperature constant for 0.5 h, then heat it to 800 °C at a heating rate of 10 °C / min, keep the temperature constant for 0.5 h, and take it out after cooling in the furnace to below 60 °C.

[0044] Example 4

[0045] A preparation method of ultra-wide bandgap semiconductor double-doped diamond, comprising the following steps:

[0046] S1. Substrate pretreatment: Select single-crystalline silicon with (100) crystal orientation as the substrate, polish the substrate to a roughness Ra < 1 nm, use an ultrasonic cleaner to ultrasonically clean the substrate with acetone, absolute ethanol and pure water for 10 min each in turn, and then at room temperature, place the cleaned substrate in a nano-diamond seed solution (an aqueous solution containing 2.5 wt% nano-diamond, and the grain size of the nano-diamond is 3 nm) for ultrasonic seeding for 30 min, and take it out for drying treatment (blow dry);

[0047] S2. Nucleation of undoped diamond: Place the pretreated substrate in a microwave plasma device, evacuate to a pressure less than 10 -5 Pa, turn on the microwave excitation source, and introduce hydrogen. Control the microwave power to be 1200 W, the deposition gas pressure to be 4.0 kPa, and the substrate temperature to be 900 °C. Then use a mixed gas of hydrogen and methane as the nucleation gas source to deposit undoped diamond for 15 min;

[0048] Among them, the flow rate of hydrogen is 250 sccm, and the flow rate of methane is 10 sccm;

[0049] S3. Growth of double-doped diamond: Keep the microwave power, deposition gas pressure and substrate temperature, and use a mixed gas of methane, hydrogen, carbon tetrafluoride and diethyl beryllium vapor as the growth gas source to epitaxially grow double-doped diamond for 4 h; then stop introducing methane, carbon tetrafluoride and diethyl beryllium vapor, and maintain the hydrogen plasma environment for 10 min;

[0050] Among them, the flow rate of hydrogen is 227.5 sccm; the flow rate of methane is 2.6 sccm; carbon tetrafluoride uses a hydrogen carrier gas (hydrogen carrying 1 vt% carbon tetrafluoride), and the flow rate is 19.5 sccm; diethyl beryllium vapor uses a hydrogen carrier gas (hydrogen carrying 1 vt% diethyl beryllium vapor), and the flow rate is 10.4 sccm;

[0051] S4. Annealing treatment: Place the product obtained in step S3 in a vacuum heating furnace, evacuate to a pressure less than 10 -2Pa, heat it to 600 °C at a heating rate of 5 °C / min, and fill the furnace with a mixed gas of methane, hydrogen and nitrogen (containing 2 vt% methane and 1 vt% hydrogen), keep the pressure at 2 MPa, keep it at a constant temperature for 0.5 h, then heat it to 700 °C at a heating rate of 10 °C / min, keep it at a constant temperature for 0.5 h, then heat it to 800 °C at a heating rate of 10 °C / min, keep it at a constant temperature for 0.5 h, and take it out after cooling in the furnace to below 60 °C.

[0052] Example 5

[0053] A preparation method of ultra-wide bandgap semiconductor double-doped diamond, comprising the following steps:

[0054] S1. Substrate pretreatment: Select single-crystalline silicon with a (100) crystal orientation as the substrate, polish the substrate to a roughness Ra < 1 nm, use an ultrasonic cleaner to ultrasonically clean the substrate with acetone, absolute ethanol and pure water for 10 min each in turn, and then at room temperature, place the cleaned substrate in a nano-diamond seed solution (an aqueous solution containing 2.5 wt% nano-diamond, and the nano-diamond grain size is 3 nm) for ultrasonic seeding for 30 min, and take it out for drying treatment (blow dry);

[0055] S2. Nucleation of undoped diamond: Place the pretreated substrate in a microwave plasma device, evacuate to a pressure less than 10 -5 Pa, turn on the microwave excitation source, and introduce hydrogen, control the microwave power to 1200 W, the deposition gas pressure to 4.3 kPa, and the substrate temperature to 900 °C, and then use a mixed gas of hydrogen and methane as the nucleation gas source to deposit undoped diamond for 15 min;

[0056] Among them, the flow rate of hydrogen is 270 sccm, and the flow rate of methane is 10 sccm;

[0057] S3. Growth of double-doped diamond: Keep the microwave power, deposition gas pressure and substrate temperature, use a mixed gas of methane, hydrogen, carbon tetrafluoride and diethyl beryllium vapor as the growth gas source, and epitaxially grow double-doped diamond for 6 h; then stop introducing methane, carbon tetrafluoride and diethyl beryllium vapor, and maintain the hydrogen plasma environment for 10 min;

[0058] Among them, the flow rate of hydrogen is 252 sccm; the flow rate of methane is 2.8 sccm; carbon tetrafluoride uses a hydrogen carrier gas (hydrogen carrying 1 vt% carbon tetrafluoride), and the flow rate is 16.8 sccm; diethyl beryllium vapor uses a hydrogen carrier gas (hydrogen carrying 1 vt% diethyl beryllium vapor), and the flow rate is 8.4 sccm;

[0059] S4. Annealing treatment: Place the product obtained in step S3 in a vacuum heating furnace, evacuate to a pressure less than 10 -2Pa, heat it to 600 °C at a heating rate of 5 °C / min, and fill the furnace with a mixed gas of methane, hydrogen and nitrogen (containing 2 vt% methane and 1 vt% hydrogen), keep the pressure at 2 MPa, keep it at a constant temperature for 0.5 h, then heat it to 700 °C at a heating rate of 10 °C / min, keep it at a constant temperature for 0.5 h, then heat it to 800 °C at a heating rate of 10 °C / min, keep it at a constant temperature for 0.5 h, and take it out after cooling in the furnace to below 60 °C.

[0060] Example 6

[0061] A preparation method of ultra-wide bandgap semiconductor double-doped diamond, comprising the following steps:

[0062] S1. Substrate pretreatment: Select single-crystalline silicon with a (100) crystal orientation as the substrate, polish the substrate to a roughness Ra < 1 nm, ultrasonically clean the substrate with acetone, absolute ethanol and pure water for 10 min each using an ultrasonic cleaner, and then at room temperature, place the cleaned substrate in a nano-diamond seed solution (an aqueous solution containing 2.5 wt% nano-diamond, and the nano-diamond grain size is 3 nm) for ultrasonic seeding for 30 min, and take it out for drying treatment (blow dry);

[0063] S2. Nucleation of undoped diamond: Place the pretreated substrate in a microwave plasma device, evacuate to a pressure less than 10 -5 Pa, turn on the microwave excitation source, and introduce hydrogen, control the microwave power to 1200 W, the deposition gas pressure to 4.3 kPa, and the substrate temperature to 900 °C, and then use a mixed gas of hydrogen and methane as the nucleation gas source to deposit undoped diamond for 15 min;

[0064] Among them, the flow rate of hydrogen is 270 sccm, and the flow rate of methane is 10 sccm;

[0065] S3. Growth of double-doped diamond: Keep the microwave power, deposition gas pressure and substrate temperature, and use a mixed gas of methane, hydrogen, carbon tetrafluoride and diethyl beryllium vapor as the growth gas source to epitaxially grow double-doped diamond for 8 h; then stop introducing methane, carbon tetrafluoride and diethyl beryllium vapor, and maintain the hydrogen plasma environment for 10 min;

[0066] Among them, the flow rate of hydrogen is 252 sccm; the flow rate of methane is 2.8 sccm; carbon tetrafluoride uses a hydrogen carrier gas (hydrogen carrying 1 vt% carbon tetrafluoride), and the flow rate is 16.8 sccm; diethyl beryllium vapor uses a hydrogen carrier gas (hydrogen carrying 1 vt% diethyl beryllium vapor), and the flow rate is 8.4 sccm;

[0067] S4. Annealing treatment: Place the product obtained in step S3 in a vacuum heating furnace, evacuate to a pressure less than 10 -2Pa, heat it to 600 °C at a heating rate of 5 °C / min, and fill the furnace with a mixed gas of methane, hydrogen and nitrogen (containing 2 vt% methane and 1 vt% hydrogen), keep the pressure at 2 MPa, hold it at a constant temperature for 0.5 h, then heat it to 700 °C at a heating rate of 10 °C / min, hold it at a constant temperature for 0.5 h, then heat it to 800 °C at a heating rate of 10 °C / min, hold it at a constant temperature for 0.5 h, and take it out after cooling in the furnace to below 60 °C.

[0068] Comparative Example 1

[0069] A method for preparing undoped diamond, comprising the following steps:

[0070] S1. Substrate pretreatment: Select single-crystalline silicon with a (100) crystal orientation as the substrate, polish the substrate to a roughness Ra < 1 nm, ultrasonically clean the substrate with acetone, absolute ethanol and pure water in turn for 10 min using an ultrasonic cleaner, and then at room temperature, place the cleaned substrate in a nano-diamond seed solution (an aqueous solution containing 2.5 wt% nano-diamond, with a nano-diamond grain size of 3 nm) and ultrasonically implant seeds for 30 min, and take it out for drying treatment (blow dry);

[0071] S2. Nucleation of undoped diamond: Place the pretreated substrate in a microwave plasma device, evacuate to a pressure less than 10 -5 Pa, turn on the microwave excitation source, and introduce hydrogen, control the microwave power to 1200 W, the deposition gas pressure to 4.0 kPa, and the substrate temperature to 900 °C, and then use a mixed gas of hydrogen and methane as the nucleation gas source to deposit undoped diamond for 15 min;

[0072] Among them, the flow rate of hydrogen is 250 sccm, and the flow rate of methane is 10 sccm;

[0073] S3. Growth of undoped diamond: Keep the microwave power, deposition gas pressure and substrate temperature, use a mixed gas of methane and hydrogen as the growth gas source, and epitaxially grow double-doped diamond for 4 h; then stop introducing methane and maintain the hydrogen plasma environment for 10 min;

[0074] Among them, the flow rate of hydrogen is 257.4 sccm; the flow rate of methane is 2.6 sccm;

[0075] S4. Annealing treatment: Place the product obtained in step S3 in a vacuum heating furnace, evacuate to a pressure less than 10 -2Pa, heat it to 600 °C at a heating rate of 5 °C / min, and fill the furnace with a mixed gas of methane, hydrogen and nitrogen (containing 2 vt% methane and 1 vt% hydrogen), keep the pressure at 2 MPa, keep it at a constant temperature for 0.5 h, then heat it to 700 °C at a heating rate of 10 °C / min, keep it at a constant temperature for 0.5 h, then heat it to 800 °C at a heating rate of 10 °C / min, keep it at a constant temperature for 0.5 h, and take it out after cooling with the furnace to below 60 °C.

[0076] Comparative Example 2

[0077] A preparation method of a super-wide bandgap semiconductor double-doped diamond, comprising the following steps:

[0078] S1. Substrate pretreatment: Select single-crystalline silicon with a (100) crystal orientation as the substrate, polish the substrate to a roughness Ra < 1 nm, use an ultrasonic cleaner to ultrasonically clean the substrate with acetone, absolute ethanol and pure water for 10 min each in turn, and then at room temperature, place the cleaned substrate in a nano-diamond seed solution (an aqueous solution containing 2.5 wt% nano-diamond, and the nano-diamond grain size is 3 nm) for ultrasonic seeding for 30 min, and take it out for drying treatment (blow dry);

[0079] S2. Nucleation of undoped diamond: Place the pretreated substrate in a microwave plasma device, evacuate to a pressure less than 10 -5 Pa, turn on the microwave excitation source, and introduce hydrogen, control the microwave power to 1200 W, the deposition gas pressure to 4.0 kPa, and the substrate temperature to 900 °C, and then use a mixed gas of hydrogen and methane as the nucleation gas source to deposit undoped diamond for 15 min;

[0080] Among them, the flow rate of hydrogen is 250 sccm, and the flow rate of methane is 10 sccm;

[0081] S3. Growth of double-doped diamond: Keep the microwave power, deposition gas pressure and substrate temperature, use a mixed gas of methane, hydrogen, carbon tetrafluoride and diethyl beryllium vapor as the growth gas source to epitaxially grow double-doped diamond for 4 h; then stop introducing methane, carbon tetrafluoride and diethyl beryllium vapor, and maintain the hydrogen plasma environment for 10 min;

[0082] Among them, the flow rate of hydrogen is 234 sccm; the flow rate of methane is 2.6 sccm; carbon tetrafluoride uses a hydrogen carrier gas (hydrogen carrying 1 vt% carbon tetrafluoride), and the flow rate is 15.6 sccm; diethyl beryllium vapor uses a hydrogen carrier gas (hydrogen carrying 1 vt% diethyl beryllium vapor), and the flow rate is 7.8 sccm.

[0083] Examples 2 to 4 are different from Example 1 in that the volume percentages of carbon tetrafluoride and diethylberyllium vapor in the growth gas source described in step S3 are changed; Examples 5 and 6 are different from Example 1 in that the deposition pressure, gas flow rate, and the time for epitaxial growth of double-doped diamond are changed; Comparative Example 1 is different from Example 1 in that step S3 is for the growth of undoped diamond; Comparative Example 2 is different from Example 1 in that the annealing treatment in step S4 is not performed. The thickness and roughness of the diamond growth are measured by an atomic force microscope. For the roughness measurement, five positions are selected on the film surface for measurement and the average value is obtained. The main parameters of the double-doped diamond growth in Examples 1 to 6 and the undoped diamond growth in Comparative Example 1 are shown in Table 1.

[0084] Table 1 Parameters of diamond growth in Examples 1 to 6

[0085]

[0086] As can be seen from Table 1, the thickness of the double-doped diamond deposited in Examples 1 to 6 is about 1.2 - 3.1 μm, and the average roughness is about 6.5 - 8.3 nm. Compared with Comparative Example 1, in Examples 1 to 6, by doping fluorine and beryllium impurities during the diamond growth process, the film deposition rate is reduced, and the roughness is also reduced. Moreover, the roughness generally shows a decreasing trend with the increase in the content of carbon tetrafluoride and diethylberyllium vapor in the mixed gas source, indicating that fluorine-beryllium double doping helps to refine the diamond grain size.

[0087] The Hall effect tests are carried out on the diamond samples grown in Examples 1 to 4 and Comparative Example 2 at room temperature to obtain the electron carrier concentration and mobility, and the hardness and modulus of the diamond samples grown in Examples 1 to 4 and Comparative Example 2 are detected. The results are shown in Table 2.

[0088] Table 2 Room temperature Hall effect test results of the samples obtained in Examples 1 to 4 and Comparative Example 2

[0089]

[0090] As can be seen from Table 2, with the increase in the amount of fluorine-beryllium double doping, the mechanical properties of the diamond film become worse, the carrier concentration increases, and the mobility first increases slightly and then decreases; compared with Comparative Example 2, the carrier concentration, mobility, hardness, and modulus of Examples 1 to 4 are significantly improved after annealing treatment. The reason may be that although fluorine-beryllium double doping will reduce the size of diamond grains, it will introduce more defects concentrated at the grain boundaries, resulting in a downward trend in mechanical properties. However, the annealing treatment has a promoting effect on both composition uniformity and defect compensation, and can significantly improve the mechanical properties.

[0091] In summary, for the double-doped diamond prepared by the present invention, the filling of fluorine and beryllium atoms can redistribute charges. There will be additional charge enrichment on the beryllium atoms, adjacent carbon atoms, and fluorine atoms, accelerating the charge flow and thus increasing the carrier mobility. The double doping with fluorine and beryllium helps improve the electrical properties and catalytic activity of the diamond film, and further promotes the application of diamond in the fields of electronic devices and catalytic electrodes.

[0092] The above embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent shall be subject to the appended claims.

[0093] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a double-doped diamond with an ultra-wide bandgap semiconductor, characterized in that: Using microwave plasma chemical vapor deposition method, diamond nucleation is carried out on the pretreated substrate, and then using methane, hydrogen, carbon tetrafluoride and diethylberyllium vapor as the growth gas source, a double-doped diamond containing fluorine and beryllium elements is grown on the substrate; It includes the following steps: S1. Substrate pretreatment: The substrate is polished, cleaned, implanted with nano-diamond seed solution and dried; S2. Nucleation of undoped diamond: Place the pretreated substrate in a microwave plasma device, evacuate to a pressure less than 10 -5 Pa, turn on the microwave excitation source, and introduce hydrogen. Control the microwave power to be 1000 - 1200 W, the deposition gas pressure to be 4.0 - 4.5 kPa, and the substrate temperature to be 850 - 950 °C. Then, use a mixed gas of hydrogen and methane as the nucleation gas source to deposit undoped diamond for 10 - 20 min; S3. Growth of double-doped diamond: Keeping the microwave power, deposition pressure and substrate temperature, using a mixed gas of methane, hydrogen, carbon tetrafluoride and diethylberyllium vapor as the growth gas source, epitaxially grow double-doped diamond for 4 - 8 h; then stop introducing methane, carbon tetrafluoride and diethylberyllium vapor, and maintain the hydrogen plasma environment for 5 - 10 min; S4. Annealing treatment: Place the product obtained in step S3 in a vacuum heating furnace, evacuate to a pressure less than 10 -2 Pa, start heating up, and introduce a mixed gas of methane, hydrogen and nitrogen into the furnace. Keep it at a temperature of 600 - 800 °C and a pressure of 1 - 3 MPa for 1 - 2 h, and then take it out after cooling in the furnace to below 60 °C.

2. The preparation method of the ultra-wide bandgap semiconductor double-doped diamond according to claim 1, wherein: In the nucleation gas source described in step S2, the total flow rate of hydrogen and methane is 220 - 300 sccm, and the volume ratio of methane to hydrogen is 2.5 - 4.5%.

3. The preparation method of the ultra-wide bandgap semiconductor double-doped diamond according to claim 2, wherein: The total flow rate of the growth gas source described in step S3 is the same as the total flow rate of the nucleation gas source described in step S2. The volume percentage of methane in the growth gas source is 1 - 2%, the volume percentage of diethylberyllium vapor in the growth gas source is 250 - 400 ppm, and the volume percentage of carbon tetrafluoride in the growth gas source is 500 - 750 ppm.

4. The preparation method of the ultra-wide bandgap semiconductor double-doped diamond according to claim 3, characterized in that: Hydrogen carrier gas is used when introducing carbon tetrafluoride and diethylberyllium vapor.

5. The preparation method of the ultra-wide bandgap semiconductor double-doped diamond according to claim 1, characterized in that: In the mixed gas of methane, hydrogen and nitrogen described in step S4, the volume percentage of methane is 1 - 5%, and the volume percentage of hydrogen is 0.5 - 2.5%.

6. The preparation method of the ultra-wide bandgap semiconductor double-doped diamond according to claim 1, characterized in that: In the nano-diamond seed solution implantation in step S1, the cleaned substrate is placed in the nano-diamond seed solution and ultrasonicated for 20 - 40 min. The nano-diamond seed solution is an aqueous solution containing 2 - 3 wt% nano-diamond, and the nano-diamond grain size is 3 - 5 nm.

7. The preparation method of the ultra-wide bandgap semiconductor double-doped diamond according to claim 1, characterized in that: In step S1, the cleaning is carried out by ultrasonic cleaning with acetone, absolute ethanol and pure water.

8. The preparation method of the ultra-wide bandgap semiconductor double-doped diamond according to claim 1, characterized in that: The substrate is single-crystalline silicon or single-crystalline diamond with a (100) crystal orientation.

9. A super-wide bandgap semiconductor double-doped diamond prepared by the method according to any one of claims 1 to 8.

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