An in-situ C-doped p-type hexagonal boron nitride thin film and its preparation method

Abstract

This invention relates to an in-situ carbon-doped p-type hexagonal boron nitride thin film and its preparation method, belonging to the field of semiconductor thin film preparation and doping technology. The invention employs low-pressure chemical vapor deposition (LPCVD) technology to grow an intrinsic hBN thin film buffer layer on a substrate via the reaction BCl3 + NH3 → hBN + HCl. Then, in-situ doping is performed on the buffer layer using Cp2Mg as a dopant source. After controlled cooling, the in-situ carbon-doped p-type hexagonal boron nitride thin film is obtained. The growth rate and thickness of the film can be controlled by the growth temperature and the growth source flow rate, while its electrical properties and doping concentration can be adjusted by the heating temperature of the dopant source and the dilution ratio. The method described in this invention is simple, stable, and produces uniform doping, enabling the preparation of p-type hBN thin films with high hole concentrations. Furthermore, through heteroepitaxial growth and other methods, various semiconductor devices can be formed with other semiconductor materials.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor thin film preparation and doping technology, specifically relating to an in-situ C-doped P-type hexagonal boron nitride thin film and its preparation method. Background Technology

[0002] In recent years, nitride semiconductor materials and devices have developed rapidly, becoming an indispensable part of fields such as ultraviolet optoelectronic devices and power electronic devices. Hexagonal boron nitride (hBN) is a synthetic III-V compound with a hexagonal layered structure similar to graphite. As an ultrawide bandgap semiconductor material with a bandgap of approximately 6.0 eV, hexagonal boron nitride (hBN) possesses many excellent properties, such as excellent physical and chemical stability, high thermal conductivity, and high dielectric strength, making its potential application value widely recognized and studied in recent years.

[0003] Doping is an important means of altering the electrical properties of semiconductor materials and is also key to whether semiconductor materials can be used in devices. However, efficient p-type doping of wide-bandgap group III nitride semiconductor materials is a recognized technical challenge. Therefore, seeking suitable doping methods and dopants to prepare p-type hBN materials is of great research significance.

[0004] Group IV element carbon (C) is an amphoteric impurity in group III-V semiconductor material hBN. Its electrical behavior depends on the state of the C atom in the hBN crystal. When C substitutes for nitrogen atoms in the hBN crystal, it can act as an acceptor impurity, ionizing and creating holes. Therefore, it is possible to prepare p-type hBN thin films using C doping. Compared with post-doping processes such as ion implantation and diffusion, in-situ doping technology has advantages such as simple process, uniform impurity distribution, and no damage to the crystal lattice, making it an important means of controlling the electrical properties of epitaxial layers.

[0005] Currently, research on C-doped hBN is relatively limited. Aside from unintentional C doping studies, most research focuses on N-type doping using methane (CH4) as the dopant. For example, Professor HX Jiang's team at Texas Tech University (Uddin,MR,Li,J.,Lin,JY&Jiang,HXProbing carbon impurities in hexagonal boron nitride epilayers. Applied Physics Letters 110,doi:10.1063 / 1.4982647(2017)) prepared C-doped N-type hBN films using MOCVD with methane as the dopant source, achieving an impurity ionization energy of 0.45 eV. No studies using other C sources or P-type doping have been reported. Summary of the Invention

[0006] The purpose of this invention is to provide a stable, efficient, and simple in-situ C-doped P-type hexagonal boron nitride thin film and its preparation method. This invention employs low-pressure chemical vapor deposition (LPCVD) technology, using boron trichloride (BCl3) and ammonia (NH3) as precursors, and magnesia pyrocene (Cp2Mg) as the dopant gas to prepare the in-situ C-doped P-type hexagonal boron nitride thin film.

[0007] The method for preparing an in-situ C-doped P-type hBN thin film according to the present invention comprises the following steps:

[0008] (1) Clean the substrate (including but not limited to silicon wafers, sapphire, etc.) with acetone, ethanol and deionized water in sequence for 3 to 8 minutes, and then put it into the chamber of the LPCVD equipment;

[0009] (2) Evacuate the chamber to a vacuum level of 5×10⁻⁶. -4 Below Pa, high-purity nitrogen gas is introduced into the chamber to stabilize the chamber pressure at 50-500 Pa, and then the chamber is heated.

[0010] (3) Growth of intrinsic hBN thin film buffer layer: After the chamber is heated to 700-900℃, N2 is used as the carrier gas to carry BCl3 and NH3 into the chamber for buffer layer growth. The flow rate of BCl3 is 1-10 sccm and the flow rate of NH3 is 1-100 sccm. The reaction principle is: BCl3+NH3→hBN+HCl. The buffer layer growth time is 1-5 min, and an intrinsic hBN thin film buffer layer with a thickness of 50-250 nm is obtained.

[0011] (4) Growth of C-doped P-type hBN thin film: Turn off all reaction sources in step (3), continue to heat the chamber to 1000-1400℃, and then turn on BCl3 and NH3 again, using N2 as carrier gas, with a BCl3 flow rate of 10-100 sccm and an NH3 flow rate of 10-1000 sccm; at the same time, Cp2Mg is heated and volatilized in a water bath at 25-50℃, and then carried into the BCl3 pipeline after dilution using N2 as carrier gas; the inlet can be either continuous inlet or pulse inlet. When using continuous inlet, the inlet flow rate of Cp2Mg is 5-25 μmol / min, and when using pulse inlet, the pulse period is 2-20 s and the duty cycle is 1 / 4-3 / 4; the growth time of this step is 0.5-5 h, and a C-doped P-type hBN thin film with a thickness of 0.5-5 μm can be prepared on the intrinsic hBN thin film buffer layer;

[0012] (5) Close all reaction sources in step (4) to end the growth; under the protection of nitrogen, first cool the chamber to 380-420°C at a cooling rate of 8-15°C / min to ensure that the thin film sample grown at high temperature and the chamber are not damaged due to excessive temperature gradient, and then allow the chamber to cool down to room temperature naturally.

[0013] (6) Fill the chamber that was cooled to room temperature in step (5) with nitrogen gas to bring the chamber pressure back to normal; open the chamber and take out the thin film sample to complete the preparation of C-doped P-type hBN thin film on the substrate.

[0014] The advantages of this invention are:

[0015] (1) The process is simple and stable, and the preparation cost is low, making it promising for large-scale production;

[0016] (2) By adjusting process parameters such as reaction source flow rate and ratio, reaction temperature, gas pressure, doping source water bath heating temperature and dilution degree, the key performance indicators such as sample quality, thickness, doping concentration, and conductivity can be precisely controlled.

[0017] (3) The in-situ doping concentration is uniform and does not require impurity activation, which enables the preparation of P-type hBN films with high hole concentration.

[0018] (4) Through heteroepitaxial growth and other methods, various semiconductor devices can be formed with other semiconductor materials, with broad application prospects. Attached Figure Description

[0019] Figure 1 : A schematic diagram of the chamber structure of the customized horizontal LPCVD equipment used in this invention. (See diagram below.) Figure 1 As shown, a graphite heating stage is provided in the quartz tube reaction chamber. An electromagnetic induction heating coil is wound around the outside of the quartz tube as a heating system, and the substrate is placed on the graphite heating stage for heating. The quartz tube reaction chamber is provided with two gas inlets to provide the reaction precursor and dopant source. In this invention, NH3 is introduced through one gas inlet, and BCl3 and Cp2Mg are introduced through the other gas inlet after they are combined.

[0020] Figure 2 XRD pattern of the in-situ C-doped P-type hBN thin film prepared in Example 1 of this invention;

[0021] Figure 3 EDS energy spectrum of the in-situ C-doped P-type hBN thin film prepared in Example 1 of this invention;

[0022] Figure 4 IV characteristic curves of the in-situ C-doped P-type hBN thin film prepared in Example 1 of this invention;

[0023] Figure 5Impurity ionization energy fitting curve of the in-situ C-doped P-type hBN thin film prepared in Example 1 of this invention. Detailed Implementation

[0024] Example 1:

[0025] (1) The sapphire substrate was ultrasonically cleaned for 5 minutes each with acetone, ethanol and deionized water, and then placed into the chamber of the LPCVD equipment.

[0026] (2) Evacuate the equipment chamber to a vacuum level of 5×10⁻⁶. -4 Below Pa. After stabilizing the chamber pressure at 100 Pa by introducing high-purity nitrogen gas, the chamber is heated using an electromagnetic induction heating system;

[0027] (3) Growth of intrinsic hBN thin film buffer layer: After the chamber was heated to 700℃, N2 was used as the carrier gas to carry BCl3 and NH3 into the chamber for reaction, with a BCl3 flow rate of 10 sccm and an NH3 flow rate of 30 sccm. The reaction principle is: BCl3 + NH3 → hBN + HCl. The buffer layer growth time is 3 min, and an intrinsic hBN thin film buffer layer with a thickness of 150 nm is obtained.

[0028] (4) Growth of C-doped P-type hBN thin film: After shutting off the reaction source and continuing to heat the chamber to 1200℃, BCl3 and NH3 were restarted. N2 was used as the carrier gas, with a BCl3 flow rate of 20 sccm and an NH3 flow rate of 60 sccm. Simultaneously, Cp2Mg was volatilized by heating in a 40℃ water bath and diluted with N2 as the carrier gas before being incorporated into the BCl3 pipeline. The incorporation was continuous, with a Cp2Mg flow rate of 18 μmol / min. This step, with a growth time of 2 h, yielded a 2 μm thick C-doped P-type hBN thin film on the buffer layer.

[0029] (5) Turn off all reaction sources in step (4) and end the growth. Under the protection of nitrogen, the chamber is first cooled to 400°C in a controlled manner at a cooling rate of 10°C / min to ensure that the sample grown at high temperature and the chamber are not damaged due to excessive temperature gradient. Then the chamber is allowed to cool down to room temperature naturally.

[0030] (6) After the chamber is cooled to room temperature, nitrogen is introduced to bring the chamber pressure back to normal. The chamber is then opened and the thin film sample is taken out, thus completing the preparation of C-doped P-type hBN thin film on the substrate.

[0031] The results of XRD characterization of the above thin films are as follows: Figure 2 As shown, the diffraction peak of the thin film is located at 25.95°, corresponding to the diffraction peak of the hBN(002) crystal plane; its half-maximum width is 1.163°, which proves that the film quality is good.

[0032] Figure 3 The EDS spectrum of the thin film clearly shows the Kα characteristic peaks of B, N, C, and O, proving that C was successfully incorporated into the hBN film. Furthermore, no characteristic peaks for Mg were observed, indicating that Mg was not incorporated into the film.

[0033] The IV characteristics of C-doped hBN films were tested at room temperature, and compared with those of intrinsic hBN films under the same conditions. The results are as follows: Figure 4 As shown. For ease of comparison with the IV properties of intrinsic hBN films, Figure 4 It uses a semi-logarithmic coordinate system. Figure 4 The inset shows the IV characteristics of the doped thin film in a linear coordinate system. At a bias voltage of 100V, the current flowing through the C-doped hBN thin film can reach 4 × 10⁻⁶. -4 A, conductivity compared to intrinsic materials (~10) -10 The performance at 100V (A@100V) is significantly improved. As shown in the inset, the IV characteristic of the C-doped hBN film is close to linear, proving that a good ohmic contact can be formed between the film and the electrode.

[0034] The impurity ionization energy of the thin film was fitted by a variable-temperature IV test, and the results are as follows: Figure 5 As shown, the fitted impurity ionization energy is 321 meV.

[0035] The results obtained from the Hall effect test of the thin film are: Hall coefficient R H =992cm 3 / C > 0 indicates that the film is P-type conductive, with a resistivity of approximately 880 Ω·cm and a hole concentration of approximately 2.01 × 10⁻⁶. 15 cm -3 Hall mobility is 3.55 cm. 2 / (V·s), with good electrical properties.

[0036] Example 2:

[0037] (1) The sapphire substrate was ultrasonically cleaned for 5 minutes each with acetone, ethanol and deionized water, and then placed into the chamber of the LPCVD equipment.

[0038] (2) Evacuate the equipment chamber to a vacuum level of 5×10⁻⁶. -4 Below Pa. After stabilizing the chamber pressure at 100 Pa by introducing high-purity nitrogen gas, the chamber is heated using an electromagnetic induction heating system;

[0039] (3) Growth of intrinsic hBN thin film buffer layer: After the chamber is heated to 700℃, N2 is used as the carrier gas to carry BCl3 and NH3 into the chamber for reaction, with a BCl3 flow rate of 10 sccm and an NH3 flow rate of 30 sccm. The reaction principle is: BCl3 + NH3 → hBN + HCl. The buffer layer grows in 2 min and a buffer layer with a thickness of 100 nm can be obtained.

[0040] (4) Growth of C-doped P-type hBN thin film: After shutting off the reaction source and continuing to heat the chamber to 1200℃, BCl3 and NH3 were restarted. N2 was used as the carrier gas, with a BCl3 flow rate of 20 sccm and an NH3 flow rate of 60 sccm. Simultaneously, Cp2Mg was volatilized by heating in a 40℃ water bath and diluted with N2 as the carrier gas before being incorporated into the BCl3 pipeline. A pulsed induction method was used, with a pulse period of 10 s and a duty cycle of 1 / 2. The growth time for this step was 2 h, and a C-doped P-type hBN thin film with a thickness of 2 μm was prepared on the buffer layer.

[0041] (5) Turn off all reaction sources in step (4) and end the growth. Under the protection of nitrogen, the chamber is first cooled to 400°C in a controlled manner at a cooling rate of 10°C / min to ensure that the sample grown at high temperature and the chamber are not damaged due to excessive temperature gradient. Then the chamber is allowed to cool down to room temperature naturally.

[0042] (6) After the chamber is cooled to room temperature, nitrogen is introduced to bring the chamber pressure back to normal. The chamber is then opened and the thin film sample is taken out, thus completing the preparation of C-doped P-type hBN thin film on the substrate.

[0043] The results obtained from the Hall effect test of the thin film are: Hall coefficient R H =1.28×10 3 cm 3 / C > 0 indicates that the film is P-type conductive, with a resistivity of approximately 2196 Ω·cm and a hole concentration of approximately 1.63 × 10⁻⁶. 15 cm -3 The Hall mobility is 1.74 cm. 2 / (V·s), with good electrical properties.

Claims

1. A method for preparing an in-situ C-doped P-type hBN thin film, comprising the following steps: (1) The substrate was ultrasonically cleaned with acetone, ethanol and deionized water for 3-8 minutes in sequence, and then placed in the chamber of the low-pressure chemical vapor deposition equipment. (2) Evacuate the chamber to a vacuum level of 5×10⁻⁶. -4 Below Pa, high-purity nitrogen gas is introduced into the chamber to stabilize the chamber pressure at 50-500 Pa, and then the chamber is heated. (3) Growth of intrinsic hBN thin film buffer layer: After the chamber is heated to 700-900℃, N2 is used as the carrier gas to carry BCl3 and NH3 into the chamber for buffer layer growth, and an intrinsic hBN thin film buffer layer with a thickness of 50-250nm is obtained. (4) Growth of C-doped P-type hBN thin film: Turn off all reaction sources in step (3), continue to heat the chamber to 1000-1400℃, and then turn on BCl3 and NH3 again, using N2 as carrier gas; at the same time, Cp2Mg is heated and volatilized in a water bath at 25-50℃, and N2 is used as carrier gas to carry it into the pipeline of BCl3 after dilution, so that a C-doped P-type hBN thin film with a thickness of 0.5-5μm is prepared on the intrinsic hBN thin film buffer layer; (5) Turn off all reaction sources in step (4) to end the growth; under the protection of nitrogen, cool the chamber in a controlled manner to 380-420°C, and then let the chamber cool naturally to room temperature. (6) Fill the chamber that was cooled to room temperature in step (5) with nitrogen gas to bring the chamber pressure back to normal; open the chamber and take out the thin film sample to complete the preparation of C-doped P-type hBN thin film on the substrate.

2. The method for preparing an in-situ C-doped P-type hBN thin film as described in claim 1, characterized in that: The substrate in step (1) is a silicon wafer or sapphire.

3. The method for preparing an in-situ C-doped P-type hBN thin film as described in claim 1, characterized in that: In step (3), the flow rate of BCl3 is 1-10 sccm, the flow rate of NH3 is 1-100 sccm, and the growth time is 1-5 min.

4. The method for preparing an in-situ C-doped P-type hBN thin film as described in claim 1, characterized in that: In step (4), the flow rate of BCl3 is 10-100 sccm, the flow rate of NH3 is 10-1000 sccm, and the growth time is 0.5-5 h.

5. The method for preparing an in-situ C-doped P-type hBN thin film as described in claim 1, characterized in that: In step (4), Cp2Mg is injected into the pipeline of BCl3 using either continuous injection or pulse injection.

6. The method for preparing an in-situ C-doped P-type hBN thin film as described in claim 5, characterized in that: When continuous injection is used, the flow rate of Cp2Mg injection is 5–25 μmol / min; when pulse injection is used, the pulse period is 2–20 s and the duty cycle is 1 / 4–3 / 4.

7. The method for preparing an in-situ C-doped P-type hBN thin film as described in claim 1, characterized in that: The cooling rate in step (5) is 8–15 °C / min.

8. An in-situ C-doped P-type hBN thin film, characterized in that: It is prepared by the method described in any one of claims 1 to 7.

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