A method for preparing cubic AlN single crystal thin film by using pulsed laser deposition technology

Abstract

The application discloses a method for preparing cubic AlN single crystal thin film by using a pulse laser deposition technology, and belongs to the field of single crystal thin film epitaxial preparation. The method uses high-power and short-wavelength pulse laser to bombard an AlN target material, so that a plasma plume is formed by evaporation of the surface of the AlN target material; then, the AlN plasma is deposited on a MgO (100) substrate to form a thin film. By precisely controlling a target-substrate distance, N2 pressure, substrate temperature, laser energy and annealing process, high-quality and high-speed epitaxial growth of the cubic c-AlN single crystal thin film is realized. The cubic AlN thin film prepared by the method has [100] orientation, and the surface roughness reaches an atomic level, and a zero-lattice-mismatch coherent interface is formed between the cubic AlN thin film and the MgO (100) substrate. The method is simple and efficient, and provides a high-quality material basis for the application of the c-AlN in semiconductor devices.

Description

Technical Field

[0001] This invention belongs to the field of single-crystal thin film epitaxial preparation, specifically relating to a method for preparing cubic AlN single-crystal thin films using pulsed laser deposition technology. Background Technology

[0002] As an ultra-wide bandgap semiconductor material, cubic aluminum nitride (c-AlN) has shown great potential in deep ultraviolet optoelectronic devices, high temperature, high frequency, and high power electronic devices due to its wide bandgap (6.2 eV), high thermal conductivity, high breakdown field strength, excellent ultraviolet transmittance, and outstanding chemical and thermal stability. It has become a cutting-edge focus of semiconductor technology research.

[0003] Current research mainly focuses on stable hexagonal aluminum nitride (h-AlN), especially its (0001)-oriented thin films. However, h-AlN exhibits significant spontaneous polarization and piezoelectric polarization along this direction, leading to a strong built-in electric field that severely limits the radiative recombination efficiency of charge carriers, thus restricting the performance improvement of AlN-based devices (such as deep ultraviolet LEDs and lasers). Compared to its stable hexagonal phase, c-AlN thin films with

[100] orientation exhibit unique advantages: the cubic structure has high crystal symmetry, fundamentally eliminating the strong built-in electric field caused by polarization electric fields (spontaneous polarization and piezoelectric polarization); the high symmetry also significantly reduces photon scattering loss and doping difficulty, making it a highly promising high-performance optoelectronic material. However, as a thermodynamically metastable phase, high-quality epitaxial growth of c-AlN is extremely challenging. Existing techniques mainly utilize buffer layers for the epitaxial growth of c-AlN. This method introduces significant process complexity: additional growth steps and the need for precise control over parameters such as the thickness of the buffer layer (too thin a layer cannot effectively relax lattice mismatch strain, while too thick a layer easily introduces defects or leads to surface roughness), severely hindering the large-scale application of c-AlN thin films. Therefore, developing a simple method to directly epitaxially grow high-quality c-AlN single-crystal thin films has become an urgent need.

[0004] To address the aforementioned core bottlenecks, this invention innovatively proposes a method for the direct epitaxial growth of high-quality cubic AlN(100) single-crystal thin films on MgO(100) substrates based on pulsed laser deposition (PLD) technology. This method achieves high-quality, high-speed epitaxial growth of c-AlN(100) thin films by precisely controlling key parameters such as target-substrate distance, N2 gas pressure, substrate temperature, laser energy, and annealing process, without the need for any buffer layer. This invention significantly reduces process complexity and technical difficulty, providing an efficient and reliable solution for the direct preparation of metastable c-AlN thin films and their application in advanced semiconductor devices. Summary of the Invention

[0005] This invention provides a method for directly epitaxially growing high-quality cubic AlN(100) single-crystal thin films on MgO(100) substrates based on pulsed laser deposition (PLD) technology. This method utilizes a pulsed laser deposition system and adjusts the target-substrate distance (50-70 mm), N2 gas pressure (2-10 Pa), substrate temperature (600-800℃), and laser energy (1-10 J / cm²). 2 The process of annealing (600-800℃, 0.5-1 h) and annealing process can achieve high-quality epitaxy of cubic AlN (100) single crystal thin films, providing an effective solution for the direct epitaxial growth of high-quality cubic AlN single crystal thin films.

[0006] The core technical solution is as follows:

[0007] 1. Preparation method:

[0008] Step (1) Substrate cleaning: The MgO(100) substrate was ultrasonically cleaned in sequence with acetone, alcohol and deionized water solution for 5-15 min each time.

[0009] Step (2) Sample delivery: Evacuate the chamber to a back-bottom vacuum, open the valve between the sample inlet chamber and the growth chamber, and use the sample delivery rod to transfer the substrate to the growth chamber of the pulsed laser deposition system;

[0010] Step (3) Deposition of c-AlN thin film: Adjust the target-substrate distance to 50-70 mm, introduce high-purity N2 (≥99.99%) into a vacuum environment (≤10-5 Pa), with the N2 pressure between 2-10 Pa, heat the substrate to 600-800℃ at a heating rate of 10-30℃ / min, and turn on the KrF excimer laser to perform epitaxial growth of single-crystal cubic AlN thin film. The laser wavelength is 248 nm, and the laser energy is 1-10 J / cm. 2 The frequency is 1-10 Hz, and the number of laser pulses is 5000-30000.

[0011] Step (4) In-situ annealing: After growth stops, maintain the temperature state of step (3), adjust the N2 gas pressure of step (3) to 50-100 Torr, and perform in-situ annealing treatment on the epitaxially grown AlN film (0.5-1 h).

[0012] Step (5) Sampling: After annealing, cool the substrate to room temperature at a rate of 10-30℃ / min, transfer the substrate to the sample delivery chamber using the sample delivery rod, close the valve between the sample delivery chamber and the growth chamber, and introduce high-purity N2 (≥99.99%) into the sample delivery chamber. The sample was then removed to complete the growth process.

[0013] 2. Technical Principles:

[0014] Substrate lattice matching: MgO with the

[100] orientation has an FCC structure (Fm3m space group) similar to cubic AlN and a lattice constant of 4.2112 Å (JCPDS card number 45-0946). The lattice constant of cubic AlN is 4.0452 Å (JCPDS card number 46-1200), and the lattice mismatch between MgO and cubic AlN films is only 4.1%.

[0015] Thin film deposition technology selection: Pulsed laser deposition technology, due to its high-energy non-equilibrium growth mechanism and flexible control of growth parameters, can achieve atomic-level fidelity transfer of complex compounds, and also possesses the capabilities of low-temperature epitaxy, precise interface control, and multi-dimensional structure adaptation. These characteristics make it an irreplaceable epitaxial method in cutting-edge fields such as ultra-wide bandgap semiconductors (e.g., cubic AlN) and silicon-based heterostructure integration, and it is the preferred technology for epitaxial metastable cubic AlN thin films.

[0016] 3. Technological advantages:

[0017] Advantage (1): The c-AlN thin film grown on the MgO (100) substrate using pulsed laser deposition technology is a single crystal and grows along the c-axis.

[0018] Advantage (2): The c-AlN thin film grown on the MgO (100) substrate using pulsed laser deposition technology has an atomically smooth surface.

[0019] Advantage (3): The c-AlN thin film grown on the MgO (100) substrate using pulsed laser deposition technology is a coherent epitaxy. The AlN atoms and MgO atoms at the interface are strictly aligned without mismatch dislocations, forming a continuous and defect-free crystal structure, which lays the foundation for the fabrication of high-performance devices.

[0020] Advantage (4): Simple growth steps. Compared with conventional and complex buffer layer-assisted growth methods, the present invention does not have complicated growth requirements. It only requires the growth of a single material once. It has low technical difficulty, is easy to operate, and has better scalability. Attached Figure Description

[0021] Figure 1 The images show the XRD patterns of the c-AlN (100) single crystal thin films prepared by pulsed laser deposition technology according to the present invention. (a) is a 2Theta scan image and (b) is a Phi scan image, which proves the crystal quality of the c-AlN thin film.

[0022] Figure 2 This is an AFM image of the c-AlN(100) single crystal thin film prepared by pulsed laser deposition technology according to the present invention, showing the atomic-level flatness of the epitaxial film surface;

[0023] Figure 3This is a TEM image of a c-AlN(100) single crystal thin film prepared by pulsed laser deposition technology according to the present invention, showing heteroepitaxial growth without mismatch dislocations. Detailed Implementation

[0024] To further illustrate the technical means of this invention, the specific implementation steps and details of the method for preparing c-AlN(100) single crystal thin films using pulsed laser deposition technology proposed in this invention will be described in detail.

[0025] Example 1:

[0026] Preparation and characterization of c-AlN(100) single crystal thin films.

[0027] 1. Substrate cleaning: MgO (100) was selected as the substrate. It was ultrasonically cleaned with acetone and alcohol solutions for 15 min in sequence, followed by ultrasonic cleaning with deionized water solution for 5 min. After cleaning, it was dried with N2.

[0028] 2. Sample delivery: Place the cleaned MgO(100) substrate into the sample delivery chamber, and evacuate the chamber to a back-bottom vacuum of 4×10⁻⁶. -7 Torr, open the valve between the sample inlet chamber and the growth chamber, and use the sample feed rod to transfer the substrate to the growth chamber of the pulsed laser deposition system;

[0029] 3. Deposition of cubic AlN thin films: Adjust the target-substrate distance to 60 mm, and perform deposition in a vacuum environment at 7 × 10⁻⁶ mm. -6 High-purity N2 (≥99.99%) was introduced into Pa at a pressure of 2 Pa. The substrate was heated to 800 °C at a heating rate of 30 °C / min. A KrF excimer laser with a wavelength of 248 nm was then used for epitaxial growth of a single-crystal c-AlN thin film at a laser energy of 5 J / cm². 2 The frequency is 3 Hz and the number of laser pulses is 15000.

[0030] 4. In-situ annealing: After growth stops, turn off the laser, maintain the temperature at 800 ℃, introduce high-purity N2 (≥99.99%) again, adjust the N2 pressure to 100 Torr, hold for 1 h, and anneal the epitaxially grown AlN film.

[0031] 5. Sampling: After annealing, the substrate is cooled to room temperature at a rate of 30 °C / min. The substrate is transferred to the sample delivery chamber using the sample delivery rod. The valve between the sample delivery chamber and the growth chamber is closed. High-purity N2 (≥99.99%) is introduced into the sample delivery chamber, and the sample is then removed to complete the growth process.

[0032] Characterization tests of cubic AlN (100) single crystal thin films:

[0033] The prepared cubic AlN(100) single-crystal thin film was characterized by X-ray diffraction (XRD). The results of Theta and Phi scans are as follows: Figure 1 As shown, the AlN thin film crystal orientation is

[100] , the crystal structure is cubic, and it grows directly along the MgO lattice without in-plane rotation, which proves the high crystal quality of the c-AlN thin film.

[0034] The prepared c-AlN(100) single-crystal thin film was characterized by atomic force microscopy (AFM), and the test results are as follows: Figure 2 As shown, the AlN film has an extremely smooth plane with a root mean square (RMS) surface roughness of only 0.2 nm, demonstrating the atomic-level flatness of the epitaxial film surface.

[0035] The prepared cubic c-AlN(100) single crystal thin film was characterized by transmission electron microscopy (TEM), and the results are as follows: Figure 3 As shown, it can be seen that at the interface, the c-AlN single crystal film is directly bonded to the MgO(100) substrate without dislocations, forming a coherent interface with zero lattice mismatch, indicating heteroepitaxialization without mismatch dislocations.

[0036] The c-AlN(100) single crystal thin film prepared by this invention exhibits good crystal quality, atomic-level flatness, and a heteroepitaxial interface without mismatch dislocations in characterization tests.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. Furthermore, various modifications can be made to the present invention for specific situations or circumstances without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed, but should include all embodiments falling within the scope of the claims of the present invention.

[0038] It should be understood that this disclosure is not limited to the features described above, and various modifications or changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for preparing cubic AlN single-crystal thin films using pulsed laser deposition technology, characterized in that, Includes the following steps: Step (1) Substrate cleaning: The MgO(100) substrate was ultrasonically cleaned (5-15 min) in sequence with acetone, alcohol and deionized water solution. Step (2) Sample delivery: Evacuate the chamber to a back-bottom vacuum, open the valve between the sample delivery chamber and the growth chamber, and use the sample delivery rod to transfer the substrate to the growth chamber of the pulsed laser deposition system; Step (3) Deposition of c-AlN cubic film: After adjusting the target-substrate distance (50-70 mm), deposit the film in a vacuum environment (≤10). -5 High-purity N2 (≥99.99%) is introduced into the substrate, and the N2 pressure is controlled at 2-10 Pa. The substrate is heated to the deposition temperature (600-800 ℃) at a heating rate of 10-30 ℃ / min, and the laser is turned on (laser energy 1-10 J / cm²). 2 Epitaxial growth of single-crystal c-AlN thin films was carried out. Step (4) In-situ annealing: After growth is completed, maintain the substrate temperature (600-800 ℃) of step (3), adjust the N2 pressure to (50-100 Torr), and perform in-situ annealing treatment on the epitaxially grown AlN film (0.5-1 h). Step (5) Sampling: After annealing, the substrate is cooled to room temperature at a rate of 10-30℃ / min. The substrate is transferred to the sample delivery chamber using the sample delivery rod. The valve between the sample delivery chamber and the growth chamber is closed. High-purity N2 (≥99.99%) is introduced into the sample delivery chamber and the sample is taken out to complete the growth.

2. The preparation method according to claim 1, characterized in that, The MgO substrate described in step (1) has a crystal orientation of [100]. The MgO (100) substrate is ultrasonically cleaned for 5-15 min in sequence with acetone, alcohol and deionized water.

3. The preparation method according to claim 1, characterized in that, The target-substrate distance mentioned in step (3) is 50-70 mm, and the vacuum environment is ≤10. -5 Pa, N2 pressure is 2-10 Pa, and the substrate is heated to 600-800℃ at a rate of 10-30℃ / min.

4. The preparation method according to claim 1, characterized in that, The KrF excimer laser mentioned in step (3) has a wavelength of 248 nm and an energy of 1-10 J / cm. 2 The frequency is 1-10 Hz, and the number of pulses is 5000-30000.

5. The preparation method according to claim 1, characterized in that, The annealing temperature in step (4) is 600-800℃, the N2 gas pressure is 50-100 Torr, and the annealing time is 0.5-1 h.

6. The preparation method according to claim 1, characterized in that, The substrate cooling rate described in step (5) is 10-30℃ / min.

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