Simulation method for improving heteroepitaxial growth of gallium nitride on diamond substrate

Abstract

The invention relates to the technical field of diamond substrate heteroepitaxy growth films, in particular to a simulation method for improving diamond substrate heteroepitaxy growth gallium nitride, which comprises the following steps of: establishing surface models of boron nitride terminal diamond films (111) with different thicknesses; performing structure optimization on the surface model, and performing first principle calculation on the surface model after the structure optimization; respectively applying a femtosecond laser field to the surface model after structure optimization, and calculating laser intensity and frequency parameter ranges when a carbon-carbon bond is not excited and a nitrogen-boron bond in boron nitride and a gallium-nitrogen bond in gallium nitride are excited; according to the obtained data, different gradient temperature fields are applied to carry out first principle calculation, and the laser intensity, frequency and temperature range in which a nitrogen-boron bond in boron nitride is broken, a gallium-nitrogen bond in gallium nitride is bonded and other bonds are kept stable are obtained. The invention provides an effective method for improving the growth of gallium nitride on the surface of the diamond substrate, and improves the development and application of the electrical properties of the diamond heterojunction.

Description

Technical Field

[0001] The invention relates to the technical field of heteroepitaxial growth of thin films on diamond substrates, and in particular to a simulation method for improving heteroepitaxial growth of gallium nitride on diamond substrates. Background Art

[0002] Diamond has great application potential in power devices and other fields due to its ultra-wide bandgap and high thermal conductivity. However, since materials with matching lattices and energy bands have not yet been found to form heterojunctions, the realization of its potential is still severely restricted. At present, surface terminal technology can not only achieve the modulation of diamond energy bands, but also provide new ideas for the growth of diamond heterojunctions. However, after the terminal is prepared, its surface is very easy to adsorb various impurities in the air, and the subsequent epitaxial process will also cause varying degrees of damage to the surface terminal. These problems seriously affect the quality of the heterojunction and prevent its performance from being fully utilized. Summary of the invention

[0003] The purpose of the present invention is to provide a simulation method for improving heteroepitaxial growth of gallium nitride on diamond substrates, which can solve the current problems of large lattice mismatch at the diamond heterojunction growth interface and poor interface growth quality, and further obtain the laser intensity, frequency and temperature range that are suitable for breaking the nitrogen-boron bond in boron nitride and forming the gallium-nitrogen bond in gallium nitride while keeping other bonds stable through first principles and molecular dynamics simulation calculations.

[0004] The solution adopted by the present invention to achieve the purpose is: a simulation method for improving heteroepitaxial growth of gallium nitride on a diamond substrate, comprising the following steps:

[0005] S1: Establishing the surface model of boron nitride terminated diamond film (111) with different thicknesses, wherein the boron nitride and diamond atoms are aligned in the top position, the boron atoms contact the carbon atoms in the diamond to form boron-carbon bonds, and the surface nitrogen atoms are not saturated but suspended separately;

[0006] S2: Optimizing the structure of the surface model of boron nitride terminated diamond film (111) with different thicknesses to obtain the lattice constant, bond length, bond angle and atomic position of the terminated diamond;

[0007] S3: Based on density functional theory, first-principles calculations are performed on the surface models of the structure-optimized boron nitride-terminated diamond films (111) with different thicknesses to obtain the ground-state electron density and wave function;

[0008] S4: applying a femtosecond laser field to the surface models of the boron nitride-terminated diamond films (111) of different thicknesses after structural optimization, setting different laser intensities and frequency parameters according to density functional theory calculations, and calculating the laser intensity and frequency parameter ranges in which the carbon-carbon bonds are not excited but the nitrogen-boron bonds in the boron nitride and the gallium-nitrogen bonds in the gallium nitride are excited;

[0009] S5: According to the laser intensity and frequency parameter range obtained in step S4, different gradient temperature fields are applied to perform first principle calculations to obtain the laser intensity, frequency and temperature range in which the nitrogen-boron bond in boron nitride is broken and the gallium-nitrogen bond in gallium nitride is formed while other bonds remain stable.

[0010] Preferably, in step S1, the surface model comprises two layers, an upper layer being a vacuum layer, and a lower layer being a growth layer with diamond as a substrate.

[0011] Preferably, the diamond substrate is divided into three parts. The first part keeps the carbon atoms fixed during the entire dynamic process, and its bottom is saturated with hydrogen atoms; the temperature of the second part is always consistent with the set temperature; the third part is a terminal layer of carbon atoms and boron nitride, allowing the surface atoms to be fully affected by the potential field.

[0012] Preferably, in the surface model, the boron nitride terminal is connected to the diamond via a carbon-boron bond, and the terminal exposes nitrogen atoms; the gallium nitride above is connected to the terminal structure via a gallium-nitrogen bond, forming a growth layer upwards.

[0013] Preferably, in step S2, the specific process is: based on the ground state surface model, with the total energy minimization of the model as the solution goal, using density functional theory to solve all lattice constants, bond lengths, bond angles and atomic positions of the two surface models.

[0014] Preferably, the specific process of step S3 is: the surface model of the boron nitride terminal diamond film (111) surface is k-space meshed using the Monkhorst-Pack method, the pseudopotentials of nitrogen, boron, carbon, gallium and hydrogen atoms are selected as ultrasoft pseudopotentials, the generalized gradient approximation exchange-correlation functional is used, the self-consistent accuracy is set and the Kohn-Sham equation is iteratively solved to obtain the ground state electron density and wave function.

[0015] Preferably, step S4 is performed by Lammps software, and the polarization direction of the laser field applied by the software is perpendicular to the model surface.

[0016] Preferably, in step S5, the molecular dynamics calculation method uses Tersoff potential to calculate the interaction force between atoms.

[0017] Preferably, in step S5, the entire simulation process adopts an NVT system, the time step △x=0.5fs, and the cut-off radius is 0.8nm.

[0018] Boron nitride not only has many advantages similar to diamond, but also performs better in thermal stability and chemical stability. Thanks to the extremely low lattice mismatch rate of the two, in order to rationally control the growth of diamond heterogeneous interface, the present invention places the boron nitride terminal on the diamond interface as a medium for its heterogeneous interface with wide bandgap semiconductors such as gallium nitride. This growth method will significantly improve the quality of heteroepitaxial growth of gallium nitride on diamond substrates, which is conducive to the innovation of high-performance components and plays an important role in promoting the further development of electronic technology.

[0019] The present invention discloses a simulation method for improving heteroepitaxial growth of gallium nitride on diamond substrates, which mainly solves the problem of poor quality of heterogeneous crystals epitaxially grown on single crystal diamond substrates in the prior art. According to density functional theory and molecular dynamics theory, first principle and molecular dynamics calculations are performed on cubic boron nitride terminal diamond film models of different thicknesses, and the microscopic process of crystal growth in the model under laser field and temperature field, as well as the corresponding photon absorption of valence electrons, valence electron transition, and chemical bond breaking are simulated. On this basis, a method for improving heteroepitaxial growth of gallium nitride on diamond substrates is further proposed. The intensity, frequency, and temperature range values ​​of femtosecond lasers that can promote the breaking of boron-nitrogen bonds in boron nitride and the bonding of nitrogen-gallium bonds in gallium nitride are calculated. Since the present invention performs surface terminal treatment on the single crystal diamond substrate, the lattice mismatch of the substrate in the subsequent epitaxial process is reduced and more dangling bonds are provided, thereby improving the quality of the heterojunction and the heat dissipation capacity of the device, and can be used for the preparation of high-power GaN-based microwave power devices.

[0020] The present invention has the following advantages and beneficial effects:

[0021] The present invention studies a method for improving heteroepitaxial growth of gallium nitride on a diamond substrate by using laser field and temperature field. By first principles and molecular dynamics simulation calculations, laser field and temperature field are applied to the surface of a model of gallium nitride grown on a diamond substrate with boron nitride terminations, and the laser intensity, frequency and temperature range in which the nitrogen-boron bond breaks, the gallium-nitrogen bond in gallium nitride forms, and other bonds remain stable are calculated. This provides an effective method for improving the growth of gallium nitride on the surface of a diamond substrate, and improves the development and application of electrical properties of diamond heterojunctions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of a diamond / boron nitride terminal / gallium nitride heterojunction structure for improving a simulation method for heteroepitaxial growth of gallium nitride on a diamond substrate provided by an embodiment of the present invention;

[0023] Figure 2 A step diagram of a simulation method for improving heteroepitaxial growth of gallium nitride on a diamond substrate provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0024] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples.

[0025] The growth of high-quality diamond heterojunctions is of great significance to improving the electronic performance of wide-bandgap semiconductors and the development of high-power electronic devices. The present invention aims to solve the problems of large lattice mismatch and poor interface growth quality in the current diamond heterojunction growth interface. The present invention simulates the temperature field changes during the growth of diamond gallium nitride interface by first principles and molecular dynamics simulation to obtain conditions suitable for interface growth. In order to determine the range of laser intensity, frequency and temperature field, Figure 1 A schematic diagram of a diamond / boron nitride terminal / gallium nitride heterojunction structure for improving a simulation method for heteroepitaxial growth of gallium nitride on a diamond substrate provided by an embodiment of the present invention; Figure 2 As shown, the present invention provides a simulation method for improving heteroepitaxial growth of gallium nitride on diamond substrates. Based on first principles and molecular dynamics analysis, the transition of valence electrons, the breaking and formation conditions of chemical bonds in the model under the action of changes in laser field and temperature field are simulated to further improve the growth quality of gallium nitride on the diamond surface of boron nitride terminal.

[0026] Specifically, a simulation method for improving heteroepitaxial growth of gallium nitride on a diamond substrate comprises the following steps:

[0027] S1: Establish the surface model of boron nitride terminated diamond film (111) with different thicknesses. Boron nitride and diamond atoms are aligned in top position, boron atoms contact with carbon atoms in diamond to form boron-carbon bonds, and surface nitrogen atoms are not saturated but suspended separately;

[0028] S2: Optimizing the structure of the surface model of boron nitride terminated diamond film (111) with different thicknesses to obtain the lattice constant, bond length, bond angle and atomic position of the terminated diamond;

[0029] S3: Based on density functional theory, first-principles calculations are performed on the surface models of boron nitride-terminated diamond films (111) with different thicknesses to obtain the ground-state electron density and wave function;

[0030] S4: applying a femtosecond laser field to the terminal surface model after structural optimization, setting different laser intensity and frequency parameters according to density functional theory calculations, and calculating the laser intensity and frequency range in which the carbon-carbon bond is not excited but the nitrogen-boron bond in boron nitride and the gallium-nitrogen bond in gallium nitride are excited;

[0031] S5: According to the laser intensity and frequency parameter range obtained in step S4, different gradient temperature fields are applied to perform first principle calculations to obtain the laser intensity, frequency and temperature range in which the nitrogen-boron bond in boron nitride is broken and the gallium-nitrogen bond in gallium nitride is formed while other bonds remain stable.

[0032] Furthermore, the surface model in step S1 is established by modeling software such as Quantum ATK, and the surface model comprises two layers, the upper layer is The upper layer is a vacuum layer, and the lower layer is a growth layer with diamond as the substrate. The entire diamond substrate has 8 layers and is divided into 3 parts. The first part is the bottom 2 layers, which keep the carbon atoms fixed during the entire dynamic process, and the bottom is saturated with hydrogen atoms; the second part is the middle 3 layers, whose atoms use the velocity calibration method to keep the temperature consistent with the set temperature; the third part is the surface 3 layers of carbon atoms and the boron nitride terminal layer, so that the surface atoms are completely affected by the potential field. Two-dimensional periodic boundary conditions are used parallel to the X and Y directions to make the particles pseudo-infinite on the horizontal plane. Among them, in the two surface models of the (111) surface, the boron nitride terminal is connected to the diamond through a carbon-boron bond, and the terminal exposes nitrogen atoms; the gallium nitride above is connected to the terminal structure through a gallium-nitrogen bond to form a growth layer upward.

[0033] Furthermore, the step S2 specifically includes: using the first-principles calculation software Quantum ATK based on the ground state surface model, with the total energy of the model minimized and the atomic free relaxation force minimized as the solution goal, solving all lattice constants, bond lengths, bond angles and atomic positions of the two surface models.

[0034] Furthermore, the step S3 specifically includes: using the first-principles calculation software Quantum ATK to perform k-space meshing on the surface model of the boron nitride terminal diamond film (111) surface using the Monkhorst-Pack method, selecting the pseudopotentials of nitrogen, boron, carbon, gallium and hydrogen atoms as ultrasoft pseudopotentials, using the generalized gradient approximation exchange-correlation functional, setting the self-consistent accuracy and iteratively solving the Kohn-Sham equation to obtain the ground state electron density and wave function.

[0035] Furthermore, the step S4 is performed by Lammps software, and the polarization direction of the laser field applied is perpendicular to the surface of the model. The growth process is simulated by molecular dynamics simulation method, using two-body distribution function, nearest neighbor coordination number and atomic trajectory method.

[0036] Furthermore, in step S5, the molecular dynamics calculation method uses Tersoff potential to calculate the interaction force between atoms. Tersoff potential is accurate for describing the diamond system of SP3 bonding type, is widely used in the simulation of semiconductor material systems, and has been successfully used in the simulation calculation of many growth systems. The entire simulation process uses NVT system, the time step △x = 0.5fs, and the cutoff radius is 0.8nm.

[0037] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A simulation method for improving heteroepitaxial growth of gallium nitride on a diamond substrate, characterized in that: The following steps are involved: S1: Establishing the surface model of boron nitride terminated diamond film (111) with different thicknesses, wherein the boron nitride and diamond atoms are aligned in the top position, the boron atoms contact the carbon atoms in the diamond to form boron-carbon bonds, and the surface nitrogen atoms are not saturated but suspended separately; S2: Optimizing the structure of the surface model of boron nitride terminated diamond film (111) with different thicknesses to obtain the lattice constant, bond length, bond angle and atomic position of the terminated diamond; S3: Based on density functional theory, first-principles calculations are performed on the surface models of the structure-optimized boron nitride-terminated diamond films (111) with different thicknesses to obtain the ground-state electron density and wave function; S4: applying a femtosecond laser field to the surface models of the boron nitride-terminated diamond films (111) of different thicknesses after structural optimization, setting different laser intensities and frequency parameters according to density functional theory calculations, and calculating the laser intensity and frequency parameter ranges in which the carbon-carbon bonds are not excited but the nitrogen-boron bonds in the boron nitride and the gallium-nitrogen bonds in the gallium nitride are excited; S5: According to the laser intensity and frequency parameter range obtained in step S4, different gradient temperature fields are applied to perform first principle calculations to obtain the laser intensity, frequency and temperature range in which the nitrogen-boron bond in boron nitride is broken and the gallium-nitrogen bond in gallium nitride is formed while other bonds remain stable.

2. The simulation method for improving heteroepitaxial growth of GaN on diamond substrate according to claim 1, characterized in that: In the step S1, the surface model includes two layers, the upper layer is a vacuum layer, and the lower layer is a growth layer with diamond as the substrate.

3. The simulation method for improving heteroepitaxial growth of gallium nitride on diamond substrate according to claim 2, characterized in that: The diamond substrate is divided into three parts. The first part keeps the carbon atoms fixed during the entire dynamic process, and its bottom is saturated with hydrogen atoms; the temperature of the second part is always consistent with the set temperature; the third part is the carbon atoms and boron nitride terminal layer, which allows the surface atoms to be fully affected by the potential field.

4. The simulation method for improving heteroepitaxial growth of GaN on diamond substrate according to claim 2, characterized in that: In the surface model, the boron nitride terminal is connected to the diamond via a carbon-boron bond, and the terminal exposes nitrogen atoms; the gallium nitride above is connected to the terminal structure via a gallium-nitrogen bond, forming a growth layer upwards.

5. The simulation method for improving heteroepitaxial growth of GaN on diamond substrate according to claim 1, characterized in that: In step S2, the specific process is: based on the ground state surface model, with the total energy minimization of the model as the solution goal, using density functional theory, all lattice constants, bond lengths, bond angles and atomic positions of the two surface models are solved.

6. The simulation method for improving heteroepitaxial growth of GaN on diamond substrate according to claim 1, characterized in that: The specific process of step S3 is as follows: the surface model of the boron nitride terminal diamond film (111) surface is k-space meshed using the Monkhorst-Pack method, the pseudopotentials of nitrogen, boron, carbon, gallium and hydrogen atoms are selected as ultrasoft pseudopotentials, the generalized gradient approximation exchange-correlation functional is used, the Kohn-Sham equation is iteratively solved after setting the self-consistent accuracy, and the ground state electron density and wave function are obtained.

7. The simulation method for improving heteroepitaxial growth of GaN on diamond substrate according to claim 1, characterized in that: The step S4 is performed by Lammps software, and the polarization direction of the laser field applied by the software is perpendicular to the model surface.

8. The simulation method for improving heteroepitaxial growth of GaN on diamond substrate according to claim 1, characterized in that: In step S5, the molecular dynamics calculation method uses Tersoff potential to calculate the interaction force between atoms.

9. The simulation method for improving heteroepitaxial growth of GaN on diamond substrate according to claim 1, characterized in that: In step S5, the entire simulation process uses the NVT system, the time step △x=0.5fs, and the cut-off radius is 0.8nm.

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