Method for analyzing electrical properties of SiC in variable-temperature semiconductor device based on first principle

Abstract

The invention discloses a method for analyzing electrical properties of SiC in a variable-temperature semiconductor device based on a first principle, and belongs to the technical field of performance analysis of semiconductor materials, and the method comprises the following steps: setting parameters and establishing a model; lattice distortion of SiC at different temperatures is simulated, cohesive energy is calculated, and stability is evaluated; analyzing the influence of lattice distortion on SiC state density and charge density; the generation of silicon defects and carbon defects in SiC is simulated, and the influence of the silicon defects and the carbon defects on cohesive energy, state density and charge density of SiC is calculated; and evaluating an electrical property change rule of SiC in a variable-temperature environment. According to the invention, the influence of lattice distortion and atomic defects of SiC at different temperatures on the electrical properties of SiC can be systematically researched, the electrical property change rule of SiC in a variable-temperature environment is disclosed, and a theoretical basis is provided for the application of SiC in a high-temperature and high-density heat flow environment.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of semiconductor material performance analysis, and specifically to a method for analyzing the electrical characteristics of SiC in a variable temperature semiconductor device based on first principles. Background Art

[0002] With the rapid development of information technology, especially in the fields of 5G communications and high-power power electronics, higher requirements are placed on the performance of semiconductor materials. As a representative of the third-generation wide bandgap semiconductor materials, SiC has shown great application potential in electronic power devices, ceramic materials, etc. due to its excellent properties such as wide bandgap, high critical breakdown electric field, and high electron saturation drift velocity. However, in the new generation of information technology represented by 5G communications, the heat dissipation problem of high-density heat flow, which has increased exponentially compared with the past, has become more prominent. In the actual use of SiC materials, the effect of temperature on its electrical properties is still unclear, which limits its widespread application in high-temperature environments. Summary of the invention

[0003] The technical solution of the present invention aims at the technical problem that the existing technical solutions are too single, and provides a solution that is significantly different from the existing technologies. It mainly provides a method for analyzing the electrical characteristics of SiC in variable temperature semiconductor devices based on first principles, so as to solve the technical problem raised in the above background technology that the influence of temperature on the electrical properties of SiC materials during actual use is still unclear.

[0004] The technical solution adopted by the present invention to solve the above technical problems is: The method for analyzing the electrical characteristics of SiC in a temperature-variable semiconductor device based on the first principle includes the following steps: S1, set parameters and build model; S2, simulate the lattice distortion of SiC at different temperatures and calculate the cohesive energy to evaluate the stability; S3. Analyze the effect of lattice distortion on SiC state density and charge density; S4. Simulate the generation of silicon defects and carbon defects in SiC and calculate their effects on the cohesive energy, state density and charge density of SiC; S5. Evaluate the changes in the electrical properties of SiC under variable temperature conditions.

[0005] Specifically, in step S1, the parameter settings include: the kinetic energy cutoff is set to 450 eV; the energy convergence standard is that the energy difference between two electron steps is less than 10 -5eV; the Hellmann-Feynman force residual between two ion steps during structure optimization was less than 0.02 eV / Å; the temperature broadening was set to 0.1 eV; 5×5×3 Gamma-centered K points were used for structure optimization, and 7×7×5 Gamma-centered K points were used for calculating the density of states.

[0006] Specifically, DFT calculations were performed using the Vienna ab initio simulation software package.

[0007] Specifically, in step S2, a deformation of the lattice from 30% contraction to 30% expansion is set, with each 5% being a step to simulate the lattice distortion caused by temperature changes in a wide range, and analyze the changes in state density and band gap.

[0008] Specifically, in step S2, the cohesive energy changes of each level of lattice-distorted SiC when lattice distortion occurs in different directions are calculated and statistically analyzed to determine the range of lattice distortion levels that produce stable deformation amounts when lattice distortion occurs in different directions.

[0009] Specifically, in step S3, the state density and charge density when deformation occurs in different directions are calculated, and the symmetry and band gap change of spin-up and spin-down are analyzed.

[0010] Specifically, in step S3, the state density and charge density when deformation occurs in different directions are calculated to explore the direction in which the distortion has the greatest impact on the state density of the material.

[0011] Specifically, in step S4, the cohesive energy of SiC and its layers introduced with silicon defects and carbon defects under different deformation amounts is counted, and the elements and temperature environment that have a greater impact on the stability of the material are analyzed.

[0012] Specifically, in step S4, the charge density and state density of SiC and its layers under different defects are calculated when the lattice is deformed, and the symmetry and band gap changes of spin-up and spin-down are analyzed.

[0013] Specifically, in step S5, the electrical performance analysis includes evaluating the change in the band gap, electronic structure, and conductive properties of SiC.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a method for analyzing the electrical properties of SiC based on first principles, which can systematically study the effects of lattice distortion and atomic defects of SiC on its electrical properties at different temperatures. Through theoretical calculation and simulation, the variation law of the electrical properties of SiC under variable temperature environment is revealed, providing a theoretical basis for the application of SiC in high temperature and high density heat flow environment.

[0015] (2) This paper uses VASP software for the first time in SiC temperature change conditions. It is a highly accurate first-principles calculation tool. It also sets calculation parameters that match the unit cell and material type, such as kinetic energy cutoff and energy convergence criteria, to ensure the accuracy, convergence and reliability of the calculation, providing a solid foundation for research. The selection of parameters makes the calculation neither too complicated nor too simplified, balancing the calculation efficiency and accuracy.

[0016] (3) The present invention uses a suitable K-point grid to ensure an accurate description of the electronic structure; evaluates the stability of the material through the change in cohesive energy, which is an effective indicator; analyzes the changes in state density and charge density under different deformation conditions, which are key parameters for evaluating electrical properties; and considers the influence of spin polarization parameters, which is crucial for understanding the behavior of materials at different temperatures. Ultimately, the simulation results of this method are reliable.

[0017] (4) This invention uses the first principles for the first time to perform theoretical calculations on the relationship between temperature parameters and performance of silicon carbide. Unlike other experimental work, the VASP calculation tool uses detailed physical logic and formulas for precise calculations, rather than summarizing the laws from macroscopic observations obtained from experiments. This also makes the factors considered in this invention, namely the influence of lattice distortion and atomic defects, a microscopic perspective that cannot be explored in similar experimental work, and cannot be intuitively summarized from experimental results. This invention simultaneously examines the influence of both on electrical properties and proposes a new, efficient, convenient, and low-cost SIC device performance analysis method. This comprehensive analysis method is more comprehensive and can provide a solid theoretical basis for similar experimental work. It greatly reduces the cost of trial and error in experiments and improves the reliability of results.

[0018] (5) During the analysis process, the present invention determined the deformation range with the best material performance through systematic research on different deformation ranges, filling the gap in existing related research.

[0019] (6) The present invention not only studies the influence of defects themselves, but also explores the differences in the effects of introducing defects in different layers of the material, which is of great significance for practical applications.

[0020] (7) Traditionally, people tend to think that the effects of lattice distortion and atomic defects on material properties are sufficiently understood, but the present invention emphasizes the importance of combining the two and breaks this prejudice. At the same time, through systematic theoretical calculations and simulations, the present invention overcomes the technical difficulty of accurately predicting the changes in SiC electrical properties at different temperatures, providing a solid theoretical basis for practical applications.

[0021] The present invention will be explained in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 4H-SiC supercell in the present invention; (a) is a top view; (b) is a side view, and the red circle in the figure represents the position of the vacancy generated due to the missing atoms in the subsequent defect calculation; Figure 2 is the state density of the material with lattice change of -30% to 30% in the present invention. The Fermi level is set to 0; Figure 3 The graph is a result of the state density of the material when the lattice in the a, b, and c directions is deformed by -5% to 10% in the present invention; wherein (a) is the total state density, and (b) is the partial wave state density; Figure 4 The charge density result diagram of the material when the lattice in the a, b, and c directions undergoes a deformation of -5% to 10% in the present invention; wherein (a) is a top view and (b) is a side view; Figure 5 The graph is a result of the state density of the material when the lattice undergoes a deformation of -10% to 15% in the a (b) direction in the present invention; wherein (a) is the total state density and (b) is the partial wave state density; Figure 6 This is a charge density result diagram of the material when the lattice undergoes a deformation of -10% to 15% in the a (b) direction in the present invention; Figure 7 The graph is a result of the state density of the material when the lattice undergoes a deformation of -15% to 20% in the c direction in the present invention; wherein (a) is the total state density, and (b) is the partial wave state density; Figure 8 This is a charge density result diagram of the material when the lattice undergoes a deformation of -15% to 20% in the c direction in the present invention; Fig. 9 The charge density result diagram of the material under different defects when the lattice is deformed in the present invention; wherein (a) is the result diagram under 5% deformation; (b) is the result diagram under -5% deformation; Fig.10 The graphs are result diagrams of the state density of the material under different defects when the lattice is deformed in the present invention; wherein (a) is the result diagram under 5% deformation; and (b) is the result diagram under -5% deformation. DETAILED DESCRIPTION

[0023] To facilitate understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings, but the present invention can be implemented in different forms and is not limited to the embodiments described in the text. On the contrary, these embodiments are provided to make the content disclosed in the present invention more thorough and comprehensive.

[0024] A method for analyzing the electrical characteristics of SiC in a temperature-variable semiconductor device based on first principles comprises the following steps: S1. Setting parameters and building models: (1) The Vienna Ab Initio Simulation Package (VASP) was used to perform the calculation based on DFT (density functional theory) with periodic boundary conditions. 2 2p 2 、Si-s 2 p 2 The electron orbitals are used as valence electrons, and the interaction between valence electrons and core electrons is described by the projected augmented plane wave (PAW) method, and the exchange correlation function is described by the PBE (Perdew Burke Ernzerhof) method in the generalized gradient approximation (GGA).

[0025] (2) In all computing tasks, parameter settings include: The kinetic energy cutoff is set to 450 eV, which can ensure the accuracy of the calculation and is the optimal choice after balancing the efficiency and economic time cost according to the calculation unit cell size; The energy convergence criterion is that the energy difference between two electron steps is less than 10 -5 eV, which ensures that the energy convergence is accurate enough, which helps to improve the reliability of the calculation; The Hellmann-Feynman force residual between two ion steps during structure optimization is less than 0.02 eV / Å, which ensures that the atomic positions are fully optimized to obtain reliable structural parameters; The Gaussian method sets the temperature broadening to 0.1 eV, which improves the convergence of electronic states close to the Fermi level in the electronic convergence step, which helps to calculate the electronic structure more accurately.

[0026] A 5×5×3 Gamma-centered K point was used for structural optimization, and a 7×7×5 Gamma-centered K point was used for density of states calculation to ensure an accurate description of the electronic structure.

[0027] Introducing spin polarization parameters during the calculation process to observe the impact of stress and defects on the density of states is crucial for understanding the behavior of materials at different temperatures.

[0028] The setting limits of these parameters jointly ensure the accuracy, convergence and reliability of the calculation, providing a solid foundation for research. The selection of parameters makes the calculation neither too complicated nor too simple, balancing the calculation efficiency and accuracy.

[0029] (3) After optimizing the bulk structure of 4H-SiC, the lattice parameters are a=b=3.088Å, c=10.111Å, α=β=90°, γ=120°, and V=83.540 Å. 3 , the space group is P63mc, which is similar to the lattice parameters a=b=3.078Å, c=10.046Å in other works, indicating that the design of the calculation parameters in the present invention is relatively reasonable. Then, the optimized primitive cell is used to expand the 2×2×1 cell, such as Figure 1 As shown, the nearest neighbors of any Si atom in 4H-SiC are four C atoms, and the nearest neighbors of any C atom are four Si atoms, forming a tetrahedral structure around the corresponding Si or C atom. Figure 1 (b) shows that the close packing of 4H-SiC is CABA. The red circles in the figure represent the positions of vacancies caused by the missing atoms in the subsequent defect calculation. In order to better distinguish the A layer, the two A layers are named A1 and A2 from top to bottom.

[0030] S2. Simulate the lattice distortion of SiC at different temperatures and calculate the cohesive energy to evaluate stability: The most obvious macroscopic effect of temperature on materials is thermal expansion and contraction, which is caused by lattice expansion and contraction. When studying lattice distortion, a deformation of lattice contraction from 30% to 30% was set up, with each 5% as a step to simulate the lattice distortion caused by temperature changes in a wide range. The results are as follows: Figure 2 shown.

[0031] Depend on Figure 2 It can be seen that the state density becomes more localized as the lattice increases from small to large (temperature increases from low to high), and even the band gap disappears in the end, indicating that increasing temperature can improve the electrical properties of 4H-SiC, but the disappearance of the band gap indicates that the temperature range is set too large.

[0032] Based on the above Figure 2 The cohesive energy is selected as the stability criterion for screening. The cohesive energy calculation results are shown in Table 1.

[0033] Table 1 Changes in cohesive energy when lattice distortion occurs in different directions

[0034] Note: Due to the symmetry between directions a and b, only one set of data is used to express it.

[0035] As shown in Table 1, when there is no lattice distortion, the cohesive energy of 4H-SiC is 6.47 eV / atom, which is greater than that of carbon phosphide (4.12 – 6.45 eV / atom) and silicene (3.71 eV / atom), and is relatively stable. When there is lattice distortion in the a (b) direction, the deformation of -10% (6.26 eV / atom) to 15% (6.16 eV / atom) is relatively stable; when there is lattice distortion in the c direction, the deformation of -15% (6.02 eV / atom) to 20% (6.05 eV / atom) is relatively stable; when there is lattice distortion in the a, b and c directions, the deformation of -5% (6.29 eV / atom) to 10% (6.00 eV / atom) is relatively stable.

[0036] S3. Analyze the influence of lattice distortion on SiC state density and charge density: When the lattice is deformed by -5% to 10% in the a, b, and c directions, the state density of the material is as follows: Figure 3 As shown, the charge density is Figure 4 shown.

[0037] Depend on Figure 3 (a) It can be seen that the state density changes significantly from small to large (temperature changes from low to high), and the spin-up and spin-down symmetry show no magnetism. Figure 3 (b) It can be clearly seen that the band gap decreases with increasing temperature, which improves the electrical properties of silicon carbide.

[0038] Depend on Figure 4 It can be seen that in silicon carbide, the charge density is mainly concentrated on Si atoms and is much greater than the charge density of C atoms. As the temperature increases, the charge density decreases because the distance between atoms increases, the bond strength weakens, the atomic position changes, and the electronic structure changes accordingly.

[0039] In order to explore which direction of distortion has a greater impact on the state density of the material, the state density and charge density when deformation occurs in the a direction (due to the symmetry between the a and b directions, only the deformation in the a direction is studied here) and the c direction respectively. The results are as follows Figure 5-8 shown.

[0040] Figure 5 It is the state density of the material when the lattice undergoes a deformation of -10% to 15% in the a (b) direction. Figure 7 is the state density of the material when the lattice undergoes a deformation of -15%-20% in the c direction. Figure 5 In (a), the peak on the right side of the Fermi level changes significantly with increasing temperature, the band gap decreases, and the change in the density of states decreases when the deformation exceeds 5%. Figure 7In (a), the peaks on both sides of the Fermi level change significantly with increasing temperature, the band gap decreases, and the degree of change in the state density decreases when the deformation exceeds 10%. Figure 6 Although the lattice shape is constantly changing, the charge density remains basically unchanged. Figure 8 As the temperature increases, the charge density decreases, the distance between atoms increases, and the electronic structure also changes. In general, the deformation in the c direction has a greater impact on the electrical properties of the material, and it can also remain stable under larger deformations (higher temperatures).

[0041] S4. Simulation of silicon defects in SiC (V Si ) and carbon defects (V C ) and calculate its influence on SiC cohesive energy, state density and charge density: The effect of defects on the electronic structure of materials is not only due to the change of atomic positions, but more to the change of coordination environment. However, at room temperature, it is not easy for materials to have defects. When the temperature rises or falls, the lattice distortion will lead to the generation of defects. Therefore, the present invention uses a 5% deformation to simulate the effect of defects on the electrical properties of materials when the temperature changes.

[0042] Table 2 gives the cohesive energy of defects introduced under different deformation amounts.

[0043] Table 2 Cohesive energy of defects introduced under different deformation amounts

[0044] As shown in Table 2, the introduction of defects will lead to a decrease in cohesive energy, but there is still good stability. At the same time, it can be seen that the introduction of silicon defects (V Si ) is always smaller than the cohesive energy of introducing carbon defects (V C ) because the atomic radius of silicon is larger than that of carbon, which has a greater impact on the stability of the material. The cohesive energy of the same structure at 5% deformation is less than that at -5%, which shows that low temperature has a greater impact on silicon carbide.

[0045] When the lattice is deformed by 5% and -5%, the charge density of the material under different defects is as follows: Fig. 9 The density of states is shown as Fig.10 shown.

[0046] Depend on Fig. 9 It can be seen that the charge density has undergone a very obvious change after the introduction of defects, indicating that the atomic bonding mode and coordination environment have undergone significant changes.

[0047] Depend on Fig.10It can be seen that the density of states has undergone deformation and movement to varying degrees after the introduction of defects. After the introduction of silicon defects, the band gap becomes smaller, the peak on the right side of the Fermi level moves to the left and crosses the Fermi level, and the density of states becomes more diffuse than before, and the spin-up and spin-down parts are still symmetrical. After the introduction of carbon defects, the peak on the left side of the Fermi level also crosses the Fermi level and generates a new peak on the right side of the Fermi level. C and B@V C The spin-up and spin-down parts in the two structures are not strictly symmetrical, which means that the introduction of carbon defects in the B and C layers can change the electronic structure to a greater extent. In general, the introduction of defects makes the band gap smaller, and the state density crosses the Fermi level, indicating that the introduction of defects can greatly improve the electrical properties of silicon carbide. Among them, the Si defects generated in the A layer at 5% deformation and the C defects generated in the B and C layers promote the electrical properties of silicon carbide.

[0048] S5. Evaluate the change of electrical properties of SiC under variable temperature environment: From the above steps, it can be seen that the change law of SiC's electrical properties under variable temperature environment is: 1. In the wide range of temperature changes, the lattice state density is more localized and the band gap decreases as the temperature changes from small to large (temperature changes from low to high), indicating that increasing temperature can improve the electrical properties of 4H-SiC; 2. When there are lattice distortions in the a, b and c directions, 4H-SiC has good stability within the deformation range of -5% to 10%, among which the deformation in the c direction has a greater impact on the overall performance and can remain stable within the deformation range of -15% to 20%.

[0049] 3. Silicon defects (VSi) have a greater impact on the stability of the material than carbon defects (VC). After the introduction of defects, the binding mode and coordination environment of the electron atoms have undergone significant changes.

[0050] 4. After the introduction of defects, the state density has undergone different degrees of deformation and movement. The band gap becomes smaller and the state density crosses the Fermi level, indicating that the introduction of defects can greatly improve the electrical properties of silicon carbide. Among them, the Si defects generated in the A layer and the C defects generated in the B and C layers at 5% deformation promote the electrical properties of silicon carbide.

[0051] It can be seen from the above content that the analysis method provided by the present invention has the advantages of high calculation accuracy and reliable simulation results, and can provide strong support for the research and development and application of SiC materials.

[0052] The above is an exemplary description of the present invention in combination with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as such non-substantial improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for analyzing the electrical characteristics of SiC in temperature-variable semiconductor devices based on first principles, characterized in that: The steps include: S1, set parameters and build model; S2, simulate the lattice distortion of SiC at different temperatures and calculate the cohesive energy to evaluate the stability; S3. Analyze the effect of lattice distortion on SiC state density and charge density; S4. Simulate the generation of silicon defects and carbon defects in SiC and calculate their effects on the cohesive energy, state density and charge density of SiC; S5. Evaluate the changes in the electrical properties of SiC under variable temperature conditions.

2. The method for analyzing electrical characteristics of SiC in a temperature-variable semiconductor device based on first principles according to claim 1 is characterized in that: In step S1, the parameter settings include: the kinetic energy cutoff is set to 450 eV; the energy convergence standard is that the energy difference between two electron steps is less than 10 -5 eV; the Hellmann-Feynman force residual between two ion steps during structure optimization was less than 0.02 eV / Å; the temperature broadening was set to 0.1 eV; 5×5×3 Gamma-centered K points were used for structure optimization, and 7×7×5 Gamma-centered K points were used for calculating the density of states.

3. The method for analyzing electrical characteristics of SiC in a variable temperature semiconductor device based on first principles according to claim 1 is characterized in that: DFT calculations were performed using the Vienna ab initio simulation software package.

4. The method for analyzing electrical characteristics of SiC in a temperature-variable semiconductor device based on first principles according to claim 1, characterized in that: In step S2, a deformation of the lattice from 30% contraction to 30% expansion is set, with each 5% being a step to simulate the lattice distortion caused by temperature changes in a wide range, and analyze the changes in state density and band gap.

5. The method for analyzing electrical characteristics of SiC in a temperature-variable semiconductor device based on first principles according to claim 4 is characterized in that: In step S2, the cohesive energy changes of each level of lattice-distorted SiC when the lattice distortion occurs in different directions are calculated and statistically analyzed to determine the range of lattice distortion levels that produce stable deformation amounts when the lattice distortion occurs in different directions.

6. The method for analyzing SiC electrical characteristics in a variable temperature semiconductor device based on first principles according to claim 1, characterized in that: In step S3, the state density and charge density when deformation occurs in different directions are calculated to analyze the symmetry and band gap change of spin-up and spin-down.

7. The method for analyzing electrical characteristics of SiC in a variable temperature semiconductor device based on first principles according to claim 6 is characterized in that: In step S3, the state density and charge density when deformation occurs in different directions are calculated to explore the direction in which the distortion has the greatest impact on the state density of the material.

8. The method for analyzing electrical characteristics of SiC in a temperature-variable semiconductor device based on first principles according to claim 1, characterized in that: In step S4, the cohesive energy of SiC and its layers introduced with silicon defects and carbon defects under different deformation amounts is counted, and the elements and temperature environment that have a greater impact on the stability of the material are analyzed.

9. The method for analyzing electrical characteristics of SiC in a temperature-variable semiconductor device based on first principles according to claim 1, characterized in that: In step S4, the charge density and state density of SiC and its layers under different defects are calculated when the lattice is deformed, and the symmetry and band gap changes of spin-up and spin-down are analyzed.

10. The method for analyzing SiC electrical characteristics in a variable temperature semiconductor device based on first principles according to claim 1, characterized in that: In step S5, the electrical performance analysis includes evaluating the change in the band gap, electronic structure, and conductivity of SiC.

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