Effect of intense laser irradiation on the electronic properties of 2H-SiC

Abstract

By using first-principles with pseudopotentials method based on the density functional perturbation theory, in this paper we calculate the electronic properties of wurtzite 2H-SiC crystal under the strong laser irradiation and analyze the band structure and the density of state. Calculations are performed by using the ABINIT code in the generalized gradient approximation for the exchange-correlation energy. And the input variable tphysel, which is a variable in the ABINIT code and relates to the laser intensity, is used to define a physical temperature of electrons Te. The size of Te is set to simulate the corresponding electron temperature of the crystal when intensive laser irradiates it in an ultrafast time. The high symmetry points selected in the Brillouin zone are along -A-H-K--M-L-H in the energy band calculations. After testing, we can always obtain a good convergence of the total energy when choosing a 20 Hartree cut-off energy and a 442 k-points grid. Then, optimizing the structure, and the structural parameters and the corresponding electronic properties of 2H-SiC in the different electron-temperature conditions are studied using the optimized equilibrium lattice constant. The calculation results indicate that the equilibrium lattice parameters a and c of 2H-SiC gradually increase as the electronic temperature Te goes up. With the electronic temperature going up, the top of valence band is still at , while the bottom of conduction band shifts from the K point with increasing electronic temperature, resulting in the fact that 2H-SiC is still an indirect band-gap semiconductor in a range of 0-2.25 eV and when the electronic temperature reaches 2.25 eV and even more than 2.5 eV, the crystal turns into a direct band-gap semiconductor. With Te rising constantly, the bottom of the conduction band and the top of valence band both move in the direction of high energy or low energy. When Te exceeds 3.5 eV, the top of valence band crosses the Fermi level. When Te varies in a range of 0-2.0 eV, the forbidden bandwidth increases with temperature rising, and when Te varies in a range of 2-3.5 eV, the forbidden bandwidth quickly decreases. This variation shows that the metallic character of 2H-SiC crystals increases with electronic temperature Te rising. The total density of states (DOS) and partial density of states are calculated at Te=0 eV and 5 eV. The DOS figures indicate that 2H-SiC is a semiconductors and its energy gap equals 2.3 eV. At Te =5 eV, the gap disappears, exhibiting metallic properties. This result shows that the crystal covalent bonds weaken and metallic bonds strengthen with temperature rising and the crystal experiences the process of melting, shifting to metallic state.