Temperature dependence of the band structure of 3C, 2H, 4H, and 6H SiC polytypes

Abstract

The temperature dependences of significant energy extrema at the high-symmetry points Γ, X, L, K, M, A, and H of the Brillouin zone in the cubic and hexagonal modifications of SiC, as well as the energies of the main interband transitions at these points, were calculated for the first time by the empirical-pseudopotential method. The effect of the temperature dependence of the electron-phonon interaction on the crystal band structure was taken into account via the Debye-Waller factors, and the contribution of the linear expansion of the lattice was accounted for via the temperature dependence of the linear-expansion coefficient. The special features of the temperature dependences of the energy levels and of energies of the interband and intraband transitions are analyzed in detail. The results of the calculations are in good agreement with the known experimental data on the characteristics of SiC-based p-n structures operating in the breakdown mode. For example, the temperature coefficient of the energy of the X1c–X3c transition, which is responsible for the narrow violet band in the breakdown-electroluminescence spectra of reverse-biased p-n junctions, was found to be significantly smaller than the temperature coefficients for the interband transitions (from the conduction to valence band). This fact is quite consistent with the experimental curve of the temperature coefficient of the emission spectrum, which has a minimum in the same wavelength range.