Linear and nonlinear optical properties of four polytypes of SiC

We calculated ε_∞ and second-order nonlinear coefficients d=χ⁽²⁾/2 for four SiC polytypes as well as ε_∞ for diamond within the local-density approximation (LDA), and using the LDA wave functions with a self-energy correction in the form of a scissors operator {Δ}Pck to adjust the band gaps. For all the wide-band-gap materials we have studied so far, we find that the {Δ} needed to reproduce the optical response properties is less than the {Δ} deduced by GW calculations or needed to reproduce the experimentally observed band gaps. This is in contrast to the small- to medium-gap semiconductors we studied previously. For nH SiC with n{≥}4, our predictions for d are close to the only experimental data. Our calculations show that both d and the local-field corrections to d for nH SiC form a trend as n{→}{∞}. The d₁₁₃/d₃₃₃ ratios we predicted for different SiC polytypes differ from those of bond-charge-model predictions.