QUASI-PARTICLE BAND-STRUCTURE OF SILICON-CARBIDE POLYTYPES

The ab initio pseudopotential method within the local-density approxim ation and the quasiparticle approach have been used to investigate the electronic excitation properties of hexagonal (6H, 4H, 2H) and zinc-b lende (3C) silicon carbide. The quasiparticle shifts added to the dens ity-functional eigenvalues are calculated using a model dielectric fun ction and an approximate treatment of the electron self-energy concern ing local-field effects and dynamical screening. The inverse dielectri c function and the auxiliary function are generalized to hexagonal cry stals. Good agreement with the experimental results is obtained for th e minimum indirect energy gaps. The k space location of the correspond ing conduction-band minima is clarified. Other excitation energies are predicted. The influence of the quasiparticle effects on band discont inuities and the electron effective masses is studied.