QUASI-PARTICLE BAND-STRUCTURE OF SILICON-CARBIDE POLYTYPES

The ab initio pseudopotential method within the local-density approximation and the quasiparticle approach have been used to investigate the electronic excitation properties of hexagonal (6H, 4H, 2H) and zinc-blende (3C) silicon carbide. The quasiparticle shifts added to the density-functional eigenvalues are calculated using a model dielectric function and an approximate treatment of the electron self-energy concerning local-field effects and dynamical screening. The inverse dielectric function and the auxiliary function are generalized to hexagonal crystals. Good agreement with the experimental results is obtained for the minimum indirect energy gaps. The k space location of the corresponding conduction-band minima is clarified. Other excitation energies are predicted. The influence of the quasiparticle effects on band discontinuities and the electron effective masses is studied.