Shallow donor levels and the conduction band edge structures in polytypes of SiC

This study focuses on the calculation of conduction band edge structures and nitrogen (N) donor levels in four polytypes of SiC: 3C, 2H, 4H, and 6H. A band-structure-based theory and a model potential are developed for the donor level calculation. A hybrid pseudo-potential and tight-binding Hamiltonian is used to obtain a set of comprehensive band structures for these four polytypes by incorporating useful experimental information in the band-structure calculation. The conduction band edge wave functions derived from these band structures and several sets of theoretical and experimental effective masses are then used to study the various effects on the donor level, which include anisotropic masses, central cell potential correction, conduction band edge wave functions, and intervalley coupling. With suitable sets of effective masses, the calculated donor energies agree semi-quantitatively with those deduced from experiments. The site dependence of the donor energies in 4H and GH is found to be dominated by the conduction band wave functions and the intervalley coupling.