OF THE ELECTRONIC STRUCTURE OF SEMICONDUCTORS?

Ah&ret--A nearest-neighbor semi-empirical tight-binding theory of energy bands in zincblende and diamond structure materials i developed and applied to the following sp3-bonded semiconductors: C, Si, Ge, Sn, SIC, GaP, GaAs, GaSb, InP, InAs, InSb, AIP, AlAs, AISb, ZnSe, and ZnTe. For each of these materials the theory uses only thirteen parameters to reproduce the major features of conduction and valence bands. The matrix elements exhibit chemical trends: the differences in diagonal matrix elements are proportional to differences in free-atom orbital energies and the off-diagonal matrix elements obey the de2 rule of Harrison et al. The lowest energy conduction bands are well described as a result of the introduction of an excited s state, s*, on each atom. Examination of the chemical trends in this sp’s * model yields a crude but “universal ” sp’s * model whose parameters do not depend explicitly on band gaps, but rather are functions of atomic energies and bond lengths alone. The “universal ” model, although cruder than the sp’s * model for any single semiconductor, can be employed to study relationships between the band structures ofdifferent semiconductors; weuse it to predict band edge discontinuities of heterojunctions. 1