Relativistic empirical tight-binding theory of the energy bands of GeTe, SnTe, PbTe, PbSe, PbS, and their alloys

The orthogonalized plane wave band structures of GeTe, SnTe, PbTe, PbSe, and PbS are fit with a nearest-neighbor, 18-orbital sp 3 d 5 , relativistic tight-binding model that exhibits chemical trends. The band gaps of Pb 1−x Sn x Te, Sn 1−y Ge y Te, and Ge 1−z Pb z Te alloys are predicted as functions of compositions x, y, and z. Bowing of the gap is expected to be substantial for Ge 1−z Pb z Te, and either Sn 1−y Ge y Te or Ge 1−z Pb z Te should exhibit a Dimmock reversal.