Electronic structure of GaSe, GaS, InSe and GaTe

Two-dimensional and three-dimensional band structures of the GaSe family of crystals have been calculated by the tight-binding method. The author's calculations fit the photoemission bandwidths well, particularly for the anion p x,y bands and, for GaSe, find similar band orderings and dispersions to those of M Schluter (1973). The tight-binding interactions are evaluated by scaling and the improved valence p bandwidths are attributed to a better ratio of p sigma :p pi for the Ga-Se bond. The band gaps are underestimated slightly but a valence maximum at Gamma and conduction minima at Gamma and M are found, in agreement with experiment. The pressure coefficients of the minimum gaps are re-interpreted in the light of the author's calculations. Tight-binding representations of the valence charge densities give polarities of: GaSe, 0.67; GaS, 0.72; GaTe, 0.60; and InSe, 0.70.