Band Structures and Optical Properties of Semiconducting Layer Compounds GaS and GaSe

Abstract

The band structures of GaS and GaSe near the Fermi levels are derived in a semiempirical way. In view of the anisotropic structures, the π band structures are mainly studied. The valence band consists of a π band with the heavy effective masses. The conduction band at the center of the Brillouin zone has the light effective masses for the both directions parallel and perpendicular to the layers, while its minimum at the zone edge has a two-dimensional character. The characteristics of the optical properties of these compounds are the existence of the sharp peaks associated with the nearly two-dimensional pair bands at the saddle points and further the limited spatial extension of an exciton along the c -axis. Most of the structures in reflectivities in GaS and GaSe and the binding energy of an exciton in GaSe are explained fairly well.