Surface deformation in films and exciton concentration

Abstract

The exciton states in a film which was cut out from an anisotropic cubic structure are analysed whereby the calculations include excitonic concentrations. It is shown that excitonic states in the bulk always exist, without any additional conditions on the type of the deformation or on exciton concentrations. It is found that under certain conditions (the surface concentration and the concentration in the bulk having approximately equal values), the effective mass of the excitons in the bulk is dependent on the azimuth in the k space i.e. the effective mass belonging to bulk excitons can alter its sign when the direction of propagation is altered. The surface excitons can exist also, but only for a specific set of values for the deformation and the concentration given by a formula quoted in this paper. It is shown that by an appropriate deformation of the film one can achieve the surface concentrations of the order of unity (i.e. C = 0.25). © 1990.