Control of intrinsic defects in molecular beam epitaxy grown CuInSe₂

CuInSe₂ epitaxial films have been grown by molecular beam epitaxy at a substrate temperature of T_S = 450 °C. The vacancy-type defects which dominate the properties of the CuInSe₂ films have been characterized and methods to control defects have been investigated. Films grown under In-flux excess conditions tend to show nonideal crystalline quality; the films are highly compensated with a high density of twins. Post-growth annealing of the films in air substantially reduced the twin density as well as the degree of compensation, implying that there is a strong correlation between Se-vacancies and the density of twins. Such improvement in the film quality was found to be responsible for in-diffused oxygen from the surface during the air-annealing process, and oxygen is considered to substitute for Se vacancies. The preliminary results showed that in situ incorporation of oxygen during the molecular beam epitaxial growth of CuInSe₂ films made possible the reduction of twin densities.