CONICET | Buscador de Institutos y Recursos Humanos

Theoretical investigations were made into the bandgap, band structure and optical properties of tin sulphide (SnS) crystal withC2mb symmetry. The SnS crystal with this symmetry though has many propertiessimilar to the well documented SnS crystal with Pnma symmetry, it does exhibitsome uniqueness in band structure. The purpose of this study was to verify andconfirm the recent experimental results of p-SnS thin films with C2mb symmetry.The p-type conductivity in SnS films is obtained due to Tin vacancies. Thesedefects invariably gives rise to residual stress in the crystal. Theoreticalinvestigations allow to address the question as to which of the two factors,stress or vacancies with stress, influences the electrical and opticalproperties more. Results of our calculations confirm that reported p-SnS filmswere oriented such that the incident light of UV-visible spectroscope fellperpendicular to the ?ab? plane and that shallow levels appear just above thevalence band edge along with a spread in the conduction band edge onintroduction of defects in the lattice. The spread in conduction band edge andappearance of shallow levels manifest themselves as Urbach spread or tail inUV-visible absorption spectra, which results in a decrease in band-gap withincreasing number of Tin vacancies. Calculations also show that while opticalproperties are essentially due to the Tin vacancies, the residual stress alsoaffects the p-SnS optical properties. The theoretical results are in goodagreement with the experimental results.