Study of SnS:Bi thin films prepared by sulfurization

We have grown Bi doped SnS thin films using a novel procedure based on sulfurization of a thin film of the Sn:Bi alloy, deposited by evaporation. The effect of the Bi concentration on the optical and structural properties, as well as on the chemical composition of the SnS:Bi thin films was studied through spectral transmittance, X-ray diffraction (XRD) and Auger electron spectroscopy (AES) depth profile, respectively. AES depth profile measurements revealed that the SnS films grow with homogeneous chemical composition. However, when Bi is incorporated in the SnS lattice, the SnS:Bi films become inhomogeneous in chemical composition; in general this type of samples are both Bi deficient and Sn rich in the region close to the surface. The studies revealed that the SnS:Bi films tend to grow with a mixture of the SnS and Bi₂S₃ phases; however, the Sn₂S₃ and SnS₂ phases were also identified in some samples. It was also found that the SnS:Bi films present a high absorption coefficient (greater than 10⁴ cm^-1) and an energy band gap of about 1.37 eV (for SnS) and 1.40 eV (for the Bi₂S₃), indicating that these compounds have good properties to perform as absorber layers in thin film solar cells.