Crystal Structure, Optical, and Electrical Properties of SnSe and SnS Semiconductor Thin Films Prepared by Vacuum Evaporation Techniques for Solar Cell Applications

Abstract

Thin films of SnSe and SnS semiconductors had been prepared by vacuum
\nevaporation techniques. All prepared samples were characterized on their structure, optical, and
\nelectrical properties in order to know their application in technology. The crystal structure of
\nSnSe and SnS was determined by X-Ray Diffraction (XRD) instrument. The morphology and
\nchemical composition were obtained by Scanning Electron Microscopy (SEM) coupled with
\nEnergy Dispersive of X-Ray Analysis (EDAX). The optical property such as band gap was
\ndetermined by DR-UV-Vis (Diffuse Reflectance-Ultra Violet-Visible) spectroscopy, while the
\nelectrical properties were determined by measuring the conductivity by four probes
\nmethod.The characterization results indicated that both SnSe and SnS thin films were
\npolycrystalline. SnSe crystallized in an orthorhombic crystal system with the lattice parameters
\nof a = 11.47 Å, b = 4.152 Å and c = 4.439 Å, while SnS had an orthorhombic crystal system
\nwith lattice parameters of a = 4.317 Å, b = 11.647 Å and c = 3.981 Å. Band gaps (Eg) of SnSe
\nand SnS were 1.63 eV and 1.35 eV, respectively. Chemical compositions of both thin films
\nwere non-stoichiometric. Molar ratio of Sn : S was close to ideal which was 1 : 0.96, while
\nmolar ratio of Sn : S was 1 : 0.84. The surface morphology described the arrangement of the
\ngrains on the surface of the thin film with sizes ranging from 0.2 to 0.5 microns. Color
\nsimilarity on the surface of the SEM images proved a homogenous thin layer.