Influence of working pressure on the structural, optical, and electrical properties of RF-sputtered SnS thin films

Abstract

We report the one-step deposition of the SnS thin films by RF-sputtering at 300 °C using a single SnS target. The influence of working pressure on the structural, optical, and electrical properties of deposited SnS films were characterized by scanning electron microscopy, electron dispersive spectroscopy, atomic force microscopy, X-diffraction, micro-Raman spectroscopy, UV–Visible spectroscopy, and Hall measurement analysis. As pressure increased, the SnS film thickness was typically reduced with increased grain size and surface roughness. All the films showed the [Sn/S] ratio close to stoichiometric SnS except the samples grown at 40 mTorr and 50 mTorr had the more atomic sulfur deficiency. XRD revealed the orthorhombic crystal phase of SnS with (111) preferred orientation. The micro Raman study confirmed the orthorhombic crystal structure of SnS without any secondary phase except the samples grown at 40 mTorr and 50 mTorr exhibited the minor impurity phase of Sn2S3. The direct energy band gap was decreased with the increase of working pressure and was varied in the range of 1.20–1.31 eV. The optical absorption coefficient was increased with pressure, and the samples grown at 50 mTorr showed the highest absorption coefficient of 1.1 ×105cm−1. The electrical properties confirmed that the SnS films exhibited the p-type conductivity with reduced resistivity and increased hole mobility with increased pressures. The SnS deposited at 30 mTorr showed highest hole concentration of 6.95 ×1015cm−3. Based on these growth properties the SnS thin films deposited at 30 mTorr was concluded as a promising absorber material for the solar cell applications.