Thickness dependent structural, electrical and optical properties of cubic SnS thin films

Abstract

This paper reports the thickness dependent structural, optical and electrical properties of tin monosulfide (SnS) films. SnS films of different thickness were grown (at 24 °C) by chemical bath deposition. Films of different thicknesses were obtained by varying the number of deposition cycles (2, 3, 4, 5 and 6 cycles; one cycle = 4.25 h). All films were examined by employing different experimental techniques. XRD results showed the occurrence of cubic π-phase in all films. FTIR spectra confirmed the occurrence of main peaks corresponding to Sn–S bond stretching in all films. Atomic force microscopy (AFM) analysis of all films showed non-uniform grain distribution with porous surface morphology. Surface roughness was found to increase (32 ± 1 nm to 72 ± 1 nm) with increase in film thickness. Optical measurements showed that the films exhibited direct energy band gap, Eg. The Eg was found to increase from 1.70 eV to 1.74 eV with increase (374 ± 5 nm to 723 ± 8 nm) in film thickness. All films exhibited high absorption coefficient α (≥104 cm−1) in the visible region. Film with lower thickness (374 nm) exhibited higher absorption coefficient. Electrical measurement of the films revealed that the electrical resistivity ρ had strong dependence on film thickness. The electrical resistivity ρ was found to increase (1.592 × 103 Ω cm to 1.785 × 104 Ω cm) with increase in film thickness. All results suggested that the optical response and electrical conductivity could be tuned through appropriate choice of film thickness by maintaining the cubic structure.