Annealing temperature effect to optimize the optical properties of SnS thin films

Abstract

The influence of annealing temperature in the range 400–550 nm on the SnS thin films, synthesized via thermal evaporation method, is investigated. The structure of tin sulfide annealed films is examined through X-ray diffraction (XRD), revealing crystalline nature with the orthorhombic structure of the main peak (111) at 2θ = 31.38Ǻ. Micro-strain and dislocation density are decreased as the annealing temperature increased. The optical energy gap of these films is computed using the data of transmittance, reflectance, and absorption spectra over a wavelength range of 300–1200 nm. The energy gap decreases with increasing annealing temperature: Eg_dir = 1.77 to 1.62 eV and Eg_ind = 1.21 to 1.08 eV. The volume and surface energy loss function increased as the annealing increased. In addition, the real and imaginary inter-band transition strength was calculated using dielectric constants. Optical conductivity (σ_opt) and penetration depth of light (δ_dp) depend on wavelength calculated using absorption coefficient: (σ_opt) = 2.4 × 10¹¹ to 0.9 × 10¹¹ Ω⁻¹.m⁻¹ at 2.25 eV and δ_dp = 0.04 to 0.006 at 1050 nm, respectively. The skin depth of these films provides a cut-off wavelength at ≈ 600 nm. Besides, the skin depth of these films decreases as annealing temperature increased.