Effect of annealing on structural and optical properties of indium sulfide thin layers produced by chemical bath deposition method

Abstract

Indium sulfide thin films were prepared by chemical bath deposition method on glass substrates for about 40 min as deposition time and 60 °C as deposition temperature. The films were post-annealed at different temperatures such as 100 °C, 200 °C, 300 °C and 400 °C, for about 1 h. Structural and optical properties of In₂S₃ thin films after post-annealing process have been investigated. The crystallinity and nanostructures of the films were studied by using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and atomic force microscopy analysis. Optical reflectance and transmittance of layers were measured in the wavelength of 300–1100 nm by spectrophotometer instrument. Kramers–Kronig relations were used to calculate the optical constants. The X-ray diffraction measurements showed transformation of an amorphous nature to a crystalline structure by increasing the annealing temperature. The atomic force microscopy images showed by increasing the annealing temperature, the roughness of the thin films increased. The scanning electron microscopy images revealed that growth rate increased consistently with the increase in annealing temperature and well-dispersed quasi-spherical nanoparticles with high agglomeration rate are formed at 400 °C. The energy-dispersive X-ray spectroscopy results show reduction in the S/In ratio from 1.61 to 1.49 when annealing temperature increased. Optical results showed the highest optical band gap of 3.65 eV was achieved at the highest annealing temperature (400 °C).