Effect of annealing temperature on the structural and optical properties of ZnS thin films deposited by CBD

Abstract EN

Zinc sulfide thin films were deposited on glass substrates by using chemical bath deposition (CBD) technique at 90oCand annealed at different temperatures (250, 300 and 350oC) in air for 30 minutes.

The chemical bath contains the solutions of thiourea, zinc sulphate, ammonia and hydrazine hydrate.

Effect of annealing temperature on the microstructure and optical properties of ZnS thin films were investigated.

The structural and optical properties of ZnS thin films were characterized using X-ray diffraction [XRD] and UV-Visible-NIR spectrometry.

The XRD analyses indicate that ZnS thin films have zinc blende (cubic) structures with (111) preferential orientation.

The structural parameters like lattice parameter, crystallite size, micro strain and dislocation density are calculated.

The crystallinity is apparently improved with the increase of annealing temperature.

The average grain size was found to be 1.9198 nm and after annealing the grain size was 2.1612 nm, 4.2821 nm and 5.7720 nm respectively (grain size increase with the increase of annealing temperatures, whereas dislocation density and micro strain decreases with the increase of annealing temperatures).

It is also found that film surface changes to ZnO after the film is annealed at 300-350oC.

The transmittance, absorbance and reflectance are recorded in the range of 300-1000 nm, the optical band gap is direct with a value of 3.85eV, but this value decreased to 3.42eV with annealing temperature at 350oC.

The result showed that the CBD ZnS thin films annealed at 350oC exhibit the highest transmittance of about 95.50 %.

The refractive index (n), extinction coefficient (k), optical conductivity and real and imaginary parts of dielectric constant are evaluated.

Additionally, the increase of annealing temperature will increase the pores in films, which results in the decrease of refractive indices and increase of extinction coefficients of the film.