EFFECT OF ANNEALING TEMPERATURE ON OPTICAL AND STRUCTURAL PROPERTIES OF ZnS THIN FILMS PREPARED BY CBD TECHNIQUE

Abstract

Zinc sulfide thin films were deposited on optical glass substrates by using chemical bath deposition (CBD) technique. The chemical bath contains the solutions of thiourea, zinc acetate, ammonia and sodium citrate. The effect of annealing temperature on the deposited films has been studied at different temperatures from 200 oC, 250 oC, 300 oC and 350 oC in 24 hours. SEM, XRD and UV-Vis were used to characterize the samples. XRD shows development of well-crystallized film with pure wurtzite structure after annealing. XRD spectrum indicates that the films are amorphous and have cubic zinc blend structure. SEM shows that the film are thicker and have bigger grains size at 350 °C compared to the film at 200 °C with the grain size between 360.0 – 392.7 nm and 329.4 – 385.0 nm respectively. UV-Vis spectra showed that the deposited ZnS thin films have more than 93% transmittance in the visible region and direct band gap of deposited films are in range of 3.01 eV to 3.90 eV. The transmittance of the film increases slightly with the increase of annealing temperature . Therefore, ZnS thin films are suitable for coating onto CIS layer as solar cell application.