The effect of annealing time on zinc selenide thin films deposited by photo-assisted chemical bath deposition

Abstract

Zinc selenide (ZnSe) thin films were deposited on non-conducting glass substrates at 80 °C for 2.0 h in an alkaline medium using photo-assisted chemical bath deposition (PCBD). The films were annealed in air at 300 °C for different time intervals ranging from 0 to 4.0 h. The annealing time had a significant effect on the structure, morphology and optical properties of the deposited films. The glancing incidence X-ray diffraction (GIXRD) analysis confirmed polycrystalline films with a hexagonal wurtzite structure. The estimated crystallite size decreased with increasing annealing time. The as-deposited sample showed secondary peaks in the GIXRD and Raman spectroscopy due to unreacted selenium, which disappeared after annealing. Changes in surface morphology with increasing annealing time were observed using scanning electron microscopy. The energy dispersive X-ray spectrometer results showed an increase in zinc with a decrease in selenium for longer annealing times. The atomic force microscopy showed that the estimated films surface roughness decreased during annealing. Blue shifts in the absorption spectra and an increase in the energy bandgaps were observed with an increase in annealing time, together with an increase in optical transmittance. Photoluminescence spectroscopy revealed blue, green and red emission peaks, which were all attributed to the intrinsic defects within the ZnSe. The estimated decay lifetime showed that the average decay lifetime of the films increased with annealing time. Annealing for 3.0 h was found to be the optimum based on the response of the investigated properties.