Optical and structural properties of vacuum annealed multilayer nanostructured CdZnS thin films deposited by thermal evaporation

Abstract

The CdS and multilayers of CdS and Zn thin films were deposited on glass substrates by thermal evaporation. Subsequently, deposited films were annealed under a high vacuum to diffuse Zn into CdS films. Vacuum annealed films of CdS and CdZnS (CZS) were characterized for structural, surface morphology and optical properties. The XRD results showed that films were polycrystalline with hexagonal and cubic structures having predominant diffraction corresponding to the (0 0 2) plane. It was also observed that the lattice constants decreased, grain size and bandgap increased as Zn content increases in deposited films. The transmittance of as-deposited films increased drastically by vacuum annealing up to 90% in visible and NIR regions. EDX results confirmed that the concentration of Zn increased with the increase of Zn layer thickness into the multilayer structure of CZS films. The results obtained suggest that the blue shift of the absorption edge of CZS films will be useful for enhancing the efficiency of photovoltaic cells and optoelectronic devices in this region. The results reported in this paper revealed that the refractive index, optical band gap and lattice constants of CZS films can be tailored by the variation of Zn concentration. The potential of vacuum annealing is also elaborated to diffuse metallic Zn into CdS films.