Bandgap engineering by substitution of S by Se in nanostructured ZnS1−xSex thin films grown by soft chemical route for nontoxic optoelectronic device applications

Thin films of nanostructured ZnS_1−xSe_x with optimized growth parameters were prepared by soft chemical route on glass substrates. Ammonia free precursors were used at 80 °C constant bath temperature. The ratio of sulphur to selenium was changed continuously by changing the composition x (0-1), while atomic concentration of zinc was kept constant. Structure, composition and surface morphology of as-deposited films were characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX) and scanning electron microscopy (SEM), atomic force microscopy (AFM) respectively. XRD studies revealed that as-deposited films were nanostructured in nature with cubic zinc blended structure. It was further observed that the preferred orientations are along (1 1 1) plane and crystallite size decreased with increase in the value of x. SEM and AFM images revealed that films were uniform and pinhole free. The optical band gap (E_g) was calculated from the observed transmittance spectra by Urbach method. It was found that the band gap varied linearly from 3.71 to 2.70 eV, as composition x varies 0-1. The electrical properties’ study revealed that the decrease in resistivity and increase in photosensitivity, as composition x varied 0-1. The observed interesting properties of ZnS_1−xSe_x thin films justified their significance in optoelectronic device fabrication and applications, and as an environment friendly alternative to the commonly used toxic material such as CdS.