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 ZnS1-xSex with optimized growth parameters were prepared by soft chemical route on glass substrates. Ammonia free precursors were used at 80 degrees 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 ZnS1-xSex 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. (C) 2011 Elsevier B.V. All rights reserved.