Structural and optical studies of hot wall vacuum evaporated CdTeSn thin films
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Bulk compounds of CdTe, Cd0.25Sn0.75Te and Cd0.25Te0.75Sn have been prepared by direct reaction of their high purity (99.9999%) elemental constituents employing rotating furnace. The hot wall system is optimized for the deposition of prepared alloys by using molecular flow studies with Monte Carlo simulation technique. Thin films have been deposited on well cleaned glass substrates using the prepared alloys by the optimized hot wall vacuum evaporation system. The compositions of the prepared bulk and thin films have been identified using energy dispersive X-ray analysis. The compositions are found to be same for both the bulk and thin films as the prepared alloys. The structural properties of the deposited films have been studied using X-ray diffraction technique. The results show that all the films are crystalline in nature and the peaks in the XRD graph of CdTe correspond to cubic zinc blende structure and that of Cd0.25Sn0.75Te and Cd0.25Te0.75Sn compounds to rock salt structure. The lattice parameters and grain sizes of all the films have been evaluated. The surface morphology of the thin films is studied using Scanning Electron Microscope (SEM). The SEM analysis shows that surface of the films are smooth and crystalline in nature. The optical transmittance spectra of thin films were recorded using spectrophotometer in the range of wavelength from 190 nm to 2500 nm. All the films exhibit direct optical band gap and their values are 1.45eV (CdTe), 0.9eV (Cd0.25Sn0.75Te) and 1.1eV (Cd0.25Te0.75Sn). Thicknesses of the thin films have been determined by multiple beam interferometric technique.
