Structural and Optical Properties of RF-Sputtered CdTe Thin Films Grown on CdS:O/CdS Bilayers

Abstract

In this work, we report the structural and optical properties of CdTe thin films on oxygenated Cadmium Sulfide (CdS:O)/Cadmium sulfide(CdS) bilayer using RF magnetron sputtering for different substrate temperatures ( 150, 200, 250, 300 and 350 °C) in Argon ambient. The XRD spectra reveal the polycrystalline nature of all the CdTe thin films with preferential cubic orientation along (111) direction. Raman Spectra show a dominant peak at 163.5 cm -1  and its overtone at 328.7 cm -1  which corresponded to the longitudinal optical (LO) phonon of CdTe. The SEM microscopy exhibits the uniform growth of CdTe films onto the entire glass substrate. The optical transmission of the CdTe films begin at the edge of 800 nm wavelength and showed interference fringe in the transmission spectra. The thickness of the deposited films and the optical constants were calculated from the fringe pattern. The thicknesses of the CdTe films are found to be increasing from 2.34 I¼m to 2.82 I¼m with increasing the substrate temperature i.e. from 150 to 250°C. Thereafter, the CdTe film thickness decreased to 2.24 I¼m while the temperature increased further up to 350°C. The optical bandgap of the deposited CdTe films follows an increasing trend of 1.46 eV to 152 eV with the increase of substrate temperature 150 to 250°C after that the bandgap decrease to 1.50 for 350°C. Hence the obtained structural and optical properties suggest that the deposited CdTe films can be used as a suitable absorber layer for the thin film-based solar cells.