Band structure controlled solid solution of spray deposited Cd_1-x Zn_xS films: Investigation on photoluminescence and photo response properties

Nano crystalline Cd_1-xZn_xS (x = 0.00–1.00 at. %) films were deposited on glass substrates through conventional chemical spray pyrolysis method at different temperatures. The films with x < 0.70 have exhibited hexagonal phase beyond which cubic phase was noticed. The shifting of XRD peaks with higher Zn content, confirmed the formation of Cd_1-xZn_xS solid solutions. The film crystallinity improved at higher deposition temperatures, while it decreased with increasing x. SEM images showed nearly spherical granular shapes for x = 0, which gradually deteriorate in size at higher x and changed to fibrous structure for x > 0.60. Further the films with x = 0.40–0.60 seem to be porous and well-suited for gas sensing applications. The EDS confirmed the presence of Cd, Zn and S with expected stoichiometry. The optical transmittance and the energy band gap increased with increasing temperature and x. The shift of absorption edge to the shorter wavelength with Zn content has made film high transparent in blue region. The extinction coefficient reduced with x and Urbach energy has shown the formation of defects. Photoluminescence spectra exhibited broad emission bands which could be deconvoluted to multiple peaks attributable to defect states. The film resistivity increased with x that resulted in decrease of carrier concentration which was determined through Hall Effect measurements. The crystallinity was found to influence the photo-response of the films. The films with high Cd contents showed excellent photo response which can be used as photo-detector due to its rapid decline of resistance in the band edge region. The smaller grain and fibrous structured films with large open surface area obtained here, can be used in gas sensing while, the films with x > 0.60 are well-suited for the fabrication of window layers of solar cells.