Heat Treatment Effect on the Structural and Optical Properties ofCdGa2S4Thin Films

Abstract

CdGa2S4was prepared in powder form by reacting CdS and Ga2S3. The powder had a tetragonal crystal structure with lattice parameters, a = 0.559 ± 0.005 nm , c = 1.008 ± 0.009 nm and c/a = 1.803. CdGa2S4films deposited by thermal evaporation of the powder were noncrystalline. After annealing, the CdGa2S4thin films contain crystals with the tetragonal crystal structure. The optical constants (the refractive index n, the absorption index k and the absorption coefficient α) were determined for CdGa2S4thin films in the thickness range 170–452 nm. It was found that both n and k are independent of the film thickness and both are slightly different as deposited and annealed films. The refractive index shows anomalous dispersion in the spectral range 300–700 nm. The high frequency dielectric constant ε∞was determined for the as-deposited and after being annealed films. It was found that ε∞= 5.12 and 5.52 for the as-deposited and after being annealed films respectively. Graphical representations of (αhν)r= f(hν) yield three linear parts, indicating the existence of two indirect and one direct allowed transitions. The values of [Formula: see text], [Formula: see text] and [Formula: see text] for CdGa2S4for the as-deposited and annealed films are presented.