Effect of doping and heat treatment on the photoluminescence of CdS films deposited by spray pyrolysis

Large area thin films of n-type CdS were prepared by spray pyrolysis technique. The films were n-type doped by having In/Cd] ion concentration ratio of 10⁻⁶, 10⁻⁵, 10⁻⁴, 10⁻³, and 10⁻² in the sprayed solution. These films were heat treated in N₂ atmosphere at 450°C for 1 h. The as-deposited undoped, doped, and heat treated were analyzed by photoluminescence (PL) at 5 K sample temperature. In general, the spectra displayed three main emission regions (green, yellow and red) with more than one band in each. The emission intensity is found to decrease with doping and the relative intensity of the bands is found to depend on the doping concentration level. The red band is only present in doped samples and its relative intensity is found to increase with doping. The effect of heat treatment in N₂ on the as-deposited undoped and the doped (10⁻⁴) samples on the relative intensity of the observed bands were compared and discussed. The results are compared with the electrical and morphological results and correlated with the probable changes in the concentration of shallow and deep radiative native defects and structural changes. These allow for better prediction of suitable doping and treatment conditions for good quality films.