Optical and electrical properties of chemically deposited CdS thin films modified by air annealing

Polycrystalline CdS thin films have been grown by chemical bath deposition (CBD) using cadmium acetate and thiourea as the Cd and S ion sources. The as-deposited films show a low degree of crystallinity, are very resistive (conductivity /spl sim/10/sup -7/ /spl Omega//sup -1//spl middot/cm/sup -1/) and possess a small degree of photosensitivity. Air annealing of the films at 100-400/spl deg/C for 1 hr converts them to n-type through partial conversion of CdS to CdO. This is accompanied by an increase in the photoconductivity by more than 6 orders of magnitude. The optical bandgaps of the as-deposited films were >2.38 eV, which decreased to /spl sim/2.24 eV after air annealing.