Effect of annealing on the structural and optical properties of indium-diffused Cd_0.7Zn_0.3Se thin films

Cadmium zinc-selenide (Cd_0.7Zn_0.3Se) thin films were deposited on the ITO substrate using chemical bath deposition techniques by optimizing the deposition parameters. The as-deposited films were annealed in air at 200, 300 and 400 °C for 1 h. The composition, surface morphology and structural properties of the as-deposited and annealed Cd_0.7Zn _0.3Se thin films were studied using x-ray photoelectron spectroscopy, scanning electron microscopy and x-ray diffraction techniques. The as-deposited films exhibited the hexagonal phase of CdSe and ZnSe. The films annealed at 200 °C showed the dominant cubic phase of CdSe and the hexagonal phase of ZnSe. However, the cubic structure of Cd_0.7Zn_0.3Se was transformed into a hexagonal structure after annealing at 300 and 400 °C. The lattice parameter a for the cubic structure was 6.0865 , whereas for the hexagonal structure a varied from 4.3035 to 4.2938 and c varied from 7.0916 to 6.9868 . The optical absorption spectra were recorded within the range 350-800 nm. The optical band gaps were 2.08 eV, 2.03 eV, 1.91 eV and 1.72 eV for the as-deposited films and those annealed at 200 °C, 300 °C and 400 °C, respectively. The drastic decrease in the optical band gap at 300 and 400 °C was due to the indium diffusion into the Cd_0.7Zn_0.3Se matrix.