Influence of thermal annealing in air on the electro-optic characteristics of chemical bath deposited non-stoichiometric cadmium zinc selenide thin films

Non-stoichiometric thin films of cadmium zinc selenide were grown onto glass substrates by the chemical bath deposition technique from elemental selenium, sodium sulphite, cadmium chloride, zinc chloride, deionised water and ammonia. As-deposited films were annealed at different temperatures up to 600 K. From their deposition temperature in air, their electrical conductivity, optical properties and microstructure were evaluated. The electrical conductivity increases rapidly with increasing annealing temperature and activation energy E A for the crystallites was calculated from the Arrhenius relation. The optical absorption edge is shifted towards higher wavelengths with increasing annealing temperature. Other optical parameters such as absorption coefficient alpha , band gap E g , refractive index n, dielectric constant epsilon and extinction coefficient k were computed from transmittance spectra. The re-growth study was also carried out from micrography obtained from optical phase contrast microscopy at different annealing temperatures and results are interpreted on the basis of grain boundaries, defects and vacancies. The fully annealed films have a hexagonal crystal structure for x or=0.6 with varying lattice constants and grain size.