ANNEALING EFFECT ON THE DARK ELECTRICAL TRANSPORT AND ABSORBANCE SPECTRA OF CHEMICAL BATH DEPOSITED CdS NANOCRYSTALLITES

We report here our investigations on dark DC resistivity and optical absorption of chemical bath deposited CdS thin films prepared by chemical bath deposition. Crystallite sizes of about 30 nm are found from XRD using Scherrer formula with an added term for strain broadening. Energy-dispersive X-ray measurement shows correct stoichiometry of Cd and S atomic ratio. The grain size of the as-deposited film determined from both AFM and TEM is found to be ~180 nm. On vacuum annealing, the dark resistivity decreases from ~109 to 106 Ω-cm. Dark resistivity variation of as-deposited and vacuum-annealed films with temperature in the temperature region (95–350 K) reveals that each film exhibits two types of conduction in this temperature region. From the optical absorption study the optical band gap of as-deposited film is found to be ~2.29 eV.