Effect of film thickness on photoconductivity in CdS thin films

Thermally deposited annealed CdS films at elevated substrate temperature exhibit good ohmic at electrode-film junctions at different film thickness. The photo-electrical property in fresh CdS films shows linear relationship with intensity of illumination, film thickness and applied bias. The photo-transport mechanism in photoconductivity process in the films revealed doubled activations due to direct and indirect transport of photo-activated carriers which co-relates with the spectral response properties of the films. The growth time (T_r) and the decay time (T_d) of photocurrents are strongly controlled by the extrinsic concentration of discrete trapped carriers being decreased with increasing film thickness. The estimated trap depths from exponential decay curves in the films are observed to decrease with increasing film thickness which transient direct relationship with the barrier modulation photo-electrical transport mechanism in the films.