Structural and photoelectronic properties of vacuum evaporated CdSe thin films

Thermally evaporated CdSe thin films deposited at high substrate temperature T-s greater than or equal to 473 K are found to be polycrystalline with hexagonal ZnS type structure. The grain size increases with T-s. Film crystallinity shows the most preferential orientation along [002] reflection. The sublinear behaviour of photocurrent - light intensity characteristics, measured at different experimental condition for the films deposited at different T-s and t, clearly confirms the defect controlled photoconductivity in CdSe films. Activation energies in dark and tinder illuminations are calculated from the temperature dependence of de conductivity of the films. The reduction of activation energy under illumination is explained on the basis of the grain boundary effect. The photocurrent in the films increases whereas the photosensitivity decreases exponentially with the rise of ambient temperature within the range 303- 403 K which is attributed to the effect of different types of scattering on carrier mobility. Spectral response shows a direct transition at 725 nm with an additional absorption around 975 not, which also confirms the existence of inherent defect states in CdSe films.