Effect of substrate temperature on film structure and photoconductivity in CdTe thin films

Photoconductivity was measured in CdTe thin films, vacuum evaporated at different temperature (Ts). High purity Al electrodes, also vacuum evaporated on thin films were found to give ohmic contact. An ECIL high input impedance (- 1014 Ω or higher) electrometer amplifier was used for the conductivity measurements. The dark conductivity of the films is found to be of the order of 10-6Ω-1m-1. The calculated grain sizes (D) increase initially with Ts and become gradually independent of Ts at higher Ts values. There is a corresponding increase in photosensitivity upto about D = 300 A beyond which the photosensitivity attains almost constant value. The observed dependence of photosensitivity on grain size has been explained on the basis of modulation of grain boundary potential barriers by photogenerated carriers. (author)