Studies on thick films of photoconducting cadmium sulphide

Abstract

Highly photosensitive films of CdS have been prepared using the thick film technique. The films obtained from the composition containing CdS-100, CdCl₂−10 and CuCl₂−0·05 parts by weight (reacted at 500° C) are found to give the best photosensitivity on firing at 600° C. The ratio of light to dark current ~10⁸-10⁹ which is considerably higher than what is reported for thin films, single crystals and sintered layers. A strong chemisorption of oxygen is found to be responsible for high photosensitivity. The spectral response for doped CdS film is similar to that obtained for thin films, single crystals and sintered layers and also shows a red shift with increasing Cu concentration. However, the undoped CdS has a broad spectral response at room temperature ranging fromλ=550 to 690 nm; unlike the thin films and single crystals which give a sharp peak atλ=510 to 520 nm. A probable explanation has been suggested for this type of behaviour.