Voltage rectification at a free surface of a cadmium sulphide crystal in different gaseous media

Abstract

Some observations are reported on voltage rectification across a barrier layer at a free surface of a high-resistivity CdS crystal traversed by a low-frequency alternating current of small constant amplitude. The rectified voltage is found to depend sensitively on the nature of the ambient gas and to quench out completely in the presence of traces of vapours of alcohols. It is confirmed that chemisorbed oxygen is largely responsible for the surface charge in crystals surrounded by atmospheric air. In addition to chemical quenching of rectification, optical quenching due to photodesorption is observed at a critical wavelength (outside the fundamental absorption band) which is characteristic of the ambient gas. The temperature dependence of the rectified voltage in the range -20-80°c exhibits a sharp drop above room temperature which may be interpreted as due to a decrease of barrier resistance rather than to thermal desorption. At low temperatures the rectified voltage is inversely proportional to the absolute temperature, in accordance with theoretical prediction.