Desorption of Oxygen and Its Effects on the Electrical Properties of CdS Single Crystal Platelets

摘要

Oxygen effects on CdS single crystal platelets are shown to manifest themselves in several ways and allow one to divide the crystals into two basic classes. Thermally stimulated desorption studies, with a sensitive partial pressure analyzer in ultra high vacuum, show that there are several layers of monatomic oxygen adsorbed on the crystal surface for the assumption that the real surface equals the geometrical surface. A sensitization and compensation model is shown to account quantitatively for the observed changes in photoconductance and rising Fermi level due to oxygen desorption. In this case some of the surface states which originally contained adsorbed oxygen act as sensitization centers after the oxygen is desorbed, whereas others act as charge compensation centers. On the other hand a model which is based on the adsorbed oxygen causing fast surface recombination is shown to be incapable of accounting for the rising Fermi level. (Author)