Surface Photoconductivity of CdS Influenced by Chemisorption and Desorption of Oxygen

Using investigations of the spectral dependence of photoconductivity and of the influence of oxygen on photoconductivity a method is developed to test the properties of space‐charge layers at the surface of CdS, at least in some extreme cases. The surface space‐charge layer of thick CdS platelets with a photoconductivity greatly sensitive to an oxygen atmosphere is found to be of accumulation type. This makes a re‐interpretation necessary of the models so far accepted for the chemisorption and desorption processes. As their rate‐ limiting steps the direct capture of electrons and holes by neutral and negatively charged oxygen, respectively, is assumed. Theoretical calculations on the basis of this model show qualitative agreement with the experimental results, but desorption seems to be a process more complex than pure photodesorption.