FIELD EFFECT STUDIES OF OXYGEN ADSORPTION ON CDS SURFACES

Oxygen adsorption on CdS surfaces is studied by field effect measurements. Under vacuum the surface is found to be practically free of acceptor-like surface states. Admission of oxygen changes the electronic structure of the surface drastically. Transition between physical and chemical adsorption at each pressure is effected by the applied electrostatic field, and the accompanying relaxation in surface conductance is analyzed to yield the electron trapping kinetics associated with the chemisorption process. The relaxation characteristics can be quantitatively accounted for by a standard rate equation. The analysis shows that at any given pressure the conduction electrons interact with a fixed density of physically adsorbed oxygen molecules throughout the relaxation process. This density, which is independent of the amount of chemisorbed oxygen, is directly proportional to ambient pressure between 10-5 Torr and atmospheric pressure. The electron capture cross section characterizing the chemisorption process is ≈ 10-23 cm2. © 1969.