Role of Cation Dissociation in Schottky Barrier Formation at II–VI Compound Semiconductor-Metal Interfaces

We used UV and X-ray photoemission spectroscopies to probe the relation between the chemical and electronic structure at ultrahigh-vacuum-cleaved CdS-metal and CdSe-metal interfaces. When combined with current-voltage and capacitance-voltage studies of the same interfaces in ultrahigh vacuum, the experimental results indicate that partially dissociated cadmium cations, produced as a consequence of interfacial chemical reaction, may be the electrically active species giving rise to the observed Fermi level stabilization at these contacts. The extent of cation dissociation, a spectroscopically determined quantity, is shown to correlate inversely with the measured Schottky barrier height. An indirect and modified doping effect is suggested as one possible mechanism to explain this behavior. Features of interdiffusion, in particular regarding the interfacial distribution of dissociated cadmium, are also described.