Chemical reactions and Schottky barrier formation at Cr/n-CdTe interfaces

The formation of Schottky barriers at Cr/n-CdTe interfaces has been investigated in detail using angle-resolved ultraviolet photo-emission, soft X-ray photo-emission and current-voltage techniques. The CdTe surfaces studied were prepared by cleaving in ultra-high vacuum, cleaving in air, and by chemical etching. The results indicate strong chemical reactions between both CdTe and its native oxide (TeO2) with evaporated Cr layers. A typical high-coverage Cr/clean-CdTe interface consists of a mixture of cadmium chromium telluride and metallically bonded cadmium. In the case of oxidised CdTe surfaces, oxides of chromium and chromium telluride also exist at the interface. The resulting barriers are less than about 0.35 eV, showing Ohmic behaviour, and are almost independent of the surface preparation. These chemical reactions at the interface are discussed on the basis of the published bulk thermodynamic data.