Correlation between Surface Properties and Detection Characteristics of Cadmium Telluride Detectors

Up to now, only very little attention has been given to the surface properties of cadmium telluride detectors, the best reported results being given When lapped surfaces, a result which is rather strange, when compared to the general behaviour of semiconductors. In order to better understand the mechanism involved at a metal-cadmium telluride contact, the properties of mechanically polished, chemically etched and also oxidized surfaces of cadmium telluride crystals have been investigated using various methods including ellipsometry, Rutherford backscattering in channelling conditions and secondary ion mass spectroscopy. Most important contaminants have been identified for each kind of preparation. Furthermore, it could be shown that if polished and certain oxidized surfaces are quite stable in air, etched surface become covered by a tellurium oxide layer, whose thickness increases even after very long periods of time. Detectors have been prepared afterwards on identical samples having received the various surface treatments and the main detectors properties investigated, especially noise, resolution, efficiency and polarization.