Recent developments and progress on electrical contacts to CdTe, CdS and ZnSe with special reference to barrier contacts to CdTe

A summary of experimental work on electrical contacts to CdTe, CdS and ZnSe is presented and recent progress of research on electrical contacts to these materials is reviewed in this paper. The surface preparation and surface characterisation prior to metallisation, interactions at the interface during contact fabrication, Schottky barrier characterisation and subsequent aging effects are considered. XPS, AES, SIMS and PL are used for surface characterisation; XPS and soft-XPS are used for interface interaction studies; I-V, C-V, DLTS and BEEM are used for Schottky barrier characterisation; and AES, GDOES and EDX profiling are used to study aging effects. The surfaces of all three materials behave in a similar way when etched in wet chemical etchants, The semiconductor cation is preferentially etched by acidic solutions and the semiconductor anion is preferentially removed by alkaline solutions. It has also been shown that the surface stoichiometry affects the Fermi level pinning position at metal/semiconductor interfaces. Furthermore, the observed Schottky barrier heights with all three materials demonstrate a multi-level pinning behaviour producing different barrier heights depending on the history of the materials used and the fabrication procedure followed. Barrier heights observed are independent of the metal work function, and their stability depends mainly on interactions occurring at the metal/semiconductor interface and are strongly related to the native defect levels within the bulk material.