Influence of chemical etching on metal contacts to II-VI compounds: CdTe and ZnSe

The chemical nature of CdTe and ZnSe surfaces prepared by various chemical treatments has been studied by X-ray photoelectron spectroscopy. It has been found that the stoichiometry of the surfaces is very sensitive to the chemical treatments and each surface shows a similar pattern. In general bromine-containing or acid-based solutions preferentially remove the semiconductor cation, leaving a semiconductor anion-rich surface. In contrast, alkaline-based systems preferentially remove the semiconductor anion to produce a semiconductor cation-rich surface. Metal contacts fabricated on these surfaces show considerable differences in current-transport properties. The stability of these metal-semiconductor contacts has also been investigated and the microscopic interactions at these interfaces studied with Auger depth profiling and secondary-ion mass spectroscopy surface imaging techniques. The influence of microscopic interactions on the macroscopic electrical properties is presented and discussed in detail.