The formation of stable ohmic contacts to MBE grown CdTe layers

Abstract

The properties of Al contacts to n-type CdTe epilayers have been compared with those for In contacts with a view to establishing a contacting technology suitable for the fabrication of stable low resistance junctions to CdTe layers and multilayer devices. It has been confirmed that, as for bulk grown n-CdTe, ohmic contacts can be formed using vacuum evaporated In but the resultant devices are unstable due to the rapid inward diffusion of In. For the case of Al contacts, simple evaporation does not yield ohmic behaviour. However, stable ohmic Al–CdTe junctions are found to be achieved making use of an ion-assisted plating technique in which the semiconductor surface is exposed to an inert gas discharge prior to and during the early stages of the Al vapour deposition process. This result is attributed to the removal of surface contamination prior to metal deposition, allowing an intimate metal–semiconductor interface to be produced.