Low resistance contacts to p-type cadmium telluride

A survey of metal contacts to p-type CdTe has revealed that the best contact is one prepared by vacuum deposition of CuAu onto a surface that has been etched with K₂Cr₂O₇:H₂SO₄ . The contact resistivity on 0.5 ohm-cm p-type CdTe is between 0.1 and 0.5 ohm-cm² . The contact resistivity does increase if subjected to heat treatment, but is stable in air at room temperature for at least several months. Contacts of CuAu and Au on a chromate etched surface were compared in detail with similar metal contacts on a methanol-bromine etched surface through measurements of current vs. voltage as a function of temperature, photovoltaic response, and Auger analysis. CuAu contacts on a chromate etched surface are describable in terms of a thermally assisted tunneling model with a barrier height of about 0.60 eV. Au contacts on either a chromate etched or a methanol-bromine etched surface can be described equally well by a thermally assisted tunneling model or by a thermionic emission model. In either case the barrier height is about 0.1 eV larger on the methanol-bromine etched surface than on the chromate etched surface. Auger analysis indicates that chromate etching produces a tellurium rich surface that plays a key role in determining subsequent contact properties.