Microscopic and macroscopic investigation of electrical contacts to n type and p type ZnSe

Surface preparation methods were established using wet chemical etching of ZnSe epilayers and the stoichiometry of the resulting surfaces was studied using X-ray photoelectron spectroscopy. It is found that the stoichiometry of the surface is very sensitive to the chemical treatment and surfaces can be produced that are rich in either Se or Zn. Electrical contacts were fabricated by vacuum evaporation of Ag, Sb, or Au on to nearly stoichiometric surfaces. Electrical properties were studied using the current-voltage technique and it has been found that the Schottky barrier heights measured vary from contact to contact, although the processing and metal used are identical. Discrete barrier heights of 1.67, 1.48, 1.20, and 0.90 eV are observed for metal/n-ZnSe contacts using the three metals studied. The first two barrier heights, 1.67 and 1.48 eV, are identical to those reported in the literature. Aging effects of current-voltage characteristics were also monitored and it was observed that the barrier height varies with time, showing one of the four values mentioned above. Ballistic electron emission miscroscopy carried out on 1.67 eV barrier contacts confirms the accuracy of the current-voltage barrier height determinations. Electrical properties of meal/p-ZnSe contacts are also presented and their aging effects discussed. (C) 1996 The Institute of Materials.