Contact properties of Ni/Au on homoepitaxial p-ZnSe with oxygen plasma treatments were investigated. The authors found that Zn distribution profiles for p-ZnSe with and without treatments were almost identical. They also found that Se concentration near the surface decreased while 0 concentration near the surface increased after oxygen plasma treatment. They also observed hillocks, which were related to Se vacancies and/or isoelectronic oxygen impurities, on the surface of 15 W oxygen plasma-treated samples. Furthermore, they found that they could achieve the lowest offset voltage from the sample treated with 15 W oxygen plasma. (c) 2007 American Vacuum Society.