Effect of arsenic pressure on solubility of copper in GaAs

Abstract

A considerable decrease in the solubility of copper has been observed when diffusion into undoped GaAs was carried to saturation at 900°C under increasing arsenic vapor pressure. Two important factors influencing the solubility are the concentration of copper in the external phase and the type of vacancy which reacts with copper. Estimates have been made of the thermodynamic properties of the Ga-As-Cu ternary liquids saturated with GaAs at 900°C from solubility measurements in the ternary system and available thermodynamic information on the Ga-As binary system. The effect of the copper concentration in the external phase on the solubility has been distinguished from that of the vacancy interaction. Thus it has enabled us to determine which vacancy reacts with interstitial copper. The simple assumption that copper is incorporated into GaAs on arsenic sites as a singly ionized acceptor, Cu − As has led to a satisfactory explanation of the experimental results. An alternative explanation leading to the same dependence of the copper solubility on arsenic pressure puts a copper atom on a gallium site associated with two arsenic vacancies to give a singly ionized acceptor complex (V AsCu GaV As) −.