Volatile metal oxide incorporation in layers of GaAs and Ga1−xAlxAs grown by molecular beam epitaxy

Abstract

A model is presented which relates the observed effects of substrate temperature and growth flux magnitudes upon layer quality to the presence of volatile oxides and the thermodynamics of the formation of nonvolatile oxides on the growth surface. A means for reducing oxide contamination is presented and the consequent benefits explored. Ga2O is shown to be a major contaminant of the gallium growth flux, on the order of 0.1%. Certain conditions, specifically low substrate temperature or high arsenic fluxes, can favor the formation of Ga2O3, a nonvolatile contaminant, on the growth surface and hence in the layer. The presence of aluminum, magnesium, or other highly reactive materials makes oxide incorporation increasingly probable. Drastically lowering the Ga2O pressure by several orders of magnitude by adding 0.1% aluminum to the gallium effusion cell should allow growth at lower substrate temperatures and higher rates. Magnesium doping of GaAs at unity efficiency is demonstrated as proof of the relevance of the model. Photoluminescence data from the doping experiment are presented.