Influence of boron on the point defect equilibrium in highly n-doped gallium arsenide single crystals

High n-type conductivity of melt-grown gallium arsenide single crystals is usually achieved by doping with tellurium or silicon. The lower carrier concentration and Hall mobility in silicon-doped crystals is attributed to the formation of acceptor defects, in particular SiAs-, the isolated gallium vacancy VGa3- and the (SiGa–VGa)2-(SiGa–VGa)2- complex. We show that the contamination of the crystals with boron, which is unavoidable in growing techniques using a boron oxide encapsulant, is decisive for the degree of compensation. In highly n-doped gallium arsenide crystals boron is not only incorporated as the isoelectronic defect BGa0. Additionally, high concentrations of BAs2- and the negatively charged BAsBAs-donor complex are formed. These acceptors can dominate the equilibrium of point defects depending on the concentration ratio of the n-dopant and boron.