On residual carbon acceptors in molecular-beam epitaxial GaAs

The unintentional background concentration in molecular-beam epitaxially grown GaAs has been found to vary between 1×1014 cm−3 n type and 2×1016 cm−3 p type when grown with solid arsenic from several different suppliers. This variation is largely due to carbon incorporation which in turn is directly traceable to the arsenic charge. Increases in arsenic flux and substrate temperature both give rise to increased carbon acceptor concentrations. We propose that this carbon arises form heavy organic molecules such as rotary pump oil incorporated during the vacuum sublimation process used by some commercial suppliers.