Identification of vacancy charge states in diffusion of arsenic in germanium

Diffusion of As into Ge from a GaAs overlayer deposited on p-type Ge substr ates has been studied by means of secondary ion mass spectrometry. A concen tration-dependent diffusion of As atoms was observed in addition to the con centration-independent diffusion of Ga and As atoms. The concentration depe ndence is explained by a Fermi-level-dependent diffusion model. Arsenic ato ms an shown to diffuse through Ge vacancies with the charge states 2- and 0 . No presence of the singly negatively charged vacancies was observed, indi cating that Ge vacancy could be a negative U center. (C) 2000 American Inst itute of Physics. [S0003-6951(00)00531-3].