The generation of native defects during the growth of heavily Si-doped material, and their effect upon heavily-doped adjacent lightly Si-doped layers, were investigated. It was found that, as the Si dopant concentration was increased, the concentrations of triply-ionized Ga vacancies, VGa3-, which were generated by a Frenkel-pair formation process, increased. It was noted that the limit of the free-carrier concentration in the heavily-doped layers was caused by VGa and not by the electron occupation of a highly localized state of the donor-related DX center. The VGa defects also led to carrier compensation in the adjoining under-layers. However, the carrier concentration in an adjoining over-layer on the heavily doped layer was unaffected. It was deduced that drift was the predominant mechanism of VGa flow into the lightly-doped layers. The drift was caused by an electric field which was induced by surface Fermi-level pinning; mainly in the early stages of growth of the heavily doped layer. On the other hand, the diffusion of VGa from the heavily doped layer during growth was negligible. Therefore, the carrier concentration in layers which were grown onto the heavily doped layer was unaffected. During annealing, the VGa (which was supersaturated in the lightly-doped under-layer) disappeared as the result of a first-order reaction.

H.Fushimi, M.Shinohara, K.Wada: Journal of Applied Physics, 1997, 81[4], 1745-51