The behavior of Ge which was pulse-diffused into high-purity epitaxial GaAs from a thin elemental source, using rapid thermal processing, was investigated. A comparison of secondary ion mass spectrometry and differential Hall effect measurements showed that the resultant n+-doped layers were highly compensated. In contrast to the case where Ge was introduced during crystal growth or by ion implantation, GeGa donors were not compensated by GeAs acceptors when Ge was pulse-diffused into GaAs. Photoluminescence spectroscopy showed that GeGa donors were compensated by VGa acceptors rather than by GeAs acceptors. At low diffusion temperatures, Ga vacancies were formed as Ga rapidly diffused into the Ge layer. These vacancies suppressed the formation of As vacancies and thus GeAs acceptors. At higher diffusion temperatures, GeGa-VGa complexes were formed more rapidly than VGa acceptors. Low-temperature Hall effect measurements suggested that these complexes were neutral. The formation of complexes, at the expense of isolated GeGa donors and VGa acceptors, was related to diffusion temperatures which exceeded 865C (the Ge-GaAs liquidus) and was explained by a marked increase in the VGa concentration in the near-surface region, due to Ga dissolution at the Ge-Ga-As liquidus.

Complex Compensation of Ge Pulse-Diffused into GaAs. C.W.Farley, T.S.Kim, S.D.Lester, B.G.Streetman, J.M.Anthony: Journal of the Electrochemical Society, 1987, 134[11], 2888-92

Table 8

Diffusivity of H in GaAs