Abstract
A series of experiments is described in which radioactive Sn was into GaAs for a wide range of conditons. Radio-tracer profiles were plotted and diffusion coefficients were calculated. At the lowest temperatures used ( approx =850 deg C), the measured diffusion coefficients depended on the doping the original GaAs slice used in the experiment. At higher temperatures ( approx =1100 deg C), however, the diffusion coefficient was independent of the substrate material. Electrical measurements were also carried out on the diffused specimens so that direct comparison could be made between Sn concentration and free carrier density. At high doping concentrations there were many more Sn atoms than electrons in the samples. The results are interpreted in terms of a model in which the Sn diffuses by way of charged vacancies. An interesting non-equilibrium effect is also reported. The surface is unstable during the diffusion unless there is a high ambient vapour pressure of As. 16 ref.--BA