The diffusion of Si was investigated by using sources from various tie-triangle regions in the Si-Ga-As phase diagram. This ensured constant chemical potentials for the 3 components under isothermal conditions. The Si profiles were determined by using secondary ion mass spectrometry, and were found to be very different for the various types of source. The Ga-Si-GaAs tie-triangle source produced p-type Si doping with a concentration-independent diffusion coefficient. A neutral As or Ga vacancy was thought to be the predominant mobile defect under these conditions. The use of As-rich sources from 2 tie-triangle regions, or a Si-GaAs tie-line source, produced Si donor diffusion with a concentration-dependent diffusion behavior. The concentration-dependent diffusion coefficients of donor Si for As-rich source diffusion were related to the net ionized donor concentration, and exhibited 3 different regions. These were an intrinsic regime, an intermediate regime, and a saturation regime. It was proposed that Ga vacancies were responsible for donor diffusion; with a VGa0 and/or VGa- mechanism for the intrinsic regime and a VGa--related mechanism for the extrinsic and saturation regimes. The use of a Si-GaAs tie-line source produced 2 branch-type profiles which were intermediate between the As-rich and Ga-rich diffusion cases.

Diffusion Kinetics of Si in GaAs and Related Defect Chemistry.  K.H.Lee, D.A.Stevenson, M.D.Deal: Journal of Applied Physics, 1990, 68[8], 4008-13