Hole-dependent diffusion of implanted Mg in GaAs

Magnesium implants in GaAs exhibit two types of diffusion during annealing: uphill diffusion in the peak of the implant and concentration-dependent diffusion into the bulk. The uphill diffusion predominates at short times and low temperatures, while the concentration-dependent diffusion is dominant at long times and high temperatures. By studying implants that were annealed at temperatures where no uphill diffusion occurs, diffused profiles could be modeled and an expression for the Mg diffusivity obtained. The activation energy for this process is 1.77 eV. Results from Fermi level experiments show that the diffusivity is hole dependent rather than concentration dependent. The hole-dependent exponent is unity for Mg implanted into semi-insulating substrates, but may change to two at high hole concentrations.