Diffusion model for Ohmic contacts to GaAs

A diffusion model based on gallium vacancy dependent diffusion assumes grain boundary diffusion of gallium in gold as the principal mechanism of diffusion. This diffusion model is tested with the experimental results on AuGe Ohmic contacts to GaAs. The grain boundary diffusion model is modified since the annealing temperature is above the AuGe eutectic point. The diffusion is better characterized by the process of capture by traps (vacancies and dislocations) created during heat treatment. The diffusion parameters for gallium diffusion in gold, and for gold and germanium diffusion in GaAs are reported. The germanium incorporation into the defect lattice structure of GaAs results in donor (Ge⁺_Ga), acceptor (Ge⁻_As), neutral pair (Ge⁺_Ga–Ge⁻_As), and acceptor complex states. The increase of the contact resistance beyond the critical annealing temperature is related to the saturation of the gold layer with gallium and excessive arsenic loss.