Anomalous diffusion profiles of zinc in GaAs

A number of workers investigating diffusion in semiconductors using radio-tracer techniques have reported a type of profile which is not easily explained by current theories of diffusion. This anomalous profile is usually found in experiments in which the solute concentration is high and has often been associated with the substitutional-interstitial diffusion mechanism. The profile shape is considered in this paper, taking the diffusion of zinc in GaAs at 1000° C as an example. The use of the Boltzman-Matano technique for analysing complex diffusion profiles is considered and experiments are described which suggest that the technique is not appropriate for this type of profile. An adaptation of the substitutional-interstitial diffusion theory is presented in which allowance is made for the possibility of the gallium vacancy concentration falling below the thermal equilibrium value. Theoretical profiles are computed and compared to experiments. Reasonable agreement is found.