Diffusion Mechanism of Zn in GaAs and GaP Based on Isoconcentration Diffusion Experiments

Abstract

Precise relationships between the diffusion coefficient D and the zinc concentration C are obtained from isoconcentration diffusion experiments performed at 900°C for zinc in GaAs and at 1000°C for zinc in GaP. It is found that D varies with C from a slightly less than cubic to a somewhat less than square dependence over the concentration range 1018 to 1020 cm−3. Possible mechanisms that result in concentration-dependent diffusion are discussed. Under the conditions given above, it is concluded that diffusion occurs by an interstitial-substitutional mechanism with the interstitial mode being dominant. The charge states of the various species involved in the diffusion are believed to be: (1) interstitial zinc atoms are doubly ionized donors; (2) substitutional zinc atoms are either neutral or singly ionized acceptors; and (3) gallium vacancies are neutral. A theoretical expression for D versus C, derived under these assumptions, fits the isoconcentration diffusion data over wide ranges of D and C through the use of only one adjustable parameter.