Diffusion of Cd in GaAs and its correlation with self-diffusion on the Ga sublattice

Cd diffusion into GaAs single crystals has been investigated in the temperature range 756–1201 °C. Penetration profiles measured by secondary ion mass spectroscopy and spreading-resistance profiling agree with each other and are numerically reproduced on the basis of the kick-out diffusion mechanism. A major involvement of vacancies via the dissociative mechanism can be excluded. This enables us to deduce from the Cd profiles effective Cd diffusivities (Dseff) as well as Ga diffusivities (DISD) mediated by doubly positively charged Ga self-interstitials (IGa2+). The Dseff values obtained from As-rich and As-poor ambients are mutually consistent. The same holds true for the DISD data. Reduced to 1 atm of As vapor pressure and electrically intrinsic conditions the Cd diffusion coefficient results as 1.76×104 exp(−4.80 eV/kB T) cm2 s−1 and the IGa2+-related self-diffusion coefficient as 3.5×104 exp(−5.74 eV/kB T) cm2 s−1. The present data provide strong evidence that in heavily p-doped GaAs atomic transport related to the Ga sublattice is governed by self-interstitials rather than vacancies.