Fermi-level effect on Ga self-diffusion studied using 69GaAs/69Ga71GaAs isotope superlattice

We have studied the Ga self-diffusion in GaAs and its dependence on Si doping using ⁶⁹GaAs/⁶⁹Ga⁷¹GaAs isotope superlattices with [Si] = 1x10¹⁷- 8x10¹⁸cm^-3 grown by molecular-beam epitaxy. The depth profiles of ⁷¹Ga atoms before and after thermal anneals at 900°C have been investigated via secondary-ion mass spectrometry (SIMS) to obtain the Ga self-diffusion coefficient as a function of the Si concentration. We find that the Fermi-level effect becomes dominant only in the high-doped regime, i.e., [Si]>1x10¹⁸cm^-3, where the Ga self-diffusion coefficient increased in proportion to the third power of the electron concentration. On the other hand, no change in the diffusion coefficient was observed in the low-doped regime. Our results show that the Ga self-diffusion is driven by the Fermi-level effect and mediated by triply charged Ga vacancies in the high-doped regime, while it is suggested that some other Fermi-level independent mechanisms are operating in the intrinsic and low-doped regime.