The superlattice intermixing of As-rich non-stoichiometric AlAs/GaAs quantum wells, which had been grown using a substrate temperature of about 300C, was found to be enhanced by several orders of magnitude relative to the diffusivity in stoichiometric structures which had been grown using normal substrate temperatures. The transient enhanced intermixing was attributed to a supersaturated concentration of group-III vacancies which had been grown into the crystal under the low-temperature growth conditions. The enhanced diffusion decayed during moderate-temperature annealing (600 to 900C, 30 to 1000s). Both first-order and second-order decay kinetics were found to agree equally well with the diffusion data which resulted from isochronal and isothermal annealing. Both of these possibilities required a thermally activated annihilation enthalpy in order to explain the temperature-insensitive behavior which was observed for the time-dependent diffusion coefficient. The activation enthalpy for the decay was between 1.4 and 1.6eV; as compared with the migration enthalpy of 1.8eV for the Ga vacancy in GaAs. Under the most extreme annealing conditions above, the diffusion length approached the self-diffusion values which were observed in isotopic superlattices of stoichiometric GaAs.

Transient Enhanced Intermixing of Arsenic-Rich Nonstoichiometric AlAs/GaAs Quantum Wells R.Geursen, I.Lahiri, M.Dinu, M.R.Melloch, D.D.Nolte: Physical Review B, 1999, 60[15], 10926-34