Energetics of Impurity-Free Vacancy-Mediated Disordering of AlGaAs/GaAs Superlattices

Abstract

ABSTRACTWe report on a systematic study of impurity-free Al-Ga interdiffusion in AlGaAs/GaAs superlattices in sealed ampoules. Three ambients were explored: along the Ga-rich solidus, with no excess Ga or As in the evacuated ampoule, and with excess As less than that required to reach the As-rich solidus limit. In each of the ambients the Arrhenius dependence of the Al-Ga interdiffusion coefficient is represented by a single activation energy throughout the temperature range investigated (700-1050 °C). These results were obtained using four structures with superlattice periods ranging from 90 to 520 Å. Excellent agreement was obtained between the Al-Ga interdiffusion coefficients measured using superlattices on Sidoped and undoped GaAs substrates. With proper normalization to a constant As overpressure, PAs4 = 1 atm, the Ga- and As-rich activation energies are 3.26±0.12 eV and 4.91±0.23 eV, respectively. These activation energies are in the range predicted for Al-Ga interdiffusion mediated by group Ill-vacancy second nearest-neighbor hopping. The increase in energy when going from Ga- to As-rich conditions is attributed to a shift in the Fermi-level position towards the valence band with an increase in the ionized group Ill-vacancy concentration.