A systematic study was made of impurity-free Al-Ga interdiffusion in superlattices which were sealed into ampoules. Four structures were used, with superlattice periods that ranged from 9 to 52nm. Three ambients were explored: along the Ga-rich solidus, with no excess Ga or As in the evacuated ampoule, or with an excess As content which was 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 could be described by a single activation energy at temperatures ranging from 700 to 1050C. Excellent agreement was obtained for the Al-Ga interdiffusion coefficients which were measured by using superlattices on Si-doped and undoped GaAs substrates. By normalization to a constant As over-pressure of 1atm, the Ga- and As-rich activation energies were deduced to be 3.26 and 4.91eV, respectively. These activation energies were in the range which was predicted for Al-Ga interdiffusion, mediated by group-III vacancy second-nearest neighbor hopping. An increase in energy which occurred upon going from Ga- to As-rich conditions was attributed to a shift in the Fermi-level position, towards the valence band; with an increase in the ionized group-III vacancy concentration.

B.L.Olmsted, S.N.Houde-Walter: Applied Physics Letters, 1993, 63[4], 530-2