Identity of the conduction-band minimum in (AlAs)₁/(GaAs)₁ (001) superlattices: Intermixing-induced reversal of states

First-principles pseudopotential calculations on the (001) (AlAs)₁/(GaAs)₁ superlattice (SL) shows that partial intermixing of the Al and Ga atoms relative to the abrupt case lowers its formation energy, making this SL even stabler at low T than the fully randomized Al_0.5Ga_0.5As alloy. Concomitantly, the conduction-band minimum (CBM) reverts from the GaAs L-derived state, to the X^xy-derived AlAs state. The previously noted discrepancy between theory (pertinent to abrupt SL’s and yielding an L-derived CBM) and experiment (yielding an X^xy-derived CBM) is therefore attributed to insufficient interfacial abruptness in the samples used to date in experimental studies.