Phase transitions in AlAs/GaAs superlattices under high pressure

Pressure-induced structural transition in AlAs/GaAs superlattices and in a bulk film of AlAs are reported for the first time. For layers thicker than a few hundred angstroms, the transition occurs in individual AlAs layers, superpressed above the bulk stability limit, with a volume change that destroys the interface coherence. However, for layers thinner than 100 AI the volume change is partially accommodated by formation of a strained-layer superlattice. The stability of strained high-pressure phases is explored with use of density-functional calculations.