Relation between phase stability and mechanical defects in InGa(Al)As/GaAs and ZnSe/GaAs heterostructures under pressure

We report pressure-Raman experiments on elastically metastable heterostructures from two systems: (i) In_xY_{1 - x}As epilayers and In_xY_{1 - x}As/GaAs multilayers (Y = Ga or Al; x ≅ 0.5) grown on GaAs or InP substrates; (ii) ZnSe epilayers and ZnSe/GaAs multilayers grown on GaAs. The LO(Γ) phonon frequencies are measured for pressure up to the α-β phase transitions in the various constituents. Several samples exhibit pressure-induced relaxation of the internal strain due either to formation of interface dislocations or to structural fluctuations antecedent to an α-β transition. Superpressing is observed for the In_xAl_{1 - x}As α-β transition in the multilayers, but it is not apparent for the ZnSe transition in our samples. A correspondence between the formation of dislocations and the absence of superpressing is discussed.