Phonon satellite strengths in the photoluminescence spectra of a type-II GaAs/Al0.3Ga0.7As superlattice at elevated pressures

We present results from a photoluminescence study of a GaAs/Al0.3Ga0.7As superlattice between 0 and 37 kbar. At 29 kbar, a type-I to type-II transition is observed, and this transition pressure is in good agreement with the predictions of the Kronig-Penney model. In the type-II regime, we detect direct X-Γ recombination and have observed three distinct phonon satellites from structures having alloy layers. By studying the laser-power dependence of the photoluminescence spectra, we demonstrate that the Xz and Xxy level separation is just 8 meV, again in close agreement with theoretical predictions. Consideration of the relative intensity of the satellites shows that the strongest satellite at high laser powers is associated with the Xxy states and overlaps three further satellites coupled to Xz. These spectra provide experimental evidence that the Xxy states can have a significant effect on the optical emission from GaAs/(AlGa)As superlattices in the type-II regime, even when the conduction-band edge has Xz character.