Above-barrier resonant transitions in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/AlAs/GaAs heterostructures

In this work we demonstrate the existence of above-barrier quasibound states in ${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As/AlAs/GaAs double-barrier quantum-well structures, by using both continuous-wave and time-resolved photoluminescence techniques in addition to reflectivity measurements. A series of clearly resolved resonances is found in the optical spectra. Their energy positions agree fairly well with the energies found for the quasibound states when analyzing the density of states of the heterostructure continuous spectrum. As shown by the analysis of the envelope wave function these resonances are localized in the ${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As barrier regions and are found to induce both an increase of the interband absorption and a reduction of the carrier capture efficiency into the wells.