Abstract
The dynamics of perpendicular transport of photoexcited carriers assisted by phonon scattering is investigated in a novel step-graded ${\mathrm{In}}_{x}({\mathrm{Al}}_{0.17}{\mathrm{Ga}}_{0.83}{)}_{1\ensuremath{-}x}\mathrm{As}$ quantum-well heterostructure by measuring the temperature dependence of spectrally and temporally resolved photoluminescence (PL). When builtin potential gradients are present in the quantum-well heterostructure due to variations in the In mole fraction (x) in the well, carriers that are thermally released by the particular well move unidirectionally from shallower to deeper wells. That is, asymmetric unidirectional motion of photoexcited carriers is possible via phonon-assisted activation above the barrier band-edge state. We have directly measured this perpendicular motion of photoexcited carriers by monitoring the transient PL signals from the different wells, which are spectrally separated. A rate equation analysis rigorously explains the dynamical changes of the PL signal intensities from the quantum wells as a function of lattice temperature. Our study of PL dynamics proves the asymmetric perpendicular flow of photoexcited carriers and the capture by the deeper quantum wells, providing firm evidence for the dynamical carrier flow and capture processes in the novel heterostructure.
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