Directional phonon-assisted cascading of photoexcited carriers in stepped In_x(Al_0.17Ga_0.83)_1-xAs/Al_0.17Ga_0.83As multiple quantum wells

Perpendicular motion of photoexcited electron and hole pairs assisted by phononscattering is investigated in a novel step-graded staircase heterostructure consisting of strained In-1(Al0.17Ga0.83)(1-x). As multiple quantum wells (QWs) with similar widths but five different x values by cw and time-resolved photoluminescence (PL) experiments. From the temperature dependence of PL spectral intensity of distinct five peaks corresponding to the QW layers. we find that, as temperature increases. the PL peaks decrease their relative intensities progressively from shorter wavelength sides, after increasing the signal amplitude in the inter-mediate temperature range, These variations reveal that the photoexcited carriers directionally move from shallower to deeper QWs via phonon-assisted activation above the barrier hand edge state. The PL dynamics directly indicate the perpendicular flowing of photoexcited carriers and the capture by the deeper QW, thus providing firm evidences for the dynamical carrier flow and capture processes.