Dynamical simulation of phonon-assisted asymmetric transfer of photoexcited carriers in step-graded multiple quantum wells

Dynamics of perpendicular motion of photoexcited electron–hole pairs assisted by phonon scattering is investigated by a rate equation analysis in a novel step-graded staircase Inx(Al0.17Ga0.83)1−xAs multiple quantum well heterostructure. When there exists built-in potential gradients in the heterostructure by changing the In mole fraction (x) in each well, those 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 realized via phonon-assisted activation above the barrier band edge state. This perpendicular motion of carriers was measured by monitoring the transient photoluminescence (PL) signals, which are spectrally discriminated between the wells. The PL dynamics is rigorously and quantitatively explained based on the dynamical simulation as a function of temperature using extracted parameters of the recombination and transfer times.