Resonance effects in the carrier-tunneling dynamics in asymmetric coupled quantum wells

We present a detailed experimental study of the tunneling times, after picosecond excitation, of electrons and holes in a large set of unbiased GaAs/Alₓ{Ga}_{1{{-}}x}$As asymmetric double-quantum-well structures, pointing out the role played by resonances in the tunneling process. In particular, fast hole tunneling is found when the quantum wells show band alignment both at k?=0 and at k?{≠}0. Referring to electrons, a resonance is found in the tunneling time, which corresponds to phonon-assisted processes. Experimental data at high excitation intensity are also reported, suggesting band-filling effects in the wider well.