Electron and hole tunneling transfer times in GaAs/Al0.35Ga0.65As asymmetric double quantum wells under electric field.

Electron and hole tunneling transfer processes in asymmetric double quantum well structures are investigated by time-resolved picosecond photoluminescence. Change from nonresonant to resonant tunneling is achieved with a perpendicular electric field. Electron transfer times decrease if the two electron subbands in the two quantum wells are energetically aligned. Both nonresonant and resonant electron transfer times decrease strongly with the barrier thickness. The resonant times are more than one order of magnitude smaller than the nonresonant times for the same barrier thickness. The buildup of delocalized coherent states at resonance would lead to much shorter resonant transfer times than we observe experimentally. This discrepancy is discussed in terms of state broadening. Hole transfer times also decrease at specific electric fields showing a resonance feature, which can be attributed either to the resonant transfer of n=1 heavy holes to an n=1 light hole level or to the onset of t he optical phonon scattering from the n=1 heavy hole level to the neighbouring n=1 heavy hole level.