Electron and hole capture in multiple-quantum-well structures

We have studied a series of modified GaAs/Alₓ{Ga}_{1{{-}}x}$As multiple-quantum-well structures, where increased capture times are obtained owing to the engineering of the band configuration. Both electron and hole capture times have been measured as a function of well width. Hole capture times are fast (typically 10 ps) and depend weakly on the structure. Electron capture times are shown to vary between 2 and 120 ps for well widths covering the whole range between 30 and 100 {}. This variation and the short time observed at resonance, when the barrier and the well levels are separated by 1 LO-phonon energy, demonstrate the importance of quantum-mechanical electron capture processes.