Long-lived light holes in GaAs/AlGaAs multiple quantum wells

Abstract

The carrier dynamics of electron-hole radiative recombination rates in quantum wells is of primary importance from physics point of view and in devices. The decay rates give the signature of the available channels (electron-phonon interaction, electronelectron) through which excited electrons and holes cascade towards the bottom of the conduction and valence subbands. Identifying these channels and finding ways to extend carrier lifetimes would possibly lead to the realization of bose condensation through bi-excitons in quantum wells. On the practical side the speed of modulation of p-n junction diode lasers is affected by this recombination rate while in quantum cascade lasers, the lasing action is facilitated by a long-lived metastable conduction electron state. Previous investigations on the radiative lifetimes of carriers in semiconductor quantum wells have concentrated on the dynamics of the excited conduction electrons.
One primary reason is that it has been contended that the holes rapidly thermalize or cascade towards the top of the valence band at a faster rate than electrons. The deexcitation process for the holes is thought to come from interaction of the holes with the rough walls of the barrier (i.e. acoustic phonons). This is also the argument used in explaining why only the excitonic recombination of the conduction band and heavy hole (1C-1HH) is normally seen in the photoluminescence (PL) spectra of GaAs/AlGaAs quantum wells.
In this study, we use time resolved photoluminescence spectroscopy to investigate the behavior of the excited light hole (LH) states in a GaAs/AlGaAs quantum well. The room temperature CW photoluminescence spectrum of the sample displays both the 1C-1HH and 1C-1LH transition at room temperature. This indicates that the acoustic phonons may not be effective in thermalizing the holes for this sample. We observed a long decay rate of the 1C-1HH PL signal when the energy of the pump beam is not in resonance with the 1C-1LH + 1LO phonon. Tuning the pump beam in resonance shows a drastic reduction in the time decay of the PL signal. These results indicate that the excited holes in the 1LH state can also be long-lived.