Effect of quantum-well confinement on acceptor state lifetime in δ-doped GaAs/AlAs multiple quantum wells

Using far-infrared time-resolved spectroscopy, we have investigated the effect of quantum-well confinement on the lifetime of shallow acceptor states in GaAs/AlAs multiple quantum wells with Be δ-doping at the well center. Low-temperature far-infrared absorption measurements clearly show three principal absorption lines due to transitions of Be acceptor states from the ground state to the first three odd-parity excited states, respectively. It is found that the lifetime of excited states monotonically reduces with decreasing quantum-well width, from 350 ps in bulk to 55 ps in a 100 A well. We suggest that the effect of quantum-well confinement on zone-fold acoustic-phonon modes increases the intra-acceptor scattering rate of acoustic-phonon-assisted relaxation.