Binding energy and dynamics of Be acceptor levels in AlAs/GaAs multiple quantum wells

We report an infrared study of the effect of quantum well confinement on the binding energy and dynamics of shallow Be acceptors in both bulk GaAs and a series of delta-doped AlAs/GaAs multiquantum well samples with well thicknesses of 20,15 and 10 nm. Low temperature far-infrared absorption measurements clearly show the three principal absorption lines due to the 1s–2p transitions of the acceptors for all four samples. The dynamics of these transitions were studied by the pump-probe technique using a free electron laser as a source of far-infrared radiation. It was found that the 2p acceptor state has a low-temperature lifetime of 360 ps in the bulk, which reduces with increasing confinement, falling to 55 ps in the case of the 10 nm well. We suggest that the increase of phonon emission rate with decreasing well width is due to the breaking of translational symmetry in the quantum well and a subsequent increase in the single-phonon emission probability