We report photoluminescence studies of internal transitions of shallow Be acceptors in bulk GaAs and a series of S-doped GaAs/ALAs multiple quantum well samples with well width ranging from 3 to 20nm. A series of Be S-doped GaAs/ AlAs multiple-quantum wells with the doping at the well center and a single epilayer of GaAs uniformly Be doped were grown by molecular beam epitaxy. The photoluminescence spectra were measured at 4,20,40, 80, and 120K, respectively. A two-hole transition of the acceptor-bound exciton from the ground state, 1S3/2 （/8）, to the first-excited state, 2S3/2 （Г6） , has been clearly observed. A variational principle is presented to obtain the 2s-1s transition energies of quantum confined Be acceptors as a function of the well width under the single-band effective mass and envelop function approximations. It is found that the acceptor transition energy increases with decreasing quantum-well width, and the experimental results agree well with the theoretical calculation.
This paper studies the dynamics of intra-acceptor hole relaxation in Be δ-doped GaAs/AlAs multiple quantum wells （MQW） with doping at the centre by time-resolved pump-probe spectroscopy using a picosecond free electron laser for infrared experiments. Low temperature far-infrared absorption measurements clearly show three principal absorption lines due to transitions of the Be acceptor from the ground state to the first three odd-parity excited states respectively. The pump-probe experiments are performed at different temperatures and different pump pulse wavelengths. The hole relaxation time from 2p excited state to ls ground state in MQW is found to be much shorter than that in bulk GaAs, and shown to be independent of temperature but strongly dependent on wavelength. The zone-folded acoustic phonon emission and slower decay of the wavefunctions of impurity states are suggested to account for the reduction of the 2p excited state lifetime in MQW. The wavelength dependence of the 2p lifetime is attributed to the diffusion of the Be atom δ-layer in quantum wells.
