Picosecond time‐resolved studies of excited state lifetime of Be acceptor in GaAs/AlAs multiple quantum wells

Abstract

The influence of the quantum well potential on the carrier dynamics of holes bound to the acceptors in Be δ-doped AlAs/GaAs multiple quantum wells is investigated by far-infrared time-resolved spectroscopy using the Free-Electron Laser for Infrared eXperiments (FELIX). The lifetime of the 2p excited state of acceptors was measured as a function of the width of the quantum well and the temperature. It is found that the lifetime decreases monotonically with decreasing well width and is independent of temperature. We suggest that the relaxation process of the 2p → 1s is non-radiative and mediated via confined acoustic phonon modes, in particular, zone-folded acoustic phonon modes which arise from the periodic nature of the multiple quantum well samples. For one particular well width the lifetime was measured across the inhomogeneously broadened D-line as 30, 30, 70, and 105 ps for 43, 44, 46, and 47 µm wavelengths, respectively. We believe the latter is due to diffusion of the Be δ-doped atomic layer in the quantum wells.Introduction In multiple quantum well or superlattice structures, the artificial period along the direction perpendicular to the layers results in Brillouin-zone folding and produces additional phonon branches and gaps in the phonon spectrum [1 -3]. Zone-folded acoustic phonons are in general accessible by the interaction with photons or carriers and have been reported in Raman scattering studies of GaAs/AlAs superlattices [1,4]. Zucker et al. has discovered a new deformation-potential electronphonon scattering in GaAs quantum wells, which does not exist in bulk GaAs [5] and is thought to arise from the change in symmetry of the crystal lattice. Such changes in symmetry can produce more efficient phonon scattering at energies which are larger than the typical bulk acoustic phonon energy of a few meV, but less than the dominant longitudinal optic (LO) phonon mode. In this paper we investigate hole scattering which is in just this regime -the influence of the quantum well potential on the carrier dynamics of holes bound to Be acceptors in δ-doped AlAs/GaAs MQW.

Donor-related third-order optical nonlinearites in GaAs/AlGaAs quantum wells at the THz region

“…The ratio of the real and imaginary parts as well as the absolute To the best of our knowledge, there is not much study in the literature on the lifetime of the carriers in the donor impurity states. In Be-doped GaAs/AlAs quantum well structures, the lifetimes of the excited impurity states have been reported as 55 ps for 10 nm well width and 350 ps for the bulk [18,19]. For a 10 nm well with 50 ps lifetime, 1.4×10 −9 , 3×10 −9 , and 4.3×10 −9 m 2 V −2 can be extracted for Re χ (3) , Im χ (3) , and χ (3) respectively at their maximum.…”

Intra-acceptor hole relaxation in Be δ-doped GaAs/AlAs multiple quantum wells

“…The pump-probe signals at λ = 43, 44, and 47 µm are observed to be two orders of magnitude weaker than that at the Dline position. [26] Fig. 4.…”

Relaxation of the impurity photoconductivity inp-Ge/Ge1−xSixquantum well heterostructures

“…In [9] the lifetime of charge carriers captured by the excited impurity states in n-GaAs in a magnetic field was studied directly, using a pulsed submillimeter gas laser. Similar investigations are being carried out currently with the use of pulsed broadband tunable (4-250 μm) free-electron lasers (FEL), but so far they have been restricted to bulk materials [10,11] and GaAs/AlAs and Si/SiGe heterostructures doped with Be and B acceptor impurities that have a rather large ionization energy-around 28 and 40 meV, respectively [12,13].…”