Electric-dipole transitions between group-III acceptor states in uniaxially compressedGe

Abstract

We study the electric-dipole transitions between group-III acceptor states in Ge understress along the [001] crystallographic direction in the effective mass approximation. Wesystematically investigate the cases of zero stress, infinitesimal stress, and finite stressincluding the low-stress and the high-stress regions. Our results show quantitativeagreement with experimental data at zero stress and at infinitesimal stress. Therelative intensities of infinitesimal-stress-induced components of transitions from the1Γ8 + state tothe nΓ8 − states do not correlate significantly with the species of acceptors except for the transition to the1Γ8 − state. The oscillator strengths of some transitions are susceptible to the stress in the low-stress region(<0.3 kbar), and could be zero at a specific stress. The behaviours of the stress dependence ofoscillator strengths for different transition lines are explained in terms of the compositionsof the wavefunctions and the dipole matrix elements. In the high-stress region ( kbar), the ground state is s-like, and only the transitions to the p-like states can havenon-negligible oscillator strengths. The photon absorbed (emitted) and associated witheach electric-dipole transition between the s-like and the p-like states is polarized eitherparallel or perpendicular to the stress direction. We also calculate the absorption spectrafor Ge:Ga at liquid-helium temperature. The results are in good agreement withexperiment.