Study of exciton localized by random potential in indirect gallium arsenide phosphide alloys

We have studied in detail a new structure Mx/0 in photoluminescence spectra from n-type indirect GaAs P alloys. The intensity of Mx/0 starts l -x x to saturate relative to that of the donor-bound exciton (Do) at very low excitation laser po\vcr. It has a low activation energy (2 meV) and prominant X-point phonon sidebands. Its wave function is effective-mass-like and is associated with the X-point in K-space. We interpret the MO band as due to excitons localized by the random potentials in the alloys. Lifetime measurements show that the Mx/0 excitons are relatively long lived (tens of microseconds) and it varies over the spectral regions of the M~ emission band. This can be understood in terms of the energy-dependence of the effective range of the excitons in the presence of impurity centers in the sample. Such characteristic is unique for the Anderson-type localized excitons. The valley-anisotropy (V-A) splitting of the localized exciton is directly observed under resonant excitation at Mx/0. The lineshape of the enhancement curves of a prolllinent longitudinal accoustic phonon (LAX) side- band of Mx/0 changes with temperature. This provides information which is necessary for the identification of the V-A split excited state. The pseudo-extended nature of the excited state plays an important role in the low activation energy of Mx/0. The asymmetric lineshape of Mx/0 is qualitatively explained.U of I OnlyThesi