Binding energies of shallow donors in semi-insulating GaAs

We have used photoluminescence from two electron satellites of donor-bound excitons as well as selective pair luminescence spectroscopy to study shallow donor levels in semi-insulating bulk GaAs. Bound exciton spectroscopy gives a donor binding energy equal to the effective mass value (5.8 meV) for all samples investigated. Selective pair luminescence, in contrast, yields a sample-dependent value for the average donor binding energy, which varies between 5.8 and ∼7 meV. This discrepancy is attributed to the fact that bound exciton spectroscopy probes all donor levels whereas selective pair luminescence is sensitive to donors close to acceptors which are therefore more strongly disturbed.