Donor bound excitons in Ge studied using photoluminescence excitation spectroscopy

Abstract

The authors report the first application of photoluminescence excitation spectroscopy to shallow donor bound excitons (BE) in Ge doped with As, P, or Bi. Transitions to the BE ground state and the first few excited states were observed by monitoring the longitudinal acoustic phonon replica of the principal bound exciton luminescence transition and scanning the laser excitation across the no-phonon region. Similar spectra were observed for Ge doped with each of the donors; an excited hole series, with states above the free exciton edge, was observed in each case. The energies of these states are in agreement with a simple hydrogenic model. From the apparent ionization limits and the bound exciton binding energies, an estimate of the D- binding energy for each donor is made. The shallowest electron and hole excited states previously observed in infrared absorption measurements are also observed for the As bound exciton, and a comparison with these earlier results is made.