Infrared Donor-Acceptor Pair Spectra Involving the Deep Oxygen Donor in Gallium Phosphide

We report the infrared radiative recombination of electrons bound to deep O donors with holes bound to C, Zn, or Cd acceptors in GaP. From the transition energies of the discrete no-phonon lines, which can be closely accounted for using a simple Coulomb donor-acceptor interaction energy term, the ionization energy of the O donor is calculated to be 893±{}2 meV. Aggregation between Zn (or Cd) acceptors and O donors in nearest-neighbor lattice sites produces strong red luminescence not observed in C-doped crystals where the closest possible donor-acceptor pairs are next-nearest neighbors. The infrared pair spectra are broad because of strong phonon-assisted transitions arising from the tight binding of the O donor. Two modes of energy 19.5 and 47.0 meV are prominent in the infrared spectra, whereas only one {~}48-meV mode is prominent in the green luminescence due to recombinations between shallow donors and C, Zn, or Cd acceptors in GaP.