Excitation Spectra and Quantum Efficiency of GaP Containing Zn and O

We have investigated the quantum efficiency for the production of red luminescence in $p$-type GaP doped with deep oxygen donors and shallow zinc acceptors. We find the luminescence can be efficiently excited by energy transfer from bound excitons, $E\approx 2.317$ eV, as well as by absorption of quanta of energy in the characteristic (phonon-assisted) absorption region $h\nu \approx 2.2$ eV, and in the pair-creation region well above the band edge. The high efficiency of the exciton-induced radiation is interpreted as a resonant transfer of energy to an exciton which is weakly bound (∼10 meV) to an O-Zn complex and which decays to the ground (red-emitting) exciton state. The temperature dependence of the efficiency for the different excitation processes is presented and discussed and the loss in efficiency above ∼70°K is interpreted in terms of an Auger process involving free holes.