Radiative and Nonradiative Recombination at Neutral Oxygen inp-Type GaP

A new near-infrared photoluminescence band attributed to the radiative capture of free holes by neutral oxygen donors has been observed in $p$-type zinc- and oxygen-doped GaP. The new emission is observed at temperatures above 70 °K and consists of a no-phonon line at 1.453±0. 002 eV and several-phonon replicas resulting from phonon energies of 23 and 52 meV. This free-to-bound luminescence is observed concurrently with the 1.40-eV luminescence band due to O-Zn donor-acceptor pair recombination, and is seen to be the dominant radiative recombination mechanism at neutral oxygen above 120 °K. The temperature dependence of the total near-infrared luminescence from neutral oxygen is found to be a strong function of zinc doping. In particular, lightly doped $p$-type crystals show an increasing luminescence quantum efficiency as the temperature is raised from 60 to 300 °K, while the more heavily doped $p$-type samples show a quenching of the luminescence with increasing temperature. These effects are explained on the basis of several nonradiative Auger processes involving the electron trapped at neutral oxygen.