Concentration Quenching of Luminescence by Donors or Acceptors in Gallium Phosphide and the Impurity-Band Auger Model

Abstract

The low-temperature photoluminescence efficiency for near band-gap transitions in GaP is shown to be a rapidly decreasing function of the donor or acceptor concentration above a well-defined threshold impurity concentration near ${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The concentration quenching is nearly temperature-independent below ∼40°K and is insensitive to the nature of the luminescence center. The threshold impurity concentration for concentration quenching lies close to the threshold predicted for intermediate-type impurity-band conduction involving shallow donors and acceptors in GaP. The luminescence quenching is attributed to radiationless Auger recombinations in which the recombination energy of the luminescence center is entirely given up to delocalized impurity electrons (or holes) in the impurity band. These free carriers are ejected deep into the electronic energy bands of GaP, and the high kinetic energy of these carriers is subsequently lost in cascade phonon-emission processes. This impurity-band Auger model for the radiationless recombination predicts the experimentally observed sharp increase in quenching above ${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$ which cannot be accounted for on the alternative hypothesis of capture competition between independent luminescent and nonradiative centers. The model is also consistent with the absence of concentration quenching at high concentrations, $\gtrsim {10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$, of isoelectronic impurities in GaP. The temperature dependence of the bismuth luminescence intensity is briefly discussed.