Eu-Mg defects and donor-acceptor pairs in GaN: photodissociation and the excitation transfer problem

We have investigated the temperature-dependent photoluminescence (TDPL) profiles of Eu3+ ions implanted in an HVPE-grown bulk GaN sample doped with Mg and of donor-acceptor pairs (DAP) involving the shallow Mg acceptor in GaN(Mg) (unimplanted) and GaN(Mg):Eu samples. Below 125 K, the TDPL of Eu3+ in GaN(Mg):Eu correlates with that of the DAP. Below 75 K, the intensity of Eu3+ emission saturates, indicating a limitation to the numbers of Eu-Mg defects available to receive excitation transferred from the host, while the DAP continues to increase, albeit more slowly in the implanted than the unimplanted sample. Prolonged exposure to UV light at low temperature results in the photodissociation of Eu-Mg defects in their Eu1(Mg) configuration, with a corresponding increase in shallow DAP emission and the emergence of emission from unassociated EuGa (Eu2) defects.