Donor-acceptor pair luminescence of nitrogen-implanted ZnO single crystal

Abstract

Donor-acceptor-pair (DAP) luminescence is a direct probe of the acceptors in ZnO. We report the near-surface doping of a ZnO single crystal by ion implantation with nitrogen and titanium. Secondary-ion-mass spectroscopy shows that the doping depth is approximately 80nm (N) and 50nm (Ti). The DAP photoluminescence centered at 3.232eV is observed from both the undoped and doped ZnO single-crystal samples. The luminescence spectrum of the nitrogen-doped sample shows enhancement of the DAP transition compared to the “pure” ZnO sample. The acceptor energy is calculated to be 177meV, consistent with nitrogen as the acceptor in DAP luminescence. The DAP recombination lifetime is found to be ∼5.5ns. The temperature evolution of spectra shows the gradual transition from DAP luminescence to electron+acceptor recombination luminescence at temperatures above 37K. Our experimental results suggest that ion implantation is an effective way of doping nitrogen into ZnO.