Time-resolved photoluminescence spectroscopy was used to study the radiative recombination of excitons that were bound to ionized donors in material that was doped with both Mg and Si to concentrations of 5 x 1018 and 1.5 x 1017/cm3, respectively. Low-temperature (7 to 10K) time-resolved and integrated photoluminescence spectra revealed an ionized donor-bound (Si) exciton peak (D+X) that was about 0.0115eV below the free exciton peak, and a neutral acceptor-bound exciton (A0X) which was 0.0205eV below the free exciton peak. A rapid decay of the free exciton emission (less than 20ps) implied that excitons were quickly captured by acceptors and ionized donors. It was found that the A0X emission lifetime was consistent with previous measurements of Mg-doped GaN epilayers, while the D+X lifetime of 160ps was longer than that of the much-studied neutral donor-bound exciton, D0X. The measured D+X lifetime, when compared with D0X and A0X, suggested that the state was stable at low temperatures.

Time-Resolved Photoluminescence Studies of an Ionized Donor-Bound Exciton in GaN. R.A.Mair, J.Li, S.K.Duan, J.Y.Lin, H.X.Jiang: Applied Physics Letters, 1999, 74[4], 513-5