Time-resolved photoluminescence in strained GaN layers

A set of GaN epilayers grown by metalorganic chemical vapor deposition on 6 H-SiC substrates was studied by time-resolved photoluminescence (PL) spectr oscopy. The PL spectra are dominated by the free A exciton (FEA) and by the neutral-donor-bound exciton (D0X) transitions. The position of FEA indicat es that the GaN layers are under tension. We observe that the recombination lifetime for the FEA is about 40-50 ps in all the layers, whereas the reco mbination time for the D0X varies for different samples. We found that the recombination lifetimes for D0X have a clear dependence on the position of FEA; i.e. the recombination lifetime increases with decreasing strain in th e layers. The results can be explained in terms of the character of the hol e states involved in the donor-bound exciton recombination.