Radiative Recombination and Ultra-long Exciton Photoluminescence Lifetime in GaN Freestanding Film via Two-photon Excitation

We have measured the photoluminescence (PL) lifetime of a freestanding GaN film using one-photon and two-photon excitation to demonstrate the dramatic difference in exciton recombination dynamics at the surface and in the bulk. An ultra-long exciton PL lifetime of 17.2 ns at 295 K is observed from a GaN freestanding film using two-photon excitation, whereas less than 100 ps lifetime is observed for one-photon excitation, suggesting that nonradiative processes from surface defects account for the short PL lifetime measured. A monotonic increase in two-photon excited PL lifetime with increasing temperature shows good agreement with the theoretical predictions, indicating that radiative recombination dominates for bulk excited state relaxation processes. © 2007 American Institute of Physics