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

Abstract

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.