Surface and Bulk Exciton Recombination Dynamics in GaN Freestanding Films Via One- and Two-Photon Excitations

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We have measured the photoluminescence (PL) lifetime of a freestanding GaN film using one- and two-photon excitations 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. The room temperature exciton lifetime of 17.2 ns is the longest ever reported for GaN film. A monotonic increase in two-photon excited PL lifetime with increasing temperature and the linear dependence of the exciton lifetime with emission wavelength show good agreement with the theoretical predictions, indicating that radiative recombination dominates for bulk excited state relaxation processes.



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