Authors: Yongchun Zhong Kam Sing Wong Weili Zhang D C Look
Publish Date: 2007/04/13
Volume: 18, Issue: 1, Pages: 453-457
Abstract
We have measured the photoluminescence PL lifetime of a freestanding GaN film using one and twophoton excitations to demonstrate the dramatic difference in exciton recombination dynamics at the surface and in the bulk An ultralong exciton PL lifetime of 172 ns at 295 K is observed from a GaN freestanding film using twophoton excitation whereas less than 100 ps lifetime is observed for onephoton excitation suggesting that nonradiative processes from surface defects account for the short PL lifetime measured The room temperature exciton lifetime of 172 ns is the longest ever reported for GaN film A monotonic increase in twophoton 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 processesThe experiments were performed in the Joyce M Kuok Laser and Photonic Laboratory at the Hong Kong University of Science and Technology The authors would like to thank S S Park of Samsung for supply the GaN sample DCL was supported by AFOSR Grant F496200310197 and Air Force Contract F3361500C5402 KSW acknowledges the support of this work by Research Grants Council of Hong Kong Project No 604405
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