Elucidation of efficiency droop mechanism in nitride semiconductorbased light emitting devices by scanning near field optical microscopy

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To clarify main factor of efficiency droop phenomena, we performed PL and time-resolved PL measurement using a scanning near field optical microscope. For the blue sample , although carriers overflow from localization centers under the high carrier density, the capture to nonradiative recombination centers (NRCs) hardly takes place because the potential barriers are formed around the NRCs. On the other hand, for the green sample, the increase of carrier density enhances the diffusion from the strong PL domains to the weak ones corresponding to high In composition area, where a large number of NRCs are distributed in association with threading dislocations. Such carrier recombination dynamics was found to be a major mechanism of the efficiency droop in the green sample due to the increase of both carrier lifetime and number of threading dislocations.