Managing trap states and understanding their role in ultrafast charge-carrier dynamics, particularly at surface and interfaces, remains a major bottleneck preventing further advancements and commercial exploitation of nanowire (NW)-based devices. A key challenge is to selectively map such ultrafast dynamical processes on the surfaces of NWs, a capability so far out of reach of time-resolved laser techniques. Selective mapping of surface dynamics in real space and time can only be achieved by applying four-dimensional scanning ultrafast electron microscopy (4D S-UEM). Charge carrier dynamics are spatially and temporally visualized on the surface of InGaN NW arrays before and after surface passivation with octadecylthiol (ODT). The time-resolved secondary electron images clearly demonstrate that carrier recombination on the NW surface is significantly slowed down after ODT treatment. This observation is fully supported by enhancement of the performance of the light emitting device. Direct observation of surface dynamics provides a profound understanding of the photophysical mechanisms on materials' surfaces and enables the formulation of effective surface trap state management strategies for the next generation of high-performance NW-based optoelectronic devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: J.I.K. and A. A. contributed equally to this work. The work reported here was supported by the King Abdullah University of Science and Technology (KAUST). The authors gratefully acknowledge the funding support from KAUST and King Abdul-Aziz City for Science and Technology TIC (Technology Innovation Center) for Solid-State Lighting at KAUST. T.K.N. and B.S.O. gratefully acknowledge contribution from Prof. Pallab Bhattacharya, University of Michigan, Ann Arbor. T.K.N. and D.P. gratefully acknowledge Rami T. Elafandy (Photonics Laboratory, KAUST) for his effort and assistance in scanning electron microscopy experiments.