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6 February 2009 Ultrafast carrier dynamics and laser action in ZnO nanowires
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We have examined ultrafast carrier dynamics and light amplification in ZnO nanowires following subpicosecond excitation at room temperature. We performed time- and wavelength-resolved pump-probe transmission and gain measurements on a 'forest' of 100- to 500-nm thick and 20-μm long nanowires, epitaxially grown on a sapphire wafer. Measurements were done using 267-nm pump pulses for direct, but inhomogeneous excitation, and 800-nm pulses to achieve homogeneous excitation via three-photon absorption. At the highest fluences, both for 267-nm and 800-nm pump pulses, a degenerate electron-hole plasma (EHP) is generated with carrier densities of 1025 m-3 or higher. We observed strong amplification of the probe, accompanied by a rapid decay (~ 1.5 ps) of the charge carriers. Below ~ 1025 m-3, the EHP becomes non-degenerate and the decay much slower. A dip in the pump-probe signal was observed, caused by ionization of probe exciton-polaritons by the pump. This effect allows for a measurement of the exciton-polariton dispersion relation and enhanced light-matter interaction in ZnO nanowires.
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Marijn A. M. Versteegh, Ruben E. C. van der Wel, Benjamin J. M. Brenny, Bas Zegers, Wouter Ensing, and Jaap I. Dijkhuis "Ultrafast carrier dynamics and laser action in ZnO nanowires", Proc. SPIE 7214, Ultrafast Phenomena in Semiconductors and Nanostructure Materials XIII, 721413 (6 February 2009);

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