Research Article Ultrafast Probe of Carrier Diffusion and Nongeminate Processes in a Single CdSSe Nanowire Peter S. Eldridge, 1 Jolie C. Blake, 1 and Lars Gundlach 1,2 1 Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA 2 Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA Correspondence should be addressed to Lars Gundlach; larsg@udel.edu Received 31 October 2014; Accepted 19 February 2015 Academic Editor: Pedro D. Vaz Copyright © 2015 Peter S. Eldridge et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We measure ultrafast carrier dynamics in a single CdSSe nanowire at diferent excitation luences using an ultrafast Kerr-gated microscope. he time-resolved emission exhibits a dependence on excitation luence, with the onset of the emission varying on the picosecond time scale with increasing laser power. By itting the emission to a model for ampliied spontaneous emission (ASE), we are able to extract the nonradiative carrier recombination lifetime and nongeminate recombination constant. he extracted nongeminate recombination constant suggests that our measurement technique allows the access to the nondifusion limited recombination regime in nanowires with low carrier mobility. 1. Introduction With the vast progress in chemical synthesis of semicon- ductor nanostructures, there is a need to understand carrier transport in the plethora of available morphologies. Ternary alloy semiconductors, such as CdS x Se 1−x , are particularly intriguing for both scientiic studies and technological appli- cations. As the bandgap of CdS x Se 1−x can span the entire visible spectrum through alloy variation, it has potential applications as a light harvester in solar cells and a tunable wavelength source in semiconductor nanolasers [1–3]. he high defect density inherent to ternary alloys in comparison to their binary counterparts has led to reports of increased density of nonradiative recombination centres (Shockley- Read-Hall states) in AlGaAs [4] while exciton localisation in CdSSe nanobelts has been attributed to bandgap variation along the nanobelt [5]. As compositional variations can occur on the single particle level for CdSSe, compositional and morphological variations within an ensemble of particles complicate interpretation of ensemble averaged measure- ments, making the need for single particle measurements all the more pertinent for carrier dynamics studies. Here, we investigate early luminescence dynamics in a single CdSSe nanowire at diferent excitation intensities using a Kerr-gated ultrafast microscope [6]. he short- lived, nonlinear emission is assigned to ampliied sponta- neous emission (ASE). Fitting the emission to a nonlinear model allows us to extract information on the impurity mediated nonradiative carrier lifetime and the nongeminate recombination coeicient. he nongeminate recombination coeicient demonstrates that our measurement technique allows the access to carrier dynamics on short enough timescales and high enough densities that recombination is not difusion-controlled. his therefore shows that the majority of the excited carriers recombine before signiicant impurity, phonon, or defect scattering. 2. Materials and Methods CdSSe nanowires were grown by the vapour liquid solid (VLS) method detailed in the previously published work [7, 8]. his technique is known to produce single crystalline nanowires with wurtzite phase and ensemble XRD measure- ments (not shown) are in agreement with the nanowires Hindawi Publishing Corporation Journal of Spectroscopy Volume 2015, Article ID 574754, 6 pages http://dx.doi.org/10.1155/2015/574754