Size-Dependent Exciton Recombination Dynamics in Single CdS Nanowires beyond the Quantum Confinement Regime

A deep understanding of the size, surface trapping, and scattering effects on the recombination dynamics of CdS nanowires (NWs) is a key step for the design of on-demand CdS-based nanodevices. However, it is often very difficult to differentiate these intertwined effects in the NW system. In this article, we present a comprehensive study on the size-dependent exciton recombination dynamics of high-quality CdS NWs (with diameters from 80 to 315 nm) using temperature-dependent and time-resolved photoluminescence (TRPL) spectroscopy in a bid to distinguish the contributions of size and surface effects. TRPL measurements revealed two distinct processes that dominate the band edge recombination dynamics-a fast decay process (tau(1)) originating from the near-surface recombination and a slower decay process (tau(2)) arising from the intrinsic free exciton A decay. With increasing NW diameters, tau(1) increases from similar to 0.10 to similar to 0.42 ns due to the decreasing surface-to-volume ratio of the NWs, whereas tau(2) increases from similar to 0.36 to similar to 1.21 ns due to decreased surface scattering in the thicker NWs-as validated by the surface passivation and TRPL studies. Our findings have discerned the interplay between size and surface effects and advanced the understanding of size-dependent optoelectronic properties of one-dimensional semiconductor nanostructures for applications in surface- and size-related nanoscale devices.