Size-dependent exciton recombination dynamics in single CdS nanowires beyond the quantum confinement regime

Abstract

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 (τ1) originating from the near-surface recombination and a slower decay process (τ2) arising from the intrinsic free exciton A decay. With increasing NW diameters, τ1 increases from 0.10 to 0.42 ns due to the decreasing surface-to-volume ratio of the NWs, whereas τ2 increases from 0.36 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.