Large defect-induced sub-bandgap photoresponse in semiconductor nanowires viawaveguiding excitation

Abstract

A large defect-induced sub-bandgap photoresponse over a broad spectral range isobserved in semiconductor single nanowires via optical waveguiding excitation. Usingan evanescent coupling technique, the excitation sub-bandgap light is efficientlytransferred from a silica fiber taper into a CdS single nanowire (bandgap ∼ 2.46 eV), and is tightly confined and guided through the whole length of thenanowire, which significantly enhances the light–defect interaction comparedwith the conventional irradiation excitation scheme. Under 593 nm wavelength (∼2.09 eV)waveguiding excitation with an input power of 10 pW level at room temperature, a 350 nm diameter150 µm-length CdS nanowire shows a responsivity of250 A W − 1, offering a sub-bandgap photosensitivity five orders of magnitude larger than by irradiationexcitation. These results may open opportunities for noninvasive characterization of defectstates in semiconductor nanowires, as well as for enabling novel sub-bandgap nanowiredevices.