Development of ZnO nanorods/Si heterojunction photodetectors for high responsivity across a wide spectral range via plasmonic Ag nanoparticles

ZnO, an<i>intrinsic n-type</i>semiconductor, has attracted considerable attention in optoelectronics. However, its application in broadband photoresponsivity is limited by its wide band gap. In this study, polyol-synthesized silver nanoparticles (Ag NPs) with controlled size were used to enhance the performance of n-type ZnO nanorods (NRs) and p-type Si heterojunction (ZnO NRs/Si) photodetectors (PDs). Photoluminescence spectra confirmed that the broadband emissions of the ZnO NRs, originating from crystal defects, efficiently overlapped with the localized surface plasmon resonance of the Ag NPs. Under illumination and a reverse bias voltage of 4.0 V, the photocurrent (<i>I</i>_ph) of the detectors increased from 2.2 × 10^-5-2.39 × 10^-4after Ag NP decoration of the ZnO NRs. The<i>I</i>_ph/<i>I</i>_darkratio of the pristine ZnO NRs/Si device was determined to be 5.5, which increased to 100 in the presence of the Ag NPs. The plasmonic-enhanced PD (Ag-decorated ZnO NRs/Si) exhibited broader and stronger spectral photoresponsivity from the UV-Vis to the NIR range. Responsivity and detectivity values of 0.39 A W^-1and 2 × 10^-11cm.Hz^1/2W^-1at 372 nm, and 0.42 A W^-1and 4.2 × 10^-11cm.Hz^1/2W^-1at 420 nm, were observed for this device. Overall, plasmon-enhanced ZnO NRs/Si PDs demonstrated enhanced broadband UV-Vis-NIR spectral response with high photocurrent values.