Dual functionality of surface plasmon resonance and barrier layer on the photosensing and optical nonlinearity of ZnO nanorod arrays

Abstract

The dual functionality of plasmonic light harvesting and barrier spacing between Au nanoparticles (NPs) and ZnO nanorod arrays (NRsA) are spotlighted to investigate their impact on the photoconversion and optical nonlinearity in the present study. The passivating Al₂O₃ barrier layer permits high-energy hot electron tunneling and injection from Au to the ZnO NRsA. The structural, vibrational, morphological/elemental, and optical properties of ZnO NRsA/a-Al₂O₃/Au were characterized by X-ray diffraction (XRD), Raman scattering, field emission scanning electron microscopy/energy dispersive X-ray spectroscopy (FE-SEM/EDX), and ultraviolet-visible-near IR (UV-Vis-near IR) absorption, respectively. The optoelectronic and nonlinear optical properties were analyzed by current–voltage measurement and z-scan tests under red laser (655 nm) irradiation, respectively. To highlight the effect of surface plasmon charge transport-based photosensing and photo-harvesting, the irradiated light source is selected to have a photon energy lower than the ZnO bandgap energy and detuning from LSPR. The transfer of photo-induced hot electrons from the Au NPs localized surface plasmon resonance (LSPR) to the ZnO NRsA translates into photocurrent generation in photosensing performance. The reverse saturable absorption process is changed to saturable absorption after intercalating the Al₂O₃ spacing layer into the ZnO NRsA/Au interface. The typical values of the nonlinear refraction index and absorption coefficient are calculated as n₂ = +2.38 × 10⁻⁵ cm² W⁻¹ and β = −0.17 cm W⁻¹ for the sandwiched ZnO NRsA/Al₂O₃/Au heterostructure, respectively. The sandwiched ZnO NRsA/amorphous Al₂O₃/Au heterostructure exhibits strong nonresonant optical nonlinearity, which has an excellent figure of merit for optical switching.