Elucidation of the unsymmetrical effect on the piezoelectric and semiconducting properties of Cd-doped 1D-ZnO nanorods

Abstract

Herein, we report the unsymmetric effect on the functional (piezoelectric and semiconducting) properties of cadmium-doped 1D-ZnO nanorods (NRs), which have a higher ionic radius (0.97 Å). The growth of Cd-ZnO NRs, which have a hexagonal wurtzite structure without any secondary CdO phases, along the c-axis was confirmed by the XRD patterns, and oxidation states observed from XPS analyses verified the diffusion of Cd²⁺ into ZnO NRs. A one-fold reduction in the piezoelectric properties was determined by the fabrication of a nanogenerator, and enhancement in the semiconducting properties was studied using an Ag/Cd-ZnO NRs/Ag device with various wt% of Cd doped into the ZnO NRs lattice. Cd-ZnO NRs improve the photogenerated charge carriers (I_ph ∼ 330 μA) compared to pure ZnO NRs (I_ph ∼ 213 μA), obtained at a bias voltage of 10 V, a wavelength of 365 nm and a light intensity of 8 mW cm⁻². The Cd-ZnO NRs (1 wt%) based sensor shows good photoresponse with a detectivity (D*) limit of 1 × 10¹¹ cm H^1/2 W⁻¹ compared to that of pure ZnO NRs (D* = 5.4 × 10¹⁰ cm H^1/2 W⁻¹). We also demonstrate a self-powered UV sensor (SPUV-S) connected parallel to the ZnO NRs based nanogenerator as an independent power source to drive the Cd-ZnO NRs UV sensor. The low-temperature hydrothermal synthesis of Cd-ZnO NRs is simple, cost-effective, and scalable for industrial applications.