Photoelectrical and thermal sensing measurement of spin coated ZnO and ZnO-RGO thin film

Abstract

This research reported the synthesis of ZnO and ZnO-RGO as well as their photo sensing and thermal sensing properties. This is with a view to reducing the electron hole recombination in ZnO and improving the sensing properties. ZnO and ZnO-RGO were synthesized by the hydrothermal method and spin coated on glass to obtain the thin film. The SEM micrograph of ZnO-RGO showed mini ZnO nanorods decorated and formed on the RGO sheet. The adherence of the nanorods were improved as the loading mass of GO increased in the hybrid. Though ZnO and ZnO-RGO had comparable thermal sensing response of 2.8 and 3.1 respectively at 573 K, ZnO-RGO showed improved electrical conductivity as temperature increased. ZnO sensors logged a negative temperature coefficient (NTC) value of 0.00236/K and a sensitivity value of 0.0139 Ω/K while ZnO-RGO had a NTC value of 0.00248/K (which is higher than values obtained in literature for silver and palladium based graphene hybrids) and a sensitivity value of 0.00769 Ω/K. A value of 0.0561eV was obtained for the activation energy of ZnO sensor while 0.0615eV was obtained for ZnO-RGO. For the photo sensing, incorporation of GO into ZnO decreased the band gap at peak wavelength of ZnO-RGO to 2.48 eV from 3.1 eV for ZnO and improved the photoconductivity to the order of 106 Ω. This research has confirmed that incorporating GO in ZnO increased the activation energy of ZnO-RGO thermistor, and consequently increased the thermal sensing response thus resulting in improved thermal and photo sensing properties of ZnO. With an improved NTC, sensor response and activation energy, ZnO-RGO can replace Pd based RGO and Ag nanoparticles based RGO as thermistors.