Investigation of High-Sensitivity NO2 Gas Sensors with Ga2O3 Nanorod Sensing Membrane Grown by Hydrothermal Synthesis Method

Abstract

In this work, Ga2O3 nanorods were converted from GaOOH nanorods grown using the hydrothermal synthesis method as the sensing membranes of NO2 gas sensors. Since a sensing membrane with a high surface-to-volume ratio is a very important issue for gas sensors, the thickness of the seed layer and the concentrations of the hydrothermal precursor gallium nitrate nonahydrate (Ga(NO3)3·9H2O) and hexamethylenetetramine (HMT) were optimized to achieve a high surface-to-volume ratio in the GaOOH nanorods. The results showed that the largest surface-to-volume ratio of the GaOOH nanorods could be obtained using the 50-nm-thick SnO2 seed layer and the Ga(NO3)3·9H2O/HMT concentration of 12 mM/10 mM. In addition, the GaOOH nanorods were converted to Ga2O3 nanorods by thermal annealing in a pure N2 ambient atmosphere for 2 h at various temperatures of 300 °C, 400 °C, and 500 °C, respectively. Compared with the Ga2O3 nanorod sensing membranes annealed at 300 °C and 500 °C, the NO2 gas sensors using the 400 °C-annealed Ga2O3 nanorod sensing membrane exhibited optimal responsivity of 1184.6%, a response time of 63.6 s, and a recovery time of 135.7 s at a NO2 concentration of 10 ppm. The low NO2 concentration of 100 ppb could be detected by the Ga2O3 nanorod-structured NO2 gas sensors and the achieved responsivity was 34.2%.