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

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)center dot 9H(2)O) 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)center dot 9H(2)O/HMT concentration of 12 mM/10 mM. In addition, the GaOOH nanorods were converted to Ga2O3 nanorods by thermal annealing in a pure N-2 ambient atmosphere for 2 h at various temperatures of 300 degrees C, 400 degrees C, and 500 degrees C, respectively. Compared with the Ga2O3 nanorod sensing membranes annealed at 300 degrees C and 500 degrees C, the NO2 gas sensors using the 400 degrees 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%.

Automated summary

In this study, GaOOH nanorods were grown using the hydrothermal synthesis method and then converted to Ga2O3 nanorods, which were used as the sensing membranes of NO2 gas sensors. The optimal surface-to-volume ratio of the GaOOH nanorods was achieved by controlling the thickness of the seed layer and the concentrations of the hydrothermal precursor. By annealing the GaOOH nanorods at different temperatures, Ga2O3 nanorods were obtained. The gas sensors using the Ga2O3 nanorod sensing membrane annealed at 400°C showed the best performance.