Investigation of High-Sensitivity NO(2) Gas Sensors with Ga(2)O(3) Nanorod Sensing Membrane Grown by Hydrothermal Synthesis Method

In this work, Ga(2)O(3) nanorods were converted from GaOOH nanorods grown using the hydrothermal synthesis method as the sensing membranes of NO(2) 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(NO(3))(3)·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 SnO(2) seed layer and the Ga(NO(3))(3)·9H(2)O/HMT concentration of 12 mM/10 mM. In addition, the GaOOH nanorods were converted to Ga(2)O(3) nanorods by thermal annealing in a pure N(2) ambient atmosphere for 2 h at various temperatures of 300 °C, 400 °C, and 500 °C, respectively. Compared with the Ga(2)O(3) nanorod sensing membranes annealed at 300 °C and 500 °C, the NO(2) gas sensors using the 400 °C-annealed Ga(2)O(3) 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 NO(2) concentration of 10 ppm. The low NO(2) concentration of 100 ppb could be detected by the Ga(2)O(3) nanorod-structured NO(2) gas sensors and the achieved responsivity was 34.2%.