Photoactivated In2O3-GaN Gas Sensors for Monitoring NO2 with High Sensitivity and Ultralow Operating Power at Room Temperature

Photoactivated gallium nitride (GaN) nanowire-based gas sensors, functionalized with either bare In2O3 or In2O3 coated with a nanolayer of evaporated Au (Au/In2O3), were designed and fabricated for high-sensitivity sensing of NO2 and low-power operation. The sensors were tested at room temperature under 265 nm and 365 nm ultraviolet illumination at several power levels and in relative humidity ranging from over 20% to 80%. Under all conditions, photoconductivity was lower in the Au/In2O3-functionalized sensors compared to that of sensors functionalized with bare In2O3. However, when tested in the presence of NO2, the Au/In2O3 sensors consistently outperformed In2O3 sensors, the measured sensitivity being greater at 265 nm compared to 365 nm. The results show significant power reduction (×12) when photoactivating at (265 nm, 5 mW) compared to (365 nm, 60 mW). Maximum sensitivities of 27% and 42% were demonstrated with the Au/In2O3 sensors under illumination at (265 nm, 5 mW) for 1 ppm and 10 ppm concentration, respectively.