Reliable anatase-titania nanoclusters functionalized GaN sensor devices for UV assisted NO ₂ gas-sensing in ppb level

Internet of Things applications require ultra-low power, integrable into electronic circuits and mini-sized chemical sensors for automated remote air quality monitoring system. In this work, a highly sensitive and selective detection of nitrogen dioxide (NO 2 ) has been demonstrated by functionalizing gallium nitride (GaN) submicron wire with titania (TiO 2 ) nanoclusters. The two-terminal GaN / TiO 2 sensor device was fabricated by top-down approach. The photo-enabled sensing makes it possible to operate this sensor at room-temperature, resulting in a significant reduction in operating power. The GaN / TiO 2 sensor was able to detect NO 2 concentrations as low as 10 ppb in air at room temperature (20 °C) with a quick response-recovery process. The sensor was found highly selective toward NO 2 against other interfering gases, such as ethanol (C 2 H 5 OH), ammonia (NH 3 ), sulfur dioxide (SO 2 ), methane (CH 4 ) and carbon dioxide (CO 2 ). Furthermore, principal component analysis has been performed to address the cross-sensitive nature of TiO 2 . The sensor device exhibited excellent long-term stability at room temperature and humidity and was quite stable and reliable at various environmental conditions. Continuous exposure of the device to siloxane for a one-month period has shown a very small degradation in sensor response to NO 2 . Finally, interaction of NO 2 gas molecules with the GaN / TiO 2 sensor has been modeled and explained under the light of energy band diagram. The photoinduced oxygen desorption and subsequent charge transfer between TiO 2 nanoclusters and NO 2 molecules modulate the depletion region width within the GaN, thus contributing to a high performance NO 2 gas sensing.