Reliable anatase-titania nanoclusters functionalized GaN sensor devices for UV assisted NO 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) has been demonstrated by functionalizing gallium nitride (GaN) submicron wire with titania (TiO) nanoclusters. The two-terminal GaN/TiO 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 sensor was able to detect NO 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 against other interfering gases, such as ethanol (CHOH), ammonia (NH), sulfur dioxide (SO), methane (CH) and carbon dioxide (CO). Furthermore, principal component analysis has been performed to address the cross-sensitive nature of TiO. 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. Finally, interaction of NO gas molecules with the GaN/TiO sensor has been modeled and explained under the light of energy band diagram. The photoinduced oxygen desorption and subsequent charge transfer between TiO nanoclusters and NO molecules modulate the depletion region width within the GaN, thus contributing to a high performance NO gas sensing.