Reliable anatase-titania nanoclusters functionalized GaN sensor devices for UV assisted NO₂ gas-sensing in ppb level

Abstract

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 (NO2) has been demonstrated by functionalizing gallium nitride (GaN) submicron wire with titania (TiO2) nanoclusters. The two-terminal GaN/TiO2 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/TiO2 sensor was able to detect NO2 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 NO2 against other interfering gases, such as ethanol (C2H5OH), ammonia (NH3), sulfur dioxide (SO2), methane (CH4) and carbon dioxide (CO2). Furthermore, principal component analysis has been performed to address the cross-sensitive nature of TiO2. 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 NO2. Finally, interaction of NO2 gas molecules with the GaN/TiO2 sensor has been modeled and explained under the light of energy band diagram. The photoinduced oxygen desorption and subsequent charge transfer between TiO2 nanoclusters and NO2 molecules modulate the depletion region width within the GaN, thus contributing to a high performance NO2 gas sensing.

Back-Gate GaN Nanowire-Based FET Device for Enhancing Gas Selectivity at Room Temperature

“…A thin layer (5-10 nm) of TiO 2 nanoclusters was deposited on the nanowire surface by RF magnetron sputtering followed by rapid thermal annealing (RTA). The fabrication details and process flow diagram of the nanowire-based two-terminal device can be found in our previous papers [16][17][18][19]. The C-doped AlGaN buffer layer (~200 nm) formed in between the GaN epilayer and the Si substrate was used as the gate dielectric here to develop a back-gate FET configuration (Figure 1).…”

Photoactivated materials and sensors for NO2 monitoring

“…The literature display numerous synthetic methods to achieve a controlled synthesis of materials with photosensitivity to NO 2 [58,62,67,113,114,118,119,[126][127][128], as noticed in Table 4.…”

Gallium Nitride (GaN) Nanostructures and Their Gas Sensing Properties: A Review

“…The ppb level detection of NO 2 was demonstrated by titania (TiO 2 ) nanoclusters-functionalized GaN submicron wire fabricated by a top-down approach [ 59 ]. The GaN/TiO 2 sensor showed a lowest detection limit of 10 ppb of NO 2 in air at room temperature (20 °C) ( Figure 4 A).…”

“… ( A ) Response fitting curves of the of GaN/TiO 2 NW sensor to NO 2 concentrations ranging from 1 ppb to 500 ppm with UV light and without UV light at room temperature (20 ºC). Figure adapted with permission from [ 59 ], Copyright 2020 IOP Publishing Ltd. ( B ) Schematic representation of the GaN/InGaN NW on Si substrate. Variation of ( C ) O 2 -response, ( D ) NO 2 -response, and ( E ) O 3 -response for GaN/InGaN NW sensor with gas concentration and operating temperature.…”