Hydrogen gas sensing performance of GaN nanowires-based sensor at low operating temperature

In this work, the effect of NH3 gas flow rate on the growth of GaN nanostructures deposited on c-plane Al2O3 substrate by chemical vapor deposition, was examined. Field effect scanning electron microscopy images showed that the morphology of GaN presented different shapes of nanostructures depending on NH3 gas flow rate, starting with thin film for low flow rate to nanowires then microstructures. Structural analysis by X-ray diffraction showed that GaN reveals a high-crystalline nature with wurtzite hexagonal structure. Raman spectroscopy indicates a good crystallinity of the prepared nanostructures with the presence of defects within the crystal lattice. For H-2 gas sensing tests, the current responses between the "on" and "off" states of H-2 gas were measured when the sensors are exposed to ultra low H-2 concentration levels in the range of 7-100 ppm at working temperature ranging from room temperature up to 75 degrees C. The sensor based on GaN-nanowires is found to be the most active for H2 sensing, with higher response value; 17 and 127%, for 7 and 100 ppm, respectively at room temperature. These values are much higher than the values reported in the literature. Additionally, the response was found to increase with increasing operating temperature. The obtained results clearly indicated that both morphology and high surfaceto-volume ratio of one-dimensional nanostructures are of the most influential parameters to improve sensing properties of a gas sensor. (C) 2014 Elsevier B.V. All rights reserved.