Capacitive sensor based on GaN honeycomb nanonetwork for ultrafast and low temperature hydrogen gas detection

Abstract Passive devices are highly desired for the detection of H2 gas due to its high safeness and low energy consumption. In this study, GaN with honeycomb nanonetwork structure (GaN-HN) epitaxially grown on Si wafer by molecular beam epitaxy technique was utilized for the fabrication of capacitive H2 gas sensors, on which 10 nm thick Pd layer was deposited as the sensing electrode. XRD, SEM, and AFM results show that the cubic phase Pd is uniformly coated on the surface of GaN-HN and maintains an interesting structure of honeycomb nanonetwork. It is found that the response time decreases gradually with the increase of the operating temperature and it reaches a steady value ∼3 s at temperatures higher than 50 °C. Ultrafast response time of 1.3 s towards 1000 ppm H2 was observed for the Pd-GaN/Si capacitive sensor operated at the temperature of 70 °C. The low limit of detection (LOD) is also evaluated by experiment and IUPAC definition, 500 ppb and 440 ppb, respectively. Moreover, the capacitive sensor exhibits ignorable response to CH4, NO2 and common VOCs gases. The long-term stability and humidity effect on H2 gas detection were also studied. Schottky junction capacitance of Pd/GaN might be dominated by the hydrogen dipole layer. The proposed Pd-GaN/Si capacitive sensor investigated here exhibits ultrafast response speed, low operating temperature, high selectivity and stability, making it attractive for applications in timely H2 leakage detection.