Abstract
Low concentration (<50 ppm) sensing of NH3 over a wide temperature range of 30-275°C using AlGaN/GaN high electron mobility transistor (HEMT) based gas sensors with Pt, Pd and Ag functionalisation layers has been studied. Pt/AlGaN/GaN HEMT exhibited the sensitivity of 0.51% and 0.83% for 50 ppm NH3 at 30°C and 275°C, respectively. The current decreased when the sensor was exposed to different concentrations of NH3 at 30°C while it increased above 200°C. The sensing mechanisms corresponding to the temperature dependent response of NH3 have been explained. The sensor with the Pd functionalisation layer exhibited higher sensitivity at 275°C as compared to Pt and Ag sensors due to higher hydrogen affinity of Pd. The sensor with the Ag functionalisation layer demonstrated faster response and recovery times (<3 min) as compared to other sensors using Pt and Pd.
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