An interesting Pt/AlGaN/GaN Schottky-type ammonia gas sensor is fabricated and studied. Both the steady-and transient-state behaviors of ammonia adsorption reactions are investigated. At 150 °C, significant ammonia detection is observed under a low ammonia concentration of 35-ppm NH3/air. Moreover, a high ammonia sensing response of 18300% and the large Schottky barrier variation ratio Δbb/air of 13.8% are observed upon exposure to a 1% NH3/air gas at 150 °C. The presence of dipoles at the metalsemiconductor interface leads to a lowering effect of Schottky barrier height and a larger current. In addition, based on thermodynamics, in contrast with a hydrogen adsorption reaction, the ammonia adsorption reaction is an endothermic reaction. Consequently, the studied NH3 sensor structure provides the promise to integrate high-performance AlGaN/GaN-based optoelectronic and microwave devices on a single chip.
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