In this paper, a method to extend the detection range of hydrogen sulfide (H2S) gas sensor is demonstrated. The sensor is based on AlGaN/GaN high electron mobility transistors (HEMTs) with Pt gate. It is observed that the as-fabricated devices exhibited sensing signal saturation at 30 ppm H2S exposure in dry air. A pre-treatment using H2 pulses in dry air ambient at 250 ºC was applied to extend the detection range of the sensor. The H2 treated H2S gas sensor was able to detect a higher H2S concentration up to 90 ppm at 250 ºC without complete saturation.

Wide bandgap gallium nitride material has highly favorable electronic properties for next generation power and high frequency electronic devices. A less widely studied application is highly miniaturized chemical and gas sensors capable of operating in harsh environment conditions. In this work we present our recent developments on design, fabrication and testing of AlGaN/GaN high electron mobility transistor (HEMT) based sensors for detection of various gases. First, the method of as-fabricated device baseline value stabilization is demonstrated. Secondly, the impact of sensor design is discussed with the emphasis on gate electrode geometry optimizations to enhance sensing performance. Then we present the sensing characteristics of Pt-HEMTs towards H2S and compare them to H2 and NO2. Finally we demonstrate recent results of NO2 detection with Ti/Au based HEMT sensors, which are superior to those using Pt based devices.