Detection of ammonia at low concentrations (0.1–2 ppm) with ZnO nanorod-functionalized AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors with ZnO nanorod functionalized gates were used for detecting NH3 in the concentration range of 0.1–2 ppm balanced with air at ambient temperatures from 25 to 300 °C. A decrease in the high electron mobility transistor drain current was observed for exposure to the NH3-containing ambients, indicating an increase in negative charge at the heterointerface. The detection sensitivity increased monotonically with ammonia concentration at all temperatures, from 0.28% (25 °C) and 3.17% (300 °C) for 0.1 ppm to 1.32% (25 °C) and 13.73% (300 °C) for 2 ppm for a drain–source voltage of 1 V. The latter condition is attractive for low power consumption. The sensitivity was also a function of applied voltage and was generally higher in the linear region of the current–voltage characteristic of the transistor. The activation energy of the sensitivity was 0.09 eV, and the sensors showed no response to O2 (100%), CO2 (10%), CO (0.1%), CH4 (4%), and NO2 (0.05%) under the same detection conditions as used for the NH3. The response was less than 1 s, and recovery times were of order ∼53 s at 25 °C.AlGaN/GaN high electron mobility transistors with ZnO nanorod functionalized gates were used for detecting NH3 in the concentration range of 0.1–2 ppm balanced with air at ambient temperatures from 25 to 300 °C. A decrease in the high electron mobility transistor drain current was observed for exposure to the NH3-containing ambients, indicating an increase in negative charge at the heterointerface. The detection sensitivity increased monotonically with ammonia concentration at all temperatures, from 0.28% (25 °C) and 3.17% (300 °C) for 0.1 ppm to 1.32% (25 °C) and 13.73% (300 °C) for 2 ppm for a drain–source voltage of 1 V. The latter condition is attractive for low power consumption. The sensitivity was also a function of applied voltage and was generally higher in the linear region of the current–voltage characteristic of the transistor. The activation energy of the sensitivity was 0.09 eV, and the sensors showed no response to O2 (100%), CO2 (10%), CO (0.1%), CH4 (4%), and NO2 (0.05%) under the same de...