Modeling and experimental study on sensing response of an AlGaN/GaN HEMT-based hydrogen sensor

A hydrogen sensor based on an AlGaN/GaN high electron mobility transistor (HEMT) structure with a Pt-decorated gate was investigated in this paper. A theoretical model of sensing response was built within the modification of Langmuir isotherm. The sensing characteristics were measured in the gaseous H2/N2 ambience of 2-6216 ppm at different temperatures, and were analyzed by the model. The approximate linear relationship between the sensing response and logarithm of hydrogen concentration in a certain range was revealed. At 130 °C, the device showed response variation of 25.8% upon 10-fold change of hydrogen concentration. Furthermore, the sensing response variations with gate bias and temperature were studied. GaN buffer leakage and gate leakage were taken into account in the model, which would seriously restrict the sensing response especially at high temperatures. At a certain level of leakage current, the sensor had an optimal gate bias as well as an operating temperature at which maximum responses could be obtained. The model was proved effective for sensing response analysis of the device.