Field effect hydrogen sensor device with simple structure based on GaN

A field effect hydrogen-sensing device with a simple structure based on GaN was fabricated by means of a simple process analogous to the fabrication process of a Schottky diode. Current–voltage characteristics between the source and the drain electrodes were studied, and response to hydrogen was measured under floating gate condition. The device has a wide detection region from a few ppm to 1% hydrogen. When oxygen and hydrogen are present at higher hydrogen concentrations, a large change in voltage occurs with an increase in oxygen concentration. The effect of gate length was investigated. When a longer gate electrode was employed, a larger change in voltage between the source and drain electrodes VDS was obtained. The sensing mechanism is discussed by reference to the channel resistance change model, and the model explains the experimental results fully. The influence of gate bias was also studied, and the results show that when the gate was connected to the source and biased, a larger change in voltage VDS was obtained.