Comprehensive study of Pd/GaN metal–semiconductor–metal hydrogen sensors with symmetrically bi-directional sensing performance

This paper reports on a new Pd/GaN hydrogen sensor with two multi-finger Schottky contacts (named metal–semiconductor–metal (MSM) hydrogen sensor). Effects of hydrogen absorption on the MSM sensor are investigated. In addition to comparisons of sensing mechanism between metal–semiconductor (MS) and MSM sensors, related current–voltage characteristics, sensor responses, Schottky barrier height variations, response transients, and switching behaviors are included. Experimentally, symmetrically bi-directional sensing performances are obtained in the newly designed MSM sensor, resulting in both widespread forward- and reverse-voltage-operating regimes. When the MSM sensor is measured in a 1080 ppm H2/N2 ambience, the voltage-independent response and barrier-height variation obtained are 51 and 102 mV, respectively. Furthermore, the measured response time is as short as 38 ± 2 s. Together with good switching behaviors, the MSM sensor studied is a promising candidate as a high-performance hydrogen sensor being easily integrated with other devices.