Hydrogen-sensitive GaN Schottky diodes

Pt/n-GaN and Pd/n-GaN Schottky diodes were characterized for their response to hydrogen as a function of measurement temperature. Even at modest temperatures (80-140 °C), an 80 μm diameter diode shows a large increase (≥0.5 mA) in forward current upon introduction of ∼10% H₂ into a N₂ ambient. The change in current increases with measurement temperature and begins essentially immediately upon introduction of the hydrogen. Cycling the ambient from N₂ to 10% H₂ in N₂ and back to N₂ produces reproducible cycling of the forward current at fixed forward bias. The decrease in barrier height of Pt on GaN was 50 mV at 25 °C and 70 mV at 150 °C upon introduction of H₂ into the ambient, with lower values for Pd. At high temperature, the time response of the sensors appears to be controlled by hydrogen diffusion to the metal/GaN interface, while at low temperatures (<100 °C), dissociation of the gas appears to be the rate-determining step.