High temperature hydrogen sensors based on AlGaN/GaN heterostructures

Schottky diodes on AlGaN/GaN heterostructures with Pt, IrPt, and PdAg catalytic metals are fabricated and characterized from 200°C to 800°C for H₂ sensing. Over this large range of temperatures, the forward current of all the diodes increases with exposure to H₂ gas, which is attributed to Schottky barrier height reduction caused by hydrogen absorption in the catalytic metals. The results indicate that AlGaN/GaN heterostructure Schottky diodes are capable of high temperature H₂ sensor operation up to 800°C. As temperature increases, the hydrogen detection sensitivity of Pt and IrPt diodes improves because H₂ dissociation is more effective. However, the sensitivity of PdAg diodes degrades with an increase of temperature due to thermal instability of PdAg. At a range of temperatures from 200°C to 300°C, PdAg diodes exhibit significant higher sensitivity compared with Pt and IrPt diodes. Above 400°C, IrPt and Pt diodes show higher sensitivity.