Hydrogen sensors based on Pt-AlGaN/AlN/GaN schottky diode

Pt/AlGaN/AlN/GaN Schottky diodes have been fabricated and characterized for H2 sensing. Platinum (Pt) with a thickness of 20nm was evaporated on the sample to form the Schottky contact. The ohmic contact, formed by evaporated Ti/Al/Ni/Au metals, was subsequently annealed by a rapid thermal treatment at 860°C for 30 s in N2 ambience. Both the forward and reverse current of the device increased greatly when exposed to H2 gas. The sensor’s responses under different hydrogen concentrations from 500ppm to 10% H2 in N2 at 300K were investigated. A shift of 0.45V at 297K is obtained at a fixed forward current for switching from N2 to 10% H2 in N2. Time response of the sensor at a fixed bias of 0.5 V was also measured. The turn-on response of the device was rapid, while the recovery of the sensor at N2 atmosphere was rather slow. But it recovered quickly when the device was exposed to the air. The decrease in the barrier height of the diode was calculated to be about 160meV upon introduction of 10% H2 into the ambient. The sensitivity of the sensor is also calculated. Some thermodynamics analyses have been done according to the Langmuir isotherm equation.