Demonstration of NOx gas sensing for Pd/ZnO/GaN heterojunction diodes

In this study, planar Pd/ZnO/GaN heterojunction diodes (HJDs) are fabricated and their capabilities for NOx (NO and NO2) gas-sensing is evaluated. The fabricated HJDs exhibit good rectifying properties at a high temperature of 250 °C and, in addition, they exhibit obvious current changes even under low-concentration 10 ppm NOx gases and respond to the on/off switching of the gas introduction. It is considered that the sensor action is owing to the electron depletion around the heterojunction caused by the absorbed gas molecules. The current changes reached relatively high values of approximately 1 mA even under exposure to a low-concentration 10 ppm NO2 gas.