Detection of C₂H₄ using wide-bandgap semiconductor sensors: AlGaN/GaN MOS diodes and bulk ZnO schottky rectifiers

The characteristics of Sc₂O₃/AlGaN/GaN metal-oxide semiconductor (MOS) diodes and Pt/ZnO Schottky diodes as detectors of C ₂H₄ are reported. At 25°C, a change in forward current of ∼40 μA at a bias of 2.5 V was obtained in response to a change in ambient from pure N₂ to 10% C₂H₄/90% N ₂. The current changes are almost linearly proportional to the testing temperature and reach around 400 μA at 400°C. The mechanism of the change in forward gate current appears to be formation of a dipole layer at the oxide/AlGaN interface that screens some of the piezo-induced channel charge at the AlGaN/GaN interface. The ZnO diodes show no detectable change in current when exposed to ethylene at 25°C but exhibit large changes (up to 10 mA) at higher temperatures. In these diodes the detection mechanism appears to also involve introduction of hydrogen donors into the near-surface region of the ZnO, increasing the effective doping level under the rectifying contact.