Sensing mechanisms of Pt/β-Ga2O3/GaN hydrogen sensor diodes

Pt/β-Ga2O3/GaN (metal/oxide insulator/semiconductor, MIS) hydrogen sensor diode was fabricated with the reactive β-Ga2O3 oxide layer grown directly on the GaN layer using a photoelectrochemical oxidation method. When the MIS hydrogen sensor diode was exposed to dilute hydrogen ambience, the reactive oxide layer not only helped to increase the number of trapping sites for the hydrogen atoms at the Pt/β-Ga2O3 interface, but its associated series resistance could also be decreased as well. Therefore, an increase in current was observed when the sensor diode was exposed to a dilute hydrogen ambience due to the changes in barrier height and series resistance. In addition, the physical and chemical hydrogen sensing mechanisms were investigated. Based on the steady-state analysis at different operating temperatures, the corresponding enthalpies for hydrogen adsorbed at the interface and also in the oxide layer were −8.5 and −7.65 kJ/mol, respectively. A negative enthalpy indicated that the kinetic reaction was exothermic in force. Therefore, the hydrogen response decreased in response to an increase in operating temperature. Furthermore, based on the kinetic analysis, the activation energy value was 1.99 kJ/mol. The small activation energy value indicated that the rapid hydrogen detection could be achieved with the Pt/β-Ga2O3/GaN hydrogen sensor diode.