Thermodynamic Sensing Mechanisms of AlGaN-Based Metal/Reactive Insulator/Semiconductor-Type Hydrogen Sensors

Thermodynamic sensing mechanisms of Pt/reactive insulator/AlGaN hydrogen sensors were studied. The reactive insulator layer of mixed
$\hbox{Ga}_{2} \hbox{O} _{3}$
and
$\hbox{Al}_{2} \hbox{O} _{3}$
was grown directly from the AlGaN layer using a photoelectrochemical oxidation method. The current of the hydrogen sensors exhibited considerable response under forward bias in a hydrogen ambient at the temperature range between 350 K and 550 K. Based on the steady-state analysis, the adsorption enthalpy of
$-11.64~\hbox{kJ}/\hbox{mol}$
for hydrogen adsorbed at the interface and in the reactive insulator layer was obtained. Because the kinetic reaction was an exothermic action, the hydrogen response decreased with an increase of operating temperatures. From the thermodynamic kinetic analysis of transient responses, the activation energy was 3.57 kJ/mol. The Pt/reactive insulator/AlGaN hydrogen sensors exhibited high performance at various temperatures.