Thermodynamic and Kinetic Analysis of Hydrogen Sensing in Pt/AlGaN/GaN Schottky Diodes at High Temperatures

Schottky diodes on AlGaN/GaN heterostructures with Pt catalytic metal are fabricated and characterized for hydrogen sensing at a wide range of temperature and hydrogen concentration. The thermodynamic and kinetic processes of hydrogen adsorption/desorption at Pt/AlGaN are analyzed based on their steady and transient state sensing characteristics. The devices have great hydrogen detection capability even at sub-ppm level reliably at temperatures up to 800. Both forward and reverse currents of Schottky diodes increase with exposure to containing ambient, which is attributed to the reduction of Schottky barrier heights resulted by hydrogen absorption at Pt/AlGaN. As temperature increases, the device sensitivity () is improved due to the more effective dissociation, but starts saturating from 600. The coverage of hydrogen at the Pt/AlGaN interface exhibits the same trend as and . The thermodynamic process of hydrogen adsorption in Pt/AlGaN is endothermic with an adsorption enthalpy of 21 . The adsorption time constant shortens as the temperature or the concentration increases. On the other hand, the desorption time constant exhibits opposite trend on the temperature and concentration. The absolute magnitudes of the activation energies for hydrogen adsorption/desertion at Pt/AlGaN increase with the concentration.