Pt/GaN based Schottky diodes for gas sensing applications

The performance of Pt/GaN Schottky diodes with different thickness of the catalytic metal were investigated as hydrogen gas detectors. The area as well as the thickness of the Pt were varied between 250 μm² and 1000 μm², 8 and 40 nm, respectively. The sensitivity to hydrogen gas was investigated in dependence on the active area, the Pt thickness and the operating temperature for 1 vol% hydrogen in synthetic air. We observed a significant increase of the sensitivity and a decrease of the response and recovery times by increasing the temperature of operation to about 350°C and by decreasing the Pt thickness down to 8 nm. Electron microscopy of the microstructure showed that the thinner platinum had a higher grain boundary density. The increase in sensitivity with decreasing Pt thickness points to the dissociation of molecular hydrogen on the surface, the diffusion of atomic hydrogen along the platinum grain boundaries, and the adsorption of hydrogen at the Pt/GaN interface as a possible mechanism of sensing hydrogen by Schottky diodes.