Response of nanostructured Pt/GaN Schottky barriers to carbon monoxide

The interaction between CO and Pt can potentially be used to generate gas-sensing signals at Pt/GaN interfaces. Here, the CO response is compared to that generated by H2, and its dependence on Pt morphology is investigated. Similar to the H2 response, exposure to CO reduces the resistance of Pt/GaN structures. On dense, pinhole-free Pt films, the magnitude of the CO resistance change increases with decreasing Pt film thickness and with increasing Pt surface area, whereas discontinuous Pt films exhibit an increasing resistance change with film thickness. These results indicate that CO sensing is greatly affected by the Pt film morphology and the interaction between adsorbed CO and the charged Pt/GaN interface. A model is proposed in which surface charge induced by the adsorption of CO on Pt affects the interfacial polarization at the Pt/GaN interface. Simulations corroborate the proposed model. Transient resistance behavior is correlated with pre-adsorbed O species on the Pt surface and CO oxidation at atmospheric pressure, leading to a decrease of the Schottky barrier height and the resistance of the structure.