Reverse bias voltage dependent hydrogen sensing properties on Au–TiO2 nanotubes Schottky barrier diodes

•Reverse bias voltage on Au-TiO2 nanotubes SBD H2 sensor was first reported.•Sensitivity reaches a balanced value by a certain voltage.•SBD barrier height and ideal factor can be altered by bias voltage.

Titania (TiO2) nanotubes array is a new kind of hydrogen (H2) sensing materials due to its unique structure, the device physics on the metal-semiconductor contact, however, is still scarce so far. In this present work, TiO2 nanotubes with diameter of 140 nm and tubular thickness of 25 nm were grown on titanium substrate using anodic oxidation in an aqueous ethylene glycol electrolyte containing 0.5 wt% NH4F. The influence of reverse bias voltage on the H2 sensing properties of such geometric TiO2 nanotubes based Schottky sensors was investigated. It was found that the contacts between gold (Au) and TiO2 nanotubes array demonstrated typical rectifying characteristic, and the barrier height decreased with the increase of hydrogen concentration. The signals of such device increased almost linearly up to a local-maximum by increasing the applied reverse bias voltage, while little improvement on gas sensitivity was observed with further increase of the applied reverse bias voltage. Based on the analysis of impedance and device characteristic, we supposed that the reverse bias voltage dependent hydrogen sensing was mainly attributed to the change of the Schottky barrier height which was intrinsically determined by the Au–TiO2 configuration, in which the thickness of the tube wall and the contact interface may govern the device sensing characteristic.

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