Oxygen Gas Sensing Properties of Metal/Nb:SrTiO 3 Mechanical Contact

An anomalous surface-barrier property of platinum on single-crystal Nb:SrTiO 3 was investigated. The metal-semiconductor mechanical contact shows a normal rectifying current-voltage characteristic in air, but a nonrectifying feature in vacuum due to the adsorption/desorption of oxygen gas at the contact interface. Considering that the depletion layer in a heavily doped semiconductor is usually very thin, we tried to interpret this phenomenon from the viewpoint of the tunnelling effect on a Schottky barrier model with the adsorbed oxygen gas taken into account. The experimental result that the depletion layer thickness decreased as oxygen gas was gradually desorbed supports the proposed barrier model. This type of diode seems promising for use in a device for detecting oxygen gas at low temperatures.