Sensing properties of gold contact in diode type gas sensors

Gold nanoparticles have been increasingly used as catalytic material since 1997, when their chemical activity was discovered. Here, chemical activity of gold contacts in Au-TiO2-Ti structures is reported and verified experimentally. Diode type Au-TiO2-Ti structures was fabricated by Au deposition on thermally oxidized titanium film. The samples demonstrated I-V characteristics of a typical Schottky diode at operated temperatures up to 400°C, the highest examined temperature. The Schottky barrier height (SBH) of different fabricated Au-TiO2 junctions was measured. It was shown that the measured SBHs depended strongly on the temperature and particle size of utilized gold contacts and could vary in the range of 1 to 1.8 eV. The hydrogen sensing properties of the samples were also investigated. The samples demonstrated high sensitivity to hydrogen; 1 Vol% of hydrogen in air could increase the reverse current of the diodes ∼1000 times. The results are described based on the reactions taking place at the Au/TiO2 interface.