MODIFIED HETEROJUNCTION BASED ON ZINC-OXIDE THIN-FILM FOR HYDROGEN GAS-SENSOR APPLICATION

Device-quality ZnO thin film is deposited by using an indigenously developed modified CVD method and a Pd/ZnO/p-Si heterojunction is fabricated. A study of the current-voltage characteristics of the heterojunction in pure air and in air with different concentrations (2000-20 000 ppm) of hydrogen reveals that the device can be used as a room-temperature hydrogen sensor down to a level of hydrogen below its explosion mixture with air. The saturation sensitivity and time response of the device with respect to the different hydrogen concentrations in air has been studied. The device operating at 1 V forward bias shows a maximum saturation sensitivity in different hydrogen concentrations. At 20 000 ppm H2 in air, the sensitivity is found to be 5 x 10(2), while the time response is 162 s. The increase of surface conductivity of ZnO at the Pd/ZnO interface due to the adsorption and chemical interaction of hydrogen is found to play a key role in sensing. This mechanism of hydrogen sensing is verified by a double-metal-gate heterojunction.