Abstract
We investigated thin catalytic metal gate Schottky diodes and pn heterojunctions for NOx detection. Thin Pt-Pd/Si/Al Schottky diodes were employed successfully to detect NO2 concentrations from 6ppm to 30ppm and NO concentrations from 50 to 250ppm, with a response roughly proportional to the logarithm of gas concentration. We investigated the fabrication of the diodes on a porous Si surface and the formation of a Si/WO3 heterojunction as possible ways to improve sensitivity. Diodes fabricated on porous Si showed slightly higher sensitivity to NO2. The sensitivity of a Pt-Pd/WO3/Si/Al heterojunction was comparable to the sensitivity of the Schottky diodes. The differences between the sensing mechanisms of these structures were also investigated and the results suggest that they provide different possibilities to enhance the sensitivity. An advantage of these sensors is to operate at room temperature. Moreover, the semiconductor junction structure is convenient to make smaller and intelligent sensors. Therefore, these structures may be considered for future development of NOx gas sensors at room temperature with miniaturization, integration and power saving features.
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