Nitrogen Monoxide Gas Sensing Characteristics of Transparent p-type Semiconductor CuAlO2 Thin Films

Abstract

We investigated the detection properties of nitrogen monoxide (NO) gas using transparent p-type <TEX>$CuAlO_2$</TEX> thin film gas sensors. The <TEX>$CuAlO_2$</TEX> film was fabricated on an indium tin oxide (ITO)/glass substrate by pulsed laser deposition (PLD), and then the transparent p-type <TEX>$CuAlO_2$</TEX> active layer was formed by annealing. Structural and optical characterizations revealed that the transparent p-type <TEX>$CuAlO_2$</TEX> layer with a thickness of around 200 nm had a non-crystalline structure, showing a quite flat surface and a high transparency above 65 % in the range of visible light. From the NO gas sensing measurements, it was found that the transparent p-type <TEX>$CuAlO_2$</TEX> thin film gas sensors exhibited the maximum sensitivity to NO gas in dry air at an operating temperature of <TEX>$180^{\circ}C$</TEX>. We also found that these <TEX>$CuAlO_2$</TEX> thin film gas sensors showed reversible and reliable electrical resistance-response to NO gas in the operating temperature range. These results indicate that the transparent p-type semiconductor <TEX>$CuAlO_2$</TEX> thin films are very promising for application as sensing materials for gas sensors, in particular, various types of transparent p-n junction gas sensors. Also, these transparent p-type semiconductor <TEX>$CuAlO_2$</TEX> thin films could be combined with an n-type oxide semiconductor to fabricate p-n heterojunction oxide semiconductor gas sensors.