Highly sensitive NOx gas sensor based on a Au/n-Si Schottky diode

For the first time it is shown, that a Au/n-Si Schottky diode based on a SiHy (y=1–3) terminated Si surface exhibits very high sensitivity to NOx at room temperature. By introducing NOx, the Schottky barrier height decreases, the ideality factor rises, and the reverse current increases. The NOx-induced increase in the reverse current at a constant applied bias voltage is considered as a measure for NOx sensitivity. The NOx response is significant, reversible, stable and fast for the NOx concentration range from about 10 ppb to 10 ppm. By introducing 0.75 ppm NOx, the diode exhibits a NOx-induced increase in the reverse current of about three orders at 1 V, a rise time τr90=134 s and a fall time τf10=45 s. The Au/n-Si Schottky diode can be used to develop semiconductor gas sensors for NOx monitoring in air.