Improvement in lifetime of pseudo-Schottky diode sensor: Towards selective detection of O3 in a gaseous mixture (O3, NO2)

This article concerns a pseudo-Schottky diode Palladium/Indium-Phosphide (Pd–InP) gas sensor. The catalytic activity of such a palladium layer coupled with a pseudo-Schottky structure enables the measurement of very low concentrations of two highly oxidant gases: nitrogen dioxide (NO2) and ozone (O3). The submission of the sensor to long O3 exposures leads to a degradation of its sensor characteristics (response time, recovery time and sensitivity) due to oxidation of the palladium metallization by O3. Therefore, to improve sensor lifetime and reduce drift, a methodology based on cyclic regeneration of the sensor's palladium surface (carbon monoxide (CO) reduction associated with thermal treatment) has been developed. The pseudo-Schottky gas sensor associated with this methodology exhibits reproducible responses, significant resolution and real time detection in the range of 20–100 ppb for NO2 and O3. Moreover, a sensor exposed to 20 ppb of O3 presented twice the response of the same sensor exposed to 100 ppb of NO2 (10.5 nA for 6.5 nA). Selectivity towards O3, with this methodology, is demonstrated in the case of atmospheric pollution monitoring.