p+-n diodes with a lateral porous layer as gas sensors

In this work an integrated p(+)-n diode, diffused on a crystalline substrate and provided with a thin adsorbing porous layer, is proposed as gas sensor. The sensor can be easily integrated by using an industrial CMOS process due to the fact that the porous film formation is the last process step. The sensitivity to isopropanol vapors has been investigated by measuring both the forward and reverse current of the diode as a function of the vapor concentration. The current variations, up to two orders of magnitude, could be explained by assuming that the adsorption of molecules in the porous layer and their interaction with localized states modify the band structure of the crystalline diode at the interface with the porous silicon, and in turn its current. Another sensor feature is that the value of the reverse current variation, induced by isopropanol vapors, depends on the voltage, so that the sensitivity can be settled by simply changing the reverse voltage itself The fabrication process, the static and dynamic behavior of the sensor are presented and discussed. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.