The lack of selectivity of chemical sensors encourages the investigations of single sensors with different mechanism of interaction with the gases. In fact, the wider the spectrum of information that can be extracted from one sensor, the more the sensor can be made selective by the analysis of the response pattern. We experimentally demonstrate that porous silicon optical microcavities (PSM) can be effectively used as multi-parametric gas sensors. Semiconductor microcavities are formed by a layer structure as a Fabry-Perot filter: a central active medium is embedded between two dielectric multilayer mirrors. The parameters monitored in our sensors are the DC electrical conductance, the photoluminescence (PL) intensity and the spectral position of the resonance cavity peak. Measurements are carried out at room temperature a) in static air saturated with various solvents and hydrocarbons, and b) under controlled flux of a mixture of dry air and gaseous traces. The examined species under controlled flux are NO{sub}2 (1-21 ppm), relative humidity (20% - 80%), ozone (200ppb) and ethanol (500 to 30000 ppm). The PSM were produced by electrochemical etching of p type (6-9 Ω cm) and p+ type (0.005-0.02 Ω cm) silicon wafers. For electrical measurements, gold contacts were evaporated on the top surface of p+ PSM. We show that the spectral position of the peak depends on the refractive index of the gas, whereas the luminescence intensity depends mainly on its low frequency dielectric constant. This indicates that independent information is available through these parameters. Moreover, the dynamics of the response of the parameters is different. Finally, in the case of ethanol, the time response of the resonance peak is discussed in detail and compared with simulated gradual filling of the cavity. The simultaneous measurement of the peak intensity and the resonance position can be used to monitor the penetration depth of the gas inside the cavity.
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