Different PSi gas sensors

Barillaro et al. (2010,2009) have presented PSi junction field effect (JFET) transistor gas sensors. They are an integrated p-channel JFET device modified with a PSi layer which acts as a sensing element to both synthetic air and NO2 with concentrations of 100,300 and 500 ppb at room temperature. The quantitative information on the effect of the NO2 adsorption/desorp-tion at the PSi surface on conductance and surface charge density of PSi was obtained. 

In Barillaro et al. (2008), nitrogen dioxide detection by using p+-n silicon diodes surrounded by a PSi layer was demonstrated. Adsorption of NO2 in the PSi layer modifies the electrical properties of the PSi/crystalline silicon interface and, in turn, the p n diode current. The device shows a higher selectivity to NOj in comparison with ethanol, at any polarization voltage and relative humidity level. 

A novel PSi sensor for the detection of 0.1-10 ppm of NO2 was sensitive simultaneously to 200 ppb of O3,1000 ppm of CO, 20 ppm of benzene, organic vapors and humidity. At low concentration (100 ppb) of NO2, the interference from ozone benzene, CO and organic vapors was not detected (Baratto et al., 2001). 

Pancheri et al. (2003) have reported sensitivity to 12-50 ppb NO2 at room temperature in the sensor, based on the change in conductivity of a single meso-porous Si layer with about 80% porosity. Meso-porous Si shows higher sensitivity and better selectivity for NO2, while macro-porous Si shows better selectivity for NH3 (Sun et al., 2012). The light-enhanced NO2 sensing properties of PSi at room temperature have been demonstrated (Chen eta/., 2012). 

Effects of surface passivation in PSi as a Hj gas sensor were also investigated (Ali et al., 2008). A peroxide-based PSi sample fabricated as a H2 gas sensor showed better electrical (I-V) sensitivity compared with those without peroxide, which has been associated with good surface passivation. Surface passivation in peroxide-based PSi is also maintained at higher temperatures (100°C). 

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