THE ROLE OF INTERFACE POTENTIALS IN DETECTION
BY METAL/SEMICONDUCTOR GAS SENSORS
I. Kocemba, S. Szafran, J. Rynkowski, T. Paryjczak
Institute of General and Ecological Chemistry, Technical University of Lodz
Zwirki 36, 90-924 Lodz, Poland
There have been various metal oxide semiconductors proposed in the literature for use as gas sensor element, but tin oxide is by far the most popular. In air, molecular oxygens are chemisorbed in form of O-2, O-, and O-2 depending upon temperature and deplete electrons from the surface of tin oxide, leading to the reduction of conductivity. Upon exposure to reducing gases, the chemisorbed oxygen reacts with the gases and electrons are subsequently reintroduced into conduction band, leading to the increase of conductivity. To improve the sensitivity and gas selectivity, catalysts such as Pt, Pd and ag are often added.
According to Morrison [1], the conductance G of a pressed pellet of an n-type material at a temperature T may be described by
G= Goexp(-eVs/kT) (1)
where eVs is the surface potential barrier energy between particles and Go is a factor that includes the bulk intragranular conductance. Experimental values of eVs and Go can be obtained by temperature-stimulated conductance measurements [2].
The aim of the present work was to study the potential barrier changes of ceramic metal/SnO2 sensors as function of temperature (250 – 500° C) and O2 concentration (100 – 106 ppm). We analysed also the correlation between the sensitivity and DeVs difference between the minimum and the maximum of the energy barrier as a function of temperature.
Acknowledgement
This work was supported by grant KBN 3 T09B 004 19.
References
1. S. R. Morrison, Sens. Actuators 11 (1987) 283.
2. V. Lantto,and P. Romppainen, S. Leppavuori, Sen. Acuators 14(1988)149
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