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1 Detected substances
Semiconductor sensors are used for measuring and detecting presence of flammable and toxic gases.
2 Principle of operation
The principle of operation of the semiconductor sensor is to change the resistance of the semiconductor in
the presence of the detected gas. The interaction of the gas phase with the surface of the semiconductor
leads to the formation of chemical bonds between the gas particles and the absorbent material (the
chemisorption process). In the air atmosphere, the surface of the semiconductor (of the n type) absorbs
oxygen atoms which constitute the so-called "electron traps" (figure 1). When a detectable gas appears in
the vicinity, the chemisorption of gas occurs in the presence of oxygen, electrons are released and an
increase in electrical conductivity of the semiconductor occurs (figure 1).
The semiconductor material is usually made of tin oxide (IV). The measuring element is heated by means of
a heater. In addition to SnO
2
other semiconductors are also applied, e. g.: TiO
2
, WO
3
, GaO, Ga
2
O
3
.
oxygen adsorption on the semiconductor
surface (without the presence of the detected
gas)
chemisorption of detected gas
Figure 1: Principle of operation of semiconductor sensor
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p. 2/4 Appendix: PU-Z-030-ENG R02
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