GAS SENSITIVITY STUDIES BY OPTICAL SPECTROSCOPY BELOW THE ABSORPTION-EDGE IN TIN OXIDE THIN-FILM SENSORS

Optical transmission spectra are investigated experimentally below the fundamental absorption edge in tin oxide thin film-based gas sensors. The spectra are studied under different conditions for gas chemisorpt ion when the resistance response to gas is modified by heating of the sensors in various atmospheres or adding of impurity metals into tin o xide. Optical bandgap, refractive coefficient and optical absorption i ndex are deduced from the experimental spectra at the conditions teste d. The changes of the optical parameters are related with the electron ic properties of the films that depend on surface defect states create d by chemisorbed oxygen species. The resistance response to the gaseou s surrounding is discussed on the basis of the analysis of the optical parameters. Some aspects of the mechanism of gas sensitivity are comm ented for tin oxide gas sensors. (C) 1998 Elsevier Science S.A. All ri ghts reserved.