MODEL FOR THE DENSITY OF SURFACE STATES AND THE SCHOTTKY BARRIER HEIGHT IN SNO_2 AND TIO_2 THICK FILM GAS SENSORS

摘要

A theoretical model has been developed to interpret the different behavior of SnO_2 and TiO_2 sensors. It is based on the determination of the surface-state density, which pins the Fermi level of the semiconductor, thus removing the linear relationship between the work function and the grain-to-grain energy barrier. To interpret these differences, measurements of the built-in potential, V_(bi), related to the Schottky barrier, were pursued at different temperatures in thick-films of SnO_2 and TiO_2, obtained via sol-gel. The model predicts a decrease in the density of surface states with the grain radius only in TiO_2, which seems to be confirmed by the experiment.