Gas sensing characterization of tellurium thin films by the kelvin probe technique

Abstract

The sensing behavior of tellurium films at room temperature was tested with environmental pollutant gases, such as NO2, CO, O3, and water vapor, using the Kelvin probe technique. A significant sensitivity was observed for nitrogen dioxide. The detection range for NO2 was between 0.5–5.0 ppm in air with controlled humidity. The response and the recovery time are rapid with good reproducibility and high sensibility. The work function measurements showed that chalcogenide semiconductors in question are well-suited materials for the detection of not only small concentrations of NO2, but also for humidity sensing. The relative humidity of 45% induces the work function change Δфof approximately 200 mV at room temperature. It is shown that the “strong” chemisorption of nitrogen dioxide results in an increase in both work function change Δф> 0 and electrical conductivity Δɕ > 0 because of the additional charging of the surface and band bending. The effect of water vapor is due to a simple physical adsorption of polar water molecules oriented perpendicular to the surface with a negative pole inward. As a result, the dipole component of the work function increases, i.e., Δф> 0, but the free lattice holes become more localized at the surface and the conductivity of the p-type chalcogenide layer decreases Δɕ