Effect of contacts and thickness on the NO2 sensing properties of tellurium based films

Abstract

The influence of contacting materials, and thickness of the tellurium based films on their electrical conductivity and sensitivity to NO2 is given. It is shown that until thickness is below 100 nm the conductivity increases with the increase of the layer thickness but becomes almost constant at thicknesses more than100nm. Scanning electron microscopy analyses indicates that grown films are compact, i.e. two-channel mechanism of current flow occurs. The sensitivity toward NO2, being controlled by gas concentration, decreases with film thickness increase but is nearly independent on contacts work function. The results are discussed taking into consideration the contributions of grain boundary as well as grain bulk and surface resistance to the total conductivity. Chemisorption of NO2 molecules is accompanied by hole enrichment of the surface and grain boundary region, due to interaction of these molecules with lone-pair electrons.