Effects of Schottky barrier height fluctuations on conductivity: Consequences on power-law response in tin oxide gas sensors

Abstract

Potential barriers formed at the intergrain of polycrystalline metal-oxide semiconductors, such as tin oxide, present fluctuations that are usually ignored in the study of gas sensors responses. Fluctuations in the Schottky-type barriers arise from the punctual character and distribution of the charges at the depletion region. Accordingly, we present a numerical model that allows to determine the distribution of the barrier heights. We then analyze the influence of fluctuations on the electrical intergrain conductivity as a function of oxygen pressure, since the signal detection in polycrystalline metal-oxide semiconductors gas sensors comes from the change of material conductivity after interaction with target gas molecules. To do so, we incorporate the fluctuation distribution found in our numerical model in the calculations of conductance. Based on these results, we could also relate the oxygen pressure with the adsorbate coverage and the fluctuating intergranular barrier. Finally, consequences on the known power-law response for gas sensors are discussed.