Sensor Effect in Oxide Films with a Large Concentration of Conduction Electrons

This paper presents a joint experimental and theoretical investigation of sensor response of nanostructured In2O3 semiconductor thin films containing a large concentration of conduction electrons. The capture of the conduction electrons by oxygen adsorbates from air causes redistribution of the electrons inside the nanoparticles, resulting in reduction of the subsurface electron density, and the drop of the conductivity of nanoparticle thin films. When CO and H2 reduced gas analytes are introduced to the system, their reaction with previously adsorbed negative atomic oxygen ions O– releases electrons back to the nanoparticles, producing a noticeable increase of thin-film conductivity, which constitutes the sensor effect. This work presents a kinetic model of such processes, which allows us to a quantitative description of the sensor effect including dependence of sensor sensitivity on temperature. Concurrently, experiments are performed to quantify the sensor response by nanostructured In2O3 thin film as a function of temperature and hydrogen concentration upon addition of hydrogen gas to the gas medium. The measured response is described well by the theoretical model developed in this work.