Numerical modelling of the potential inside the cylindrical shaped nanocrystallite metal oxide semiconductors and its effect on gas sensor response

Abstract

The surface of metal oxide semiconductors exhibits great gas sensing response when the size of the grains becomes much smaller, i.e. in the range of the Debye length. In the presented work, the gas sensing properties of nanocrystalline cylindrical shaped metal oxide semiconductors have been studied. The effect of crystal size and surface states on gas sensor response has been investigated. The electric potential inside the grains has been calculated by solving the Poisson’s equation coupled with electroneutrality condition. The relationship between the electric potential and the size of the nanograins has been established as a function of available surface states, surface temperature and occupied surface states. It has been found that the critical value of available surface state density increases with an increase in the size of nanograins. Total carrier concentration inside the grain volume has been simulated as a function of available surface state density and grain size. Eventually, the sensitivity of the gas sensor has been simulated and compared for different sizes of nanocrystals. From the simulated studies, it is clear that the smaller cylindrical-shaped nanostructured grains could result in better gas sensing performances. Presented model has universal application for all metal oxides (both n-type and p-type) based semiconductors and can be extended for both oxidising and reducing gases with essential modifications.