Numerical Analysis of Oxygen Vacancy Distribution in Semiconductor Gas Sensors in the Cooling Process Based on the Model of Gradient-Distributed Oxygen Vacancies

Abstract

The oxygen vacancies (V_O) play an essential role in the gas-sensing mechanism of semiconductor devices. A diffusion equation is established to describe the V_O behaviors during a cooling process based on the model of gradient-distributed oxygen vacancies. Numerical solutions of the diffusion equation are found to illustrate the V_O distribution in grains. The gradient of V_O distribution is of negative dependence on the cooling rate, which also influences the average V_O density in the depletion layer. The migration of oxygen vacancies in cooling process could be interrupted by quenching and it is restarted by the re-annealing process. The V_O distributing process is illustrated by three stages from initial uniform distribution to final gradient profile via a transient stage. The influence of V_O distribution on gas-sensing characteristics of semiconductor grains is discussed. Potential opportunities are found to control the gas sensor characteristics by a designed annealing process.