Size Effects of Vacancy Formation and Oxygen Adsorption on Gas-Sensitive Tin Oxide Semiconductor: A First Principle Study

Abstract

Background: Oxygen behaviors play essential roles in the receptor function in the gassensing mechanism of SnO2 semiconductors, the size effect of which is a fundamental phenomenon for the development of gas sensors. Objective: This article discusses the size effect on the oxygen behaviors in the gas-sensitive SnO2 semiconductor. Methods: : The first principle calculation was used to investigate size effect on formation of oxygen vacancies and adsorption of oxygen species in the SnO2 semiconductor. The electrical characteristics of conductivity, band gap and electron transfer in SnO2 crystallites were analyzed by density of states and the Mulliken population. Results: The defect of surface bridge oxygen has the lowest formation energy, and it is most likely to form in the SnO2 semiconductor. The adsorption energies for O- and O2 - are from 1.717 to 3.791 eV and 2.371 to 4.683 eV, respectively. The Mulliken population distribution illustrates that O 2p orbit captures the electrons from the orbits of Sn 5s and 5p as well as O 2s. Conclusion: The formation energies of oxygen defects in complete and defective SnO2 super cells are of positive correlation with crystallite size. The carrier concentration and conductivity are improved by the incremental crystallite size. The adsorption energies of O- and O2 - species on defective SnO2 super cells increase with crystallite size. With the assistance of connecting Sn atoms, the adsorbates of O- and O2 - are able to capture electrons from the inner region of crystallites, resulting in an expansion of depletion layer.