Adsorption of CO, NH3, NO, and NO2 on pristine and defective g-GaN: Improved gas sensing and functionalization

The adsorption behaviors of gas molecules, including CO, NH3, NO, and NO2 on pristine and defective g-GaN, and their adsorption energy, charge transfer, and magnetic moment are investigated using first-principles calculations. The small adsorption energy of all the gas molecules on pristine g-GaN suggests the physisorption characteristics. Among these gas molecules, the binding between NH3 and pristine g-GaN is stronger than the other molecules owing to the hybridization of its frontier orbitals with the 2p orbital of N atoms in pristine g-GaN. To improve the sensing ability of g-GaN, the adsorption behaviours of these gas molecules on g-GaN with Ga and N single vacancies are also examined. All these gas molecules exhibit much larger adsorptions energy on the defective g-GaN than that on the pristine form. For most of the gas molecule adsorption on defective g-GaN, the charge transfer is more significant that in the corresponding gas molecule adsorption on pristine g-GaN. Besides, the magnetisms are found in many gas molecules adsorbed defective g-GaN. Our work not only provides an effective approach to improve the sensing ability of g-GaN but also offers an effective approach for functionalization of g-GaN.