Defects and oxidation of group-III monochalcogenide monolayers

Among various two-dimensional (2D) materials, monolayer group-III monochalcogenides (GaS, GaSe, InS, and InSe) stand out owing to their potential applications in microelectronics and optoelectronics. Devices made of these novel 2D materials are sensitive to environmental gases, especially O₂ molecules. To address this critical issue, here we systematically investigate the oxidization behaviors of perfect and defective group-III monochalcogenide monolayers by first-principles calculations. The perfect monolayers show superior oxidation resistance with large barriers of 3.02-3.20 eV for the dissociation and chemisorption of O₂ molecules. In contrast, the defective monolayers with single chalcogen vacancy are vulnerable to O₂, showing small barriers of only 0.26-0.36 eV for the chemisorption of an O₂ molecule. Interestingly, filling an O₂ molecule to the chalcogen vacancy of group-III monochalcogenide monolayers could preserve the electronic band structure of the perfect system-the bandgaps are almost intact and the carrier effective masses are only moderately disturbed. On the other hand, the defective monolayers with single vacancies of group-III atoms carry local magnetic moments of 1-2 μ_B. These results help experimental design and synthesis of group-III monochalcogenides based 2D devices with high performance and stability.