A Family of Two-Dimensional Quaternary Compounds A2BXY2 (A = K, Na; B = Li, Na; X = Al, Ga, In; Y = P, As, Sb) for Optoelectronics Applications.

Expanding material types and developing two-dimensional (2D) semiconductor materials with high performance have been hotspots in the field. In this research, it is found that the 12 existing semiconductors A₂BXY₂ (A = K, Na; B = Li, Na; X = Al, Ga, In; Y = P, As, Sb) have a pronounced layered structure. We predict their 2D structures and properties, using first-principles calculations. Lower exfoliation energies confirm the feasibility of mechanical exfoliation from their bulk phases and that the 2D structures can be stabilized independently at room temperature. Interestingly, A₂BXY₂ has an anionic tetrahedral one-dimensional chain or two-dimensional mesh structure of [XY₂]^3- composed of elements III-V. All A₂BXY₂ monolayers exhibit direct or indirect band gap features (0.78-1.94 eV). More encouragingly, the A₂BXY₂ monolayers possess ultrahigh carrier mobilities (∼10⁵ cm² V^-1 s^-1) at room temperature. Furthermore, the results based on the nonequilibrium Green's function indicate that 2D A₂BXY₂ exhibits a high ON/OFF ratio (∼10⁴). To sum up, the A₂BXY₂ family is an outstanding promising candidate for optoelectronics application.