Strain Tunable Bandgap and High Carrier Mobility in SiAs and SiAs₂ Monolayers from First-Principles Studies

Searching for new stable free-standing atomically thin two-dimensional (2D) materials is of great interest in the fundamental and practical aspects of contemporary material sciences. Recently, the synthesis of layered SiAs single crystals has been realized, which indicates that their few layer structure can be mechanically exfoliated. Performing a first-principles density functional theory calculations, we proposed two dynamically and thermodynamically stable semiconducting SiAs and SiAs₂ monolayers. Band structure calculation reveals that both of them exhibit indirect band gaps and an indirect to direct band even to metal transition are found by application of strain. Moreover, we find that SiAs and SiAs₂ monolayers possess much higher carrier mobility than MoS₂ and display anisotropic transportation like the black phosphorene, rendering them potential application in optoelectronics. Our works pave a new route at nanoscale for novel functionalities of optical devices.