Monolayered Silicon and Germanium Monopnictide Semiconductors: Excellent Stability, High Absorbance, and Strain Engineering of Electronic Properties.

The discovery of stable two-dimensional (2D) semiconductors with exotic electronic properties is crucial to the future electronic technologies. Using the first-principles calculations, we predict the monolayered Silicon- and Germanium-monopnictides as a new class of semiconductors owning excellent dynamical and thermal stabilities, prominent anisotropy, and high possibility of experimental exfoliation. These semiconductors, including the monolayered SiP, SiAs, GeP, and GeAs, possess wide bandgaps of 2.08-2.64 eV obtained by hybrid functional calculation. Under small uniaxial strains (-2 to 3%), dramatic modulations of their band structures are observed, and furthermore, all the 2D monolayers (MLs) can be transformed between indirect and direct semiconductors. The monolayered GeAs and SiP exhibits extraordinary optical absorption in the range of visible and ultraviolet (UV) light spectra, respectively. The exfoliation energies of these monolayers are comparable to graphene, implying a strong probability of successful fabrication by mechanical exfoliation. These intriguing properties of the monolayered silicon- and germanium-monopnictides, combined with their highly stable structures, offer tremendous opportunities for electronic and optoelectronic devices working under UV-visible spectrum.