Mechanically-Controllable Strong 2D Ferroelectricity and Optical Properties of Semiconducting BiN Monolayer

Structural, electronic, ferroelectric, and optical properties of two-dimensional (2D) BiN monolayer materials with phosphorene-like structure are studied in terms of the density functional theory and modern Berry phase method of ferroelectric calculation. Phonon spectra, molecular dynamics simulations, and total energy comparison indicate that the BiN monolayer is a stable 2D ferroelectric with polarization as large as 580 pC/m, with ferroelectric polarization being sustainable up to 500 K. Further study shows that the polarization in the BiN monolayer can be easily switched from [100] to [010] direction over the bridging saddle phase by applying a tensile [010] stress of 2.54 N/m or compressive [100] stress of −1.18 N/m. This phase transition makes its lattice constants vary in a large range compared to other nonferroelectric 2D materials. Moreover, through applying uniaxial tensile stress parallel to the polarization, one can fix the polarization and change the semiconductor energy gap from direct to indirect. The optical properties feature a very strong anisotropy in reflectivity below the photon energy of 4 eV. All these significant ferroelectric, mechanical, electronic, and optical properties make us believe that the 2D BiN monolayer can be used to make stretchable electronic devices and optical applications