A new phase of monolayer group-V binary compounds with direct bandgap and giant piezoelectric properties

Abstract

Since the successful isolation of black phosphorus in 2014, the investigation of two-dimensional (2D) materials consisting of group-V elements has aroused wide interest. In this paper, by applying first-principles calculations, we predict a new stable phase of monolayer 2D group-V binary compounds (MX), which we call the β phase. Our calculations show that these β-MXs (β-AsP, β-SbN, β-SbP, β-SbAs, and β-BiP) are semiconductors with direct bandgaps, and this direct bandgap property is stable under a larger strain along both x and y directions. Furthermore, these β-MXs are also piezoelectric materials due to the lack of inversion symmetry. The piezoelectric coefficients of β-AsP, β-SbP, β-SbAs, and β-BiP are about one order of magnitude higher than other commonly used piezoelectric materials. Therefore, the combination of direct bandgap property and giant piezoelectric effect may make β-MXs promising materials for future optical and electronic devices.