Self-energy corrected band-gap tuning induced by strain in the hexagonal boron phosphide monolayer

Abstract: We performed a first-principles study of the electronic behavior of a 2D hexagonal boron phosphide monolayer (2D-h-BP). The system was deformed isotropically by applying a simultaneous tensile strain along the a and b crystal axes. We analyzed the band-gap evolution as function of the deformation percentage, ranging from 1% to 8%. Results show that the system behaves as a direct band-gap semiconductor, with the valence band maximum and conduction band minimum located at the K point (1/3, 1/3, 0) of the Brillouin zone. This behavior is unchanged despite the strain application. The band gap underestimation, as computed within the standard DFT, was corrected by applying the G0W0 approach. Trends in the band-gap behavior are the same within both approaches: for low deformation percentages, the band-gap grows linearly with a small slope, and at higher values, it grows very slow with a tendency to achieve saturation. Therefore, the band-gap is less sensitive to tensile strain for deformations near 8%. The origin of this band gap behavior is explained in terms of the projected density of states and charge densities, and it can be attributed to Coulomb interactions, and charge redistributions due to the applied tensile strain. To study the carrier mobility, we computed the electron and hole effective masses, finding high mobility for both carriers. Finally, the stability analysis of each strained system includes the calculation of phonon spectra, to assure the dynamical stability, the computation of elastic constants to evaluate the mechanical stability, and cohesive energies for exploring the thermodynamical stability. Results indicate that the boron phosphide monolayer is stable under the calculated tensile strains.