  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.
