Strain-engineering of bandgaps in pristine and fully hydrogenated hexagonal boron phosphide

Based on density functional theory, the structural, electronic, and phonon properties of the pristine and three conformers of fully hydrogenated h-BP sheets are investigated. The results demonstrate that they are all dynamically stable because of no imaginary frequencies in their phonon spectra. The pristine h-BP sheet is a semiconductor with a direct bandgap of 1.377 eV calculated by Heyd–Scuseria–Ernzerhof (HSE06). The variation tendency of its bandgap vs uniaxial strains is very slow due to conduction band minimum and valence band maximum insensitive to strains. However, the uniaxial strain can effectively tune the bandgaps of the fully hydrogenated counterparts. An indirect to direct bandgap transition can occur in the chair conformer by adding a tiny x- or y-axial strain. A direct bandgap can remain in stirrup conformer no matter whether x-axial or y-axial strain is added. The HSE06 bandgap can be tuned in a wide range from 4.592 eV to 2.919 eV (chair), from 4.151 to 3.362 eV (boat), and from 4.344 eV to 3.134 eV (stirrup) in the range of 8% to − 8 %. The discussions above demonstrate that their bandgaps are controllable as long as the uniaxial strain is chosen in proper direction and size. Our findings suggest the great potential of a strain-engineered hydrogenated h-BP sheet in electronic and optoelectronic device applications.