Enhanced ultraviolet absorption in BN monolayers caused by tunable buckling

Abstract

The optical properties of a hexagonal Boron Nitride, BN, monolayer across the UV spectrum are studied by tuning its planar buckling. The strong σ-σ bond through sp2 hybridization of a flat BN monolayer can be changed to a stronger σ-π bond through sp3 hybridization by increasing the planar buckling. This gives rise to the s- and p-orbital contributions to form a density of states around the Fermi energy, and these states dislocate to a lower energy in the presence of an increased planar buckling. Consequently, the wide band gap of a flat BN monolayer is reduced to a smaller band gap in a buckled BN monolayer enhancing its optical activity in the Deep-UV region. The optical properties such as the dielectric function, the reflectivity, the absorption, and the optical conductivity spectra are investigated. It is shown that the absorption rate can be enhanced by ≈15% for intermediate values of planar buckling in the Deep-UV region, and ≈20% at higher values of planar buckling in the near-UV region. Furthermore, the optical conductivity is enhanced by increased planar buckling in both the visible and the Deep-UV regions depending on the direction of the polarization of the incoming light. Our results may be useful for optoelectronic BN monolayer devices in the UV range including UV spectroscopy, deep-UV communications, and UV photodetectors.