Optical absorption and excitation spectra of monolayer blue phosphorene

Abstract

We study the optical absorption and excitation spectra of monolayer blue phosphorene with two approaches. The first is based on the approximation in conjunction with the Bethe–Salpeter equation theory. The second is based on the time-dependent density-functional theory in the adiabatic local density approximation and the random phase approximation. The spectra from the two approaches are quite similar. The optical absorption spectrum is dominated by a single peak at 4.2 eV, which originates from direct interband transitions at the point of the Brillouin zone. The excitation spectrum is dominated by a plasmon peak at 9.2 eV, which arises from collective excitations of valence electrons. The plasmon shows a positive dispersion at finite momentum transfer. The in-plane electron is responsible for the optical absorption, whereas the out-of-plane electron is responsible for the plasmon dispersion. Monolayer blue phosphorene has an indirect band gap of 2.98 eV and an exciton binding energy of 1.03 eV.