Monolayer and bilayer BP as efficeiant optoelectronic materials in visible and ultraviolet regions

Abstract

Utilizing first-principles calculations, the effects of interlayer interaction and biaxial strain on the phonon dispersion and optical properties of BP sheet are investigated. The calculated phonon spectra shows that the monolayer and bilayer structures are dynamically stable. The phonon bandgap of monolayer BP decreases under tensile strain and increases under the compressive strain. The LO and TO modes harden under compressive strain and soften under tensile strain. The interlayer coupling in bilayer BP causes the splitting of out-of-plane ZA and ZO modes at the Γ point and the phonon band gap decreases with increasing the tensile strain. The absorption edge of bilayer BP is located around 0.6 eV, and it is at a lower energy with respect to the monolayer BP. The results indicate that the optical absorption may be enhanced by applying the compressive strain. These results demonstrate that the phonon dispersion and optical properties of BP sheet could as well be tuned with both interlayer interaction and biaxial strain that are promising for optoelectronic and thermoelectric applications.