Quasi-particle energies and excitonic effects in bilayer of hexagonal boron nitride

First-principles calculations based on the density functional theory (DFT), GW and Bethe–Salpeter equations are performed on the bilayer of hexagonal boron nitride (bilayer h-BN) to investigate the electronic structure and optical properties. Due to the quantum confinement effect and the less efficient electronic screening, the value of direct (indirect) band gap increases from a value of 4.45 eV (4.37 eV) within the density functional theory to a value of 6.74 eV (6.67 eV) within the GW many-body Green׳s function theory. The calculated optical absorption spectra are dominated by exciton states with a binding energy about of 1.67 eV. The enhanced excitonic effects in bilayer h-BN have the potential to be used in optoelectronic and excitonic devices.