Functionalized hexagonal boron nitride bilayers: desirable electro-optical properties for optoelectronic applications

Structural, electronic, and optical properties of functionalized hexagonal boron nitride (h-BN) bilayer were deeply explored by carrying out the PBE + G₀W₀ + BSE calculations. Hydrogenation/hydrofluorination/fluorination can cause the planar h-BN bilayer to form a novel diamane-like monolayer by interfacial sp³ atom bonding. These functionalized h-BN bilayers are estimated to be stable dynamically due to their phonon dispersions. The functionalization on h-BN bilayer can induce its electronic nature to be transformed from an indirect wide-gap insulator to direct narrow-gap semiconductor, which is desirable for its application in optoelectronics. In particular, hydrogenated and hydrofluorinated h-BN bilayers have strong absorbance coefficients for the near-infrared and visible part of the incident sunlight (larger than 10⁵ cm^-1). More interestingly, the binding energy of the observed first bright exciton can achieve a value beyond 1 eV, which can effectively reduce the recombination of photogenerated electron-hole pairs. These results are potentially important for extending the applications of the h-BN bilayer in optoelectronic devices.