Phonon-Mediated Superconductivity near the Lattice Instability in Hole-Doped Hydrogenated Monolayer Hexagonal Boron Nitride*

Employing the density-functional theory with local density approximation, we show that the fully hydrogenated monolayer-hexagonal boron nitride H₂BN has a direct-band gap of 2.96 eV in the blue-light region while the pristine h-BN has a wider indirect-band gap of 4.78 eV. The hole-doped H₂BN is stable at low carrier density (n) but becomes dynamically unstable at higher n. We predict that it is a phonon-mediated superconductor with a transition temperature (T_c) which can reach ~31 K at n of 1.5x10¹⁴ holes cm^-2 near the lattice instability. The T_c could be enhanced up to ~82 K by applying a biaxial tensile strain at 6% along with doping at n of 3.4x10¹⁴ holes cm^-2 close to a new lattice instability.