Optical Properties of Defect-Laden Single-Layer Hexagonal Boron Nitride

By employing density functional theory (DFT) and time-dependent DFT (TDDFT), we study the electronic and optical properties of monolayers of pure (h-BN) and defect-laden hexagonal Boron Nitride dh-BN (with boron vacancy (V_B), nitrogen vacancy (V_N), boron substitution for nitrogen (B_N), nitrogen substitution for boron (N_B), carbon substitution for boron (C_B) and carbon substitution for nitrogen (C_N)). The DFT analysis traces the defect-induced changes to the orbital- and spin-projected density of states of h-BN and their implications for the optical properties of the system. The TDDFT results show that the long-range nature of the exchange-correlation kernel significantly affects the excitation energy, and hence the absorption and emission properties of the systems. We demonstrate that experimental data on the emission in dh-BN can be explained by the V_N defects only. Namely, the conduction band-to-V_N electron transitions give the dominant contribution to the photoluminescence spectrum, observed experimentally [1]. We discuss possible applications of the results in optoelectronic single-photon emitting devices.

[1] T.T. Tran et al., Nature Nanotech. 11, 37 (2016)