Atom Substitution Defects of Hexagonal Boron Phosphide Suppress Charge Recombination

Point defects, during e-h recombination, are a key factor in impacting optoelectronic device performance. Using nonadiabatic molecular dynamics (NAMD), here we investigate the nonradiative recombination of pristine, missing atom defects, including phosphorus vacancies (V_P) and phosphorus and boron vacancies (V_BP), and atom substitution defects, containing boron on the phosphorus site (B_P) and phosphorus on the boron site (P_B) of 2D monolayer hexagonal boron phosphide (h-BP). Carrier dynamics in the pristine h-BP and the defect engineered systems reveal that atom substitution defects B_P and P_B can suppress e-h nonradiative recombination. This is caused by the introduction of several low-frequency phonons in defect states. Electron-phonon coupling between the electronic state and these low-frequency phonons shortens the decoherence time and the nonadiabatic coupling. Also, the atom substitution systems with one defect state introduce fewer carrier recombination channels. Such a mechanism can be extended to other 2D materials with the same structure as h-BP.