Rapid bimolecular and defect-assisted carrier recombination in hexagonal Boron Nitride

Hexagonal boron nitride (hBN) is an indirect wide band gap semiconductor that holds great promise for optoelectronic devices in the ultraviolet regime. Here we report the dynamics of photoexcited charge carriers at room temperature in exfoliated monoisotopic ¹⁰B enriched hBN. Two recombination mechanisms were identified, and their associated time scales measured, using ultrafast two-photon pump, infrared probe transient transmission spectroscopy. Initially, when the free carrier density is high, bimolecular decay dominates recombination with a rate constant of (1.33 ± 0.09) × 10^-7 cm^-3/s. At later times, the recombination of the free carriers is characterized by an exponential decay with a time constant on the order of a nanosecond, determined by the density of the impurities/defects in the lattice.