Ultra-slow recombination of carriers at low density and energy in neutral graphene-hBN van der Waals heterostructures

We report on carrier lifetimes in graphene/hBN heterostructures of ~30 ps for photoexcited carriers at low density and energy, using mid-infrared photoconductivity measurements. We further demonstrate the switching of carrier lifetime from ~30 ps (attributed to interband Auger) down to a few picoseconds upon ignition of hyperbolic phonon polaritons relaxation at finite bias and/or with infrared excitation power. Our study opens interesting perspectives to exploit graphene/hBN heterostructures for THz lasing and highly sensitive THz photodetection as well as for phonon polariton optics.