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Hot carrier recombination close to the Dirac point in graphene-hBN van der Waals heterostructures

We investigate the photoconductive regime in graphene-hBN heterostructures close to the Dirac point. We demonstrate recombination lifetimes of non-equilibrium carriers in excess of 30 ps under continuous mid-infrared illumination (i.e. with photon energy below optical phonon energy in graphene). We also demonstrate the onset of an effective recombination channel relying on electron-hyperbolic phonon coupling by increasing bias. This study opens interesting perspectives to exploit graphene-hBN van der Waals heterostructures with long carrier lifetimes for THz lasing and highly sensitive THz photodetection. Our work also paves the way to develop graphene-based sources for phonon polariton optics.