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Graphene/hBN heterostructures are very attractive materials for advanced optoelectronic devices at THz frequencies. The recombination dynamics of non-equilibrium carriers in graphene, which rely on carrier–carrier and carrier-optical phonon scattering, have shown to possess only sub-picosecond characteristic times in the case of large non-equilibrium carrier density at high energy. An additional channel has been recently demonstrated in graphene/hBN heterostructures by emission of hBN hyperbolic phonon polaritons (HPhPs) with <2 ps decay time. However, for the development of THz emitters and photodetectors based on interband transitions, long carrier lifetimes are needed. Here, using mid-infrared photoconductivity measurements we investigate carrier recombination processes for non-equilibrium carriers at low density and energy in graphene/hBN Zener-Klein transistors. We report on carrier lifetimes in excess of 30 ps, ultimately limited by interband Auger processes. We also unveil the possibility to switch on at finite dc bias or mid-infrared optical power the very efficient electron-hyperbolic phonon recombination channel. This allows the control of carrier lifetime which falls below few picoseconds upon ignition of HPhP relaxation. Furthermore, we have investigated the interplay between optical and electrical pumping and demonstrated the opto-electrical pumping of HPhPs in the hBN layer at high Joule power and high optical power. This works may promote graphene/hBN heterostructures as a platform for phonon polariton optics and nanoscale thermal management.
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