Graphene/hBN heterostructures are promising active materials for devices in the THz domain, such as emitters and photodetectors based on interband transitions. Their performance requires long carrier lifetimes. However, carrier recombination processes in graphene possess sub-picosecond characteristic times for large non-equilibrium carrier densities at high energy. An additional channel has been recently demonstrated in graphene/hBN heterostructures by emission of hBN hyperbolic phonon polaritons (HPhP) with picosecond decay time. Here, we report on carrier lifetimes in graphene/hBN Zener-Klein transistors 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 HPhP 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.

Electromagnetic resonators, which are based on optical cavities or electronic circuits, are key elements to enhance and control light-matter interaction. In the THz range, current optical cavities exhibit very high-quality factors with (λ/2) 3 mode volumes limited by diffraction, whereas resonant electronic circuits show low quality factor but provide strong subwavelength effective volume (10 −6 λ 3 ). To overcome the limitations of each type of resonator, great efforts are being devoted to improving the performances of current methods or to the emergence of original approaches. Here, we report on an optical resonator based on Tamm modes newly applied to the THz range, comprising a metallic layer on a distributed Bragg reflector and demonstrating a high-quality factor of 230 at ~1THz. We further experimentally and theoretically show a fine-tuning of the Tamm mode frequency (over a 250 GHz range) and polarization sensitivity by subwavelength structuration of the metallic layer. Electromagnetic simulations also reveal that THz Tamm modes are confined over a λ/2 length within the distributed Bragg reflector and can be ideally coupled to both bulk materials and 2D materials. These THz Tamm cavities are therefore attractive as basic building blocks of lasers, for the development of advanced THz optoelectronic devices such as sensitive detectors, high-contrast modulators, narrow filters, and polarizers, as well as for THz cavity quantum electrodynamics in nanostructures.