Electrical detection of hyperbolic phonon-polaritons in heterostructures of graphene and boron nitride

Light properties in the mid-infrared can be controlled at a deep subwavelength scale using hyperbolic phonons-polaritons of hexagonal boron nitride. While propagating as waveguided modes hyperbolic phonons-polaritons can concentrate the electric field in a chosen nano-volume. Such a behavior is at the heart of many applications including subdiffraction imaging and sensing. Here we employ HPPs in heterostructures of hexagonal boron nitride and graphene as new nano-optoelectronic platform by uniting the benefits of efficient hot-carrier photoconversion in graphene and the hyperbolic nature of hexagonal boron nitride. We demonstrate electrical detection of hyperbolic phonons-polaritons by guiding them towards a graphene pn-junction. We shine a laser beam onto a gap in metal gates underneath the heterostructure, where the light is converted into hyperbolic phonons-polaritons. The hyperbolic phonons-polaritons then propagate as confined rays heating up the graphene leading to a strong photocurrent. This concept is exploited to boost the external responsivity of mid-infrared photodetectors, overcoming the limitation of graphene pn-junction detectors due to their small active area and weak absorption. Moreover this type of detector exhibits tunable frequency selectivity due to the hyperbolic phonons-polaritons, which combined with its high responsivity paves the way for efficient high-resolution mid-infrared imaging. Optoelectronics: guided hyperbolic phonon-polaritons in h-BN boost mid-infrared graphene photodetectors h-BN hyperbolic phonon-polaritons can be probed electrically in a van der Waals photodetector by guiding them towards a graphene junction. A team led by F.H.L. Koppens at ICFO developed a nano-optoelectronic device whereby light from a laser beam, shone on a heterostructure of monolayer graphene encapsulated in h-BN, is converted to hyperbolic phonon-polaritons. Once the latter are launched at the edge of a metallic bottom split gate, they propagate as highly confined and directional rays towards graphene, where they are absorbed. This results in the generation of hot carriers which diffuse spatially towards the graphene junction, giving rise to an inhomogeneous temperature distribution which, in turn, leads to a strong photo-response. Besides enhanced responsivity and room temperature operation, this mid-infrared photodetector possesses tunable frequency selectivity, making it appealing for imaging and sensing applications.