High-speed bolometry based on Johnson noise detection of hot electrons in cavity-coupled graphene (Conference Presentation)

Abstract

Since the invention of the bolometer, its main design principles relied on efficient light absorption into a low-heat-capacity material and its exceptional thermal isolation from the environment. While the reduced thermal coupling to its surroundings allows for an enhanced thermal response, it in turn strongly reduces the thermal time constant and dramatically lowers the detector's bandwidth. With its unique combination of a record small electronic heat capacity and a weak electron-phonon coupling, graphene has emerged as an extreme bolometric medium that allows for both, high sensitivity and high bandwidths. Here, we introduce a hot-electron bolometer based on a novel Johnson noise readout of the electron gas in graphene, which is critically coupled to incident radiation through a photonic nanocavity. This proof-of-concept operates in the telecom spectrum, achieves an enhanced bolometric response at charge neutrality with a noise equivalent power NEP < 5pW/ √Hz, a thermal relaxation time of < 34ps, an improved light absorption by a factor~3, and an operation temperature τ up to T=300K. High sensitivity and fast response are the most important metrics for infrared sensing and imaging and together form the primary tradeoff space in bolometry [1]. To simultaneously improve both characteristics requires a paradigm shift on the thermal properties of bolometric materials. Due to a vanishingly small density of states (DOS) at the charge neutrality point (CNP) [2,3] , graphene has a record-low electronic heat capacity which can reach values approaching one Boltzmann constant C e ~k b [4-6]. In addition, its small Fermi surface and the high energy of its phonons result in an extremely weak electron-phonon (e-ph) heat exchange [7-9] ., The combination will allow a strong thermal isolation of the electrons in graphene for higher sensitivity without sacrificing the detector response time. These unique thermal properties and its broadband photon absorption [10] , make graphene a promising platform for ultrasensitive and ultra-fast hot electron bolometers, calorimeters and single photon detectors for low energy light [11-13]. While there already have been device concepts demonstrating bolometric response of graphene [14-16] , many challenges remain on the way to practical applications, like the very low light absorption of only 2.3% [10] and low measurement bandwidths. Previous work