Ultra-long carrier lifetime in neutral graphene-hBN van der Waals heterostructures under mid-infrared illumination

P Huang,T Taniguchi,J Mangeney,B Plaçais,S Dhillon,K Watanabe,R Ferreira,J Tignon,S Messelot,H Graef,E Riccardi,F Valmorra

doi:10.1038/s41467-020-14714-1

Abstract

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.

Highlights

Graphene/hBN heterostructures are promising active materials for devices in the THz domain, such as emitters and photodetectors based on interband transitions
It is essential in this experiment to keep a low doping; to this end, we compensate for drain doping by a careful calibration of the gate voltage at the charge neutrality point (CNP) as function of VDS19
Using mid-infrared photoconductivity measurements we have investigated recombination processes of carriers photoexcited at low density and energy in graphene/hBN Zener–Klein transistors

Summary

Introduction

Graphene/hBN heterostructures are promising active materials for devices in the THz domain, such as emitters and photodetectors based on interband transitions. We use continuous mid-infrared laser excitation (ħω = 117 meV) and set graphene at charge neutrality point (CNP) where transport is dominated by interband Zener tunneling[18,19] This provides weak incident photon density and corresponds to a photon energy between the Fermi-level fluctuations (typically ~20 meV in graphene/hBN heterostructures) and the optical phonons of graphene and hBN (ħΩ ≈ 170–200 meV). Focusing on this lowenergy domain, we unveil on a strong photoconductive regime involving a remarkably long Auger recombination time (~30 ps) and a switching to a short HPhP emission time at a finite dc bias or mid-infrared optical power. It allows to investigate the interplay between optical and electrical pumping

Methods

Results

Conclusion