Synchrotron-like THz emitters based on corrugated 2D materials – STEM2D

TeraHertz (THz) radiation is of importance for both fundamental science and for technology with promising applications in astronomy,
chemistry, bio-security and communications. However, the THz frequency range (especially from 1 to 10 THz) remains one of the
least technologically developed spectral regions owing to the lack of compact powerful sources.

The STEM2D project tackles the
challenge to achieve an integrated powerful THz–submillimeter wave emitter based on 2D materials operating at room temperature. The novelty here will be to exploit synchrotron-like radiation process in corrugated 2D materials. Synchrotron-like radiation process is well established in the context of vacuum electron-beam devices such as free-electron lasers but represents an original concept for light emission in condensed matter. Moreover, the use of geometrical constraints (corrugation) as opposed to the application of an external magnetic field (such as in wigglers) to obtain radiation via angular motion is innovative.

2D materials (such as graphene) are very attractive for this concept. Indeed, due to their ultra-small thickness (i.e., single-atomic-layer), the conformal adhesion of 2D materials to a corrugated surface can be expected with sub-micron grating periodicities. More specifically, in graphene, the carrier velocity is about an order of magnitude larger than the maximum drift velocities achievable in typical semiconductors so the output THz power is expected to be high. In addition, the other 2D materials, such as MoS2 and black phosphorus (BP), even if the carrier motilities are lower, possess a band gap providing a large control of the carrier-density using a gate electrode. So, synchrotron-like emitters based on these 2D materials could emit THz light modulated at GHz frequency with a high contrast that is particularly attractive for communication applications.

Combining cutting-edge nanofabrication techniques, advanced THz experiments and sophisticated microscopic modeling, we will investigate fundamentally interesting and technologically promising corrugated 2D materials radiation devices. Therefore, this proposal relies on three major objectives: i) the theoretical study of corrugated 2D materials and of their coupling with optical cavity, ii) the demonstration of fully integrated THz emitters based on corrugated graphene and iii) the extension of this concept to other 2D materials to efficiently modulate the THz emitted radiation at high frequencies using a gate.

To achieve these objectives, several challenges will have to be tackled. The main technological challenge is to achieve high quality corrugated substrates and efficiently transfer the 2D materials onto them. The instrumental challenge is to detect the weak THz radiation that will be emitted by the first series of devices (not yet optimized). The main scientific challenge is to theoretically investigate the coupling of corrugated 2D materials to an optical cavity. Indeed, innovative approach has to be proposed to synchronize the THz radiation emitted by the device (of micrometer dimensions) to the run-trip time of the THz waves propagating in the optical cavity (of few hundreds micron length).

The global impact of STEM2D will be considerable by pointing the route for a new concept exploiting corrugated 2D materials and demonstrating its pertinence in THz technology.

The project STEM2D will be carried out by 1 industrial partner Thales Research and Technology (TRT), 3 academic partners as (a) Institut d’Electronique et des Systèmes (IES) from Montpellier University, (b) Laboratoire de Physique de l’ENS (LPENS) and (c) Unité Mixte de Physique CNRS/Thales (UMPhy).