ATRAP 2D – optical Assessment of TRAnsport Properties in 2D materials and devices

Research project selected under the 2020 call for proposals

Principal Investigator : Laurent LOMBEZ

Involved Teams :

LPCNO / Quantum optoelectronics

Type of project : Disruptive Project

Date (start/end) : 2020 – 2023

Schematic representation of multiple particles optically generated in 2D materials. The optical generation is local and generates a lateral diffusion of the species that can be optically probed through luminescence signal. The aims at probing and controlling such transport in monolayer and Van der Waals heterostructures

Following the example of the graphene craze, the scientific community is interested in the properties of new 2D materials, associated in Wan der Waals hetrostructures, that have extraordinary optical and electrical properties. As the fundamental

properties of such materials is becoming more and more understood, it is important to measure charge and spin(valley) transport properties in order to develop optoelectronic and/or spin(valley)tronic devices.

For optoelectronic application with 2D semiconductor materials, most of the research is focused on transition metal dichalcogenides (MoS₂, MoSe₂, WSe₂, WS₂…). Their optical properties are particularly remarkable (ex: very high absorption up to 20% per monolayer) and lead to the design of new ultra-thin optoelectronic devices. Also, good electrical conductivity is expected and recent progress has been made in particular thanks to the control of the dielectric environment via encapsulation with hexagonal boron nitride (h-BN) layers. Moreover, for the design of ultra-thin devices it is important to focus on excitons: strongly bound electron-hole pairs with binding energy of a few hundreds of meV, much larger than in conventional semiconductors. Therefore, the analysis of such a material will mainly measure the excitonic transport, which is thought to be at the basis of a new electronics. However, there are many challenges to understand the creation, transport and dissociations of the different excitonic particles. It is therefore fundamental to understand this complex transport and then try to control it; this is the main purpose of the project.

Yet it is important to measure carrier/excitonic transport and spin/valley properties in order to develop an optoelectronic and/or spintronic device. We should demonstrate the control of the transport properties via external factors such as strain, dielectric environment, electrical/chemical doping, temperature and obviously electric and magnetic field.

To face these challenges, optical measurement methods are ideal because they can be quantitative and measure electronic properties without electrical contacts (early stages of design), so before the creation of a final device.