Description du sujet de thèse

Metal (M) mono-chalcogenide (X) III-VI compound (MX), as InSe, GaSe, GaS and GaTe, have emerged as a promising two-dimensional (2D) semiconductors. Their crystal structure consists in covalently-bound “X-M-M-X” sheets, stacked vertically through van der Waals (vdW) interaction. The electronic band structure of many 2D vdW materials changes as the thickness is reduced down to a few layers. One well known example is the indirect to direct gap transition that occurs at monolayer thickness of Mo and W transition metal dichalcogenides (TMDs).
At odds with the dichalcogenide (MX2) compounds, MX (I.e. GaSe and InSe) are direct bandgap semi-conductors in the bulk (2.1eV and 1.2eV) but they evolve to be indirect bandgap when thinned down to few layers. Being optically active in the infrared or visible range is a significant advantage for 2D materials since graphene (gapless) and hexagonal boron nitride (over 5eV) are not very practical for optoelectronic applications. The indirect band gap transition has not deterred the successful use of few-MLs GaSe and InSe as fast photodetectors. This kind of indirect bandgap transition is also a subject of unusual physics, where a near flat valence band pinches down at the Γ point ('Mexican hat') and creates a Van Hove singularity close to the valence band maximum. This peculiar density of states singularity could lead to interesting effects such as tunable magnetism depending on the doping of the single layer or other instabilities. Some recent works highlight the potential applications of InSe and related III−VI 2D materials in optoelectronics. Also, InSe-based devices can be used in Field Effect transistors (FET) as InSe exhibits one of the highest electron mobility among the 2DMs.
Although optical and transport studies of MX have made rapid progress, the intrinsic electronic structure is still not precisely understood. Fortunately, Angle Resolved Photoemission Spectroscopy (ARPES) and Scanning Tunneling Microscopy (STM) have the potential to answer these questions. The coupling of InSe to other 2DMs van der Waals crystals from the TMD family (WSe2, WS2, etc..) will be studied to expand the electronic properties for InSe to more complex van der Waals heterostructures.
The research activities will be centered on
* 2D materials transfer and heterostructure fabrication via a dedicated setup
* 2D material characterization using photoluminescence, Raman, SHG
* 2D material characterization using Angle-Resolved Photoemission Spectroscopy
* 2D material growth by Chemical Vapor Deposition

Contexte de travail

The work will be conducted at the Centre de Nanosciences and Nanotechnologies (C2N) in Palaiseau (France). The C2N is a joint research lab between Université Paris-Saclay and the Centre National de la Recherche Scientifique (CNRS) which is home to about 200 research staff and 200 PhD and post-doc.

Contraintes et risques

Laser risks, chemical risks.