Atomically sharp junctions based on stacked 2D materials : new building blocks for the electronics – J2D

J2D project aimed at mastering the whole process from materials growth to devices with special attention given to fundamental issues. The work plan developped along 4 main axis: materials growth, stacking, cristalline and electronic properties of junctions and phototransport.
Samples were obtained either from growth ( CVD on different substrate, SiC surface graphitisation) for planar junctions or by exfoliation for vertical structures. Their quality, size and electronic properties were checked.
Different experimental techniques combining atomic scale (AFM, STM) and macroscopic probes ( KPFM, Raman, Photoluminescence, transport) were used in direct link with modelling.

Technological locks were solved  for growth and intercalation control, doping, transfer, devices fabrication.
Coupled experimental techniques and modeling allowed us to determine the nature of an observed defect but also to study in-plane junction properties and demonstrate their quality.
Stacking under controlled atmosphere enables the fabrication of well controlled heterostructure and demonstrate their quality and interest for optoelectronic devices.
Two outreach operations on these materials are now running.

The properties of 2D materials and especially the effect of rotation in bilayers will go on ( ANR FlatMoi submitted at the new ANR project call)
Optoélectronic properties will go on in collaboration between Néel and SyMMES ( project MATRA2D ANR 2020)

One PhD was funded by the project and defended in 2019. two other thesis also benefited from the project.
22 articles have been published and 9 of them have authors from at least two partners.

Graphene isolation in 2004 and the following apparition of the related 2D materials family (h-BN, transition metal dichalcogenides (TMDC)) open up the way to novel high performance electronic devices. One-atomic-layer-thick 2D materials can be artificially stacked nearly at will, creating heterostructures that combine the properties of each constituent. The J2D project aims at creating heterojunctions using different types of 2D materials (metal, semiconductor, insulator) to explore the interface properties at the atomic scale and correlate them to photo-transport measurements. It covers all the steps from materials to device, focusing on fundamental issues. At each stage, different experimental techniques (AFM, STM, KPFM, Raman, Photoluminescence, transport) and modeling will be coupled in a back and forth way to benefit from each other and help choose the best direction for the next step.
Materials will be either grown in situ - by CVD on different types of substrate or by SiC graphitisation - or exfoliated and then characterized by different experimental techniques and ab initio modeling to determine their crystalline quality, size and check for their electronic properties. In situ growth will be developed for TMDC monolayer ( in-plane junctions while transfer will enable vertical structures. The consortium already masters exfoliation of many of the 2D materials and graphene growth on different substrate. The approaches will be adapted to tackle TMDC and possible in plane re-epitaxy.
Van der Waals stacking either by micromanipulation or in situ by CVD will then be used to create heterostructures (step 2). We already have the skills for transfer of graphene and will have to extend them to other 2D materials. The electronic, optic and transport properties of the van der Waals stacked heterostructures will be studied in step 3.
For each of the 3 first steps, related practical but core questions will be addressed: doping of materials (since this has been the key in semiconductor electronics for many years), stacking orientation and possible species trapping between transferred layers during the stacking step , effect of true 2D character in junctions since all junctions model are for 3D.
Beyond classical 3D designs (pn junctions, Schottky junctions, field effect transistor) that have been the building blocks of the electronic industry since its beginning, new geometries and new concepts enabled by 2D will be explored such as truly 2D quantum wells for original devices (light emitting diode) in the fourth step.
Each task of the project will provide materials for popularization with a main goal, explain to a broad audience what two-dimensionality means and offers. This will take the form of a demonstrator for the physiquarium, a popularization platform developed at Institut Néel with an augmented reality nanomanipulator simulator to make visitors “feel” differences between Van der Waals and covalent bonds and lead to a reflexion on bonding.
The scientific expertise of the three partners (Institut Néel, LPTM, SPrAM) in 2D materials, their complementary skills covering all the steps and their already existing relationships ensure the success of the project.