Transport of Excitons in van der Waals heterostructures!
Context and subject:
In most of semiconductor opto-electronic devices, photons are converted into electrons and holes which are drained in opposite directions by an electric field. The situation is drastically different when considering excitons (coupled electron–hole pairs). In excitonic devices, electrons and holes move in the same direction, enabling new paradigm for the design energy-efficient devices.
However, despite its potential importance, the investigation of exciton transport in common semiconductors is still much less understood than its electronic counterparts, and research work must be urgently carried out to solve this issue.
2D materials based on transition metal dichalcogenides (TMDs), in which binding energy of excitons is much larger than in common semiconductors, represent a great opportunity to bridge this gap. The properties of TMD heterostructures being adjustable by the choice of the layers and their relative orientations, they are promising candidates for various applications in opto/nano-electronics. For instance, very recently, the strong excitonic character of those materials led to a remarkable ultrafast fluid flow effect .
At IM2NP, we have developed several “in-house” quantum transport codes based on the Non-Equilibrium Green's Function (NEGF) formalism to describe the electronic [2-5] and phononic [6-9] transport. The NEGF approach is one of the best-suited methods to realistically describe quantum transport in nano-devices. The PhD candidate will then extend those codes to the treatment of excitons and will theoretically investigate the excitonic transport in TMDs and their heterostructures (i.e. stacked 2D layers). He/she will have i) to answer open questions about the transport mechanisms of excitons in those systems and ii) to propose disruptive energy-efficient devices in the field of opto-electronics (photovoltaics, light collection etc…).
The thesis will be done in close collaboration with Dr. Sebastian Volz from the LIMMS, IRL CNRS at the University of Tokyo [4-5].
Eligibility criteria of the applicants:
Applicants must hold a master degree in physics, material science or electrical engineering. Experience in programming would be appreciated.
References on the topic:
1) A. Granados del Águila, Y. R. Wong, I. Wadgaonkar, A. Fieramosca, X. Liu, K. Vaklinova, S. Dal Forno, T. Thu Ha Do, H. Y. Wei, K. Watanabe, T. Taniguchi, K. S. Novoselov, M. Koperski, M. Battiato, Q. Xiong, “Ultrafast exciton fluid flow in an atomically thin MoS2 semiconductor,” Nat. Nanotechnol. (2023) https://doi.org/10.1038/s41565-023-01438-8
2) M. Bescond, G. Dangoisse, X. Zhu, C. Salhani and K. Hirakawa, “Comprehensive analysis of electron evaporative cooling in double-barrier semiconductor heterostructures,” Phys. Rev. Appl. 17, 014001(2022). https://doi.org/10.1103/PhysRevApplied.17.014001
3) A. Yangui, M. Bescond, T. Yan, N. Nagai, and K. Hirakawa, “Evaporative electron cooling in asymmetric double barrier semiconductor heterostructures,” Nature Commun. 10, 4504 (2019). https://doi.org/10.1038/s41467-019-12488-9
4) N. Cavassilas, D. Logoteta, Y. Lee, F. Michelini, M. Lannoo, M. Bescond, M. Luisier, “A dual-gated WTe2/MoSe2 van der Waals tandem solar cell,” J. Phys. Chem. C, 122 (50) 28545 (2018). https://doi.org/10.1021/acs.jpcc.8b09905
5) M. Moussavou, M. Lannoo, N. Cavassilas, D. Logoteta and M. Bescond, “Physically based diagonal treatment of polar optical phonon self-energy: performance assessment of III-V double-gate transistors,” Phys. Rev. Appl. 10, 064023 (2018). https://doi.org/10.1103/PhysRevApplied.10.064023
6) Y. Guo, M. Bescond, Z. Zhang, M. Luisier, M. Nomura, and S. Volz, “Quantum mechanical modeling of anharmonic phonon-phonon scattering in nanostructures,” Phys. Rev. B, 102, 195412 (2020). https://doi.org/10.1103/PhysRevB.102.195412.
7) Guo, M. Bescond, Z. Zhang, S. Xiong, K. Hirakawa, M. Nomura, S. Volz, “Thermal conductivity minimum of graded superlattices due to phonon localization,” APL Materials 9 (9), 091104 (2021). https://doi.org/10.1063/5.0054921
8) Y. Guo, Z. Zhang, M. Bescond, S. Xiong, M. Nomura, S. Volz, “Anharmonic phonon-phonon scattering at the interface between two solids by nonequilibrium Green's function formalism,” Phys. Rev. B 103 (17), 174306 (2021). https://doi.org/10.1103/PhysRevB.103.174306
9) Y. Guo, Z. Zhang, M. Bescond, S. Xiong, M. Wang, M. Nomura, S. Volz, “Size effect on phonon hydrodynamics in graphite microstructures and nanostructures,” Phys. Rev. B 104 (7), 075450 (2021). https://doi.org/10.1103/PhysRevB.104.075450
Application deadline: The 15th of November 2023.
Dr. Marc BESCOND: supervisor
Prof. Fabienne MICHELINI: co-supervisor at Aix-Marseille University
Dr. Sebastian VOLZ: co-supervisor at the University of Tokyo