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| Home > Articles > Published articles > Hot-carrier cooling in high-quality graphene is intrinsically limited by optical phonons |
(Politecnico di Milano. Dipartimento di Fisica) (University of Manchester. School of Physics and Astronomy) (Institut Català de Nanociència i Nanotecnologia) (RWTH Aachen University) (Institut de Ciències Fotòniques) (Politecnico di Milano. Dipartimento di Fisica) (Center for Nanotechnology Innovation (Pisa, Itàlia)) (Institució Catalana de Recerca i Estudis Avançats) (Max-Planck-Institut für Polymerforschung) (Max-Planck-Institut für Polymerforschung) (Institució Catalana de Recerca i Estudis Avançats) (Université de Liège. CESAM) (Beijing Graphene Institute) (Beijing Graphene Institute) (RWTH Aachen University) (Politecnico di Milano. Dipartimento di Fisica) (Institut Català de Nanociència i Nanotecnologia)
| Date: | 2021 |
| Abstract: | Many promising optoelectronic devices, such as broadband photodetectors, nonlinear frequency converters, and building blocks for data communication systems, exploit photoexcited charge carriers in graphene. For these systems, it is essential to understand the relaxation dynamics after photoexcitation. These dynamics contain a sub-100 fs thermalization phase, which occurs through carrier-carrier scattering and leads to a carrier distribution with an elevated temperature. This is followed by a picosecond cooling phase, where different phonon systems play a role: graphene acoustic and optical phonons, and substrate phonons. Here, we address the cooling pathway of two technologically relevant systems, both consisting of high-quality graphene with a mobility >10 000 cm 2 V -1 s -1 and environments that do not efficiently take up electronic heat from graphene: WSe-encapsulated graphene and suspended graphene. We study the cooling dynamics using ultrafast pump-probe spectroscopy at room temperature. Cooling via disorder-assisted acoustic phonon scattering and out-of-plane heat transfer to substrate phonons is relatively inefficient in these systems, suggesting a cooling time of tens of picoseconds. However, we observe much faster cooling, on a time scale of a few picoseconds. We attribute this to an intrinsic cooling mechanism, where carriers in the high-energy tail of the hot-carrier distribution emit optical phonons. This creates a permanent heat sink, as carriers efficiently rethermalize. We develop a macroscopic model that explains the observed dynamics, where cooling is eventually limited by optical-to-acoustic phonon coupling. These fundamental insights will guide the development of graphene-based optoelectronic devices. |
| Grants: | European Commission 881603 European Commission 873028 European Commission 804349 European Commission 670949 Agencia Estatal de Investigación PID2019-111673GB-I00 Ministerio de Economía y Competitividad RYC-2017-22330 Ministerio de Economía y Competitividad SEV-2017-0706 Ministerio de Ciencia e Innovación CEX2019-000910-S Ministerio de Ciencia e Innovación PGC2018-096875-BI00 Agència de Gestió d'Ajuts Universitaris i de Recerca 2017/SGR-1369 |
| Note: | ICFO was supported the Generalitat de Catalunya through the CERCA program. |
| Rights: | Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, i la comunicació pública de l'obra, sempre que no sigui amb finalitats comercials, i sempre que es reconegui l'autoria de l'obra original. No es permet la creació d'obres derivades.  |
| Language: | Anglès |
| Document: | Article ; recerca ; Versió publicada |
| Subject: | Graphene ; Cooling dynamics ; Hot electrons ; Transient absorption microscopy ; Optical phonons ; Phonon bottleneck |
| Published in: | ACS nano, Vol. 15, issue 7 (July 2021) , p. 11285-11295, ISSN 1936-086X |
