The ultrafast dynamics and conductivity of photoexcited graphene at different Fermi energies

Tomadin A, Hornett SM, Wang HI, Alexeev EM, Candini A, Coletti C, Turchinovich D, Klaeui M, Bonn M, Koppens FHL, Hendry E, Polini M, Tielrooij KJ (2018)

Publication Type: Journal article

Publication year: 2018

Journal

Science Advances American Association for the Advancement of Science

Book Volume: 4

Article Number: eaar5313

Journal Issue: 5

DOI: 10.1126/sciadv.aar5313

Abstract

Formany of the envisioned optoelectronic applications of graphene, it is crucial to understand the subpicosecond carrier dynamics immediately following photoexcitation and the effect of photoexcitation on the electrical conductivity-the photoconductivity. Whereas these topics have been studied using various ultrafast experiments and theoretical approaches, controversial and incomplete explanations concerning the sign of the photoconductivity, the occurrence and significance of the creation of additional electron-hole pairs, and, in particular, howthe relevant processes depend on Fermi energy have been put forward.We present a unified and intuitive physical picture of the ultrafast carrier dynamics and the photoconductivity, combining opticalpump-terahertz probemeasurements on a gate-tunable graphene device, with numerical calculations using the Boltzmann equation. We distinguish two types of ultrafast photo-induced carrier heating processes: At low (equilibrium) Fermi energy (EF ≤ 0.1 eV for our experiments), broadening of the carrier distribution involves interband transitions (interband heating). At higher Fermi energy (EF ≥ 0.15 eV), broadening of the carrier distribution involves intraband transitions (intraband heating). Under certain conditions, additional electronhole pairs can be created [carriermultiplication (CM)] for lowEF, and hot carriers (hot-CM) for higher EF. The resultant photoconductivity is positive (negative) for low (high) EF, which in our physical picture, is explained using solely electronic effects: It follows from the effect of the heated carrier distributions on the screening of impurities, consistent with the DC conductivity beingmostly due to impurity scattering. The importance of these insights is highlighted by a discussion of the implications for graphene photodetector applications.

Involved external institutions

Italian Institute of Technology / Istituto Italiano di Tecnologia (IIT) IT Italy (IT) Johannes Gutenberg-Universität Mainz (JGU) DE Germany (DE) University of Sheffield GB United Kingdom (GB) Consiglio Nazionale delle Ricerche (CNR) / National Research Council of Italy IT Italy (IT) University of Exeter GB United Kingdom (GB) Max-Planck-Institut für Polymerforschung (MPI-P) / Max Planck Institute for Polymer Research DE Germany (DE) Autonomous University of Barcelona (UAB) / Universitat Autònoma de Barcelona ES Spain (ES)

How to cite

APA:

Tomadin, A., Hornett, S.M., Wang, H.I., Alexeev, E.M., Candini, A., Coletti, C.,... Tielrooij, K.-J. (2018). The ultrafast dynamics and conductivity of photoexcited graphene at different Fermi energies. Science Advances, 4(5). https://doi.org/10.1126/sciadv.aar5313

MLA:

Tomadin, Andrea, et al. "The ultrafast dynamics and conductivity of photoexcited graphene at different Fermi energies." Science Advances 4.5 (2018).

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