Electron dynamics in graphene in the presence of an electrical field
Licentiatavhandling, 2017

Graphene as atomically thin two-dimensional material exhibits remarkable optical and electronic properties that suggest its technological application in novel optoelectronic devices, such as graphene-based lasers and photodetectors. The linear electronic bandstructure and the vanishing band gap at the Dirac point open up new relaxation channels, such as Auger scattering. Here, optically excited carriers can eciently bridge the valence and the conduction band, which might result in an increase of the number of charge carriers (electrons and holes), i.e. by absorbing a single photon one can create multiple electron-hole pairs through internal scattering. This many-particle process is called carrier multiplication (CM) and has a large technological potential. In the presence of an electric eld, carriers become accellerated in the momentum space depleting the region around the Dirac point and providing optimal conditions for Auger scattering and CM. To investigate ultrafast phenomena characterizing the carrier dynamics in graphene, we develop a microscopic approach based on the density matrix formalism and the semiconductor Bloch equations, which provides microscopic access to the timeand momentum resolved carrier dynamics in the presence of an electric eld. The aim of the thesis is to investigate the many-particle processes behind the ultrafast electron dynamics in graphene. The focus lies on understanding the dynamics in the presence of an electrical eld and in particular providing a microscopic foundation for the photoconduction eect, which is crucial for the application of graphene as an ultrafast photodetector. The highlight of the thesis is the proposal of a very ecient dark carrier multiplication in the presence of an electrical eld. While scattering processes are generally considered to reduce the eld-induced current, we have revealed that in graphene Auger processes give rise to a signicant current enhancement via dark CM. Furthermore, we have investigated the interplay of optical excitation, many-particle scattering and eld-induced acceleration of carriers resulting in asymmetric scattering processes and generation of photocurrents.

Bloch equations

density matrix formalism

graphene

relaxation dynamics

photoconduction effect

carrier multiplication

PJ-Salen, Origo, Kemigården 1, Chalmers University of Technology
Opponent: Assistant Professor Witlef Wieczorek, Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, Sweden

Författare

Roland Jago

Chalmers, Fysik, Kondenserade materiens teori

Graphene as gain medium for broadband lasers

Physical Review B - Condensed Matter and Materials Physics,; Vol. 92(2015)

Artikel i vetenskaplig tidskrift

Experimentally accessible signatures of Auger scattering in graphene

Physical Review B: covering condensed matter and materials physics,; Vol. 94(2016)p. 235430-

Artikel i vetenskaplig tidskrift

Current enhancement due to field-induced dark carrier multiplication in graphene

2D Materials,; Vol. 4(2017)

Artikel i vetenskaplig tidskrift

Recombination channels in optically excited graphene

Physica Status Solidi (B): Basic Research,; Vol. 252(2015)p. 2456-2460

Artikel i vetenskaplig tidskrift

Jago, R., Wendler, F. and Malic, E., Microscopic understanding of the photoconduction effect in graphene

Styrkeområden

Nanovetenskap och nanoteknik

Infrastruktur

C3SE (Chalmers Centre for Computational Science and Engineering)

Ämneskategorier

Den kondenserade materiens fysik

Utgivare

Chalmers tekniska högskola

PJ-Salen, Origo, Kemigården 1, Chalmers University of Technology

Opponent: Assistant Professor Witlef Wieczorek, Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, Sweden

Mer information

Skapat

2017-08-08