Get excited about hot carriers – then relax and dissipate

The interaction between graphene and light reveals some interesting physics, and an understanding of the fundamentals is imperative if researchers are to realise the potential of graphene in device applications. Some of the leading experts in hot carrier research have contributed their latest papers to a JPCM special issue on hot carriers in graphene. The issue was Guest Edited by Bernard Plaçais and Christophe Voisin.

Hot carriers may be created when a photon of sufficient energy impacts on a semiconductor. This photon energy transfers to an electron, exciting it out of the valence band, and forming an electron-hole pair (the hot carriers). The hot carriers then relax and the energy is lost to phonons or by carrier-carrier scattering.

Graphene device

Schematic of measured device (a) and image of a typical graphene device (b). C B McKitterick et al 2015 J. Phys.: Condens. Matter 27 164203

As Plaçais and Voisin write in their preface:

“The advent of graphene, a decade ago, has shed a new light in this field, offering genuine 2D materials where both electrons and phonons are ultimately confined at the atomic scale. Furthermore, the nature of the carriers is new: in monolayer graphene one deals with massless Dirac fermions characterized by a linear dispersion with a large Fermi velocity, whereas multilayer graphene supports low-mass carriers but still with a gapless spectrum. Furthermore graphene is ambipolar and widely tunable with an electron-hole symmetry inherited from the crystal structure. Dirac Fermion physics is served in graphene by robust material parameters providing large energy scales suitable for physical characterization and valuable for applications. Put together, these symmetry and material properties have promoted graphene as a remarkable platform for hot carrier physics, attracting large interest from both optics and transport communities.”

Specific aspects of the topic covered in the special issue are: electron cooling, relaxation by magneto-transport, THz detection, population inversion and optical gain, Zener tunnelling and photo-detection.

 


Images:

Thumbnail image on homepage adapted from: Figure 1, Isabella Gierz et al 2015 J. Phys.: Condens. Matter 27 164204.  Equilibrium band structure of a hydrogen-intercalated graphene bilayer.  (Copyright IOP Publishing 2015.)

Image in blog post from: Figure 4, C B McKitterick et al 2015 J. Phys.: Condens. Matter 27 164203.  (Copyright IOP Publishing 2015.)



Categories: Journal of Physics: Condensed Matter

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