Working Group Device Physics

Current research interests:

 

Nanoscale Light Emission and Detection

Photons are the fastest carriers of information possible. For this reason a large proportion of mid- and long-distance electrical communication connections have been replaced by fiber optics in the last decades. The next evolutionary step will be the replacement of short-distance electrical connections by optical waveguides, to enhance on-chip data transfer rates, for example between processor and memory. We are currently working on the development of electrically-driven nanoscale light emitters and detectors and their integration into waveguide/device structures.

A promising material for optoelectronics is single-walled carbon nanotubes, which can be stimulated electrically to emit light. Depending on the type of nanotubes (metallic or semiconducting) and the mode of operation, the emission can be narrowband (electroluminescence) or broadband (incandescence). We use electric-field assisted placement (dielectrophoresis) of solution-processed carbon nanotubes into lithographically pre-defined structures. Using this approach we can demonstrate efficient coupling of light emitted from an electrically-stimulated carbon nanotube into photonic circuits [3]. We are also exploring electroluminescence from nanotube-molecule-nanotube contacts [4].

Graphene is another nanocarbon material of interest for optoelectronics. It can also be stimulated electrically to emit light. However lacking a band gap the emission is of a broadband type, unless the photonic mode density is tailored, forcing emission into a specific wavelength range. We generate such an optical confinement by integrating a graphene transistor into a microcavity and induce electrically-stimulated narrow-band thermal light emission [5]. We are also studying incandescence from nanocrystalline graphene as an easy-to-synthesize alternative to crystalline graphene [6].

Complementary to light emission studies we are exploring the potential of carbon nanotubes and graphene for nanoscale light detection. Depending on the type of nanotube, photocurrents are generated in a narrow or in a wide wavelength range, and are hence envisioned as nanoscale on-chip waveguide integrated transducers. We are exploring the photocurrent response of solution-processed carbon nanotubes [7], of graphene [5] and of nanocrystalline graphene [6]. Furthermore we are studying the photoresponse of nanotube-molecule and graphene-molecule hybrid structures.

 

Fig. 1:  The schematic visualizes how thermal light emission is generated by applying a drain bias and how thermal radiation couples to the optical cavity mode [5].
Fig. 2:   3D schematic of the measurement setup. A focused light beam of variable wavelength is scanned across a carbon nanotube film interfaced with metallic contacts [7].

Graphene-based Devices

We are interested in various aspects of the physics of graphene from its fundamental properties to potential applications. While we investigate mesoscopic effect in graphene-based systems like van der Waals heterostructures, we also develop different approaches to design new type of electronic devices that can be integrated in real electrical circuits. We are currently exploring the possibilities to design microwave amplifiers based on our graphene field effect transistors on sapphire substrate [10][11]. We explore the charge carrier conduction at millikelvin temperature, at high magnetic field and microwave frequency and design graphene based devices to eventually observed excitonic condensates or reach the ultimate limit of charge detection.

Some of our interests:

- Electronic transport and noise properties

- Graphene van der Waals heterostructures

- Proximity induced superconductivity

- Towards full sp2 carbon circuits

- Graphene at microwave frequency

- Topological insulators