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19 december 2018

Approved FOM programme

Number 152.
Title Designing Dirac carriers in semiconductor honeycomb superlattices (DDC)
Executive organisational unit BUW
Programme management Prof.dr. D. Vanmaekelbergh
Duration 2014-2019
Cost estimate M€ 2.3

The objective
The goal of this programme is to investigate the electronic properties of conventional, well-known 2-D semiconductors, which, however, obtain a rich Dirac band structure by their honeycomb nanogeometry. To reach this goal, we propose further efforts in the theoretical development, fabrication and electronic characterization of such systems.

Background, relevance and implementation
The effect of nanoscale geometry on the electronic properties of 2-D semiconductors has been overlooked, despite the fact that it can be a dominant factor in the electronic band structure. The most prominent nanoscale geometry is the honeycomb, for which theory predicts Dirac-type electronic conduction and/or valence bands, while the bandgap of the semiconductor is preserved. Furthermore, strong intrinsic spin-orbit coupling in heavy compounds results in the quantum spin Hall effect for holes and/or electrons. Hence, such systems combine all virtues of a semiconductor with Dirac-type electrons and/or holes.

A recent discovery by one of us will be further developed to a mature technology for the preparation of atomically coherent 2-D honeycomb semiconductors of metal-chalcogenides with strong (intrinsic) spin-orbit coupling. By continuous feedback between synthesis and spectroscopy, we will optimise the samples such that band-like transport is achieved and the experimental spectroscopic results can be compared with the theoretical predicted (Dirac)-type band structure.

The programme has three main challenges: (1) Predicting and understanding the electronic band structure of 2-D semiconductors compounds with a given atomic lattice and (honeycomb) nanogeometry. This includes calculation of the effects of spin orbit coupling, and the understanding of the effects of atomic and nanoscale disorder. (2) Development of a robust and broadly applicable fabrication route for 2-D semiconductor superlattices with tunable nanoscale honeycomb geometry; optimization of the samples in terms of the carrier mobility. (3) Investigation of the opto-electronic band structure, and transport characteristics by three complementary types of (opto, magneto-) electrical spectroscopy: scanning tunnelling spectroscopy, micro-wave and tera-hertz spectroscopy, and spectroscopy in a field-effect transistor set-up. More 'mundane' but very useful applications of these 2-D systems, such as sensitive photon detection from the mid-IR to the visible, and very promising thermo-electrics will not be overlooked.

The final evaluation will be based on the self-evaluation report initiated by the programme leader and is foreseen for 2019.

Please find a research highlight that was achieved in 2013 within this FOM programme here.