Synthesis of 2-d semiconductors with honeycomb nanogeometry, and study of their dirac-type band structure and opto-electronic properties
Graphene redirected the pathways of solid-state physics with a revival of 2-D materials showing Dirac
physics due to their honeycomb geometry. The charge carriers are fundamentally different from those
in conventional electronic systems: the energy vs. wave vector relationship is linear instead of
quadratic, resulting in Dirac bands with massless carriers. A genuinely new class of materials will
emerge provided that classic semiconductor compounds can be molded in the nanoscale honeycomb
geometry: The Dirac-type band structure is then combined with the beneficial properties of
semiconductors, e.g. a band gap, optical and electrical switching, and strong spin-orbit coupling. The
PI recently prepared atomically coherent 2-D PbSe and CdSe semiconductors by nanocrystal assembly
and epitaxial attachment. Moreover, he showed theoretically that these systems combine a
semiconductor gap with Dirac-type valence and conduction bands, while the strong spin-orbit
coupling results in the quantum spin Hall effect. The ERC advanced grant will allow him to develop a
robust bottom-up synthesis platform for 2-D metal-chalcogenide semiconductor compounds with
honeycomb nanoscale geometry. The PI will study their band structure and opto-electronic properties
using several types of scanning tunnelling micro-spectroscopy and optical spectroscopy. The Fermilevel
will be controlled with an electrolyte-gated transistor in order to measure the carrier transport
properties. The results will be compared directly with those obtained on the same 2-D semiconductors
without honeycomb geometry, hence showing the conventional band structure. This should
unambiguously reveal the Dirac features of honeycomb semiconductors: valence band and conduction
band Dirac cones, non-trivial band openings at the K-points that may host the quantum spin Hall
effect, and non-trivial flat bands. 2-D semiconductors with massless holes and electrons open new
opportunities in opto-electronic devices and spintronics.