Carbon nanotube-based light emitting FETs could yield cheap organic lasers

July 26, 2017 //By Julien Happich
Carbon nanotube-based light emitting FETs could yield cheap organic lasers
Improving on previous research, a team of researchers from the University of Heidelberg (Germany) and the University of St Andrews (UK) has demonstrated electrically pumped near-infrared exciton-polariton emission at room temperature, using a SWCNT-based ambipolar LEFET embedded in an optical microcavity.

Publishing their results in Nature Materials under the paper title "Electrical pumping and tuning of exciton-polaritons in carbon nanotube microcavities", the researchers disclose a seemingly simple to manufacture device with a strong potential for laser applications.

The authors explain that while organic semiconductors are actively researched to design exciton-polariton lasing devices, low charge carrier mobilities have been hindering the applicability of such devices. Here they used single-walled carbon nanotubes (SWCNTs) embedded in a polymer matrix as a planar semiconducting material between source and drain electrodes, topping it up with a gate doubling up as a top mirror to form a light-emitting field-effect transistor (LEFET). The carbon nanotubes are readily processed from solution and boast exceptionally high electron and hole mobilities.

Schematic geometry of a bottom-contact/top-gate
LEFET (top stack). By extending the structure with a
bottom mirror an optical microcavity is formed
between the top gate and the bottom mirror.

They built the whole device within an optical cavity formed perpendicular to the direction of charge transport, by the top gate mirror and a semitransparent bottom mirror electrically isolated by a layer of aluminium oxide, on a glass substrate. Through multiple experiments, they were able to tune the narrow-band polariton electroluminescence (EL) from 1,060 nm up to 1,530, by simply adjusting the cavity through different spacer thicknesses. 

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