A new type of light-emitting diode has been developed at TU Wien.
Light is produced from the radiative decay of exciton complexes in
layers of just a few atoms thickness.
When particles bond in free space, they normally create atoms or molecules. However, much more exotic bonding states can be produced inside solid objects.
Researchers at TU Wien have now managed to utilise this: so-called
"multi-particle exciton complexes" have been produced by applying electrical pulses
to extremely thin layers of material made from tungsten and selenium or
sulphur. These exciton clusters are bonding states made up of electrons
and "holes" in the material and can be converted into light.
The result
is an innovative form of light-emitting diode in which the wavelength
of the desired light can be controlled with high precision. These
findings have now been published in the journal Nature Communications.
Electrons and holes
In a semiconductor material,
electrical charge can be transported in two different ways. On the one
hand, electrons can move straight through the material from atom to atom
in which case they take negative charge
with them. On the other hand, if an electron is missing somewhere in
the semiconductor that point will be positively charged and referred to
as a "hole." If an electron moves up from a neighbouring atom and fills
the hole, it in turn leaves a hole in its previous position. That way,
holes can move through the material in a similar manner to electrons but
in the opposite direction.
"Under certain circumstances, holes and electrons can bond to each
other," says Prof. Thomas Mueller from the Photonics Institute (Faculty
of Electrical Engineering and Information Technology) at TU Wien.
"Similar to how an electron orbits the positively charged atomic nucleus
in a hydrogen atom, an electron can orbit the positively charged hole
in a solid object."
Even more complex bonding states are possible: so-called trions,
biexcitons or quintons which involve three, four or five bonding
partners. "For example, the biexciton is the exciton equivalent of the
hydrogen molecule H2," explains Thomas Mueller.
More: https://phys.org/news/2019-04-exotic-particle-states.html
