Visualization of the probability of finding an excited electron in zinc-oxide in the vicinity of the hole (indicated by the black dot). In order to understand the exciton in this transparent conducting oxide (TCO), the hole is assumed to be localized at an oxygen atom. Image: Lawrence Livermore National Laboratory
By looking at the way
electrons are excited, researchers can gain a better understanding of the new
field of transparent electronics.
Postdoctoral student Andre
Schleife, who works in Lawrence Livermore National Laboratory’s Quantum
Simulations Group, developed a new approach to investigate the interplay of
excitonic effects and electron doping. In semiconductor production, doping
intentionally introduces impurities into an extremely pure semiconductor for
the purpose of modulating its electrical properties.
These interactions are
critical to learning more about transparent conducting oxides (TCOs), which are
used in a range of fields including green-energy, intelligent materials or
flexible and transparent electronics. Companies like GM, for instance, are
currently exploring possible applications for TCOs, such as back seat passenger
windows for cars that are displays at the same time. These displays could be
used to entertain (games, movies, etc) back seat passengers and also display
information about the environment or the city you are driving in.
exploiting and eventually tailoring the properties of these unique materials
would be analogous to creating ‘transparent gold’ with a plethora of technical
applications,” Schleife said. Excitons are the most important pair excitations
that occur in several optical spectroscopies of non-metals and molecules and
dominate the absorption properties of the TCOs.
While the TCOs are
transparent in the visible spectral range (due to large fundamental band gaps),
they have to be doped (intentionally or unintentionally) to be conductive. In
other words, doping of a semiconductor introduces a large number of free
electrons and, therefore, leads to high conductivity.
The field of
semiconductor optoelectronics is expected to continue its rapid growth in the
future, driven by the demand for efficient photovoltaics or semiconductor
lasers for high-bandwidth optical communication.
“The effect of these
free carriers on the optical properties is widely unknown,” Schleife said.
“Dramatic changes are expected in the spectral region, which is the most interesting
Other researchers include
those from Friedrich-Schiller-Universität in Germany and the European Theoretical
The paper appears in Physical