Abstracts Book - IMRC 2018

• SD1-O026
AMORPHOUS ZnO: STRUCTURE, ELECTRONIC PROPERTIES AND
CHARGE TRAPPING
David Mora Fonz 1 , Alexander L. Shluger 1
1 University College London, Department of Physics and Astronomy, United Kingdom, Channel
Islands & Isle of Man.
ZnO is a very important transparent conducting oxide, which has been shown
to have particularly interesting physical and chemical properties. Amorphous
ZnO (a-ZnO), however, have been studied in much less detail and their structural
and electronic properties still remain unclear. One of the possible applications
of a-ZnO is as a semiconductor layer in thin-film transistors, which are key
components in at panel displays (FPD). To date, InGaZnO is one of the most used
materials as a TCO in FDP, due to its high level of conductivity and optical
transparency. The cost of these elements has, however, motivated the scientific
community to search for replacements, for example, a-ZnO. Moreover, a-ZnO
can be synthesised at low temperatures, reducing the production cost, and it is
the base of very important amorphous electronic materials, such as ZnSnO,
InGaZnO, InZnO. We report a detailed theoretical study of the a-ZnO. We
provide information on the atomic and electronic structure of a-ZnO spanned
across several amorphous structures. More than 500 a-ZnO structures were
created using highly accurate interatomic potentials (IP) and a molecular
dynamic melt and quench technique. We analyse fourteen cooling rates (0.75-
800 K/ps) and eight cell sizes (containing 96-768000 atoms). 90 amorphous
structures in total, consisting of 96 and 324 atoms, were subsequently fully reoptimised
using a hybrid DFT approach. Our IP amorphous structures show an
excellent agreement with hybrid DFT calculations. After fully hybrid DFT
optimisation, these 90 structures were tested for electron and hole trapping. We
tested our hybrid DFT functional by calculating the localised states of the wellknown
Li Zn defect in ZnO, its absorption spectrum and its thermodynamic
transition level (Li-O) -/0 . Studies have shown that ZnO does not have an affinity
for charge trapping. In agreement with our inverse participation ratio analysis,
hybrid DFT calculations for ZnO show that charge trapping is not stable. In the
amorphous configuration, however, we show that hole trapping processes take
place due to under-coordinated oxygen ions. Trapping energies range 0.57 to
1.30 eV, with an average of 0.87 eV. We also show that our qualitative results do
not change using two different amount (25% and 37.5%) of HF exchange.
Electron trapping remains unstable in a-ZnO.