Download Electronic structure and optical properties of Transparent

Electronic structure and optical properties of Transparent
Conducting Oxides
Hemant Dixit
Electron Microscopy for Materials Science – EMAT, Universiteit Antwerpen ,
Campus Groenenborger, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium.
Transparent Conducting Oxides (TCO’s) are technologically important materials and
have wide range of application in transparent electronics, solar cells, flat panel
displays, touch screens and so on. These materials combine the unique material
property of being optically transparent (property of an insulator) and electrically
conductive (property of a metal). The systematic study of the correlation between the
structure of the material with its electronic and optical properties, using firstprinciples electronic structure calculations, is important to understand the physics of
these materials and to design new materials cost effectively.
We have applied Density-functional theory (DFT) successfully onto basic TCO
materials like zincoxide, indiumoxide and cadmium oxide. DFT results show that the
structural properties can be accurately described. However the electronic structure,
using DFT, shows some discrepancies compared to experiment due to intrinsic
complexities involved in the theoretical description of oxides. It is an open area of
research and an accurate theoretical description is still not available in literature. To
calculate the band gap of these oxides we have used the GW approximation. The GW
technique involves the ejection or injection of electrons that links the N particle
system with the (N+/-1)-particle system. Thus, the GW approximation offers a strong
physical basis to correlate the band energies obtained using Green's function with the
experimental band gap measured using photoemission spectroscopy techniques. The
GW approximation to many body perturbation theory represents the state of the art
technique to calculate the quasiparticle correction to the band gap of solids and has
been successfully applied to many materials. Although the GW approximation often
works well with pseudopotentials and plane wave basis sets used within Density
Functional Theory – Local density approximation (DFT-LDA), the II-VI materials
are particularly challenging due to the strong p-d hybridization between the cation 'd'
and anion 'p' states. We discuss the modification required in the pseudopotentials for
correct description of the GW gap. In this talk we will show the GW results on
systems like ZnO, ZnX2O4 (X=Al, Ga and In) spinel oxides and SnO2.