Designing Materials for Optoelectronics and Energy Applications

A prerequisite towards the design of novel materials in the fields of energy efficient optoelectronics, power electronics, catalysis, or superconductivity, is to understand, describe and predict the complex interplay between their structural, thermodynamic, magnetic, optoelectronic and electronic properties. Apart from bulk, interfaces (solid-solid, solid-liquid, and solid-gas) and surfaces, both at the nano- and the micro-meter scales, are of paramount importance in the design and the properties of these materials. Density functional theory calculations constitute the working horse in addressing and exploring the aforementioned interplay.

Screw dislocation induced nanopipes are investigated by combining elasticity theory with density functional theory calculations. Based on these calculations a c-type screw dislocation phase diagram is constructed which describes the energetically most favorable core structures as function of the Ga, N and H chemical potentials. We find that nanopipes with diameters ranging from ≈1 to ≈2 nm are energetically favorable for high values of the H chemical potential and conditions that correspond to MOCVD and MOVPE growth. [more]
We use ab initio based molecular dynamics simulations to understand the thermodynamic driving forces triggering electrochemical reactions that involve hydrogen adsorption on Pt electrodes to gain fundamental understanding of processes at solid/liquid interfaces and aid the design of better electrocatalysts. [more]
The synthesis of InGaN digital alloys in the form of short period InGaN/GaN superlttices is investigated by combining ab/initio and empirical potential calculations with PAMBE growth , Photoluminescence Spectroscopy, and HR(S)TEM characterization. [more]
The aim of this project is to resolve the interplay of real space structure and electronic states in combination with magnetic disorder for iron-based superconductors.  We apply a combination of density-functional theory calculations and effective tight-binding models for the electronic energy dispersion. [more]
The thermodynamic stability of computationally designed multicomponent compounds against decomposition into structures with less favorable properties is often unclear. In this project, we have used sophisticated finite temperature ab initio methods to determine the relative phase stabilities of promising Ce-Fe-Ti hard-magnetic materials. [more]
The fundamental mechanisms of V-pits formation on epitaxially grown GaN polar surfaces are investigated combining state-of-the-art first-principles calculations and elasticity theory.
Electronic Passivation Schemes for Materials Exhibiting Spontaneous Polarization
Using technologically interesting examples, such as wurtzite surfaces, we develop a robust passivation scheme for density-functional-theory surface calculations of materials exhibiting spontaneous polarization. The novel approach enables computationally efficient and accurate surface electronic structure calculations. more
Designing Material Properties by Controlling Impurity Content in Structural Defects
We study the impurity incorporation mechanisms in metallic nano-aerogels is expected to identify routes to the targeted design of specimens with desired concentrations of impurities. more
Phase Diagram of Grain Boundary Facet and Line Junctions in Silicon
Faceting of grain boundaries has a strong impact on the properties of structural, functional, and optoelectronic materials. In this project, we employ density-functional theory and modified embedded atom method calculations to investigate the energetics and thermodynamic stability of facets and line junctions in Silicon. We find that higher energy metastable GB phases can be stabilized by thermodynamics and not kinetics when constituting the facets at line junctions. This is in contrast to the common perception that the properties of faceting are merely driven by the anisotropic GB energies.  more
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