*Application Area AA2 – Materials, Light, Devices *organizes a research seminar which takes place every second week. In the seminar, current research topics within the thematic scope of the application area are presented and discussed. Every interested person is encouraged to participate in the seminar.

**Organizers**

**Time**

Friday 13:00 – 14:00

**Room**

Meeting-ID: 683 2463 1385

Password: 318636

**Next occurrence**

February 26th at 13:00

February 26th, 2021

**Modeling of concentration and electric field dependent susceptibilities in electrolytes**

February 12th, 2021

**Material Parameter Identification and Sensitivity Optimization for Piezoelectric Ceramics**

Benjamin Jurgelucks (HU Berlin)

Recent material parameter identification methods for piezoelectric ceramics rely on the solution of an inverse problem with the electrical impedance as the measurable quantity. A common complaint is that the sensitivity of impedance with respect to some material parameters is small or zero. Thus, some material parameters cannot be identified reliably. However, the sensitivity of impedance can be increased with the help of Algorithmic Differentiation by optimizing the shape of the electrodes attached to the ceramic. This greatly improves the accuracy of current material parameter identification methods for piezoelectrics. Furthermore, based on pre-optimized electrode shapes one can even achieve arbitrary sensitivity.

January 29th, 2021

**Thermoelectric transport in semiconductor devices: Modeling and numerical methods
**

Many challenges faced in the development of today’s semiconductor devices are related to self-heating phenomena, which become increasingly important with the on-going miniaturization of the device’s feature size. The spatio-temporal dynamics of the underlying charge and heat transfer processes are well-described by the non-isothermal drift-diffusion system, where the magnitude of the thermoelectric cross-effects is determined by the Seebeck coefficient. We show that by choosing a new model for the Seebeck coefficient (the so-called “Kelvin formula”), the corresponding system of partial differential equations takes a remarkably simple form with several appealing properties. In the second part of the talk, we present a novel non-isothermal generalization of the finite-volume Scharfetter-Gummel method for efficient numerical simulation of the fully coupled thermoelectric transport problem. The discretization scheme guarantees all important structural properties of the continuous system on the discrete level and is shown to be more accurate than traditional approaches. The approach is illustrated by numerical simulations of a heterojunction bipolar transistor.

January 15th, 2021

**Influence of random alloy fluctuations on the electronic properties of semiconductor nanostructures**

Statistical fluctuations in the alloy composition on the atomic scale can have important effects on electronic and optical properties of semiconductor properties. We review previous approaches to model atomistic effects in a continuum framework and give an introduction and outline to the mathematical modeling and computational approaches based on the k.p method to understand and quantify these effects.