Dr. Lutz Kirste Successfully Completes Habilitation

Dr. Kirste studied mineralogy at RWTH Aachen University, graduating with distinction in 1998. He then continued his scientific training as a research associate and doctoral candidate at the Freiburg Materials Research Center (FMF) before joining Fraunhofer IAF in 2001. In 2003, he earned his Dr. rer. nat. degree with distinction from the University of Freiburg for his dissertation on the growth and real structure of epitaxial (Al,Ga)N layers. His scientific collaboration with IHPP PAS, which continues to this day, began during his doctoral studies.

Advanced methods for defect analysis of GaN substrates

The habilitation is based on the publication series “Advanced Bragg Diffraction Imaging of Defects in GaN Substrates for High-Power Electronics.” It focuses on the development and application of advanced Bragg diffraction imaging methods—X-ray topography techniques—for investigating defects and lattice distortions in bulk GaN crystals and substrates. Laboratory and synchrotron techniques enabled both the imaging of large-area defect structures and the quantitative determination of local lattice distortions at high submicrometer resolution. A particular focus was the use of synchrotron rocking-curve imaging (RCI) to characterize defect structures in GaN in detail and quantitatively.

A key finding of this work is that the choice of seed crystals has a decisive influence on the structural quality of GaN. A comparison of different growth methods shows that the use of native GaN seed crystals enables particularly high crystal quality and very low dislocation densities. Furthermore, dynamic diffraction phenomena such as the Borrmann effect and Kato fringes were demonstrated for the first time in high-quality GaN crystals and used for structural assessment. Certain defect types, such as the “honeycomb defect,” were also observed in GaN for the first time. These findings provide an important basis for characterizing and further developing high-quality GaN substrates for future GaN-on-GaN power electronics.

Time and again, I am fascinated by how closely a material’s structural properties are linked to the properties of devices made from it. This understanding helps us further develop GaN substrates in a targeted manner, thereby laying the foundation for more powerful and reliable power electronics,” says Dr. Lutz Kirste, describing his enthusiasm for the research.  

With his successful habilitation, Dr. Kirste has reached another important milestone in his many years of scientific work in the field of structural analysis of semiconductor materials.