Improvement of S/TEM-based methods for reliable and accurate measurement of strain and electric potentials

• Applicant: Dr. Laura Niermann
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 492463633

This project has the goal to develop reliable and quantitative methods within the (scanning-) transmission electron microscope (S/TEM) for measurements of strain and electrostatic potentials in nanostructured devices. Present day lighting technology from general purpose up to dedicated applications like optical data transmission is based on light emitting diodes (LED) and laser diodes built from semiconductor heterostructures, which allow shaping the electrostatic potential landscape by means of semiconductor doping in combination with different material properties. Accurate knowledge of the strain induced by material differences and the knowledge of the actual electric potential in these structures is essential for further understanding the underlying physics and hence opening doors for precise modeling and further development of these devices.S/TEM based methods, in principle, allow the rather unique possibility of a direct and spatially resolved measurement of strain and electric potential. However, these methods are far away from providing reliable quantitative data. Within this project they will be further developed for the investigation of state-of-the-art AlGaN based LEDs emitting in the ultraviolet wavelength range. In the nitrides the electric potential landscape does not only result from doping, but also from electrical polarization. In the devices under investigation the polarization influences the light emitting region of the LED and is also exploited to optimize tunnel junctions (TJ), which are used as highly efficient electrical p-contact. The developed techniques will also be applicable to many other device classes, since the electron microscopic challenges root in physical effects like diffraction or inhomogeneous strain fields and are not inherent to material specific properties of AlGaN heterostructures per se.

• DFG Programme: Research Grants
• Major Instrumentation: S/TEM-Probenhalter mit elektrischen Kontakten
• Instrumentation Group: 5140 Hilfsgeräte und Zubehör für Elektronenmikroskope