Spectroscopy setup for optical thermometry

• Subject Area: Condensed Matter Physics
• Term: Funded in 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 511416444

The requested piece of major instrumentation is a spectroscopy setup for optical thermometry, which needs to be assembled from various components by the tenure-track research group of the applicant. The projected implementation will be based on experience with a prototype of this spectroscopy setup, which was constructed by the applicant at the École Polytechnique Fédérale de Lausanne (EPFL, Switzerland), providing first experimental results. It is the aim to combine standard optical characterization of a semiconductor specimen by, e.g., (time-resolved) photoluminescence spectroscopy with an analysis of thermal material properties in order to derive a mutual physical understanding. Therefore, the experimental setup will enable thermal characterization techniques that rely on the Raman or reflection signal, providing access to spatially and temporarily resolved temperature distributions. As a result, most vital thermal material parameters like the thermal conductivity κ and diffusivity α can be derived. It is exactly this possibility of a simultaneous analysis of optical and thermal material properties that constitutes an important feature of the envisaged piece of major instrumentation. The complexity of the specimen in focus of this interdisciplinary characterization approach must be risen in a careful step-by-step approach, not only from a materials points of view (e.g., from Ge to InGaN), but also from a structural perspective (e.g., from bulk semiconductors to nanobeam laser structures). As a result, the selected set of characterization techniques will be established based on thermal simulations performed in the group of the applicant. Consequently, the different contributions to thermal transport given by, e.g., electrons, excitons, and thermal, i.e., acoustic THz-phonons must be disentangled for different semiconductor structures. It is exactly this present lack of understanding for the balance of these different contributions to thermal transport at a given environmental temperature, which prevents any thorough analyses of, e.g., the wave-like and coherent propagation of heat. In this connection, the envisaged spectroscopy setup will facilitate the experimental access to the interconnected different transport regimes for thermal phonons (ballistic, hydrodynamic, diffusive, etc.) in preparation of an analysis of interference effects related to thermal phonons in semiconductor nanostructures. The rich feature set of the projected piece of major equipment will directly enable its flexible use for numerous seminal research endeavors, which rely on mutual optical and thermal characterizations. As most direct consequence, the infrastructure related to experimental solid-state physics will strongly be bolstered at the host institution, while the rich set of flexible spectroscopic techniques will even benefit all research groups with a focus on material science at the University of Bremen.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Messplatz für optische Thermometrie
• Instrumentation Group: 8690 Sonstige Meßgeräte für thermische Größen (außer 860-868)
• Applicant Institution: Universität Bremen
• Leader: Professor Dr. Gordon Callsen