Laboratories
Optical and thermal (micro)-characterization I
In this laboratory samples like semiconductor nanostructures can be characterized by Photoluminescence and Raman spectroscopy, yielding optical and thermal material properties. The methods used in the fully customized setup include one- and two-Laser Raman Thermometry (1LRT and 2LRT) in addition to micro-photoluminescence (µPL) and conventional Raman spectroscopy. In addition, also time-resolved µPL measurements are possible, enabling an estimation of the internal quantum efficiency, which is often a vital parameter for quantitative thermometry. The lab features a large variety of different lasers suitable for time-resolved spectroscopy and Raman spectroscopy. Furthermore, also a ultra-low vibration He-cryostat is installed, which enables measurements down to 4 K. Mapping of all structures with sub-µm spatial resolution is enabled by a variety of piezo-stages.
Optical and thermal (micro)-characterization II
In this lab we commonly perform one-laser (1LRT) and two-laser Raman thermometry (2LRT) to map out the thermal properties of, e.g., semiconductor membranes made by Si, SiC, Ga2O3, and GaN. For the heating we apply a 266 nm cw laser, which is also Raman compatible (relevant for 1LRT measurements). For the temperature probing during the acquisition of 2LRT mapscan we utilize a 561 nm diode laser. As a special feature, this lab also possesses a heating stage (sample temperature: 295 K - 1100 K) and a closed-cycle He cryostat (sample temperature: 9 K - 295 K). For the detection of the spectra we utilize a triple monochromator and a UV-enhanced CCD.
Ellisometry
For quantitative optical thermometry it is of utmost importance to know the absorption coefficient related to the heating laser. As most of our samples are not fully underetched, we perform ellipsometry to measure the absorption and reflectivity of our samples. Furthmore, many other aspects of our samples can be analyzed by ellipsometry. Therefore, we utilize a UVISEL 2 ellipsometer from Horba, which is a micro-spot phase modulation ellipsometer operating from the FUV to the NIR (190 nm - 2100 nm).