The project addresses the exploration of fundamental material properties for the improvement of crystal quality, revised microscopic understanding of bulk properties, and controlling the parameters for applications. The main focus of research is the influence of lattice structure, alloying and doping on the vibrational, electronic and magnetic characteristics of oxides studied by optical spectroscopy. Particularly regarding heterostructures as well as ternary alloys, Raman spectroscopy is utilized to study the frequency and splitting of phonon modes as a function of chemical composition or heterostructure design. As a consequence of these investigations, the occurance of miscibility gaps will be clarified for various alloy systems. Regarding heterostructures, the determination of strain states by Raman scattering is an important subject of research. Spatial variations of chemical composition and strain, both in the surface plane and along the growth direction, are addressed by confocal micro-Raman spectroscopy. Regarding electrical doping, Raman scattering by free-carrier related excitations is utilized to study the electrical characteristics of various oxide structures. The impact of magnetic doping is studied by magnetometry as well as magneto-optical spectroscopy. The actual incorporation of dopant atoms into the crystal lattice as well as unintentional point defects and adsorbates are studied using Raman scattering by characteristic vibrational modes. Optionally, spatially resolved photoluminescence may be utilized in order to obtain a more complete picture of the sample characteristics in certain cases.
The doping-related Raman spectroscopic study is complemented by investigations using infrared spectroscopic ellipsometry (IRSE). One target is the determination of intrinsic electron and hole effective masses and their anisotropies as well as non-parabolicities in different material systems. Particular attention is paid to the role of polarons and their influence on effective carrier masses.
Our results will provide input and benchmarks for theoretical calculations, for the optimization of the fabrication conditions and for a proper understanding of optical and transport properties required for devices.
Major accomplishments expected:
Collaboration with partners in the project:
Collaboration with partners in other projects:
If you have queries about the project, please contact the PI:
Oliver Bierwagen, Paul-Drude-Institut
Leibniz-Insitut im Forschungsverbund Berlin e.V.
10117 Berlin, Germany
The Leibniz ScienceCampus GraFOx is a network of two Leibniz institutes, two universities and one institute of the Max Planck Society. The Network is based in Berlin, Germany.