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Current Status of Carbon‐Related Defect Luminescence in GaN
2021, Zimmermann, Friederike, Beyer, Jan, Röder, Christian, Beyer, Franziska C., Richter, Eberhard, Irmscher, Klaus, Heitmann, Johannes
Highly insulating layers are a prerequisite for gallium nitride (GaN)-based power electronic devices. For this purpose, carbon doping is one of the currently pursued approaches. However, its impact on the optical and electrical properties of GaN has been widely debated in the scientific community. For further improvement of device performance, a better understanding of the role of related defects is essential. To study optically active point defects, photoluminescence is one of the most frequently used experimental characterization techniques. Herein, the main recent advances in the attribution of carbon-related photoluminescence bands are reviewed, which were enabled by the interplay of a refinement of growth and characterization techniques and state-of-the-art first-principles calculations developed during the last decade. The predicted electronic structures of isolated carbon defects and selected carbon-impurity complexes are compared to experimental results. Taking into account both of these, a comprehensive overview on the present state of interpretation of carbon-related broad luminescence bands in bulk GaN is presented.
Melt Growth and Physical Properties of Bulk LaInO3 Single Crystals
2021, Galazka, Zbigniew, Irmscher, Klaus, Ganschow, Steffen, Zupancic, Martina, Aggoune, Wahib, Draxl, Claudia, Albrecht, Martin, Klimm, Detlef, Kwasniewski, Albert, Schulz, Tobias, Pietsch, Mike, Dittmar, Andrea, Grueneberg, Raimund, Juda, Uta, Schewski, Robert, Bergmann, Sabine, Cho, Hyeongmin, Char, Kookrin, Schroeder, Thomas, Bickermann, Matthias
Large bulk LaInO3 single crystals are grown from the melt contained within iridium crucibles by the vertical gradient freeze (VGF) method. The obtained crystals are undoped or intentionally doped with Ba or Ce, and enabled wafer fabrication of size 10 × 10 mm2. High melting point of LaInO3 (≈1880 °C) and thermal instability at high temperatures require specific conditions for bulk crystal growth. The crystals do not undergo any phase transition up to 1300 °C, above which a noticeable thermal decomposition takes place. The good structural quality of the crystals makes them suitable for epitaxy. The onset of strong optical absorption shows orientation-dependent behavior due to the orthorhombic symmetry of the LaInO3 crystals. Assuming direct transitions, optical bandgaps of 4.35 and 4.39 eV are obtained for polarizations along the [010] and the [100], [001] crystallographic directions, respectively. There is an additional weak absorption in the range between 2.8 and 4 eV due to oxygen vacancies. Density-functional-theory calculations support the interpretation of the optical absorption data. Cathodoluminescence spectra show a broad, structured emission band peaking at ≈2.2 eV. All bulk crystals are electrically insulating. The relative static dielectric constant is determined at a value of 24.6 along the [001] direction.