Clemens Petersen

• Petersen, Clemens; Vogt, Sofie; Fernandez, Javier Garcia; Vines, Lasse; Kano, Taisei & Grundmann, Marius [Vis alle 8 forfattere av denne artikkelen] (2026). Single-domain, semiconducting κ-Ga2O3 grown on isostructural ε-GaFeO3 templates. Applied Physics Letters. ISSN 0003-6951. 129(17). doi: 10.1063/5.0343866. Fulltekst i vitenarkiv Vis sammendrag

  The epitaxial growth of a phase-pure, single-domain, semiconducting κ-Ga2O3 thin film is demonstrated. Multiferroic ε-GaFeO3, being isostructural to κ-Ga2O3, was used as a substrate and was initially covered by a high-temperature MIST-CVD κ-Ga2O3 seed layer. Subsequently, tin-assisted pulsed laser deposition at 550 °C was applied to grow the single-crystalline epilayer with a thickness of 400 nm. The structural properties were investigated by x-ray diffraction and transmission electron microscopy. A reciprocal space map revealed that the κ-Ga2O3 layer sustains residual strain and is only partially relaxed. Consistently, misfit dislocations were observed, indicating ongoing but incomplete strain relaxation. Secondary ion mass spectrometry confirmed efficient Sn incorporation and revealed Fe diffusion from the ε-GaFeO3 substrate. The Fe impurities segregate predominantly at the advancing growth front, resulting in only moderate bulk compensation of the κ-Ga2O3/ε-GaFeO3 layer. Temperature-dependent in-plane transport measurements revealed freeze out of free electrons with activation energies of Ea,1=48 meV and Ea,2=253 meV at intermediate and high temperatures, respectively. No measurable in-plane conductivity was observed for a reference sample deposited on c-plane sapphire, which exhibited in-plane rotational domains and nanocolumnar growth. These results demonstrate that epitaxial growth on isostructural ε-GaFeO3 enables single-crystalline, semiconducting κ-Ga2O3 and establishes the κ-Ga2O3/ε-GaFeO3 heterostructure as a promising platform for exploring polarization-charge-induced two-dimensional electron gases in multifunctional ferroelectric/ferrimagnetic oxide systems.

• Andreassen, Magnus; Rosnes, Andreas; Petersen, Clemens; Schenk, Richard Justin; Both, Kevin Gregor & Bergum, Kristin [Vis alle 7 forfattere av denne artikkelen] (2026). Combinatorial Synthesis and Characterization of Lattice-Matched Ga2O3–Cr2O3 and Ga2O3–V2O3 Sesquioxide Alloys for Ultrawide-Bandgap Semiconductor Applications. Physica Status Solidi (a) applications and materials science. ISSN 1862-6300. 223(15). doi: 10.1002/pssa.70437. Fulltekst i vitenarkiv Vis sammendrag

  Gallium sesquioxide is a wide‐bandgap semiconductor of high interest for power electronics and deep UV‐sensing applications. The α‐phase ( E g  = 5.6 eV) can be synthesized with excellent crystal quality on isostructural Al 2 O 3 substrates, removing the need for expensive homoepitaxial growth that is required for the thermodynamically stable β‐phase ( E g  = 4.9 eV). Here, continuous composition spread material libraries of (Ga 1‐ x V x ) 2 O 3 and (Ga 1‐ x Cr x ) 2 O 3 with 0.05 <  x  < 0.45 are synthesized by pulsed laser deposition, and characterized structurally and optically with the aim of decreasing the optical absorption edge of α‐Ga 2 O 3 to expand the range of potential optoelectronic applications. The (Cr x Ga 1‐ x ) 2 O 3 material library remained stable in the rhombohedral α‐phase throughout the investigated compositional range, exhibiting high crystal quality with minimal changes to the unit cell parameters. A systematic shift in optical absorption edge from 5.5 to 3.9 eV is observed, as determined by spectrophotometry. The (Ga 1‐ x V x ) 2 O 3 material library exhibits a systematic shift from 5.2 to 2.9 eV with increasing x V , but a region of decreased crystal quality is observed for 0.11 ≤  x V  ≤ 0.20. Additionally, a secondary V 2 O 5 phase is observed for x V  > 0.23. Overall, bandgap engineering of α‐(Ga 1‐ x V x ) 2 O 3 and α‐(Ga 1‐ x Cr x ) 2 O 3 is demonstrated, and chromium substitution is identified as especially promising due to high crystallinity and systematic change of optical absorption edge.

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• Petersen, Clemens; Rosnes, Andreas; Fernandez, Javier Garcia; Grundmann, Marius & Wenckstern, Holger Von (2026). ETC-PLD for high-throughput mapping of spatially addressable transparent oxide heterostructures. doi: https:/research.uni-leipzig.de/hlp/TCO2026/. Fulltekst i vitenarkiv
• Fernandez, Javier Garcia; Bergsbak, Ingvild; Rosnes, Andreas; Petersen, Clemens; Løvoll, Marte & Øyvik, Lea [Vis alle 7 forfattere av denne artikkelen] (2026). Combinatorial Thin-Film Libraries: Correlating Composition, Structure, and Defects by TEM. doi: https:/research.uni-leipzig.de/hlp/TCO2026/. Fulltekst i vitenarkiv

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