The Leibniz ScienceCampus Growth and Fundamentals of Oxides (GraFOx) for electronic applications seizes the unique chance to fuse excellent individual activities and competences on oxides in five partner institutions based in Berlin.
Oxides are among the materials with the widest tunability of physical properties. Spanning insulators, semiconductors, metallic conductors and superconductors, magnetic materials, ferro-/antiferro- and other dielectrics, oxides are a materials class with high potential for a new generation of electronic devices and energy applications. These applications can very likely show outstanding properties. Initially, the emerging class of sesquioxides (In2O3, Ga2O3 and Al2O3) and their alloys is the main focus of our work while the more complex and versatile class of perovskites, e.g. SrTiO3, LaAlO3, BaSnO3 will increasingly be addressed. Detailed information on all planned activities is provided in the GraFOx booklet.
The ScienceCampus model promotes cooperation on an equal footing between Leibniz institutions and universities in the form of thematically-focused, complementary regional partnerships. The networks aim to strengthen the scientific environment for the relevant themes by conducting strategic research, encouraging interdisciplinarity in their topics, projects and methods, and ultimately enhancing the visibility of the respective location.
The workgroup “Chemistry of Inorganic Materials” at Ruhr-Universität Bochum (RUB) lead by Prof. Anjana Devi develops and provides the precursors for MOCVD of complex oxides at IKZ.
Based on their large experimental device-oriented activity using crystalline and amorphous oxides, Prof. Marius Grundmann's group at Universität Leipzig (UL) collaborates towards real applications of the oxides and growth of reference samples by PLD.
Prof. Günther Tränkle of Ferdinand Braun Institut (FBH) supports the ScienceCampus in all device related questions using its competence in scientific investigations and full-technological semiconductor device processing of wide-band-gap semiconductors for optoelectronics and power electronics.
Prof. Rüdiger Goldhahn at Otto-von-Guericke-Universität Magdeburg (UM) is a leading expert in spectroscopic ellipsometry, which provides essential information on the optical materials and band-structure properties.
Prof. Norbert Esser of the Leibniz-Institut für Analytische Wissenschaften (ISAS) closely collaborates with Prof. Goldhahn by providing unique expertise in synchrotron-based ellipsometry in Berlin.
Prof. Catherine Dubourdieu, head of the institute “Functional Oxides for Energy-Efficient Information Technology” at the Helmholtz-Zentrum Berlin, strengthens the activities of GraFOx on complex oxides by contributing her long-standing expertise with multifunctional perovskites on various substrates including on silicon.
Semiconductor heterostructures are the basis of almost any electronic device. With their band gaps from 2.7 eV for In2O3 to 4.8 eV for Ga2O3 to 8.8 eV for Al2O3, these sesquioxides are a promising model system for band-gap engineering by the formation of solid solutions and the realization of heterostructures with large band offsets by stacking different oxides. Our research addresses the crystal structure analysis, miscibility, solid solution and metastable structures investigation, interface formation, and layer stack investigation. As hole-doping has so far proven impossible, likely due to polaronic localization, the scattering mechanisms, transport at heterointerfaces, and phonons need to be understood.
Surfaces play an essential role for epitaxial growth, electrical contacts and gas sensor function. In order to obtain high-quality layers for heterostructures and devices, not only the bulk properties but also the surface properties need to be understood in detail. Growth relies on the incorporation and diffusion of atoms at the surface. Growth condition dependent surface reconstruction electronic properties, and chemistry are usually crucial for the deposition of further layers. Surface electronic states are essential in view of electronic applications of oxides as they can pin the Fermi level. The resulting surface charge accumulation or depletion layers as well as the surface work function strongly impacts electrical contacts to the oxide and are at the root of the gas sensor functionality. Reconstruction, band bending, interplay with adsorbates, contacts, surface defects, surface diffusion, and surface reactions will be addressed in this cluster.
During oxide growth, control of growth stoichiometry, surfaces, interfaces, and atomic defects poses major challenges. For bulk growth, the critical issues are the growth stability and mechanisms, defect formation, impact of growth conditions on crystal properties, as well as diameter. In thin-film deposition using molecular beam epitaxy, substantial differences in sticking coefficients, and tendency to form volatile suboxides may require tight growth windows. Metal-organic chemical vapour deposition (MOCVD) allows conditions closer to thermodynamic equilibrium and higher oxygen pressures, decreasing intrinsic defect concentrations. Thermodynamics and kinetics of oxygen incorporation, the role of surface steps, facet formation and film nucleation need to be understood. Our goal is a profound theoretical and experimental understanding of fundamental growth processes during oxide epitaxy, which will be crucial to fully exploit the potential of this materials system.
Doping to define charge carrier concentrations and Fermi level positions is an essential ingredient for (opto-)electronic applications of oxide materials. The proper dopant atom and doping limits are key doping issues. Intrinsic atomic point defects, such as vacancies and interstitials essentially influence materials properties. Oxygen vacancies and cation interstitials can act as unintentional or compensating donors, whereas cation vacancies or oxygen interstitials can act as unintentional or compensating acceptors, they can act as deep levels that trap carriers and limit carrier mobility. Ordering clustering and precipitation as well as intermixing of cations at interfaces are crucial to understand and strongly influence physical properties. Details of these processes strongly depend on the specific materials and need to be studied as dependent on the materials system considered experimentally and by theory. The investigated materials will be bulk crystal and homoepitaxial layers, including semiconducting group III sesquioxides as well as complex oxides (SrTiO3).
Z. Galazka, R. Uecker, R. Fornari,
“Method and Apparatus for Growing Indium Oxide (In2O3) Single Crystals and Indium Oxide (In2O3) Single Crystal”,
a) No. EP 2841630 (granted on 16.03.2017)
b) No. JP 6134379 (granted on 28.04.2017)
Z. Galazka, R. Uecker, D. Klimm, M. Bickermann,
“'Method for growing beta phase of gallium oxide (β-Ga2O3) single crystals from the melt contained within a metal crucible”,
International Patent Applications No. PCT/EP2015/079938, publication No. WO 2016/110385A1 (14.07.2016)
The Leibniz ScienceCampus GraFOx will be present at the following events:
The Leibniz ScienceCampus GraFOx is a network of two Leibniz Institutes, two universities and one institute of the Max Planck Society. It is based in Berlin, Germany.
Paul-Drude Institut für Festkörperelektronik (PDI)
Leibniz-Institut im Forschungsverbund Berlin e.V.
Tel.: +49 30 20377-342
Prof. Dr. Henning Riechert, PDI
Dr. Oliver Bierwagen, PDI
Dr. Martin Albrecht, IKZ