Modern society relies on a wide range of electrical and electronic systems. To achieve this, the conversion of electrical energy must be carried out as efficient as possible. The material system β-Ga₂O₃ has due to its high bandgap of approx. 4.8 eV and the resulting theoretically high breakdown field strength the best prerequisites to become the high-performance material for next generation power applications. Therefore our mission is to achieve the predicted material properties through process development to pave β-Ga₂O₃ the way into power electronics.

The β-Ga₂O₃ MOVPE process development is focused on the investigation of the effects of the growth parameters and the type of doping on the electrical properties of the layers. Another focus is the homoepitaxial growth on differently oriented substrates and the influence on the generation of crystal defects. In addition, there are studies on increasing the growth rate by maintaining the good layer quality. In future, also alloys of the material with aluminium are planned to improve the positive properties of β-Ga₂O₃ even further.

Offer: Gallium oxide substrates and epi-layers

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Functional oxide films with perovskite structure exhibit a variety of functional properties depending on their chemical composition and structure. In contrast to bulk crystals, in epitaxial layers additional degrees of freedom are given by incorporating lattice strain (strain engineering by heteroepitaxy) or intentional defects (defect engineering) to deliberately modify material properties and to develop new technologies. Our mission is to make promising materials with perovskite structure, such as the lead-free ferro/piezoelectric material Potassium-Sodium-Niobate ((K,Na)NbO₃) or the dielectric Strontium-Titanate (SrTiO₃), available in thin film form for potential applications, e.g. for highly sensitive sensors or neuromorphic computing.

In close collaboration with the sections "Oxides & Fluorides" and "Experimental Characterization", we grow (K,Na)NbO₃ and SrTiO₃ based films using the metal-organic vapor phase epitaxy (MOVPE) method as the only group worldwide. By introducing lattice strain or off-stoichiometry, material properties (such as piezoelectric constants, phase transition temperature, dielectric permittivity) are deliberately modified. In particular, film characterization using scanning probe microscopy techniques such as piezoelectric force microscopy (PFM) and conductive atomic force microscopy (CAFM), provides insight into ferroelectric domain formation and electrical properties at the nanometer scale.

Alternatively, to strain engineering by heteroepitaxial film growth on lattice mismatched substrates, local lattice strain and strain gradients on the nanometer scale can be generated by the formation of artificial twist boundaries in oxide thin films. This is provided by the transfer of freestanding ultrathin oxide films on a single-crystal or another epitaxial oxide film with a controlled twist angle. Our mission is to explore the impact of the generated dislocation network on the dielectric and ferroelectric properties of thin complex oxides.

Um freistehende nanometerdünne Oxidschichten zu erzeugen wird das Konzept der Opferschicht (Sacrificial Layer), hergestellt mit Hilfe der gepulsten Laserdepositionstechnik (PLD), und dem Überwachsen der funktionellen Oxidschicht durch PLD oder MOVPE angewandt. Der Schichttransfer erfolgt mit unserer neu entwickelten Layer-Transferstation, die unter Hochvakuumbedingungen arbeitet (siehe Abschnitt "Nanostrukturen"). Wir wenden Rastersondenverfahren an um grundlegende Erkenntnisse über die Domänenbildung nach dem anschließenden Bonden auf einem neuen Substrat oder nach dem Anlegen einer externen Spannung zu gewinnen.