Fluoride single crystals are key components for a variety of photonics applications such as laser materials, high power optical isolators, as well as nonlinear frequency converters and optical windows with superior properties in the deep-UV region. Fluoride compounds can overcome the current limitation in handling power of optical isolators. They are also very promising for solid state laser cooling (optical refrigeration), a technique enabling to cool down solid materials to cryogenic temperature by laser excitation.

The Junior Research Group is particularly engaged in melt growth of high-quality fluoride single crystals doped with rare-earth ions for laser cooling. Main challenges are to mitigate formation of foreign phases and color centers and to minimize oxygen contamination and internal strain. Fluorination of raw materials helps to prepare highest purity crystals. The application-relevant properties of grown crystals are demonstrated in collaboration with the IKZ Center for Laser Materials.

We manufacture transparent conducting or semiconducting oxide single crystals. The topic is primarily known from our pioneering work on 2" β-Ga₂O₃ single crystals (Czochralski method), and other binary oxides (In₂O₃, SnO₂). In recent years, we have developed gallium based spinels (MgGa₂O₄, ZnGa₂O₄, CoGa₂O₄), barium stannate (BaSnO₃) and lanthanum indate (LaInO₃). As substrates and thin films, these crystals enable new device structures in power electronics, optoelectronics, for sensors and ferrimagnetic thin layers, and as scintillator material.

The growth of these crystals is hampered by the tendency to decompose at high temperatures near the melting point. We therefore use novel and proprietary methods and technologies (e.g. dynamic gas atmospheres) to increase compound and growth stability to enable large crystal volumes. A special focus is on the control and characterization of the electrical and optical properties in dependence on growth, doping and annealing conditions.

Our primary focus is to develop new bulk crystals with tailored lattice parameters, mainly with perovskite, pyrochlore or magnetoplumbite structure. As substrates, such crystals serve as the literal foundation for the preparation of epitaxially grown oxide thin films with interesting ferroelectric, superconducting, ferromagnetic, piezoelectric, multiferroic, or electron transport properties. Some of the bulk crystals are attractive for optical applications as well. Most of the compounds are exclusively grown at IKZ for our academic and industrial research partners.

The growth temperature is typically in the range between 1500°C and 3000°C. Depending on the material properties at such high temperatures and the requirements on structural quality and purity, the crystals are grown by crucible-based or crucible-free methods from the melt or from melt fluxes. Insufficient heat transport, internal strain in the crystals and crucible stability are critical issues that must be carefully controlled. The crystals are investigated by their structural quality and chemical composition.

Individual single crystals are demanded as benchmark and reference materials in different fields of science, e.g. geology, materials science, solid-state chemistry and physics. They are used by research institutions, companies and technology ventures for detailed investigation, to demonstrate their application potential or to assess conditions for a commercial production. If the required material falls within our range of capabilities and is not commercially available, we can prepare and provide it.

We have expertise in crystal growth for a number of different compounds and provide crystals with highest quality and purity. While our core area of research is melt growth at high temperatures, we can employ a variety of growth approaches and techniques. In-house characterization provides a thorough assessment of the crystals’ properties. Depending on the target and effort of the research, we can operate by joint development agreement, full-cost accounting or scientific collaboration.

We use thermochemical analysis to determine how a particular material can be best grown as a single crystal with desired properties. Incongurent melting, material decomposition, or metal oxidation state instability are common problems that can be mitigated by establishing proper phase diagrams. We optimise source material compositions for the respective growth methods and suggest the optimal growth atmosphere. With our expertise we also support the other IKZ activities regarding their process technologies.

The optimal crystal growth conditions are found by determining the phase diagram of binary or ternary systems with Differential Thermal Analysis (DTA), Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG) in oxidising, reducing or inert atmospheres up to 2400 °C. DTA analysis can be supplemented with evolved gas analysis using a quadrupole mass-spectrometer. Additionally, we employ X-ray diffraction, thermal conductivity (laser-flash) measurements and provide thermodynamic calculations.