The main task of the department is the growth of bulk crystals of the elementary semiconductors silicon, germanium, and their solid solutions, as well as classical semiconductor compound materials. Basically, Floating Zone (FZ), Czochralski (Cz) and Vertical Gradient Freeze (VGF) are the methods used. All the VGF- and several CZ-growth furnaces are equipped with special KRISTMAG© heater-magnet modules in order to produce traveling magnetic fields. The Lorentz forces are generated in order to control the melt convection.
In the groups 'Multi-Crystalline Silicon“ and 'Gallium Arsenide' the influence of these non-stationary magnetic fields on growth conditions and hence, the crystal quality are investigated. Silicon ingots of different sizes have been directionally solidified. Solidification processes have been developed to reduce recombination active defect structures in multi-crystalline or even quasi-mono silicon used for photovoltaic applications. The research activities of the group Gallium Arsenide are focused in particular on the efficiency increase of the VGF growth process. Different strategies are pursued to tackle these technological and scientific challenges, e.g., the simultaneous growth in several crucibles as well as an increase in the crystallization rate.
The group 'Silicon and Germanium' is focused on the growth of silicon crystals and also isotope-pure silicon crystals applying the Float Zone method up to 150 mm in diameter. Furthermore, the process development of highly pure germanium single crystals is another main research task. Single crystalline silicon has been grown for power electronics, germanium for detectors as well as Si1-xGex for radiation detectors and diffraction gratings. SiGe crystals have been grown as gradient crystals and as mosaic crystals with controlled mosacity.
Modelers are integrated in the different groups of the department to support the process developments by numerical simulations. Primarily, global temperature fields are simulated and the influence of magnetic fields on the growth conditions is studied. The actual shape of the growth interface can then e.g. be diagnosed at the crystal material by the Lateral Photovoltage Scanning method.
The Department is interested in cooperating with national and international partners from industry and research institutes on challenging projects.
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