Fluid flow analysis and vertical gradient freeze crystal growth in a travelling magnetic field

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Introduction. In bulk crystal growth of semiconductors the concept of remote flow control by means of alternating magnetic fields has attracted considerable interest (see, e.g., [1-6]). In this way the melt flow can be tailored for growth under optimised conditions to improve the crystal properties and/or the growth yield. A promising option is to apply an axially travelling magnetic wave to the melt (Travelling Magnetic Field – TMF). It introduces a mainly axial Lorentz force which leads to meridional flow patterns. In recent numerical studies [3],[6] the TMF has been recognised to be a versatile and efficient tool to control the heat and mass transport in the melt. For the Vertical Bridgman/Vertical Gradient Freeze (VB/VGF) growth, the beneficial effect of an adequately adjusted, TMF induced flow was clearly demonstrated in [6] in terms of the reduction of thermal shear stress at the solid-liquid interface. In this paper we present experimental and numerical results on the TMF driven convection in an isothermal model fluid as well as first VGF-TMF crystal growth experiments. The model investigations are focused on the transition from laminar to instationary flow conditions that should be avoided in crystal growth applications. The VGF experiments were performed growing Ga doped germanium single crystals under the influence of the travelling field in a newly developed VGF-TMF equipment.