| Crystal Research and Technology |
Thermal buoyancy driven flow in semiconductor melts contained in closed silica glass ampoules was studied experimentally in dependence on the height of the molten zone. The onset of temperature oscillations in the melt and further transitions of the temporal convective behaviour were detected by in-situ temperature measurements. It was shown for low PRANDTL number melts that the flow in stationary vertical molten zones strongly tends to become unsteady. For the periodic unsteady flow regime two fundamentally different periodic oscillation modes were revealed. Transitions to chaos are announced in nearly all cases by period doubling events. First return maps of selected typical time series are used to characterize the temporal dynamics of the non-linear dynamic system. Based on the phase relations and amplitudes of the signals measured simultaneously in axial and azimuthal direction spatio-temporal oscillating flow structures can be carefully interpreted. “Mode switching“ and the rotation of a vortex configuration are assumed to be the preferred oscillation mechanisms.
Keywords: temporal flow, molten zone, Bi-Sb-Te, measurements
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