Thermal characterization of an optical floating zone furnace: A direct link with controllable growth parameters

The variations in temperature induced along the length of a sample in a four-mirror image furnace have been studied as a result of altering the lamp power, gas pressure, type of atmosphere and zoning rate. Temperature profiles measured under different gas atmospheres (oxygen, argon and helium) revealed that although a higher lamp power is required to attain a particular temperature under higher thermal conductivity atmospheres such as helium, the temperature profiles along the sample were similar for different gas types at the same pressure once lamp powers were adjusted to give the same maximum temperature. Increasing the gas pressure from 1 to 5 bar decreased the maximum temperature attained for any given lamp power. When the lamp power was adjusted to give the same maximum temperature at higher gas pressure, a sharper temperature gradient along the sample was created. Increasing the zoning speed increased the cooling rate, but had little effect upon temperature profiles. The temperature characterization results are discussed with a view to indicating how varying the growth parameters can affect crystal quality and growth stability in different ways during optical float zoning. (c) 2009 Elsevier B.V. All rights reserved.