Potential for growth of Si-Ge bulk crystals by modified FZ technique

The technique for crucibleless crystal growth of silicon and its alloy with germanium is developed on the basis of the floating zone (FZ) setup equipped with an additional so-called axial heating process (AHP) heater. The heater forms around itself the melt zone being suspended by forces of surface tension between its top surfaces and the growing crystal, as well as between the top surfaces of the AHP heater and the feeding rod. To investigate into the problem of the capillary stability of the pulling process, numerical computations of shaping of the free Si and Ge melt surface during the crystal pulling were performed. The dependences of the crystal radius and the thickness of the melt film on the parameters of the process are analyzed. It is demonstrated that, in the modified FZ method, the thickness of the melt layer between the crystal and the heater can be considerably larger than the capillary constant. A number of Si and Si-Ge crystals with a diameter up to 15 mm are grown. The range of a Si-Ge melt layer, which one could establish as high as possible, was found to be equal to 11-18 mm.