Growth of large single crystals using the improved lamp-image floating-zone furnace: application to

We grew large single crystals of reproducibly over a wide doping range using an improved travelling solvent floating zone (TSFZ) method. We performed a simulation on the lamp-image focusing to find an optimum condition for a steep temperature gradient along the rod. Based on the results of simulation, we adapted smaller lamps and shielded the partial area of the mirror surfaces. The improvement of the focusing had a great effect on keeping the molten zone stable for more than 100 h. Stabilization of the molten zone improves both the reproducibility of the crystal growth and the quality of the grown crystals.