Floating zone process

Silicon is prepared commercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be prepared as a brown powder, which can be easily melted or vaporized. The Gzochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Hyperpure silicon can be prepared by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone process. 

The next step is to produce nearly perfect single-crystal boules of silicon from the ultrapure polycrystalline silicon. Many techniques have been developed to accomplish this, and they all rely on a similar set of concepts that describe the transport process, thermodynamically controlled solubility, and kinetics [8]. Three important methods are the vertical Bridgman-Stockbarger, Czochralski, and floating zone processes, fully described in Fundamentals of Crystal Growth by Rosenberger [9]. 

Very pure, low-defect crystals are produced by the alternative float zone process in which a cylindrical polysilicon rod has a seed crystal melted into its lower end with an encircling inductive heating coil. The heater is then raised along the rod length, entraining a molten zone and a monocrystalline solidified region below. Impurities have higher solubility in the molten silicon and are carried with it to the top. The process may be repeated to enhance the purity and crystallinity. 

Float-Zone Process - In reference to solar photovoltaic cell manufacure, a method of growing a large-size, high-quality crystal whereby coils heat a polycrystalline ingot placed atop a single-crystal seed. As the coils are slowly raised the molten interface beneath the coils becomes a single crystal. 

Three processes are known to fabricate continuous yttrium aluminum garnet (YAG) fibers. Single crystal YAG fibers are obtained by the edge defined film fed growth process and by the laser heated float zone process (Chapter 4.5). Both are slow processes. Amorphous YAG glass fibers have recently been demonstrated by a containerless laser heated melt process (Chapter 4.4). Polycrystalllne YAG fibers can be obtained with sol-gel and related processes (this chapter). These are potentially fast processes. 

Laser heated float zone process In this process, a circumferential laser is placed around a preform rod to zone refine a segment of the material while simultaneously updrawing a single crystal fiber. 

Dislcxation-free silicon single crystals are the basic material of microelectronics and nanoelectronics. Physical properties of semiconductor silicon are determined by the structural perfection of the crystals grown by the Czochralski and float-zone processes (Huff, 2002). In such crystals during their growth are formed grown-in microdefects. 

Mutual alloying and doping improve the mechanical properties. Hardness values of the TiC-VC system with carbon-to-metal ratios close to 0.84 obtained for various cooling rates in a floating-zone process indicated that the variation in hardness of pure VCo,84 obtained by chang-... 

Y Kumashiro, Y Nagai, H Kato, E Sakuma, K Watanabe, S Misawa. The preparation and characteristics of ZrC and TaC single crystal using an r.f. floating-zone process. J Mater Sci 16 2931, 1981. 

Y Kumashiro, A Itoh, S Misawa. TiC single crystals prepared by the radio frequency floating zone process. J Less Common Met 32 21, 1973. 

De la Puente, G. F., Diez, J. C., Angurel, L. A., Pena, J., Sotelo, A., Navarro, R. (1995). Wavelength dependence in laser floating zone processing. A case study with bi-SR-CA-CU-0 superconductors. Advanced Materials, 7(10), 853-856. doi 10.1002/adma. 19950071008. 

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