Silicon ultrapure single-crystal

Large-scale synthesis of materials Ultrapure single-crystal silicon Ultrapure glass... 

Challenge Problem. According to Kenny et al., Avogadro s number may be calculated from the following equation using measurements on a sphere fabricated from an ultrapure single crystal of silicon. 

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]. 

Since the electrical properties of semiconductors are strongly influenced by the incorporation of heteroelements, ultrapure semiconductor grade silicon is obtained by the reduction of SiCL, or SiHCh with very pure Mg or Zn, followed by the growth from the molten silicon of a columnar single crystal which is further purified... 

Ultrapure silicon is the product of a very expensive multistage purification process (see Section 3.4.1.1.2). The price for this material therefore increases strongly with the degree of refining. 1 kg of polycrystalline ultrapure silicon ( polysilicon ) from the pyrolysis of SiHCly cost ca. 80 DEM in 1997, silicon single crystals ca. 600 DEM/kg and silicon wafers used in semiconductor technology ca. 1700 DEM/kg. 

The specific resistance of ultrapure silicon single crystals of up to 150 000 12 cm decreases upon doping with 1 ppb of phosphorus to 100 Q cm. Therefore the purity... 

With solar cells on the basis of ultrapure silicon, sunlight can be direetly converted into direct current electricity utilizing the photovoltaic effect. Silicon wafers from single crystal or cheaper directionally crystallized polycrystalline ultrapure silicon are utilized for solar cell manufacture. Solar cell electricity production efficiencies up to 18% are attained with single crystal material and up to 16% with polycrystalline material. 

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