Growth of Boron Crystals by the Czochralski and Floating-Zone Methods

Abstract

An investigation has been made of various ways to densify and grow crystals of boron. Induction heating methods were used to densify the boron in boron nitride crucibles and on pedestals of boron and boron nitride. Crystals approximately 6 in. in length were grown by the Czochralski method from densified charges.

Floating-zone studies were carried out on bars prepared by (a) the Czochralski growth process from boron nitride crucibles and (b) crystal bars as deposited in the vapor phase deposition. Five zone passes were normally made, with the liquid zone moving from the top to the bottom of the vertical ingot. The zoned bars grown from boron nitride crucibles by the Czochralski procès s tended to crack with zoning after one or two zone passes.

Spectrographs analysis of the zoned bar s showed that Si, Fe, Cu, V, and Ca concentrated in the bottom end of the zoned bar, indicating that these impurities had segregation coefficients less than unity. The concentration of magnesium decreased toward the lower end of the bar. Electrical measurements made on the zoned bars showed that the resistivity ranged from 10⁷ to 10⁴ ohm-cm, decreasing toward the bottom portion of the bar. Small monocrystalline areas were found in the float-zoned bars which x-ray studies showed to be of the rhombohedral structure. Comparison is made of properties of the bars zoned in vacuum and ambient gases.