A new technique is proposed, in which the thin neck formation process is adopted after the seeding process in the vertical Bridgman growth of sapphire crystals.

   The process stages of the new technique are shown in figure 1. The raw materials are put into a Mo or W crucible from above and a c-axis seed crystal is inserted in the seed well at the bottom of the crucible as shown in Fig.1 (a). The growth processes consists of first seeding, after melting of all raw material and a part of seed crystal, as shown in Fig1(b) and then, as the crucible is pulled down, formation of thin neck, as shown in Fig1(c), and growth of the crystal body, as shown in Fig1(d). After cooling to room temperature, it was found that the seed and the body grown could be easily separated and released from the crucible¹⁾.

   Samples cut from grown crystals were polished to mirror finish on both side and were characterized using a crossed polarizer and X-ray topography. It was confirmed that low angle grain boundaries generated at the periphery of seeding portion were eliminated at the thin neck and c-axis crystals free from low angle grain boundaries in the main body were successfully grown.

   We concluded that the proposed new technique incorporating a thin neck formation process in the vertical Bridgman growth method promises high potential in growth of large-size and high quality c-axis sapphire crystals with high reproducibility.

(1)   C. Miyagawa et.al: Demonstration of crack-free c-axis sapphire crystal growth using vertical Bridgman method, Journal of Crystal Growth. (in printing)

1. POSTER: Vertical Bridgman Growth of Sapphire Crystals with Thin Neck Formation Process, JPEG image data, JFIF standard 1.02, 0.1MB

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