Filamentary sapphire

Abstract

The “edge-defined, film-fed growth” (EFG) technique was used to grow filamentary sapphire from tungsten growth orifices in the 〈0001〉 growth direction. The higher thermal conductivity of tungsten, compared with molybdenum orifices, results in more efficient heat removal at the growth interface and allows the stable growth of filamentary sapphire at rates up to 15 cm/min. More important, at rates as high as 3.0 cm/min, sapphire was grown entirely free of microvoids. This void-free sapphire acted as a light pipe and had average tensile strength as high as 3.3 x 10⁹ N/m² (480 × 10³ lb/in.²). The role of tungsten in creating the planar solid/liquid growth interface necessary for void-free growth was investigated using tungsten orifices having different ratios of feed capillary to outside diameter. Finally, the conditions necessary for void-free growth are discussed in terms of the thermal generation and heat transfer processes occurring within the liquid film from which the crystal is withdrawn.