Crystal Growth and Design of Sapphire: Experimental
and Calculation Studies of Anisotropic Crystal Growth upon Pulling
Directions
- Publication date
- Publisher
Abstract
The anisotropic growth of large-size
sapphire single crystals along
different pulling directions was studied on the basis of the chemical
bonding theory of single crystal growth and practical Czochralski
growth. The projection of thermodynamic morphology of sapphire single
crystal respectively along [210], [110], [001], and [001] rotated
57.62° directions can be used to confirm the growth directions
of surfaces that are preferred to be exposed thermodynamically in
Czochralski growth. Starting from these thermodynamically preferred
directions, the possible radial directions that are normal to the
four typical pulling directions by kinetic controls have been identified
by anisotropic chemical bonding distributions of sapphire single crystal.
Chemical bonding calculations demonstrate that the lower pulling rate
should be designed when <i>R</i><sub>axial</sub>/<i>R</i><sub>radial</sub> > 1, whereas the higher pulling rate
should be designed when <i>R</i><sub>axial</sub>/<i>R</i><sub>radial</sub> < 1. The anisotropic chemical bonding
conditions demonstrate the lowest chemical bonding density along the
radial directions of sapphire single crystal when it grows along the
[001] pulling direction. Taking [001] as the pulling direction in
practical growth, a ϕ 2″ sapphire single crystal was
grown via the Czochralski method with a growth rate of 2–3
mm/h. Our present work shows the effect of anisotropy on the Czochralski
growth of large-size single crystals, which can provide a theoretical
guide in practical growth from both thermodynamic and kinetic viewpoints