Choice of the dimensions of the Te zone and control of its interface shape are considered essential in determining the crystallinity. For example, for the growth of rods 10 mm in diameter and ~60 mm long, Schoenholtz demonstrate that a 3 mm wide Te zone generates polycrystalline boules, the grain size being 0.5 of the diameter of the rod. Using of a 4 or 6 mm wide zone generated sing crystals ro..