Effects of ampoule rotation on flows and dopant segregation in vertical Bridgman crystal growth

Computer simulation is conducted to study the effects of ampoule rotation on the flows and the dopant segregation in vertical Bridgman (VB) crystal growth. A benchmark problem for the growth of gallium-doped germanium in a graphite ampoule is used as an example. Both pseudo-steady state and fully transient calculations are conducted. It is found that the convection and dopant segregation can be affected significantly by ampoule rotation, and the effect is similar to that by an axial magnetic field. Ampoule rotation decreases the intensity of convection and stretches the flow cell axially. As a result, both radial and axial segregations are affected. When the convection is weak, the flow can be suppressed almost completely by moderate ampoule rotation and the dopant segregation becomes diffusion-controlled For stronger convection, the elongated flow cell by ampoule rotation may bring dopant mixing into the bulk melt reducing axial segregation at the early stage of the growth. However, if the cellular flow cannot be suppressed completely, ampoule rotation may induce larger radial segregation due to poor mixing. (C) 1999 Elsevier Science B.V. All rights reserved.