Suppressing three-dimensional unsteady flows in vertical zone-melting by steady ampoule rotation

Three-dimensional (3D) unsteady heat flow and molten zone induced by nonlin ear bifurcations or imperfect growth conditions are typical in vertical zon e-melting crystal growth or refining. Through flow modification, we find th at the use of steady ampoule rotation is effective in suppressing these 3D characteristics. Even with only 10 RPM ampoule rotation, numerical simulati on indicates that the steady axisymmetric (or nearly) mode can be easily re tained for 2-in GaAs under a typical growth condition, in which the 3D unst eady flows prevail for no rotation. A model gallium zone is also examined, and its 3D bifurcations are significantly suppressed by rotation as well. H owever, if the rotation is not sufficient to suppress the unsteadiness, bar oclinic waves may appear. The effects of ampoule rotation for imperfect gro wth conditions, including asymmetric heating and ampoule tilting, are furth er illustrated. The ampoule rotation is also found useful. (C) 2000 Elsevie r Science B.V. All rights reserved.