Influence of ampoule rotation on three-dimensional convection and segregation in Bridgman crystal growth under imperfect growth conditions

Three-dimensional (3D) convection and segregation due to imperfect growth c onditions, such as ampoule tilting and asymmetric heating, are common probl ems in vertical Bridgman crystal growth. How to suppress the 3D effects has been an important task for better growth control. To investigate the possi bility of using steady ampoule rotation to damp the 3D flows, numerical sim ulation is conducted. It is found that the low-speed rotation (e.g., 10 RPM ) can reduce significantly the 3D flows, but may result in larger radial se gregation due to less dopant mixing, as well as rotational growth and melti ng. For weaker convection, which corresponds to a low-thermal-gradient or r educed-gravity growth, ampoule rotation is particularly effective. This is especially true in space, where the 3D flows and segregation induced by an arbitrary residual gravity can be significantly suppressed by only several RPM of ampoule rotation leading to a nearly diffusion-controlled growth. Ho wever, if the growth interface is not axisymmetric, which is often caused b y an asymmetric heating, rotational segregation can be quite severe, even w ithout the buoyancy convection. (C) 2000 Elsevier Science B.V. All rights r eserved.