Tailored magnetic damping of g-jitter driven buoyant convection during bridgman growth of semiconductor crystals in space

In the Bridgman process, a single crystal is grown by the directional solidification of an initially molten semiconductor (melt) contained in a cylindrical ampoule. A crystal-growth experiment in an earthorbiting vehicle is subjected to residual accelerations (g-jitters) which drive an undesirable oscillatory buoyant convection in the melt. Since many molten semiconductors have electrical conductivities which are comparable to that of mercury, the magnitude of the buoyant convection is dramatically reduced by applying a magnetic field during crystal growth. The magnetic field can be produced by a permanent magnet or by a solenoid around the crystal-growth furnace. We treat the buoyant convection driven by periodic g-jitters whose direction is parallel to the axis of the ampoule. There is a non-uniform magnetic field which is axisymmetric around the ampoule axis. We compare the magnitudes and characteristics of the buoyant convections for various non-uniform magnetic fields to those for a uniform axial magnetic field. Fringing fields with the largest or smallest magnetic fiux density at the crystal-melt interface are considered.