Floating-zone growth of silicon in magnetic fields - I. Weak static axial fields

Silicon floating-zone experiments, employing P- and Sb-doped crystals of 8 mm diameter and zones of 10-12 mm length, were carried out in a mirror furnace under static axial magnetic fields (magnetic induction B less than or equal to 500 mT). A strong influence of the magnetic field on the formation of dopant striations could be detected: Whereas crystals grown without field show an irregular striation pattern implying a broad frequency range of the melt flows (0.1-5 Hz), fields as small as 60 mT already show an influence by reducing the frequency spectrum to a range of 0.1-1.5 Hz. Higher fields reduce the spectrum even further and at fields of 220 mT only one frequency remains, producing a periodic striation pattern. Above 240 mT, nearly striation-free crystals could be obtained. In addition to changes in the microsegregation, the transient part of the axial macrosegregation is steeper because of the reduced mixing of the melt. The radial segregation is changed by a flattening of the interface curvature and the formation of a core region in the crystal. The core diameter is directly dependent on the magnetic induction. (C) 1998 Elsevier Science B.V. All rights reserved.