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 m irror furnace under static axial magnetic fields (magnetic induction B less than or equal to 500 mT). A strong influence of the magnetic fie ld on the formation of dopant striations could be detected: Whereas cr ystals grown without field show an irregular striation pattern implyin g a broad frequency range of the melt flows (0.1-5 Hz), fields as smal l as 60 mT already show an influence by reducing the frequency spectru m to a range of 0.1-1.5 Hz. Higher fields reduce the spectrum even fur ther and at fields of 220 mT only one frequency remains, producing a p eriodic striation pattern. Above 240 mT, nearly striation-free crystal s could be obtained. In addition to changes in the microsegregation, t he 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 reg ion in the crystal. The core diameter is directly dependent on the mag netic induction. (C) 1998 Elsevier Science B.V. All rights reserved.