Float zone growth and characterization of Ge1-xSix (x <= 10 at%) single crystals

Ge1-xSix (x less than or equal to 10 at%) single crystals were grown with t he float zone technique using a monoellipsoid mirror furnace. The feed rod consisted of pre-synthesized Ge0.95Si0.05 polycrystalline material with an initial composition of pure germanium. Several boron-doped (1-2 x 10(17) at cm (-3)) crystals were grown using (1 0 0) Ge seeds. Taking advantage of t he pre-synthesized feed rods, a defined macrosegregation could be achieved in the grown crystals with a linear slope at the beginning (approximate to 0.5 at% mm (-1)) followed by a plateau region with a constant silicon distr ibution (Si concentration up to 10 at%, fluctuation rate: less than or equa l to +/-0.3 at%). The etch pit density was in the range of 7 x 10(3)-2 x 10 (4)cm(-2) Micrographs of the etched crystals show sharp changes in interfac e curvature at the crystal edges. These distortions of the interface morpho logy are a direct function of the Si concentration; they are considered to be caused by solutal Marangoni convection. Theoretical considerations show that the flow direction and strength vary significantly from a solutal Mara ngoni convection regime directly in front of the solid-liquid interface to a thermal Marangoni convection regime within the bulk melt. (C) 2001 Elsevi er Science B.V. All rights reserved.