Mat. Res. Bull., Tol. 24, pp. 995-1004, 1989. Printed in the USA. 0025-5408/89 $3.0, + .00 Copyright (e) 1989 Pergamon Press plc. THE CRITICAL MARANGONI NUMBER FOR THE ONSET OF TIME -DEPENDENT CONVECTION IN SILICON A. CrSll, W. Mfiller-Sebert and tk Nitsche Kristallographisches Institut der Universitgt Hebelstr. 25, D-7800 Freiburg i. Br., FRG (Received May 10, 1989; Refereed) ABSTRACT A novel technique has been developed for evaluation of the critical Marangoni number Ma~ for time-dependent convection in silicon. This was achieved by ob- serving the onset of formation of dopant striations in silicon crystals grown by the floating-zone-technique with small free melt surfaces. A value of about 200 was found for Ma2 c. MATERIAI,S INDEX: semiconductors, silicon Introduction The perfection and homogeneity of crystals is influenced by flows in the fluid nutri('ut during the growth process. Such flows affect the transport of dopants to and their segrega- tion at the growing interface. Thus, the macroscopic and microscopic dopant distributions in semiconductor crystals are related to the flow patterns which prevailed in the melt dur- ing growth. Whereas steady flows influence only the macroscopic segregation, timc~-~le pendent flows lead to dopant inhomogeneities in the ~m range, the so-called striations. More specifically , they are called type--I-striations, in contrast to the type-II-striations of kinetic origin (1). Commonly, such flows are caused by buoyancy convection, driven by gravity or by thermocapillary convection (Marangoni convection), driven by the tempera 995