The paper discusses a possibility to use different types of rotating magnetic fields (RMF) and combinations of these to control the hydrodynamics and heat/mass transfer in the processes of bulk semiconductor single crystal growth. Some factors contributing to the efficiency of RMF and their influence on different technologies are analyzed. Their specific practical application is illustrated by some examples.
KEYWORDS
Rotating magnetic field; Eleetroconducting liquid; Hydrodynamics; Single crystal growth; Solidification front 1. Introduction. Recently rotating magnetic fields (RMF) are used more often to control the heat and mass transfer in single crystal growth (Gelfgat and Priede, 1995; Dold and Benz, 1997;Friedrich et al, 1997). Certain simplicity of the devices' design and the adjustment of these to growth facilities that usually have an axially symmetric configuration mostly explain the application of RMF. Besides, RMF consume less power compared, for example, to the devices employing steady magnetic fields (SMF).
The present report describes some peculiarities of RMF influence on the melt in an ampoule or in a crucible. The efficiency of such influence for different geometrical ratios of the system "RMF inductor -vessel with the melt" is considered. The paper also discusses some combinations of RMF which enhance the influence of RMF on the growth process quantitatively and qualitatively. In all cases the initial melt is assumed to have an electrical conductivity of about 104-106 Ohrn'lm "1 that is characteristic for semiconductor mono-and multi-component materials when these are molten.
- Some peculiarities of hydrodynamic flows in RMF. As a rule, the RMF is generated by a cylindrical inductor resembling the stator of a three-phase asynchronical electrical engine. A melt-filled ampoule is placed along the axis of the inductor. An alternating magnetic field induces currents in a conducting fluid. These interact with the field of the inductor and generate an azimuthal electromagnetic force in the melt. The RMF efficiency and the pattern of hydrodynamic flows due to RMF in a cylindrical volume depend on the distribution of electromagnetic forces in the melt. This distribution is determined by a number of pole pairs of the inductor, the frequency of work current as well as the relations between H (melt's height) and H= (inductor's height) and R (ampoule's radius) and R1 (inductor's radius) -Fig. 1.