The Critical Growth Rate for Particle Incorporation during the Directional Solidification of Solar Silicon under Microgravity

Int. J. Microgravity Sci. Appl. 2017p340115
Tina SORGENFREI , Thomas JAUSS , Arne CRÖLL , Christian REIMANN , Jochen FRIEDRICH and Martin VOLZ
Crystallography, University of Freiburg, Hermann-Herder-Str.,Fraunhofer Institute for Integrated Circuits and Devices, Schottkystr.,NASA Marshall Space Flight Center,
Foreign phase particles, which are engulfed by a growth front and then incorporated into a growing crystal, can cause a variety of problems. These problems can influence the crystal growth process and the preparation of the crystal or reduce the performance of resulting devices. In photovoltaics, the incorporation of SiC particles in VGF silicon leads to a relatively high material loss due to wire saw damages and shunts in the resulting solar cells. Due to the setup of the directional solidification the formation of SiC particles can hardly be avoided. Therefore, it is important to control the incorporation of the particles. It is known that the incorporation is dependent on the size of the particles and on the velocity of the moving solid-liquid interface. Existing theoretical models describe the transition between pushing and engulfment, but growth experiments show that the experimental values for the transition between these two states deviate significantly from the theoretical ones. In this work, several experiments under 1 G conditions and an experiment under µg conditions were done to investigate this question. The µg setup is necessary to get as close as possible to diffusive conditions which are the basic parameters for the theoretical calculations.
Foreign phase particle, Particle engulfment, Particle pushing, Melt growth, Silicon, VGF, Directional solidification

Received 24 December 2015, Accepted 12 October 2016, Published 31 January 2017

© The Japan Society of Microgravity Applicaiton

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