2008In situ observation of Si faceted dendrite growth from.pdf

Available online at /locate/actamat Acta Materialia 56 (2008) 2663–2668In situ observation of Si faceted dendrite growth from low-degree-of-undercooling melts Kozo Fujiwara *, Kensaku Maeda, Noritaka Usami, Gen Sazaki, Yoshitaro Nose, Akiko Nomura, Toetsu Shishido, Kazuo Nakajima Institute for Materials Research (IMR), Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan Received 13 July 2007; received in revised form 30 January 2008; accepted 30 January 2008 Available online 6 March 2008Abstract We directly observed the transition of crystal growth behavior of Si in a low undercooling region. We succeeded in observing the initiation of faceted dendrite growth from a portion of parallel twins with increasing degrees of undercooling. The critical undercooling for growing a faceted dendrite was experimentally determined to be DT = 10 K. We also confirmed that parallel twins associated with faceted dendrite growth were formed between grain boundaries and not at grain boundaries during melt growth. The parallel-twin for- mation was explained in terms of a model of twin formation on the {111} facet plane at the growth interface.  2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Faceted dendrite; Solid/liquid interface; Silicon; Undercooling; Twin boundary1. Introduction Many fundamental studies of faceted dendrites of Si and Ge have been carried out over the last 50 years [1–21]. These have shown that faceted dendrite growth occurs when a crystal with more than two parallel twins grows from an undercooled melt. Recently, dendrites grown from a highly undercooled Si or Ge melt have been extensively investigated by flux methods [9–12] or electromagnetic lev- itation (EML) methods [13–20]. Aoyama and coworkers directly observed crystal growth processes from under- cooled Si melts by an EML method with a high-speed cam- era [14,15]. They succeeded in determining the relationship between growth velocity, V, and degree of under