Crystallization kinetics in Si-1 at%Sn during rapid solidification in undercooled melt
Crystallization kinetics in Si-1 at%Sn during rapid solidification in undercooled melt
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DOI：
10.1016/j.jcrysgro.2016.11.041
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发表时间：
2017-06-15
影响因子：
1.8
通讯作者：
Inatomi, Y.
中科院分区：
文献类型：
--
作者：
Kuribayashi, K.;Ozawa, S.;Inatomi, Y.
为了阐明半导体材料过冷熔体中晶体生长形态转变的原因，我们采用CO2激光电磁悬浮器（EML）对未掺杂Si和Si-1at%Sn进行了无容器凝固。在控制过冷度下成功地实现了这些材料的结晶。Si-1at%Sn中生长晶体的形状与过冷度之间的关系与未掺杂Si中的相似，即在低过冷度下观察到板状针状晶体，而在中等和高过冷度下生长晶体的形状变为块状树枝晶。与未掺杂的Si相比，Si-1at%Sn的凝固样品的晶粒尺寸显著地小。通过将熔体滴在镜面抛光的硅的冷却板上凝固的样品的表面形貌由典型的孪晶相关的< 110 >枝晶组成。另一方面，从过冷状态落下的样品由无孪晶的< 100 >枝晶组成。基于两种机制（孪晶重入刃机制和无孪晶机制）计算的二维形核率表明，< 100 >< 110 >当过冷度大于临界值时，发生了由孪晶相关枝晶向无孪晶枝晶的形态转变。这些结果表明，过冷熔体中Si生长形态转变的原因不是晶液界面的粗糙化转变，而是形核动力学从孪晶相关机制向无孪晶机制的转变。
In order to elucidate the cause of the morphological transition of crystals growing in an undercooled melt of semiconducting materials, we carried out the containerless solidification of undoped Si and Si-1 at% Sn using a CO2 laser-equipped electromagnetic levitator (EML). The crystallization of these materials was successfully achieved under controlled undercooling. The relation between the shape of growing crystals and the degree of undercooling in Si-1 at% Sn was similar to that in undoped Si; that is, plate-like needle crystals were observed at low undercooling, whereas at medium and high undercooling the shape of growing crystals changed to massive dendrites. The grain-size of as-solidified samples of Si-1 at% Sn was remarkably small compared with that of undoped Si. The surface morphologies of samples solidified by dropping the melt onto a chill plate of mirror-polished silicon consisted of typical twin-related < 110 > dendrites. On the other hand, samples that were dropped from the undercooled state consisted of twin-free < 100 > dendrites. The nucleation rate of two-dimensional nuclei calculated on the basis of two mechanisms, which are the twin-plane re-entrant edge mechanism and the twin-free mechanism, suggested that the morphological transition to twin-free < 100 > dendrites from twin-related < 110 > dendrites occurs when the degree of undercooling becomes larger than the critical value. These results indicate that the cause of the morphological transition of Si growing in the undercooled melt is not the roughening transition of the crystal-melt interface but the transition of the nucleation kinetics to the twin-free mechanism from the twin-related mechanism.