Direct production of silicon crystals for solar cells from the melt of silicon alloys using self-shape maintaining characteristics of a crystal

该研究旨在证明通过从硅基合金熔体中拉晶来生产板或棒硅晶体的新工艺的可能性，该工艺将在低温下进行，并且需要比常规工艺更少的能耗。作为模型实验，使用Si-45wt%Ni合金进行晶体提拉。在深过冷条件下，硅晶体生长的择优取向是<211>晶体学方向，实验中使用了具有晶体学方向的籽晶板<211>。当熔体过冷时，小面枝晶沿熔体的自由表面沿着生长，因此难以生长板状硅晶体。当熔体稍微过热时，在从1到5摄氏度的过热和低于0.015 mm/min的提拉速度的条件下，成功地提拉外延生长到籽晶的硅晶体。所得晶体按形状分为针状、棒状和玉米状三种晶体。部分针状和棒状晶体内部含有Si-Ni共晶。对籽晶和生长晶体中的温度分布进行了估算，结果表明，晶体是在热稳定状态下生长的。熔体对晶体的润湿行为对晶体的稳定提拉起着重要作用。生长条件的详细检查表明，硅多晶体在生长速度低于0.03mm/分钟的范围内稳定生长。晶体学分析表明，在拉晶过程中，缩角机制占主导地位。结果表明，从硅基合金熔体中拉晶是可行的。还有人建议，将棒状晶体和抛物面镜结合起来，就有可能形成一种新的太阳能电池系统。

The research was aimed to demonstrate the possibility of the new production process of plate or rod silicon crystals by crystal pulling from the melt of silicon-based alloys, which would be conducted at low temperature and need less energy consumption than usual processes. As model experiments, the crystal pulling was performed using Si-45wt%Ni alloy. The preferred orientation for silicon crystal growth at low undercooling was a <211> crystallographic direction and a seed crystal plate with a <211> direction was used in the experiments. When the melt was undercooled, facet dendrites grew along the free surface of the melt and thus it was difficult to grow a plate silicon crystal. When the melt was slightly superheated, silicon crystals epitaxially grown to the seed crystal were successfully pulled up under the conditions of superheating from one to five degrees Celsius and pulling velocity under 0.015 mm per minute. The obtained crystals were classified into three types of needle-, rod- and corn-shape-crystal in their shapes. Some of needle- and rod-crystals contained Si-Ni eutectics inside. The temperature distribution estimated in the seed and the growing crystal showed that the crystal was grown in thermally steady state. The wetting behavior of the melt to the crystal played an important role for the stable crystal pulling. The examination of the growth condition in detail showed that a silicon multi-crystal was stably grown in the range of growth velocity under 0.03 mm per minute. From the crystallographic examination revealed the re-entrant corner mechanism was dominant in the crystal pulling process. It was concluded that the crystal pulling from the melt of silicon-based alloys was practically possible. It was also suggested that a new solar cell system would be possible by combining a rod-crystal and a parabolic mirror.