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

这项研究的目的是论证从硅基合金熔体中拉晶生产板状或棒状硅晶体的可能性，这种新工艺将在较低的温度下进行，并且比通常的工艺需要更少的能耗。作为模型实验，用Si-45wt%Ni合金进行了晶体拉拔。在低过冷度条件下，硅晶体生长的择优取向为a-lt；211&gt；晶向，实验中采用的是晶种晶片。当熔体过冷时，小平面树枝晶沿着熔体的自由面生长，因此很难生长出板状硅晶体。当熔体略有过热时，在1~5℃的过热度和拉拔速度低于0.015 mm/min的条件下，外延生长到种子晶体上的硅晶体成功地被拉出。得到的晶体在形状上分为针状、棒状和角状三种类型。部分针状和棒状晶体内部含有Si-Ni共晶。晶种和晶体生长过程中温度分布的估算表明，晶体生长处于热稳定状态。熔体对晶体的润湿行为对晶体的稳定拉拔起着重要作用。对生长条件的详细考察表明，在0.03 mm/min的生长速度范围内，可以稳定地生长出硅多晶。结晶学分析表明，在拉晶过程中，再入拐角机制占主导地位。结果表明，从硅基合金熔体中拉出晶体是可行的。也有人建议，将棒状晶体和抛物面反射镜相结合，将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.