毕业设计（论文）-铸造多晶硅晶体生长速率对杂质分布的影响研究.doc

铸造多晶硅晶体生长速率对杂质分布的影响研究
摘要
目前,铸造多晶硅是最主要的光伏材料,其结晶组织、缺陷、和杂质含量显著影响着太阳能电池的转换效率。杂质的浓度和分布是影响光电转换效率的重要因素。由于多晶硅锭的质量好坏主要取决于长晶过程中的固液界面形状及晶体生长速率大小,固液界面形状及晶体生长速率大小对定向凝固的排杂效果起决定作用,一般认为微凸的固液界面更有利于多晶硅杂质和位错的排除。因此深入研究多晶硅生长速率对杂质分布的影响,分析它对多晶硅锭结晶学及电学性能的影响,不仅有利于生长出高成品率的铸造多晶硅锭,而且可以降低铸造多晶硅硅片的制造成本。
本工作利用微波光电导衰减仪(μ-PCD)、二次离子质谱仪(SIMS),以及红外扫描仪(IR)等方法对铸造多晶硅的杂质以及少子寿命的分布进行了系统的研究。实验发现,硅锭中的氧浓度随硅锭高度的增加而逐渐降低,而碳的分布情况正好相反。研究发现,在低速凝固条件下杂质的排除效果很好,平均少子寿命较高,但多晶硅锭的红区较长,铸锭周期长。而高速凝固杂质的排除效果不佳,硅锭红区较短,但平均少子寿命较低。。
关键词:铸造多晶硅,杂质,少子寿命,长晶速率
The investigation on the crystal growth rate of casting polycrystalline silicon influencing on the distribution of impurity
ABSTRACT
At present, casting polycrystalline silicon is the main PV materil. It affects
are the important factors of photoelectric conversion quality of poolycrystalline silicon ingots is determined by the position of the solid/liquid interface and growth rate of crystal. The shape of solid/liquid interface and growth rate determined the quality of rejecting of ,small protruding liquid-solid interface is more advantageous to the reject of dislocation and further research on the influence of polysilicon growth rate on the impurity distribution and electrical behaviour of polycrystalline silicon ingots will help us improve the yield of the ingots and reduce the cost of casting polycrystalline silicon.
In this thesis, we investigate the distribution of impurity and minority carrier lifetime of the ingots by Microwavephoto Conductive Decay(μ-PCD), ScanningInfrared Microscopy(IR), Scanning Infrared Microscopy(SIRM) . In the experiments, oxygen content increases in vetical direction, While carbon distribution is exactly thepposite. We find that low-speed solidification conditions is good to the reject of all the reject of all the metal inpurity,minority carrier lifetime is higher, but the casting cycle is longer. Whle High-speed solidification to the disadvantage of the reje