硅凝固生长过程中孪晶和位错形成与演变模拟研究
发布时间：2019-06-26 20:33
【摘要】：多晶硅太阳能电池因生产成本低和光电转换效率较高而成为光伏市场主流。但多晶硅太阳能电池因位错等晶体缺陷的存在,比单晶硅太阳能电池光电转换效率要低。降低定向凝固多晶硅中位错等缺陷密度成为业界努力的目标之一,然而实验上尚难以在硅晶体生长过程之中观测分析缺陷的形成,对缺陷形成机理缺乏深入的认识。本文运用分子动力学模拟方法,硅原子间相互作用采用Tersoff势函数进行计算,就多晶硅中位错和孪晶这两类最重要的晶体缺陷开展了模拟研究,结果表明:(1)硅生长孪晶形成于{111}密排面上,是一个在密排面上HCP结构和FCC结构竞争生长,且HCP结构逐渐占优直至占据整个区域的过程。能量分析发现,硅原子在{111}密排面上的错排能非常低,生长过程两种结构同时出现的概率非常高。当硅晶体沿{111}面生长时,固液界面保持稳定并为密排面,形成孪晶概率最高;沿(110)和(112)面生长时,固液界面均会转化成被{111}小面包围的之字型界面,孪晶在{111}小面上形成,形成概率比沿{111}面生长时低;沿(100)面生长时,固液界面稳定,未能形成{111}小面,整个生长过程中也没有形成孪晶。(2)硅晶体生长过程中位错的形核是伴随在孪晶的形成过程之中,在{111}小面上竞争生长的HCP结构和FCC结构之间容易形成位错。不同面位错形核的难易程度由大到小的顺序为:(100)面(110)面(112)面(111)面。硅晶体沿相同晶面生长时,生长温度越高,位错越难形成。(3)硅晶体生长过程中易形成三种位错,它们是伯氏矢量为1/6112、1/12111的不全位错和1/6110梯杆位错。这些位错在晶体生长过程中伴随着分解和合成复杂变化,如伯氏矢量为1/2110的全位错会分解为两个伯氏矢量为1/6112的不全位错;伯氏矢量1/6112的不全位错仍会分解为亚稳态的1/12111的不全位错;而两个伯氏矢量为1/6112的不全位错会合成一个伯氏矢量为1/6110的梯杆位错。(4)位错形成后会反作用于硅晶体的生长过程。当硅晶体沿(110)面生长时,与生长面垂直的刃位错对硅晶体生长速率影响不大,而螺位错和60°位错则因对生长面的小面化有影响,而降低了硅晶体生长速率。
[Abstract]:Polysilicon solar cells have become the mainstream of photovoltaic market because of their low production cost and high photoelectric conversion efficiency. However, the photoelectric conversion efficiency of polysilicon solar cells is lower than that of single silicon solar cells due to dislocation and other crystal defects. Reducing the density of defects such as dislocation in directionally solidified polysilicon has become one of the goals of the industry. However, it is difficult to observe and analyze the formation of defects in the process of silicon crystal growth, and there is a lack of in-depth understanding of the mechanism of defect formation. In this paper, the molecular dynamics simulation method is used to calculate the interaction between silicon atoms by Tersoff potential function. The two most important crystal defects, dislocation and twinning in polysilicon, are simulated. The results show that: (1) the silicon growth twin is formed on the {111} dense row surface, which is a competitive growth process between HCP structure and FCC structure on the dense arrangement surface, and the HCP structure gradually dominates until it occupies the whole region. Energy analysis shows that the misarrangement energy of silicon atoms on {111} dense arrangement surface is very low, and the probability of simultaneous appearance of the two structures in the growth process is very high. When the silicon crystal grows along the {111} plane, the solid-liquid interface is stable and dense, and the probability of twinning is the highest, and when the solid-liquid interface grows along (110) and (112) planes, the solid-liquid interface is transformed into a zigzag interface surrounded by {111} facets, and the twins are formed on the {111} facet, which is lower than that along the {111} plane. When the solid-liquid interface grows along the plane, the solid-liquid interface is stable and the {111} facet is not formed, and no twins are formed during the whole growth process. (2) the nucleation of dislocation in the process of silicon crystal growth is accompanied by the formation of twins, and it is easy to form dislocations between the competitive growth of HCP structure and FCC structure on {111} facets. The order of difficulty of dislocation nucleation in different planes is (100) face (110) surface (112) surface (111) surface. When silicon crystals grow along the same crystal plane, the higher the growth temperature is, the more difficult it is to form dislocations. (3) three kinds of dislocations are easy to form during the growth of silicon crystals, which are incomplete dislocations of 1: 6112, 1: 12111 and 1: 6110 ladder dislocations. These dislocations are accompanied by complex changes in decomposition and synthesis during crystal growth, such as the total dislocation of 1 鈮，
本文编号：2506469
[Abstract]:Polysilicon solar cells have become the mainstream of photovoltaic market because of their low production cost and high photoelectric conversion efficiency. However, the photoelectric conversion efficiency of polysilicon solar cells is lower than that of single silicon solar cells due to dislocation and other crystal defects. Reducing the density of defects such as dislocation in directionally solidified polysilicon has become one of the goals of the industry. However, it is difficult to observe and analyze the formation of defects in the process of silicon crystal growth, and there is a lack of in-depth understanding of the mechanism of defect formation. In this paper, the molecular dynamics simulation method is used to calculate the interaction between silicon atoms by Tersoff potential function. The two most important crystal defects, dislocation and twinning in polysilicon, are simulated. The results show that: (1) the silicon growth twin is formed on the {111} dense row surface, which is a competitive growth process between HCP structure and FCC structure on the dense arrangement surface, and the HCP structure gradually dominates until it occupies the whole region. Energy analysis shows that the misarrangement energy of silicon atoms on {111} dense arrangement surface is very low, and the probability of simultaneous appearance of the two structures in the growth process is very high. When the silicon crystal grows along the {111} plane, the solid-liquid interface is stable and dense, and the probability of twinning is the highest, and when the solid-liquid interface grows along (110) and (112) planes, the solid-liquid interface is transformed into a zigzag interface surrounded by {111} facets, and the twins are formed on the {111} facet, which is lower than that along the {111} plane. When the solid-liquid interface grows along the plane, the solid-liquid interface is stable and the {111} facet is not formed, and no twins are formed during the whole growth process. (2) the nucleation of dislocation in the process of silicon crystal growth is accompanied by the formation of twins, and it is easy to form dislocations between the competitive growth of HCP structure and FCC structure on {111} facets. The order of difficulty of dislocation nucleation in different planes is (100) face (110) surface (112) surface (111) surface. When silicon crystals grow along the same crystal plane, the higher the growth temperature is, the more difficult it is to form dislocations. (3) three kinds of dislocations are easy to form during the growth of silicon crystals, which are incomplete dislocations of 1: 6112, 1: 12111 and 1: 6110 ladder dislocations. These dislocations are accompanied by complex changes in decomposition and synthesis during crystal growth, such as the total dislocation of 1 鈮，
本文编号：2506469
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