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首页> 外文学位 >Hierarchy of Grain Boundary Impurity Gettering and Passivation in Photovoltaic Multicrystalline Silicon.
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Hierarchy of Grain Boundary Impurity Gettering and Passivation in Photovoltaic Multicrystalline Silicon.

机译：光伏多晶硅中晶界杂质吸收和钝化的层次结构。

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摘要

This thesis examines grain boundaries, dislocations and metallic impurities in photovoltaic multicrystalline silicon (PV mc-Si). The interaction dynamics between hierarchy of grain boundaries (GBs), nickel, iron, and intragrain defects during thermal and hydrogenation processes have been studied. Localized Deep Level Transient Spectroscopy (DLTS) analysis was applied to quantify the changes induced by rapid thermal annealing (RTA) in trap states and accompanying decrease of carrier recombination in respect to the hierarchy of GBs and the dislocation density. A unique in-situ microscopic masking process for Schottky diode preparation which practically enables the localized probing of specific electrical active defect structure has been developed to investigate the local properties of mc-Si wafers. The reduction of recombination activity at GBs after RTA was found to be dominated by impurity decoration and less influenced by the relative structural mismatch for a specific type of GB. A new type of spectra was observed in PV thin mc-Si and its origins are attributed to the additional barrier height caused by GB hetro-junction.;The gettering capabilities of GBs were found to follow the sigma order in high sigma GB group but no consistent gettering relationship was found between gettering strength and low sigma group (O3 and twins). Electron bean induced current (EBIC) result shows that most of dislocation sites and twins (intragrain defects) present a weak or no impurity gettering tendency if they co-exist with GBs. GBs present as a more favored gettering sites to attract impurities under annealing condition. GB gettering strength presents a higher dependence on the hierarchy of crystal defect and lower dependence on the impurity type. GB plane also plays an influential role in the gettering behavior of GBs. On the other hand, the concentration of electrically "inactive" metals due to the presence of structural defect was quantified by subtracting the difference between the bulk metallic impurity concentration and electrical trap concentration. The electrical inactive level of nickel was found a least one order of magnitude higher than iron.;Silicon nitride hydrogenation was found to be effective on both coincidence site lattice (CSL) GBs and random GBs (R). This passivation also demonstrated significant passivation effects on dislocations, small angle (SA) GBs and twin boundaries (TBs) in mc-Si. Besides GB character, the local conditions like stress field also demonstrate an essential influence on the hydrogenation result. It was found that the main mechanism of SiN passivation at GB is to shift the trap energy level toward a shallower level so that the minority carrier recombination decreases. Relatively smaller grains present higher lifetime and also a better lifetime improvement after hydrogenation. The pure impact of GB mismatch on the density of interfacial states and deep level states were characterized by multi-frequency IV/CV and DLTS by using bonded wafer as GB model. The density of interfacial states at hetero -- GB was found to be 1.5 times higher than homo -- GB. Dislocations from GB misfit and induced by oxidation process were found to present different trap energy levels.
机译：本文研究了光伏多晶硅（PV mc-Si）中的晶界，位错和金属杂质。研究了热和加氢过程中晶界（GBs），镍，铁和晶粒内缺陷层次之间的相互作用动力学。局部深层瞬态光谱法（DLTS）分析用于量化由快速热退火（RTA）引起的陷阱态的变化以及随之而来的相对于GBs和位错密度的载流子复合减少。已经开发出一种独特的用于肖特基二极管制备的原位微观掩膜工艺，该工艺实际上能够对特定的电活性缺陷结构进行局部探测，以研究mc-Si晶片的局部特性。发现RTA后GBs的重组活性降低主要受杂质修饰的影响，而不受特定类型GB相对结构不匹配的影响。在PV薄mc-Si中观察到一种新型光谱，其起源归因于GB异质结引起的附加势垒高度。;在高sigma GB组中发现GBs的吸杂能力遵循sigma顺序，但没有吸气强度与低西格玛组（O3和双胞胎）之间存在一致的吸气关系。电子豆感应电流（EBIC）结果表明，如果与GBs共存，大多数位错位点和孪晶（晶格缺陷）呈现出弱的或没有杂质吸收的趋势。 GB在退火条件下作为更有利的吸气部位存在，以吸引杂质。 GB的吸杂强度对晶体缺陷的等级依赖性较高，对杂质类型的依赖性较低。 GB平面在GBs的吸杂行为中也起着重要作用。另一方面，由于结构缺陷的存在，电“惰性”金属的浓度通过减去体金属杂质浓度和电陷阱浓度之间的差来量化。发现镍的无电水平比铁高至少一个数量级。氮化硅氢化作用对重合点晶格（CSL）GB和随机GBs（R）均有效。该钝化还显示出对mc-Si中的位错，小角度（SA）GB和孪晶边界（TB）的显着钝化作用。除GB特性外，应力场等局部条件也显示出对氢化结果的重要影响。发现GB处的SiN钝化的主要机理是使陷阱能级向较浅的级移动，从而减少了少数载流子的复合。相对较小的晶粒具有较高的寿命，并且在氢化后也具有较好的寿命改善。以键合晶圆为GB模型，通过多频IV / CV和DLTS表征了GB失配对界面态和深能级态密度的纯影响。发现异质GB的界面态密度是同质GB的1.5倍。发现GB失配引起的位错和由氧化过程引起的位错表现出不同的陷阱能级。

著录项

  • 作者

    Yu, Liya.;

  • 作者单位

    North Carolina State University.;

  • 授予单位 North Carolina State University.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 203 p.
  • 总页数 203
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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