P型掺杂晶体硅的低温液相外延生长研究
发布时间：2018-11-23 06:05
【摘要】：晶体硅太阳电池是现代光伏电力的主要支撑,其中以p型硅为衬底的p型太阳电池因其传统材料与工艺优势占绝对主导地位。然而近年来n型晶体硅太阳电池因其固有突出优势而逐受重视,成为未来晶硅太阳电池技术的发展方向。n型晶硅太阳电池的技术障碍之一是p型掺杂制结困难。从Al-Si熔体向n型硅晶体衬底表面外延生长Al掺杂的硅晶层是一个有潜在发展前景的低成本解决方案。该方法的原理实际已成功应用于p型太阳电池丝网印刷铝浆烧结制备Al背场,但用于制备pn结则还存在连续均匀性问题,而且铝浆成本相对熔体生长需要的铝锭也要高得多。为此我们开展了Al-Si合金熔体中(001)n型单晶硅衬底上低温液相外延生长p型掺杂硅实验研究,研究集中于(001)外延的原因是单晶硅太阳电池所用均为(001)硅片。我们设计制作了垂直升降浸渍法液相外延生长装置,生长体系内部用流动高纯氩保护。用垂直浸渍法进行了过冷恒温生长与连续降温生长两种模式的低温液相外延生长实验,所考察的生长条件包括衬底表面状态、熔体成分(决定液-固平衡温度)、过冷度、生长时间或降温幅度、以及衬底预热温度等,对所得外延生长晶体进行了结构和形貌显微分析,测定了所形成的pn结开路电压,并运用计算模拟方法分析了影响pn结开路电压的因素。研究取得了以下主要结果。在Al-Si熔体中能够实现硅晶体(001)液相外延生长,但在各种衬底表面状态下过冷恒温外延生长时都呈离散的岛状生长形态,岛的形状为以四个{111}面为表面的金字塔型或屋顶型,显示它是生长中表面能最小化选择结果。这种形态只有在这些岛生长到相互密切接触时才合乎pn结的基本连续性要求,因此较高和均匀的形核密度应是工艺优化的方向。实验中各衬底表面状态所能影响的是岛的疏密和大小,较平整光滑的衬底表面有利于外延形核密度的提高及形核均匀化,衬底表面涂覆铝助焊剂可促进外延形核;熔体硅含量提升、过冷度减小和硅衬底预热温度提高有利于均匀密布岛状生长的发生;随外延生长时间延长,后期金字塔外形开始逐渐平滑化。连续降温生长方式下,可以实现衬底在略高于液-固平衡温度下回熔处理后再原位连续降温外延生长的方案。回熔处理实验显示它可以获得平滑清洁的表面。回熔处理后的原位连续降温生长在初期可以获得连续外延薄膜层,之后在其表面出现岛状形核生长,与Stranski-Krastanov生长模式相合。连续降温生长所形成的pn结的开路电压比恒温生长的有大幅度提高,而且在初期就形成了质量较高的连续均匀外延层,后续岛状形核生长反而使开路电压明显降低。提高降温生长速率会使所得pn开路电压降低,但该影响并不十分敏感。计算模拟结果显示,本研究中采用回熔处理后原位连续降温生长方法进行低温液相外延所得pn结的开路电压平均值为524mV,最高达529mV,已颇为接近理论计算值(538 mV);计算模拟还显示,只要p型外延层厚度小于10μm,则外延层材料少子寿命只要大于1μs就能保证pn结开路电压处于高水平范围,因此低温液相外延制结的n型晶硅太阳电池发展前景是可以十分乐观的。
[Abstract]:The crystalline silicon solar cell is the main support of modern photovoltaic power, and the p-type solar cell with p-type silicon as the substrate is dominated by its traditional material and process advantage. However, in recent years, the n-type crystalline silicon solar cell has become the development direction of the future crystal silicon solar cell technology because of its inherent outstanding advantages. one of the technical barriers to n-type crystalline silicon solar cells is the difficulty of p-type doping. The epitaxial growth of Al-doped silicon crystal layer from the Al-Si melt to the surface of the n-type silicon crystal substrate is a low-cost solution with a potential development prospect. The principle of the method has been successfully applied to the preparation of the Al back field by the p-type solar cell screen printing aluminum paste sintering, but the method for preparing the pn junction also has the problem of continuous uniformity, and the aluminum paste cost is much higher than that of the aluminum ingot required by the melt growth. In this paper, we carried out a high-temperature liquid-phase epitaxial growth p-type doped silicon experiment on the (001) n-type single-crystal silicon substrate in the Al-Si alloy melt. The liquid-phase epitaxial growth device of the vertical lifting and dipping method is designed and manufactured, and the inside of the growth system is protected by flowing high pure argon. the low-temperature liquid phase epitaxial growth experiment of the two modes of supercooled constant-temperature growth and continuous cooling and growth is carried out by a vertical impregnation method, and the investigated growth conditions include the surface state of the substrate, the melt composition (determining liquid-solid equilibrium temperature), the subcooling degree, the growth time or the cooling amplitude, The structure and morphology of the resulting epitaxial growth crystal were analyzed, the open-circuit voltage of the pn-junction was measured, and the factors that influence the open-circuit voltage of the pn-junction were analyzed by means of the calculation and simulation method. The following main results were obtained. in that Al-Si melt, the liquid phase epitaxial growth of the silicon crystal (001) can be realized, it is shown that it is the surface in growth that minimizes the selection result. This form only meets the basic continuity requirements of the pn-junction when these islands are grown to close contact with one another, so that the higher and uniform core density should be the direction of the process optimization. the surface state of each substrate in the experiment can influence the density and the size of the island, the surface of the substrate with the smooth and smooth surface is favorable for improving the density of the epitaxial core and the shape core, the surface of the substrate is coated with the aluminum soldering flux, the epitaxial core is promoted, and the content of the melt silicon is improved, The reduction of the subcooling and the increase of the preheating temperature of the silicon substrate are favorable to the occurrence of uniformly distributed island-like growth, and the shape of the later-stage pyramid is gradually smooth with the extension of the epitaxial growth time. in that continuous cool-down growth mode, the substrate can be re-melted at a slightly higher temperature than the liquid-solid equilibrium temperature, and the scheme of the epitaxial growth in-situ continuous cool-down can be realized. a reflow process experiment shows that it can obtain a smooth, clean surface. the in-situ continuous cooling and growth after the reflow treatment can obtain the continuous epitaxial thin film layer at the initial stage, and then the island-shaped nuclear growth on the surface of the continuous epitaxial thin film layer is matched with the Sranski-Krastanov growth mode. the open-circuit voltage of the pn-junction formed by continuous cooling and growth is greatly improved than that of the constant-temperature growth, and a continuous uniform epitaxial layer with higher quality is formed in the early stage, and the subsequent island-shaped nuclear growth can obviously reduce the open-circuit voltage. Increasing the rate of cooling growth can reduce the resulting pn-open voltage, but the effect is not very sensitive. The simulation results show that the average of the open-circuit voltage of the pn-junction obtained by the in-situ continuous cooling and growing method after the reflow treatment in this study is 524mV, up to 529mV, which is close to the theoretical calculation value (538 mV), and the calculation simulation also shows that, As long as the thickness of the p-type epitaxial layer is less than 10. m u.m, the short-life of the epitaxial layer material can ensure that the open-circuit voltage of the pn-junction is in a high-level range as long as the thickness of the p-type epitaxial layer is more than 1. m
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ127.2;TM914.4
本文编号：2350540
[Abstract]:The crystalline silicon solar cell is the main support of modern photovoltaic power, and the p-type solar cell with p-type silicon as the substrate is dominated by its traditional material and process advantage. However, in recent years, the n-type crystalline silicon solar cell has become the development direction of the future crystal silicon solar cell technology because of its inherent outstanding advantages. one of the technical barriers to n-type crystalline silicon solar cells is the difficulty of p-type doping. The epitaxial growth of Al-doped silicon crystal layer from the Al-Si melt to the surface of the n-type silicon crystal substrate is a low-cost solution with a potential development prospect. The principle of the method has been successfully applied to the preparation of the Al back field by the p-type solar cell screen printing aluminum paste sintering, but the method for preparing the pn junction also has the problem of continuous uniformity, and the aluminum paste cost is much higher than that of the aluminum ingot required by the melt growth. In this paper, we carried out a high-temperature liquid-phase epitaxial growth p-type doped silicon experiment on the (001) n-type single-crystal silicon substrate in the Al-Si alloy melt. The liquid-phase epitaxial growth device of the vertical lifting and dipping method is designed and manufactured, and the inside of the growth system is protected by flowing high pure argon. the low-temperature liquid phase epitaxial growth experiment of the two modes of supercooled constant-temperature growth and continuous cooling and growth is carried out by a vertical impregnation method, and the investigated growth conditions include the surface state of the substrate, the melt composition (determining liquid-solid equilibrium temperature), the subcooling degree, the growth time or the cooling amplitude, The structure and morphology of the resulting epitaxial growth crystal were analyzed, the open-circuit voltage of the pn-junction was measured, and the factors that influence the open-circuit voltage of the pn-junction were analyzed by means of the calculation and simulation method. The following main results were obtained. in that Al-Si melt, the liquid phase epitaxial growth of the silicon crystal (001) can be realized, it is shown that it is the surface in growth that minimizes the selection result. This form only meets the basic continuity requirements of the pn-junction when these islands are grown to close contact with one another, so that the higher and uniform core density should be the direction of the process optimization. the surface state of each substrate in the experiment can influence the density and the size of the island, the surface of the substrate with the smooth and smooth surface is favorable for improving the density of the epitaxial core and the shape core, the surface of the substrate is coated with the aluminum soldering flux, the epitaxial core is promoted, and the content of the melt silicon is improved, The reduction of the subcooling and the increase of the preheating temperature of the silicon substrate are favorable to the occurrence of uniformly distributed island-like growth, and the shape of the later-stage pyramid is gradually smooth with the extension of the epitaxial growth time. in that continuous cool-down growth mode, the substrate can be re-melted at a slightly higher temperature than the liquid-solid equilibrium temperature, and the scheme of the epitaxial growth in-situ continuous cool-down can be realized. a reflow process experiment shows that it can obtain a smooth, clean surface. the in-situ continuous cooling and growth after the reflow treatment can obtain the continuous epitaxial thin film layer at the initial stage, and then the island-shaped nuclear growth on the surface of the continuous epitaxial thin film layer is matched with the Sranski-Krastanov growth mode. the open-circuit voltage of the pn-junction formed by continuous cooling and growth is greatly improved than that of the constant-temperature growth, and a continuous uniform epitaxial layer with higher quality is formed in the early stage, and the subsequent island-shaped nuclear growth can obviously reduce the open-circuit voltage. Increasing the rate of cooling growth can reduce the resulting pn-open voltage, but the effect is not very sensitive. The simulation results show that the average of the open-circuit voltage of the pn-junction obtained by the in-situ continuous cooling and growing method after the reflow treatment in this study is 524mV, up to 529mV, which is close to the theoretical calculation value (538 mV), and the calculation simulation also shows that, As long as the thickness of the p-type epitaxial layer is less than 10. m u.m, the short-life of the epitaxial layer material can ensure that the open-circuit voltage of the pn-junction is in a high-level range as long as the thickness of the p-type epitaxial layer is more than 1. m
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ127.2;TM914.4
【参考文献】
相关期刊论文 前1条
1 ;QE and Suns-V_(oc) study on the epitaxial CSiTF solar eelis[J];Science in China(Series E:Technological Sciences);2005年01期
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