P型摻雜晶體硅的低溫液相外延生長研究
發(fā)布時間：2018-11-23 06:05
【摘要】：晶體硅太陽電池是現(xiàn)代光伏電力的主要支撐,其中以p型硅為襯底的p型太陽電池因其傳統(tǒng)材料與工藝優(yōu)勢占絕對主導(dǎo)地位。然而近年來n型晶體硅太陽電池因其固有突出優(yōu)勢而逐受重視,成為未來晶硅太陽電池技術(shù)的發(fā)展方向。n型晶硅太陽電池的技術(shù)障礙之一是p型摻雜制結(jié)困難。從Al-Si熔體向n型硅晶體襯底表面外延生長Al摻雜的硅晶層是一個有潛在發(fā)展前景的低成本解決方案。該方法的原理實際已成功應(yīng)用于p型太陽電池絲網(wǎng)印刷鋁漿燒結(jié)制備Al背場,但用于制備pn結(jié)則還存在連續(xù)均勻性問題,而且鋁漿成本相對熔體生長需要的鋁錠也要高得多。為此我們開展了Al-Si合金熔體中(001)n型單晶硅襯底上低溫液相外延生長p型摻雜硅實驗研究,研究集中于(001)外延的原因是單晶硅太陽電池所用均為(001)硅片。我們設(shè)計制作了垂直升降浸漬法液相外延生長裝置,生長體系內(nèi)部用流動高純氬保護(hù)。用垂直浸漬法進(jìn)行了過冷恒溫生長與連續(xù)降溫生長兩種模式的低溫液相外延生長實驗,所考察的生長條件包括襯底表面狀態(tài)、熔體成分(決定液-固平衡溫度)、過冷度、生長時間或降溫幅度、以及襯底預(yù)熱溫度等,對所得外延生長晶體進(jìn)行了結(jié)構(gòu)和形貌顯微分析,測定了所形成的pn結(jié)開路電壓,并運(yùn)用計算模擬方法分析了影響pn結(jié)開路電壓的因素。研究取得了以下主要結(jié)果。在Al-Si熔體中能夠?qū)崿F(xiàn)硅晶體(001)液相外延生長,但在各種襯底表面狀態(tài)下過冷恒溫外延生長時都呈離散的島狀生長形態(tài),島的形狀為以四個{111}面為表面的金字塔型或屋頂型,顯示它是生長中表面能最小化選擇結(jié)果。這種形態(tài)只有在這些島生長到相互密切接觸時才合乎pn結(jié)的基本連續(xù)性要求,因此較高和均勻的形核密度應(yīng)是工藝優(yōu)化的方向。實驗中各襯底表面狀態(tài)所能影響的是島的疏密和大小,較平整光滑的襯底表面有利于外延形核密度的提高及形核均勻化,襯底表面涂覆鋁助焊劑可促進(jìn)外延形核;熔體硅含量提升、過冷度減小和硅襯底預(yù)熱溫度提高有利于均勻密布島狀生長的發(fā)生;隨外延生長時間延長,后期金字塔外形開始逐漸平滑化。連續(xù)降溫生長方式下,可以實現(xiàn)襯底在略高于液-固平衡溫度下回熔處理后再原位連續(xù)降溫外延生長的方案�；厝厶幚韺嶒烇@示它可以獲得平滑清潔的表面�；厝厶幚砗蟮脑贿B續(xù)降溫生長在初期可以獲得連續(xù)外延薄膜層,之后在其表面出現(xiàn)島狀形核生長,與Stranski-Krastanov生長模式相合。連續(xù)降溫生長所形成的pn結(jié)的開路電壓比恒溫生長的有大幅度提高,而且在初期就形成了質(zhì)量較高的連續(xù)均勻外延層,后續(xù)島狀形核生長反而使開路電壓明顯降低。提高降溫生長速率會使所得pn開路電壓降低,但該影響并不十分敏感。計算模擬結(jié)果顯示,本研究中采用回熔處理后原位連續(xù)降溫生長方法進(jìn)行低溫液相外延所得pn結(jié)的開路電壓平均值為524mV,最高達(dá)529mV,已頗為接近理論計算值(538 mV);計算模擬還顯示,只要p型外延層厚度小于10μm,則外延層材料少子壽命只要大于1μs就能保證pn結(jié)開路電壓處于高水平范圍,因此低溫液相外延制結(jié)的n型晶硅太陽電池發(fā)展前景是可以十分樂觀的。
[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
【學(xué)位授予單位】：南昌大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TQ127.2;TM914.4
本文編號：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
【學(xué)位授予單位】：南昌大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TQ127.2;TM914.4
【參考文獻(xiàn)】
相關(guān)期刊論文 前1條
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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