本文關(guān)鍵詞： 晶體生長 位錯形核 應(yīng)變 硅 分子動力學(xué)　出處：《南昌大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：晶體硅是當前和未來相當一個時期主要的光伏材料。它一般通過直拉法和定向凝固法獲得。前者得到單晶硅棒,后者得到多晶硅錠。后者因相對成本低而更具競爭力,但也因其結(jié)晶缺陷形成更難于控制而在技術(shù)上更具有挑戰(zhàn)性。本文主要針對硅晶體的定向凝固生長進行研究,包括其生長動力學(xué)各向異性和對晶體硅電學(xué)性能影響最大的位錯缺陷的形成條件與形成機制。采用的方法為分子動力學(xué)計算模擬,這是迄今為止唯一能夠在原子尺度模擬跟蹤位錯形成動態(tài)過程的方法。本研究選擇Tersoff勢函數(shù)描述硅原子間的相互作用,構(gòu)建了晶體硅定向凝固的NPT系綜生長模型和外加應(yīng)力施加方法,以Nose-Hoover算法控制和恒定溫度,以Andersen算法控制和恒定壓強,應(yīng)用LAMMPS軟件進行模擬實驗。模擬研究結(jié)果顯示,晶體硅凝固生長速率及其受應(yīng)力影響情況有明顯的各向異性,不同方向晶體生長速率大小關(guān)系為[100][110][112][111]???????;對于同一生長方向,在壓應(yīng)變條件下,隨著應(yīng)變的增大晶體生長速率降低,而在拉應(yīng)變條件下,晶體生長速率先隨著應(yīng)變的增大而增大,再隨著應(yīng)變的增大而減小,不過110生長中,在壓應(yīng)變條件下晶體生長速率出現(xiàn)反常。模擬結(jié)果揭示,不同方向晶體生長過程中位錯形核情況也存在各向異性。在100、110、111、112方向自然生長中,112和111生長過程中能觀察到位錯的形核,另外兩個方向上,在多次模擬生長試驗中都未出現(xiàn)位錯;112生長中,固液界面呈{111}小面化特征,生長過程中會出現(xiàn)沿{111}面的堆垛層錯,而位錯即在{111}面上于層錯邊沿處形成;111生長中位錯直接形核于固液界面。在外加應(yīng)力條件下,100、110、111和112生長過程中均能觀察到位錯形核;在較大的應(yīng)變條件下,100和110生長中的位錯形核概率會顯著提升;而一定的應(yīng)變范圍內(nèi),112和111生長中的位錯形核概率卻會降低。在應(yīng)變下的晶體生長過程中會出現(xiàn) V‖型固液界面,而位錯形核于 V‖型凹槽附近的晶體無序化—重結(jié)晶的過程中,而且形成的位錯是位于生長面內(nèi)的垂直于生長方向的一對位錯偶極子;但110生長中還有沿生長方向的位錯形核。另外,對112晶體生長中的過冷度和溫度梯度條件模擬結(jié)果表明,當過冷度和溫度梯度達到一定值時,112方向自然生長中才會觀察到位錯形核。
[Abstract]:Crystal silicon is the main photovoltaic material at present and in the future. It is usually obtained by Czochralski method and directional solidification method. The latter is more competitive because of its low cost. However, the formation of crystalline defects is more difficult to control, so it is more challenging in technology. This paper mainly focuses on the directional solidification growth of silicon crystals. The formation conditions and mechanism of dislocation defects, which have the greatest influence on the electrical properties of silicon crystal, are discussed in this paper. The molecular dynamics method is used to simulate the formation of dislocation defects. This is the only way to simulate the dynamic process of dislocation formation at atomic scale. In this study, the Tersoff potential function is chosen to describe the interaction between silicon atoms. The NPT ensemble growth model of directional solidification of crystal silicon and the method of applying applied stress are constructed. The Nose-Hoover algorithm is used to control the temperature. Andersen algorithm is used to control and constant pressure, and LAMMPS software is used to simulate the experiment. The simulation results show that. The solidification growth rate of crystal silicon and its effect on stress have obvious anisotropy. The relationship between crystal growth rate and crystal growth rate in different directions is as follows. [100]. [110]. [112]. [111]? ? ? ? ? ? ? ; For the same growth direction, with the increase of strain, the growth rate of crystal decreases with the increase of strain, while under the condition of tensile strain, the growth rate of crystal increases with the increase of strain. With the increase of strain, however, the growth rate of the crystal is abnormal in the growth of 110. The simulation results show that the growth rate of the crystal is abnormal. Anisotropy also exists in the case of dislocation nucleation during crystal growth in different directions. Dislocation nucleation can be observed during the growth of 112 and 111. In the other two directions, there is no dislocation in many simulated growth tests. During the growth of 112, the solid-liquid interface has the characteristics of {111} facture, and the stacking faults along the {111} surface will occur during the growth process, while the dislocation will be formed on the {111} plane at the edge of the stacking fault. Dislocation nucleation was observed at the solid-liquid interface during the growth of 111. The probability of dislocation nucleation in the growth of 100 and 110 increases significantly under the condition of large strain. However, the probability of dislocation nucleation will decrease in a certain strain range. The dislocation nucleation is in the process of disorderation-recrystallization near the V-shaped grooves, and the resulting dislocation is a pair of dislocation dipoles perpendicular to the growth direction in the growth plane. However, there are dislocation nucleation along the growth direction in 110 crystal growth. In addition, the simulation results of undercooling and temperature gradient conditions in 112 crystal growth show that when the undercooling and temperature gradient reach a certain value. Dislocation nucleation is observed only in natural growth in the 112 direction.
【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

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相關(guān)博士學(xué)位論文 前1條

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本文編號：1491210