本文選題：第一性原理計算 + 彈性性質　； 參考：《昆明理工大學》2017年碩士論文

【摘要】：研究半導體材料Ge和GaAs的彈性性質和動力學性質具有重要的科學意義和實際價值。本論文以線性與非線性彈性理論為基礎,結合第一性原理的密度泛函理論,采用廣義梯度近似和局域密度近似方法,數(shù)值計算了Ge和GaAs的二階和三階彈性常數(shù)�？紤]不弛豫和原子弛豫的方法,計算Ge和GaAs中glide部分位錯在112{111}滑移系統(tǒng)和GaAs中shuffle位錯在110{111}}滑移系統(tǒng)中的廣義層錯能,并通過擬合得到廣義層錯能曲線�；谖诲e晶格理論,結合計算得到的二階彈性常數(shù)和廣義層錯能,研究Ge和GaAs中glide 90°部分位錯和GaAs中shuffle 60°位錯的力學性質。獲得的研究成果如下:對Ge和GaAs彈性性質研究的主要結果:計算所得Ge和GaAs的晶格常數(shù)和二階彈性常數(shù)與實驗值及先前的理論結果都符合的很好。當應變超過1.5%時就不能再運用線性彈性理論,這時就需要用到非線性彈性理論。三階彈性常數(shù)除了C456與實驗值及理論結果較大偏差,其他都符合的很好,并且當考慮到三階彈性常數(shù)時,能量-應變的關系并不是對稱的,正應變的能量總是小于負應變的能量,這也說明了大多數(shù)三階彈性常數(shù)都是負值。對Ge和GaAs位錯性質研究的主要結果:對于Ge和GaAs中glide部分位錯的不穩(wěn)定層錯能,局域密度近似方法計算得到的不穩(wěn)定層錯能略高于用廣義梯度近似方法計算得到的結果,考慮弛豫得到的不穩(wěn)定層錯能比不弛豫的低,通過弛豫方法得到的不穩(wěn)定層錯能大約是不弛豫的2/3,考慮到Ge和GaAs中的glide 90°部分位錯通過鍵的旋轉來滑動,在滑動過程中,會發(fā)生很大程度的弛豫,因此通過原子弛豫得到的廣義層錯能更合理。計算了GaAs中shuffle 60°位錯的不穩(wěn)定層錯能,用局域密度近似計算的不穩(wěn)定層錯能比廣義梯度近似計算的略大,且原子弛豫方法計算得到的不穩(wěn)定層錯能略小。對于Ge和GaAs中的glide 90°部分位錯,不弛豫的位錯寬度比原子弛豫的窄,考慮原子弛豫的位錯寬度約為不弛豫的1.4倍,考慮原子弛豫的Peierls應力比不弛豫的小。計算得到的GaAs中shuffle 60°位錯的位錯寬度和Peierls應力在弛豫和不弛豫的情況下相差不大�？梢�,不穩(wěn)定層錯能越低,位錯越寬,Peierls應力越小,則位錯越容易滑動;對于具有金剛石及閃鋅礦結構晶體中的glide位錯,原子弛豫的結果對位錯芯結構及Peierls應力影響較大,因此需考慮原子弛豫;而對于shuffle位錯,原子弛豫對結果影響很小,從而可以忽略。
[Abstract]:It is of great scientific significance and practical value to study the elastic and dynamic properties of GE and GaAs semiconductor materials. Based on the linear and nonlinear elastic theory and the first-principle density functional theory, the second and third order elastic constants of GE and GaAs are numerically calculated by using generalized gradient approximation and local density approximation. In this paper, the generalized stacking fault energy of glide partial dislocation in 112 {111} slip system and shuffle dislocation in 110 {111} slip system in GE and GaAs are calculated by considering the method of nonrelaxation and atomic relaxation. The generalized laminated fault energy curves are obtained by fitting. Based on dislocation lattice theory, the mechanical properties of glide 90 擄partial dislocation in GE and GaAs and shuffle 60 擄dislocation in shuffle are studied by combining the second order elastic constant and generalized stacking fault energy. The results obtained are as follows: the main results of the study on the elastic properties of GE and GaAs are as follows: the calculated lattice constants and second-order elastic constants of GE and GaAs are in good agreement with the experimental values and previous theoretical results. The linear elastic theory can not be applied when the strain exceeds 1.5 and the nonlinear elastic theory is needed. The third order elastic constant is in good agreement with the experimental data and theoretical results except C456, and when the third order elastic constant is considered, the relationship between energy and strain is not symmetrical. The energy of positive strain is always smaller than that of negative strain, which indicates that most third-order elastic constants are negative. The main results of the study on the dislocation properties of GE and GaAs are as follows: for the unstable layer fault energy of GE and glide partial dislocations, the local density approximation method is slightly higher than the generalized gradient approximation method. The unstable stacking fault energy obtained by considering relaxation is lower than that by unrelaxation. The unstable stacking fault energy obtained by relaxation method is about 2 / 3 of that of unrelaxation. Considering that the partial dislocation in GE and glide 90 擄glides through the rotation of the bond, during the sliding process, A large degree of relaxation occurs, so the generalized stacking fault energy obtained by atomic relaxation is more reasonable. The unstable stacking fault energy of shuffle 60 擄dislocation in GaAs is calculated. The unstable layer fault energy calculated by local density approximation is slightly larger than that calculated by generalized gradient approximation, and the unstable layer fault energy calculated by atomic relaxation method is slightly smaller. For the partial dislocation of glide 90 擄in GE and GaAs, the width of unrelaxation dislocation is narrower than that of atomic relaxation. The width of dislocation considering atomic relaxation is about 1.4 times that of non-relaxation, and the Peierls stress considering atomic relaxation is smaller than that of non-relaxation. The calculated dislocation width of shuffle 60 擄dislocation and Peierls stress have little difference in the case of relaxation and non-relaxation. It can be seen that the lower the unstable stacking fault energy, the smaller the Peierls stress of the dislocation, the easier it is to slide the dislocation, and for the glide dislocation with diamond and sphalerite structure, the effect of atomic relaxation on the dislocation core structure and Peierls stress is greater. Therefore, atomic relaxation should be considered, while for shuffle dislocations, atomic relaxation has little effect on the results, so it can be neglected.
【學位授予單位】：昆明理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN304

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本文編號：2024133