以x光繞射儀研究(111)銻砷化鎵內的相分離與雙晶缺陷

Abstract

先前研究在(1 1 1) GaAsSb的(3 3 3)面ω-2θ HRXRD量測中看到雙峰圖形並歸因於相分離，之後在(1 1 1) GaAsSb TEM量測發現雙晶的存在。由於雙晶也有可能在ω-2θ譜中造成雙峰圖形，為了確認相分離現象，我們在本論文中實驗了(1 1 1)面的ω-2θ掃描。結果發現雙峰秒差會隨著(1 1 1)面或是(3 3 3)面掃描而有所不同。因為雙晶造成晶面的偏斜並不會隨著(1 1 1)面或是(3 3 3)面掃描有所改變，因此我們認為是相分離現象造成雙峰圖形。接著我們計算出(3 3 3)面和(1 1 1)面ω-2θ XRD譜中峰值對應的銻濃度，兩者銻濃度相近，確認了相分離的存在。 本論文也進行了高解析度X光繞射儀(220)面的ϕ掃描量測與分析。經由(2 2 0)面ϕ掃描我們能觀察到三個(2 2 0)原始晶格點以及雙晶造成的三個(2 2 0)雙晶晶格點。在雙晶最少的樣品中沒觀察到雙晶晶格點；當雙晶稍微增加時，我們觀察到一個雙晶晶格點。當雙晶變得更多時，能觀察到三個雙晶晶格點；而且原始晶格點的平均寬度會比雙晶晶格點更寬。這是因為原始晶格點會與三種雙晶晶格點重疊，而雙晶晶格點只是單一一種雙晶晶格點。當雙晶還不嚴重時原始晶格點僅有晶體本身的晶格圖形且較為陡峭，但隨著雙晶增加半寬會明顯地增大。在雙晶較少的樣品中，原始晶格點出現不對稱的圖形。我們對雙晶晶面、原始晶面和基板偏斜三者的關係作討論，分析後認為在材料內部雙晶情況不嚴重時基板偏斜方向會影響到雙晶晶面偏斜方向，而此偏斜的雙晶晶格點與原始晶格點重疊，造成ϕ XRD譜中不對稱的圖形。當雙晶更增加時，雙晶晶面偏斜不再受到基板偏斜影響。在雙晶更嚴重的樣品中不再有不對稱的圖形。我們也發現雙晶較少的樣品因為雙晶區域的繞射強度太弱，只會出現一個雙晶晶格點訊號。

Previous researches observed dual peaks in (1 1 1) GaAsSb using (3 3 3) and (1 1 1) ω-2θ HRXRD scans, and claimed it as phase separation. After that a research found existence of twinning in (1 1 1) GaAsSb by using TEM. Because twin could possibly result in dual peaks in (3 3 3) ω-2θ HRXRD scans. To confirm the phase separation in our samples, we examined the (1 1 1) ω-2θ HRXRD scans. The results show that angle differences of dual peaks varies with (1 1 1) or (3 3 3) scans, and this suggests that dual peaks observed in ω-2θ scans are due to not twin but phase separation. Then we evaluated the corresponding Sb content from both (3 3 3) and (1 1 1) ω-2θ scans. And we found that two Sb contents coincide, which allow us to affirm the existence of phase separation. We also examined HRXRD (2 2 0) ϕ scans. Three original lattice points and three twin lattice points can be observed by (2 2 0) ϕ scans. In the sample with minimal twin showed no twin point. In the sample with bit more twin, one twin point was observed. Sample with most twin gave three twin points. Original points were broader than twin points, which is because that three kinds of twin points coincide with the original point and only one kind of twin is included in twin point. When twinning is not severe, the almost original region makes original point a sharp peak. Peaks width increases with increasing twin in samples. Moreover, asymmetric peaks were found at specific angles. We evaluated the relation between directions of twin planes, original planes and miscut, and we inferred that the tilting of twin planes is related with the direction of miscut when twinning is not severe. When twinning becomes severe, tilting of twin planes are no longer affected by surface step, which results in symmetric line shapes. We also observe that the sample with less twin gives only one twin point due to the weak diffraction intensity.