利用X光繞射研究(111)B銻砷化鎵內雙晶缺陷生成的機制

Abstract

本論文利用HRXRD提出一套重新判定基板斜切方向的方法，並藉由{220} 360° phi角掃描來研究[111]B GaAsSb內部雙晶缺陷成長的結構特性。 首先，我們經由phi角掃描中{220}繞射點出現的位置，將樣品分為兩類，分別為類型1：phi=60°、180°和300°，以及類型2：phi=0°、120°和240°。接著，由於樣品基板有經過[001]方向斜切處理，在量測HRXRD前須先進行[111]向量的校正，我們藉此反推出樣品平放時的[111]方向及基板斜切方向[001]，並推測基板表面因斜切處理產生的台階，會朝[001]反方向降階。最後，也討論了此判定方法可靠性。 在{220} 360° phi角掃描部份，我們觀察到隨著成長溫度降低，Sb成分比例會上升，雙晶缺陷密度也會提高，此顯示高Sb成分比例的晶體在成長時，會傾向藉由產生雙晶缺陷以釋放應力。此外，當雙晶密度逐漸提高，樣品的{220}繞射點寬度會急遽增加，其中(202)和(022)繞射點譜形會由對稱形狀轉變為不對稱，最後再變回對稱分布。我們認為因為雙晶區域受邊緣缺陷影響而傾斜後，會使{220}繞射點中的雙晶訊號偏移造成譜形改變。同時，也觀察到不對稱譜形的分布和基板斜切方向有關，並利用台階成長模型分析[1-1-1]、[-1 1-1]以及[-1-1 1]三種方向下成長的雙晶，其受台階影響而產生的偏轉效應，成功地解釋當雙晶密度中等時的{220}繞射點寬度不對稱變化。

In this work, we utilized the HRXRD measurement to recover the missing off-cut direction of substrates and qualitatively compared the twin defects density of [111]B GaAsSb samples to study its growth mechanism by the {220} 360° phi-scans. First, we classified the samples into two categories by the phi angles of {220} diffraction points. The one is for phi= 60°, 180°, and 300°; the other is for phi= 0°, 120°, and 300°. Later, from the analyses of calibration angles of [111] vector, which is deviated from the sample normal direction under the substrate off-cut, we suggested that the surface steps of substrate would terrace down in the direction against to the [001]. In addition, the reliability of this re-determination method was also discussed. Second, in the {220} 360° phi-scan, we observed the twin defect density increases as the sample growth temperature decreases, which reveals that the formation of twin defects is good for strain releasing during the sample growth of high Sb composition. Furthermore, we found that the higher the twin defect density, the much broader the {220} diffraction peaks. We suggest that the broadening behavior is resulting from the shift of twin signals, which coincide with the original {220} diffraction points firstly, under the tilting of defects at twin domain boundaries. Also, we noticed that the broadenings of (202) and (022) points are asymmetric at first, becoming symmetric eventually. And, the asymmetric broadening is related to the substrate off-cut direction. Thus, the step-growth model was used successfully, in the regime of medium twin defect density, to explain the asymmetry of {220} line-shapes by examining the tilting influences coming from surface steps during the twin defect growth.