Growth mechanism of twin defects in (111)B GaAsSb studied by X-ray diffraction spectroscopy

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.