We systematically investigate the compositional uniformity, degree of strain relaxation (DSR), defect structure and surface morphology of GeSn epitaxial layers with 16% Sn, grown by low temperature molecular beam epitaxy (MBE) on Ge-buffered Si(001) substrates. Combining atom probe tomography, reciprocal space mapping, cross-sectional transmission electron microscopy, and atomic force microscopy analyses, we demonstrate that for a layer thickness of , a high DSR (∼70%) can be achieved, while maintaining compositional uniformity at the atomic scale. We find no evidence of Sn clustering in the bulk, or Sn segregation to the surface, for at least this value of . The observed compositional uniformity contrasts the well-established phenomenon of strain-relaxation enhancement of Sn content in chemical vapour deposition (CVD) growth of GeSn. The defect structure leading to strain relaxation in these MBE-grown GeSn epitaxial layers is also distinctly different from that observed in CVD growth of the alloy. We observe the co-existence of highly strain-relaxed and pseudomorphically strained regions in the grown epilayers, tentatively explained by bunching of threading dislocations. Considering that MBE growth of GeSn epitaxial layers, with such high-Sn content and layer thickness, has not been reported before, our results are encouraging for future improvements in design and fabrication of group-IV-based mid-infrared photonic devices.

我们系统地研究了由低温分子束外延（MBE）在Ge缓冲的Si（001）衬底上生长的16％Sn的GeSn外延层的组成均匀性，应变松弛度（DSR），缺陷结构和表面形态。结合原子探针层析成像，相互空间映射，横截面透射电子显微镜和原子力显微镜分析，我们证明，对于的层厚度为，可以实现高DSR（〜70％），同时保持原子的组成均匀性规模。对于至少这个值，我们没有发现大量锡聚集或表面锡偏析的证据。。观察到的成分均匀性与公认的GeSn化学气相沉积（CVD）生长中Sn含量的应变松弛增强现象形成了鲜明对比。在这些MBE生长的GeSn外延层中导致应变松弛的缺陷结构也与合金的CVD生长中观察到的明显不同。我们观察到在生长的外延层中存在高度松弛的应变和拟晶应变区域的共存，并通过线程位错的束缚进行了初步解释。考虑到以前从未报道过具有如此高的Sn含量和层厚的GeSn外延层的MBE生长，我们的结果令人鼓舞，这将进一步改善基于IV组的中红外光子器件的设计和制造。