AI 中文总结
研究六方IV族半导体在平面异质结构中稳定的挑战，通过低能等离子体增强化学气相沉积在CdS衬底上生长平面六方锗，研究生长温度作用，揭示其晶体结构、缺陷机制等，确立CdS为稳定模板并提供应变弛豫见解。
AI 中文摘要
六方IV族半导体因其与立方金刚石相相比具有非常规的电子和光学性质而受到越来越多的关注。然而，在平面异质结构中稳定这些亚稳态同素异形体仍然是一个重大挑战。在这项工作中，我们通过低能等离子体增强化学气相沉积在非基面m平面CdS衬底上演示了平面六方锗的外延生长。研究了生长温度在六方相形成和稳定中的作用。X射线衍射、扫描透射电子显微镜和偏振分辨拉曼光谱揭示了具有预期晶体对称性的外延六方锗的形成。特别是，拉曼响应表现出六方Ge的E$_\text{2g}$声子模式的特征偏振选择规则。相反，光致发光光谱没有揭示任何与Ge相关的发射特征。结合透射电子显微镜观察和原子模型表明，应变弛豫由一组有限的位错机制控制，这些机制在距界面几纳米内有效地缓解了大部分失配应变，并且可能涉及局部立方堆叠插入。在距界面更远的距离处，六方有序的逐渐丧失越来越多地由堆垛层错无序主导，特别是I3型缺陷。这些结果确立了CdS作为六方Ge平面稳定的有前途的模板，并提供了对亚稳态IV族异质结构中应变弛豫的缺陷机制的深入了解。
英文摘要
Hexagonal group-IV semiconductors have attracted increasing interest owing to their unconventional electronic and optical properties compared to the cubic diamond phase. However, the stabilization of these metastable allotropes in planar heterostructures remains a major challenge. In this work, we demonstrate the epitaxial growth of planar hexagonal germanium on non-basal $m$-plane CdS substrates by low-energy plasma-enhanced chemical vapor deposition. The role of growth temperature in the formation and stabilization of the hexagonal phase is investigated. X-ray diffraction, scanning transmission electron microscopy, and polarization-resolved Raman spectroscopy reveal the formation of epitaxial hexagonal germanium with the expected crystal symmetry. In particular, the Raman response exhibits the characteristic polarization selection rules of the E$_\text{2g}$ phonon mode of hexagonal Ge. Conversely, photoluminescence spectroscopy does not reveal any Ge-related emission feature. Combined transmission electron microscopy observations and atomistic modeling show that strain relaxation is governed by a limited set of dislocation mechanisms, which efficiently relieve most of the mismatch strain within a few nanometers from the interface and can involve localized cubic stacking insertions. At greater distances from the interface, the progressive loss of hexagonal order is increasingly dominated by stacking-fault disorder, particularly I3-type defects. These results establish CdS as a promising template for the planar stabilization of hexagonal Ge and provide insight into the defect mechanisms governing strain relaxation in metastable group-IV heterostructures.
Comments10 pages, 6 figures
