Bending and precipitate formation mechanisms in epitaxial Ge-core/GeSn-shell nanowires
Bending and precipitate formation mechanisms in epitaxial Ge-core/GeSn-shell nanowires
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DOI：
10.1039/d1nr04220c
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发表时间：
2021-10-05
期刊：
影响因子：
6.7
通讯作者：
McIntyre, Paul C.
中科院分区：
文献类型：
--
作者：
Meng, Andrew C.;Wang, Yanming;McIntyre, Paul C.
核-壳Ge/GeSn纳米线提供了一种获得具有所需发光性能的无位错单晶锗锡合金的途径，因为Ge核在失配GeSn壳生长期间充当弹性顺应性衬底。然而，在减压化学气相沉积过程中锡结合的均匀性可能受到GeSn生长过程中向壳的传质动力学的限制。锡前体通量和GeSn成核和生长的可用表面之间的平衡决定了是否形成缺陷及其类型。一方面，当Sn前体递送不足时，在GeSn生长期间Sn到达纳米线表面的速率的局部变化在壳生长中产生不对称性，这引起线弯曲。这种不均匀的弹性膨胀，由于变化的组合物发生通过沉积的Sn-贫区的纳米线的{112}侧壁刻面的一些。另一方面，当可用的纳米线表面积不足以容纳到达的Sn前体通量时，导致富Sn沉淀物形成。在这两个极端之间，存在允许无缺陷GeSn壳生长的生长条件和纳米线密度的制度。
Core-shell Ge/GeSn nanowires provide a route to dislocation-free single crystal germanium-tin alloys with desirable light emission properties because the Ge core acts as an elastically compliant substrate during misfitting GeSn shell growth. However, the uniformity of tin incorporation during reduced pressure chemical vapor deposition may be limited by the kinetics of mass transfer to the shell during GeSn growth. The balance between Sn precursor flux and available surfaces for GeSn nucleation and growth determines whether defects are formed and their type. On the one hand, when the Sn precursor delivery is insufficient, local variations in Sn arrival rate at the nanowire surfaces during GeSn growth produce asymmetries in shell growth that induce wire bending. This inhomogeneous elastic dilatation due to the varying composition occurs via deposition of Sn-poor regions on some of the {112} sidewall facets of the nanowires. On the other hand, when the available nanowire surface area is insufficient to accommodate the arriving Sn precursor flux, Sn-rich precipitate formation results. Between these two extremes, there exists a regime of growth conditions and nanowire densities that permits defect-free GeSn shell growth.