The Stranski–Krastanow transition in SiGe epitaxy investigated by scanning transmission electron microscopy
The Stranski–Krastanow transition in SiGe epitaxy investigated by scanning transmission electron microscopy
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通过扫描透射电子显微镜研究 SiGe 外延中的 Stranski-Krastanow 转变
DOI：
10.1002/pssa.201200363
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
D. Leadley
中科院分区：
文献类型：
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作者：
T. Walther;D. Norris;Y. Qiu;A. Dobbie;M. Myronov;D. Leadley
Stranski-Krastanow生长模式描述了从二维平面应变层外延到可以在技术上用作量子点的岛屿形成的转变。迄今为止，这已被用于In(Ga)As/GaAs和Ge/Si异质外延。在这里，我们研究了不同锗含量和厚度的SiGe合金的多层样品，并发现在x≈0.28时Si1−xGex‐on‐Si体系中可以发现类似的转变。利用分析透射电子显微镜中的环形暗场成像和能量色散X射线能谱相结合的方法，我们证明了沉积的Ge总量决定了层是否保持平坦或粗糙，锗偏析决定了是否以及何时发生转变。名义上纯Ge的层在厚度为~ 0.5 nm时变得粗糙，而x≥0.28的Si1−xGex层保持平坦的时间更长，直到表面分离的Ge导致孤岛。低于临界浓度（x≤0.27）的层可以保持平坦直至更高的厚度，可能直到形成位错。x = 0.28处stranski - krstanow跃迁的临界厚度为d = 1.7 nm。
The Stranski–Krastanow growth mode describes the transition from two‐dimensional flat strained layer epitaxy to the formation of islands that can be technologically used as quantum dots. This has so far been utilized for In(Ga)As/GaAs and Ge/Si heteroepitaxy. Here, we investigate multilayer samples of SiGe alloys grown with different germanium content and thicknesses by reduced pressure chemical vapor phase epitaxy and show that a similar transition can be found in the Si1−xGex‐on‐Si system at x ≈ 0.28. Using a combination of annular dark‐field imaging and energy‐dispersive X‐ray spectroscopy in an analytical transmission electron microscope, we demonstrate that it is the total amount of Ge deposited that determines whether the layers stay flat or roughen, and it is germanium segregation that determines whether and when the transition occurs. While layers with nominally pure Ge roughen at a thickness of ∼0.5 nm, Si1−xGex layers with x ≥ 0.28 stay flat for much longer, until segregated Ge at the surface leads to islanding. Layers below that critical concentration (x ≤ 0.27) can stay flat up to even higher thicknesses, possibly until dislocations will be formed. The critical thickness for the Stranski–Krastanow transition at x = 0.28 is d = 1.7 nm.