Microstructure and strain relief of Ge films grown layer by layer on Si(001).
Microstructure and strain relief of Ge films grown layer by layer on Si(001).
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DOI：
10.1103/physrevb.42.11690
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发表时间：
1990-12
期刊：
影响因子：
--
通讯作者：
F. Legoues;Matthew Copel;R. Tromp
中科院分区：
文献类型：
--
作者：
F. Legoues;Matthew Copel;R. Tromp
本文研究了在Si（001）表面上逐层生长Ge薄膜的微结构。通过用1个单层砷钝化表面，将生长模式从Sttranski-Krastanov模式（3个单层的逐层生长，然后岛化）改变为逐层生长模式。这种生长形态的变化导致应变消除机制的急剧变化。与裸硅上生长的薄膜不同，这些薄膜保持赝晶应变高达约10个单层的厚度。在12单层的膜厚度，我们观察到灾难性的应变诱导缺陷的形成。这些由垂直于衬底倾斜的几个{111}平面组成。缺陷是ssV形的，因此，随着薄膜的生长，逐渐减轻失配。在50单层的膜厚度，我们观察到的ssV形缺陷作为成核位置的位错爬下到Si衬底。这些位错然后滑过薄膜，以减轻先前未缺陷区域的错配。因此，部分地通过位于Ge层中的ssV形缺陷和部分地通过位于Si衬底中的边缘位错来缓解失配。对于厚膜，我们观察到，大部分的ssV形缺陷已被覆盖的Ge取向外延与衬底，但他们也产生了双胞胎和堆垛层错，延伸到整个膜。这项工作具有根本性的影响，应变救济的理解在“正常”的增长。事实上，它表明，所谓的临界厚度必须考虑应变消除缺陷（一般来说，位错）的形成能量，而不仅仅是移动缺陷的能量，如到目前为止通常所做的。
We have studied the microstructure of Ge films grown layer by layer on Si(001) surfaces. The growth mode was changed from a Stranski-Krastanov mode (layer by layer for 3 monolayers, followed by islanding) to a layer-by-layer growth mode by passivation of the surface with 1 monolayer of arsenic. This change in growth morphology results in drastic changes in the mechanism of strain relief. Unlike films grown on bare Si, these films remain pseudomorphically strained up to a thickness of about 10 monolayers. At a film thickness of 12 monolayers, we observe the catastrophic formation of strain-induced defects. These consist of several {111} planes tilted perpendicular to the substrate. The defects are ssV-shaped and, consequently, relieve the misfit progressively as the film grows. At a film thickness of 50 monolayers, we observe that the ssV-shaped defects serve as nucleation sites for dislocations that climb down into the Si substrate. These dislocations then glide through the film to relieve the misfit in previously undefected areas. Thus, the misfit is relieved partly by ssV-shaped defects located in the Ge layer and partly by edge dislocations located in the Si substrate. For thick films, we observe that most of the ssV-shaped defects have been covered by Ge oriented epitaxially with the substrate, but they have also generated twins and stacking faults that extend throughout the whole film. This work has fundamental implications for the understanding of strain relief during ``normal'' growth. Indeed, it demonstrates that the so-called critical thickness has to take into account the formation energy of the strain-relieving defects (in general, dislocations), and not only the energy to move the defects, as has generally been done up to now.