Formation and interaction of epitaxial Ge structures on Ge(001)
Formation and interaction of epitaxial Ge structures on Ge(001)
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DOI：
10.1103/physrevb.66.115313
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发表时间：
2002-09-15
影响因子：
3.7
通讯作者：
Altman, EI
中科院分区：
文献类型：
--
作者：
Li, M;Altman, EI
用扫描隧道显微镜研究了Ge(001)同质外延的初始阶段。当在310K下沉积0.12ML的Ge时，表面以[130]和[310]取向的亚稳团簇为主。将Ge覆盖率增加到0.18ML，增加了外延二聚物行的密度。在420K时，亚稳团簇完全被外延结构取代，包括比亚稳团簇更小的岛。这些结果是由两个相互竞争的过程解释的：(1)亚稳态团簇的形成，然后它们转化为外延岛；(2)亚稳态二聚体转化为顶部(B)和谷底(D)的外延二聚体，然后它们相互碰撞，直接成核稳定的岛屿。后者在温度升高时占主导地位。在420K时，观察到了无数的外延结构，包括单个屈曲的B二聚体、末端由B和D二聚体或仅由D二聚体终止的单个未屈曲的二聚体列；单屈曲的二聚体列；具有局部c(4x2)对称性的一对屈曲的二聚体列；由一个屈曲的和一个未屈曲的二聚体列组成的对；以及更大的外延岛。尽管沿1x方向的扩散速度更快，但岛沿衬底2x方向拉长。这是由于平行于上阶地二聚体排列的S-A台阶相对于垂直的S-B台阶具有较低的能量而导致的捕获概率不对称。这些岛屿还表现出邻近和奇异的Ge(001)面所不存在的台阶结构，包括未屈曲的S-A台阶和未结合的S-B台阶。研究了外延岛与衬底之间的相互作用，发现外延岛与衬底之间的相互作用导致了p(2x2)对称性，而不是有利的c(4x2)对称性。
The initial stages of Ge(001) homoepitaxy were studied using scanning tunneling microscopy. When 0.12 ML of Ge was deposited at 310 K, [130]- and [310]-oriented metastable clusters dominated the surface. Increasing the Ge coverage to 0.18 ML increased the density of epitaxial dimer rows. At 420 K, the metastable clusters were completely replaced by epitaxial structures, including islands that were smaller than the metastable clusters. These results were explained by two competing processes: (1) formation of metastable clusters followed by their conversion to epitaxial islands; and (2) conversion of metastable dimers to epitaxial on-top (B) and trough (D) dimers which then collide to directly nucleate stable islands. The latter dominated at elevated temperatures. At 420 K a myriad of epitaxial structures were seen including single buckled B dimers, single unbuckled dimer rows with ends terminated by either B and D dimers or only D dimers; single buckled dimer rows; pairs of buckled dimer rows with local c(4x2) symmetry; pairs composed of one buckled and one unbuckled dimer row; and larger epitaxial islands. The islands were elongated along the substrate 2xdirection even though diffusion along the 1xdirection is faster. This was attributed to an asymmetric capture probability due to the lower energy of S-A steps oriented parallel to the upper terrace dimer rows versus the orthogonal S-B steps. The islands also displayed step structures that do not exist on vicinal and singular Ge(001) surfaces including unbuckled S-A and nonbonded S-B steps. The interactions between the epitaxial islands and the substrate were also studied and it was found that these interactions led to p(2x2) symmetry due to dimer buckling rather than the favored c(4x2) symmetry.