Rebonded SB step model of Ge/Si()1×2: A first-principles theoretical study

Si/Ge exchange mechanisms at the Ge(105) surface

“…2 ͑see caption for actual values͒. After averaging over several trajectories, an estimate for the exchange rate k ex is readily obtained as k ex =1/ ͗ ͘, where ͗ ͘ is the average time needed to reach M 6 a from M 1 a . As shown in Fig.…”

“…2 More investigations followed, demonstrating that the Ge͑105͒ surface is indeed an optimal alternative to ͑001͒: owed to a peculiar rebonded-step ͑RS͒ reconstruction, the ͑105͒ surface energy competes with the ͑001͒ one, particularly so under the compressive-strain conditions experienced by Ge on Si. [3][4][5][6][7][8][9] In order to get more insights into the kinetics of ͕105͖ Ge islands growth, also Ge-adatom mobility at such facets was investigated, [10][11][12] and a step-flow model allowing for fast facet enlargement was proposed. 13 Nowadays it is well known that, despite the deposition of pure Ge on Si͑001͒, islands tend to be alloyed with temperature-dependent SiGe distributions.…”

Fast isotropic adatom diffusion on Ge(105) dot facets

“…Since then, several other experimental evidences revealed how easily {105} orientations appear in Ge or Si x Ge 1−x growth on Si(001). [4][5][6][7] Very recently, it has been shown that a rebonded-step (RS) reconstruction 8 is energetically favored [9][10][11] on the Ge(105) surface. In particular, it was demonstrated that the RS reconstruction actually takes place at Ge pyramids facets, 9 and that it plays a key role in determining the dots stability.…”

“…9,12 Such a reconstruction dramatically changes the as-cut geometry, virtually eliminating the step stucture, flattening the (105) surface, and causing enhanced stability under compressive strain. [11][12][13][14] If the above mentioned references provide detailed theoretical information about surface thermodynamics, kinetics at the RS(105) surface is still unexplored. Since kinetics often plays a key role in determining the morphology of growing films, 15,16 understanding how and how fast atoms move at the RS(105) surface should be regarded as a crucial step towards a comprehensive microsopic modeling of the observed dot growth modes.…”

Atomic-scale modeling of next-layer nucleation and step flow at the Ge(105) rebonded-step surface

“…The RS reconstruction strongly influences the morphology of the ͑105͒ surface, in eliminating the typical stepped profile of the as-cut geometry. As a result, the surface appears as rather flat, and it is characterized by a low surface energy, 13,14 further decreased by compressive strain. [15][16][17] Recent experiments 18 showed that a very efficient step-flow growth mode must take place at the Ge-pyramid facets, since, before starting the transition to the dome shape, they always appear unstepped and very ordered in scanning tunneling microscopy ͑STM͒ images.…”