Si(111) strained layers on Ge(111): evidence for c(2x4) domains

TL;DR

This study investigates tensile strained Si(111) layers on Ge(111) substrates, revealing c(2x4) domain structures and proposing a model that explains their formation through surface energy considerations and atomic substitutions.

Contribution

It provides the first combined experimental and theoretical analysis of c(2x4) domains in strained Si(111) layers on Ge(111), including a proposed structural model.

Findings

Identification of c(2x4) domains separated by domain walls along <-110> directions.

Proposed model structure with low formation energy consistent with experimental data.

Surface strain transition from compressive to tensile changes surface reconstruction from dimer-based to adatom-based structures.

Abstract

The tensile strained Si(111) layers grown on top of Ge(111) substrates are studied by combining scanning tunneling microscopy, low energy electron diffraction and first-principles calculations. It is shown that the layers exhibit c(2x4) domains, which are separated by domain walls along <-110> directions. A model structure for the c(2x4) domains is proposed, which shows low formation energy and good agreement with the experimental data. The results of our calculations suggest that Ge atoms are likely to replace Si atoms with dangling bonds on the surface (rest-atoms and adatoms), thus significantly lowering the surface energy and inducing the formation of domain walls. The experiments and calculations demonstrate that when surface strain changes from compressive to tensile, the (111) reconstruction converts from dimer-adatom-stacking fault-based to adatom-based structures.