Models for Si (111) Surface upon Ge Adsorption

In view of the chemical similarity between Ge and Si one would expect the surface structures observed following deposition of Ge onto the Si(111) substrate to be of complexity comparable to that of the clean Si(111)7 × 7 surface. It is therefore remarkable that a simpler reconstruction has been observed by Chen et al. [51.1] for room temperature deposition of Ge onto the Si(111)2 × l surface. They observed a $$\sqrt 3 \times \sqrt 3 $$ pattern corresponding to 0.2–0.4 monolayers of Ge. From the symmetry, coverage, and the fact that Ge-Si intermixing does not occur at this temperature, Chen et al. proposed an adatom model for the structure. Motivated by these experiments, we have carried out total energy calculations for two types of $$\sqrt 3 \times \sqrt 3 $$ adatom models. The results of these calculations are discussed in Sect.51.2. Ultimately, we hope to provide a definitive characterization of the Si (111)$$\sqrt 3 \times \sqrt 3 $$3-Ge surface, since this will provide insight into the more complicated 5 × 5 and 7 × 7 reconstructions which have been observed on Si and SiGe alloys [51.2].