Kinetic and Strain-Induced Self-Organization of SiGe ...

4 CHAPTER 1. SILICON-GERMANIUM MATERIAL SYSTEM
senide (GaAs) and heterostructures based on it, are used mainly for microwave and photonic
applications. Nevertheless silicon is one of the most investigated elements in the periodic
table and the whole silicon technology is by far the most advanced among all semiconductor
technologies. [2]
1.1 Structural Properties
Silicon and germanium crystallize in a diamond lattice structure. This structure belongs to
the cubic-crystal family and can be seen as two interpenetrating fcc sublattices with one sub-
lattice displaced from the other by one quarter of the distance along the diagonal of the cube
(i.e. a displacement of √ 3/4 along [111]). In a diamond lattice all atoms are identical, and
each atom in the diamond lattice is surrounded by four equidistant nearest neighbors that
lie at the corners of a tetrahedron (see Fig. 1.1, refer to the spheres connected with darkened
bars [2]).
In a hard sphere model only 34% of the available space is filled, and therefore the diamond
lattice structure is not very compact. Si and Ge have, like any other group IV element,
four electrons in the outer orbit, and each atom shares these valence electrons with its four
neighbors. This sharing of electrons is called covalent bonding and occurs between atoms of
either the same element or between atoms of different elements that have similar outer-shell
electron configurations (in our case: Si, Ge, C). [2].
Figure 1.1: Diamond lattice structure of Si and Ge [2].
� Source: SiGe crystalstructure.jpg