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

10 CHAPTER 1. SILICON-GERMANIUM MATERIAL SYSTEM
Silicon (Si)
Figure 1.8: Band structures for the most prominent group IV semiconductors
Si (a) and Ge (b), both featuring an indirect bandgap [12, 20].
� Source: SiGe bandstructure.jpg
In Si the conduction band is characterized by six equivalent minima along the 〈100〉-directions
of the Brillouin zone located at about k0 = 0.85 (2π/a). The constant energy surfaces are
ellipsoids of revolution with major axes along 〈100〉. The valence band of Si has its minimum
at the Γ-point where the warped heavy and light hole bands are degenerate. The indirect
gap energy Eg,ind is 1.12 eV (300 K). In Fig. 1.8 [12, 20] the Si band structure and the indirect
band gap are shown. [3]
Germanium (Ge)
In Ge the conduction band is characterized by eight equivalent minima at the end points of
the 〈111〉-directions of the Brillouin zone and the constant energy surfaces are ellipsoids of
revolution with major axes along 〈111〉. The valence band of Ge has its minimum, like Si, at
the Γ point. The indirect gap energy of Ge is with Eg,ind = 0.66 eV (291 K) smaller than in
Si (see also Fig. 1.8 [12, 20] for the Ge band structure).
In Tab. 1.1 some important properties for Group IV elements are listed. For the sake of
completeness additionally to Si and Ge also values for carbon (diamond) are tabulated. [3]