Some Polytypes of Germanium and a Tight Binding Model for the Electronic Structure of Amorphous Solids
There is now considerable evidence1–3 that a useful, although idealized, model of amorphous silicon and germanium is the random tetrahedral network (RTN). In this model, each atom is bonded to four nearest-neighbors at very nearly the nearest-neighbor distance R0, of the crystal. The tetrahedral bonding is very nearly preserved in the RTN with the rms deviation in angle being about 10°–15° and a maximum deviation in angle of about twice this amount Thus, on a local scale, the atomic arrangements in the RTN are much like those of the diamond lattice of crystalline Si and Ge. However, on a larger scale significant differences between the diamond lattice and the RTN become apparent. For example, the diamond lattice consists entirely of “staggered” arrangements of bonds on nearest-neighbors whereas the dihedral angle in the RTN is random. In addition, the RTN contains five-, six-, and seven-member rings whereas the diamond lattice contains only six-member rings.
KeywordsDihedral Angle Radial Distribution Function Amorphous Solid Tight Binding Model Diamond Structure
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