An icosahedral quasicrystalline model for amorphous semiconductors

In the first article of this series an icosahedral quasicrystal with a tetracoordinated decoration of atoms was introduced as a model for amorphous semiconductors. The electronic structure is one of its most interesting features. Based upon a LCAO tight binding scheme with five orbitals sp³s* per atom the electronic density of states (DOS) is calculated by use of the recursion method. Various effects of the specific geometry on the DOS are investigated, including the topology of the tetracoordinated network, the corresponding dihedral angles, bond angles, bond lengths, and dangling bonds. These geometrical parameters are treated separately and therefore reveal their distinct influences on the DOS. The resulting effects are discussed regarding the DOS as a whole, while details are provided about variations of the outer band edges, shifts of maxima and first moments of uppermost valence band and lowest conduction band, and — most important — changes in the central gap. The properties of single wave functions are subject of the third article in this series.