KINDS OF DISORDER AND THE ELECTRONIC STRUCTURES OF TETRAHEDRAL AMORPHOUS SEMICONDUCTORS.

In an elemental tetrahedral amorphous semiconductor, such as Si or Ge, there is both quantitative and topological disorder. The topological disorder includes both coordination defects and the ring statistics. The quantiative disorder includes bond-length, bond-angle, and dihedral-angle variation. Using an accurate tight-binding representation for Si, authors show that the bond-length and bond-angle disorder are relatively unimportant. Extensions of these results enable one to understand semiquantitatively the differences in density of states between crystalline and amorphous Si as well as predict variations among different amorphous semiconductors.