Topology of Amorphous Tetrahedral Semiconductors on Intermediate Length Scales

Using the recently proposed ``activation-relaxation technique,'' we develop a structural model for a-GaAs almost free of odd-membered rings, i.e., wrong bonds, having an almost perfect coordination of four. This model is found to be superior to structures from tight-binding or quantum molecular dynamics simulations. Comparing with a-Si, as described by a Polk-type continuous random network, we find that the cost of wrong bonds is such that the two materials should have different topologies. Our study provides direct information on the intermediate-range topology of amorphous tetrahedral semiconductors.