AB-INITIO STUDY ON THE AS-STABILIZED SURFACE-STRUCTURE IN ALAS MOLECULAR-BEAM EPITAXY

The dimer structure of an As-stabilized (001) AlAs surface was analyze d based on the cluster model by using ab initio molecular orbital calc ulations. The surface As dimer was modeled by Al4As4H12 (cluster 1) an d Al7As8H19 (cluster 2) clusters. It was shown that the electron count ing model was satisfied for cluster 2, while it was not satisfied for cluster 1. In both clusters, the electronic state of the reconstructed surface was shown to be differ greatly from that of the non-reconstru cted surface. The ground state of cluster 2 was (1)A(1), where a a bon d was formed between the two surface As atoms, and each surface As ato m had a doubly occupied dangling bond. The bond length of the dimer wa s calculated to be 2.7 Angstrom. The mechanism whereby the electron co unting model was satisfied for cluster 2, but not for cluster 1, was c larified.