Lattice Gas Model Analysis of the (111) Surface Structures of Si, Ge and Related Systems. II. On the DAS Model

Abstract

The interrelation among the (7×7), (5×5) and c(2×8) reconstructions of the (111) surface of Si, Ge and related systems is discussed by extending previous analysis of the lattice gas model on a triangular net to a multi-layer model to the purpose of analyzing the DAS structure of the (7×7) restruction of Si (111) surface proposed by Takayanagi et al. It is concluded that the stacking fault characterizing the DAS structure has a good reason to appear and that it can solve the difficulties encountered in the previous analysis concerning the stability of the (7×7) state and also that of the c(2×8) state of Ge(111) whose DAS like atomic configuration is newly proposed. The atomic configuration of the (1×1) disordered state at high temperatures is discussed also. The possibility of the floating phase discussed previously is reexamined thereby.