Theory of transition from the dihydride to the monohydride phase on the Si(001) surface

Abstract

Recent studies have revealed interesting properties of the dihydride phase coexisting with the monohydride phase on the hydrogenated Si surfaces. In this work, we report self-consistent total-energy calculations within the framework of the local density functional theory, which provide a rigorous basis for understanding the transition between the dihydride and monohydride phases, and the desorption of hydrogen from Si surfaces. We found that the energy associated with the rotation of SiH2 in the plane bisecting the angle between two back bonds is rather small. The equilibrium configuration is not the ideal SiH2 which completes the tetrahedral coordination, and the total energy is lowered when all SiH2 radicals are tilted in the same direction. The forces exerted on the atoms, as well as the results of the geometry optimization indicate that the outermost Si plane relaxes inwards even at full coverage of SiH2. The charge-density analysis shows how the H2 bond is formed from the two adjacent SiH2 radicals approaching each other. © 1986.