ELECTRONIC STATES OF SI(001) STEPPED SURFACE UNDER ELECTRIC-FIELD PARALLEL TO SURFACE

Electronic states of the 2 x 1 terrace, the unreconstructed S(a) buckled S(a), reconstructed S(b) and unreconstructed S(b) steps under electric fields parallel to the Si(001) surface are calculated by the DV-Xalpha-LCAO method. If an electric field is applied in parallel and perpendicular to dimers, electron transfer between neighboring atoms of two dimers is larger and smaller, respectively. For both S(a) and S(b) steps, electric field induces large electron transfers between dimers on the higher and lower terraces near the step edge. Furthermore, it changes the charge density of valence bonds between surface and subsurface atoms near the step edge. For the S(a) steps, electric field applied in the step-down (-up) direction induces a large shift of energy levels to the lower (higher) energy side. For the Sb StePS, electric field induces a shift of energy levels in opposite direction to that of the S(a) steps.