Electronic excitations on Ge_xSi_1−x(100)(2×1)

The presence of a reconstruction of a higher order than the nominal (2×1) superstructure has been observed for the (100) surface of Ge/Si alloys at room temperature. High‐resolution electron energy loss spectroscopy (HREELS) has been used to study electronic excitation on these surfaces. Transitions were observed both between the valence band and the unoccupied surface state and between the occupied surface state and the conduction band at a variety of points in the two‐dimensional Brillouin zone. Heating produced segregation of the Ge to the surface leaving a Si rich subregion. Therefore, the bulk transitions strongly resemble those from pure Si. Rather surprisingly, transitions between bulk and surface states also resemble those from pure Si and may be taken as a good indication that the Ge atoms have the same electronic and geometric structure as do the Si atoms on the pure substrate. Supportive evidence for a metallic surface state at the Γ point associated with the loss of long‐range order is also presented.