Localized excess negative charges in surface states of the clean Ga-rich GaAs(100)c(8×2)/4×2 reconstruction as imaged by scanning tunneling microscopy

Scanning tunneling microscopy images of the Ga-rich GaAs(100)c(8×2)/(4×2) surface exhibit vivid long-range patterns consisting of bright spots (“ghosts”) which are attributed to localized excess charge rather than atomic clusters. The nearly planar geometry of the sp2-hybridized gallium dimer atoms results in localized π states made up of a combination of the Ga pz orbitals. These states in the upper half of the band gap form the lowest …