Scanning tunneling microscopy studies of Si donors (SiGa) in GaAs

We report scanning tunneling microscopy (STM) studies of Si substitutional donors (${\mathrm{Si}}_{\mathrm{Ga}}$) in GaAs that reveal delocalized and localized electronic features corresponding to ${\mathrm{Si}}_{\mathrm{Ga}}$ in the top few layers of the (110) cleavage surface. The delocalized features appear as protrusions a few nm in size, superimposed on the background lattice. These features are attributed to enhanced tunneling due to the local perturbation of the band bending by the Coulomb potential of subsurface ${\mathrm{Si}}_{\mathrm{Ga}}$. In contrast, STM images of surface ${\mathrm{Si}}_{\mathrm{Ga}}$ show very localized electronic structures, in good agreement with a recent theoretical prediction [J. Wang et al., Phys. Rev. B 47, 10 329 (1993)].