Charged defects on an n-GaAs(110) surface were investigated by using light-modulated scanning tunnelling spectroscopy. Tunnelling via a single defect-induced gap state under photo-illumination was observed for the isolated atomic defects. Screened Coulomb potentials induced around a charged Ga vacancy and a step edge were visualized, for the first time, with nanometer spatial resolution.Furthermore, the charge states of the individual defects were determined at the atomic level.

Probing Nanoscale Potential Modulation by Defect-Induced Gap States on GaAs(110) with Light-Modulated Scanning Tunneling Spectroscopy. S.Yoshida, Y.Kanitani, O.Takeuchi, H.Shigekawa: Applied Physics Letters, 2008, 92[10], 102105