AVS 45th International Symposium
    Electronic Materials and Processing Division Wednesday Sessions
       Session EM2-WeA

Paper EM2-WeA1
Oscillating Contrasts Surrounding Charged Defects and Dopant Atoms in (110) Surfaces of III-V Semiconductor at Room-Temperature

Wednesday, November 4, 1998, 2:00 pm, Room 316

Session: Application of Scanning Probes to Electronic Materials
Presenter: Ph. Ebert, Forschungszentrum Jülich, Germany
Authors: Ph. Ebert, Forschungszentrum Jülich, Germany
C. Domke, Forschungszentrum Jülich, Germany
M. Heinrich, Forschungszentrum Jülich, Germany
K. Urban, Forschungszentrum Jülich, Germany
Correspondent: Click to Email
Positively and negatively charged defects and dopant atoms in n-doped GaAs(110) surfaces give rise, at room temperature, in occupied-state scanning tunneling microscope images to a bright elevation, which is surrounded by a dark depression ring. This oscillating contrast is not observed in empty-state images. A similar effect is found on n-doped GaP(110) surfaces. In order to explain the origin of this contrast behavior we simulated the spatial variation of the tunnel current as a function of the tunneling voltage, the polarity of the charge, and the doping of the material. The calculation of the tunnel current takes into account the tip-induced band bending, the local potential change induced by the screening of the charge, and the extension of the Tersoff-Hamann model for larger voltages. The results suggest that the oscillation in room-temperature STM images can be explained as the image of the local potential change (screened Coulomb potential) induced by the presence of the charge on (110) surfaces of III-V semiconductors. It is found that the oscillating contrast behavior occurs only if competing contributions to the tunnel current from the valence and conduction bands exist. The simulation also reproduces qualitatively all presently known contrast features of charged defects and dopant atoms on III-V and II-VI compound semiconductor cleavage surfaces in STM images.