C. Domke

Oscillating contrast in room-temperature scanning tunneling microscope images of localized charges in III–V semiconductor cleavage surfaces

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. A simulation of the contrast induced by localized charges on (110) surfaces of III–V semiconductors suggests that the oscillation in room-temperature scanning tunneling microscope images can be explained as the image of the local potential change (screened Coulomb potential) induced by the presence of the charge.

Direct observation of electrical charges at dislocations in GaAs by cross-sectional scanning tunneling microscopy

We demonstrate the possibility of simultaneous determination of the type and electrical charge state of dislocations in GaAs by cross-sectional scanning tunneling microscopy (STM). The methodology is demonstrated for a dissociated perfect dislocation in highly Si-doped GaAs(110) surfaces. The STM images of the dislocation penetrating GaAs cleavage surface show that both partial dislocation cores as well as the stacking fault between the two partial dislocation cores are negatively charged.

Atomic-scale properties of the amphoteric dopant Si in GaAs(110) surfaces

Abstract The electronic properties of positively charged Si Ga donors and negatively charged Si As acceptors in different subsurface layers as well as Si donor–Si acceptor dipoles and uncharged Si pairs in GaAs(110) surfaces were investigated by scanning tunneling microscopy. The subsurface location of the dopant atoms is determined from the observed symmetry. Localized states of the dopant atoms are identified. The fraction of Si atoms incorporated in GaAs on As sites increases with increasing Si concentration. Si pairs are found to be incorporated substitutionally in GaAs and their contrast indicates the presence of half-filled dangling bonds. The Si Ga donor–Si As acceptor dipoles are surrounded by a height change indicating a dipole screening field.

Point defects, dopant atoms, and compensation effects in CdSe and CdS cleavage surfaces

Abstract We investigated point defects and dopant atoms in (11–20) and (100) cleavage surfaces of CdSe using atomically resolved scanning tunneling microscopy images. Positively charged dopant atoms give rise to elevations of up to 5 nm in diameter in the empty and occupied state images. Uncharged Se and Cd vacancies exhibit an isolated missing occupied and empty dangling bond, respectively. In CdS (100) surfaces we observed In dopant atoms and acceptors. On the basis of the observed defects and dopant atoms and their concentrations the origin of the electrical compensation is discussed.