TUNNELING MICROSCOPY OF POINT-DEFECTS ON GAAS(110)

The structure of point defects situated at nominal arsenic or gallium sites on the (110) cleavage face of GaAs has been studied by scanning tunneling microscopy (STM). Alternate-bias imaging was used to simultaneously resolve the arsenic and gallium sublattices corresponding to filled and empty states, respectively, on both p- and n-type material. There, is an interesting symmetry in the characteristic features associated with the most commonly observed defect of each type. Both types appear in the STM images as a missing surface atom, or, more precisely, a highly localized reduction in the corresponding filled- or empty-state density. For both types of defect, nearest neighbors within the same zigzag chain appear to be raised out of the surface, while second nearest neighbors show a slight depression. No large lateral displacements are detected in either the nearest or second nearest neighbor atoms. Point defects with this structure are observed exclusively at arsenic sites on p-type material, and exclusively at gallium sites on n-type material. The band bending accompanying the defects reveals that the arsenic defect on p-type samples is positively charged whereas the gallium defect on n-type samples is negatively charged. Migration of these defects in the [110BAR] direction along the zigzag chains, as well as in the [001] direction perpendicular to them, is occasionally observed in the STM scans.