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 simulta neously resolve the arsenic and gallium sublattices corresponding to f illed and empty states, respectively, on both p- and n-type material. There, is an interesting symmetry in the characteristic features assoc iated 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-s tate density. For both types of defect, nearest neighbors within the s ame zigzag chain appear to be raised out of the surface, while second nearest neighbors show a slight depression. No large lateral displacem ents are detected in either the nearest or second nearest neighbor ato ms. Point defects with this structure are observed exclusively at arse nic sites on p-type material, and exclusively at gallium sites on n-ty pe material. The band bending accompanying the defects reveals that th e arsenic defect on p-type samples is positively charged whereas the g allium defect on n-type samples is negatively charged. Migration of th ese defects in the [110BAR] direction along the zigzag chains, as well as in the [001] direction perpendicular to them, is occasionally obse rved in the STM scans.