Detection of doping atom distributions and individual dopants in InAs(110)by dynamic-mode scanning force microscopy in ultrahigh vacuum

We investigate the influence of near-surface doping atoms of in situ cleave d n- and p-doped InAs(110) on images acquired with constant frequency shift by dynamic mode scanning force microscopy (DM-SFM) in ultrahigh vacuum. Th e local arrangement of doping atoms near the surface determines the distrib ution of mobile charge carriers and thus the electrostatic surface potentia l, which affects the contrast observed in DM-SFM images. The experiments re veal a strong dependence of the type and density of these charge carriers o n the sign and magnitude of the applied bias voltage. Additionally, we find that the achieved resolution is directly related to the,overlap of the scr eened Coulomb potential of ionized neighboring doping atoms. On n-InAs(110) , the overlap is very strong, and the contrast observed in large-scale DM-S FM images acquired on atomically flat terraces reflects the density distrib ution of the doping atoms. The bias dependence of the contrast can be inter preted by the presence of an accumulation, depletion, or inversion zone und erneath the probe tip. On a p-InAs(110) sample with a nearly identical dopi ng concentration, however, a screened Coulomb potential around individual d oping atoms could be detected, since the screening length is smaller than t heir mean distance between dopings; In atomically resolved images, charged doping atoms as well as charged As vacancies could be identified.