Switching the charge of a single Mn-Dopant in InAs with the STM in experiment and model

We performed low-temperature scanning tunneling microscopy and -spectroscopy on Mn-doped InAs. We looked at (110) surfaces prepared by in-situ cleavage of InAs samples with Mn doping densities of 1.1017 cm-3 and 1.1019 cm-3. We find rings of increased differential conductance surrounding each Mn dopant with bias-voltage dependent diameter. When the ring crosses the acceptor, the well known anisotropic shape of the bound-hole wave function appears in topographs. We take the rings as evidence for a charge-change of the acceptors caused by the tip-induced potential. A very simple Tersoff-Hamann based model, integrating the voltage dependent tip-induced quantum dot and the decharging, was used to accurately reproduce our observations. Our understanding allows interpreting the observed ring shapes as equipotential lines of the tip-induced quantum dot and the ring intensity as a direct measure for the screened Coulomb potential of the charged acceptor