Enhanced binding energy of manganese acceptors close to the GaAs(110) surface

Scanning tunneling spectroscopy was performed at low temperature on buried manganese (Mn) acceptors below the (110) surface of gallium arsenide. The main Mn-induced features consisted of a number of dI/dV peaks in the band gap of the host material. The peaks in the band gap are followed by negative differential conductivity, which can be understood in terms of an energy-filter mechanism. The spectroscopic features detected on the Mn atoms clearly depend on the depth of the addressed acceptor below the surface. Combining the depth dependence of the positions of the Mn-induced peaks and using the energy-filter model to explain the negative resistance qualitatively proves that the binding energy of the hole bound to the Mn atom increases for Mn acceptors closer to the surface.