Electronic structure of Ge(111)-(2$\times$1) surface in the presence of doping atoms. Ab initio analysis of STM data

We present the result of first principles modeling of the Ge(111)-($2{\times}1$) surface electronic structure in the presence of donor doping atom at certain position in the surface bi-layer of ($2{\times}1$) reconstruction. We briefly compare these results with the data of experimental low temperature STM investigations. Ab initio calculations demonstrate that doping atom strongly disturbs local electronic structure. The separate state, most probably split off conduction band, appears in the bandgap. Surface LDOS reveals spatial oscillations in vicinity of foreign atom. We also show that the spatial extent of non-negligible inter-atomic interaction between neighboring donor atoms is not less then 70 Å.