Surface band-bending and Fermi-level pinning in doped Si observed by Kelvin force microscopy

The workfunction change in doped Si was examined using Kelvin force microscopy in a wide range of doping concentrations from p-type ∼10 ¹⁹ to n-type ∼10²⁰cm^-3 corresponding to the bulk Fermi-level positions from near the valence-band top to conduction-band minimum. Experimental data can be reproduced by model calculations using an appropriate surface-state density composed of the donor- and acceptor-like gap states. These results indicate that no appreciable surface-band bending occurs for doping concentrations less than ∼10¹⁴cm^-3 while the bending becomes prominent and the surface Fermi-level is eventually pinned in the midgap region as the concentration increases to ∼10 ²⁰cm^-3.