Electrostatic screening near semiconductor surfaces
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abstract
We have developed a semimicroscopic theory for the electrostatic potential due to an isolated charge near a semiconductor surface whose surface states do not contribute free carriers. It employs the linearized version of the Debye-Hckel (or, equivalently, the Thomas-Fermi) approximation. This includes the screening effects both of the plasma of free carriers due to bulk donors or acceptors, and of the bound polarizable charge associated with the bulk dielectric, but does not include free charge from intrinsic or extrinsic surface states. Results are obtained for a source charge above the semiconductor, within the semiconductor, and on the semiconductor surface, but we emphasize the last case. Although there is a dipole moment associated with source charge on the surface, the surface potential at long distances is quadrupolar; at intermediate distances greater than a characteristic atomic dimension it is a screened exponential, with screening length equal to the bulk value. The case of intermediate distance provides a rigorous basis for the exponentially screened surface potential commonly employed to analyze scanning tunneling microscopy images of the depletion or accumulation regions surrounding isolated charges on III-V(110) cleavage surfaces. Certain of these results also apply to colloids. 2000 The American Physical Society.
