Geometric Frustration of 2D Dopants in Silicon: Surpassing Electrical Saturation

A novel application of scanning transmission electron microscopy, combined with data from x-ray absorption spectroscopy, establishes that high concentrations of $n$-type Sb dopants distributed within a two-dimensional (2D) layer in Si can contribute up to an order of magnitude higher free-carrier density than similar dopant concentrations distributed over a three-dimensional region. This difference is explained using a simple model in which formation of electrically deactivating centers is inhibited by solely geometric constraints. It should be possible to extend these ideas for obtaining even higher free-carrier densities in Si from 2D layers of Sb and other group V donors.