  Recent work on atomic-precision dopant incorporation technologies has led to
the creation of both boron and aluminum $\delta$-doped layers in silicon with
densities above the solid solubility limit. We use density functional theory to
predict the band structure and effective mass values of such $\delta$ layers,
first modeling them as ordered supercells. Structural relaxation is found to
have a significant impact on the impurity band energies and effective masses of
the boron layers, but not the aluminum layers. However, disorder in the
$\delta$ layers is found to lead to significant flattening of the bands in both
cases. We calculate the local density of states and doping potential for these
$\delta$-doped layers, demonstrating that their influence is highly localized
with spatial extents at most 4 nm. We conclude that acceptor $\delta$-doped
layers exhibit different electronic structure features dependent on both the
dopant atom and spatial ordering. This suggests prospects for controlling the
electronic properties of these layers if the local details of the incorporation
chemistry can be fine tuned.
