Impurity doping in
silicon (Si) ultra-large-scale integration is
one of the key challenges which prevent further device miniaturization.
Using ultraviolet photoelectron spectroscopy and X-ray absorption
spectroscopy in the total fluorescence yield mode, we show that the
lowest unoccupied and highest occupied electronic states of ≤3
nm thick SiO2-coated Si nanowells shift by up to 0.2 eV
below the conduction band and ca. 0.7 eV below the valence band edge
of bulk silicon, respectively. This nanoscale electronic structure
shift induced by anions at surfaces (NESSIAS) provides the means for
low-nanoscale intrinsic Si (i-Si) to be flooded by electrons from
an external (bigger, metallic) reservoir, thereby getting highly electron-
(n-) conductive. While our findings deviate from the behavior commonly
believed to govern the properties of silicon nanowells, they are further
confirmed by the fundamental energy gap as per nanowell thickness
when compared against published experimental data. Supporting our
findings further with hybrid density functional theory calculations,
we show that other group IV semiconductors (diamond, Ge) do respond
to the NESSIAS effect in accord with Si. We predict adequate nanowire
cross-sections (X-sections) from experimental nanowell data with a
recently established crystallographic analysis, paving the way to
undoped ultrasmall silicon electronic devices with significantly reduced
gate lengths, using complementary metal–oxide–semiconductor-compatible
materials.