  We report the transport characteristics of both electrons and holes through
narrow constricted crystalline Si "wall-like" long-channels that were
surrounded by a thermally grown SiO2 layer. Importantly, as a result of the
existence of fixed oxide charges in the thermally grown SiO2 layer and the
Si/SiO2 interface, the effective Si cross-sectional wall widths were
considerably narrower than the actual physical widths, due the formation of
depletion regions from both sides. These nanostructures were configured into a
metal-semiconductor-metal device configuration that was isolated from the
substrate region. Dark currents, dc-photo-response, and carrier
"time-of-flight" response measurements using a mode-locked femtosecond laser,
were used in the study. In the narrowest wall devices, a considerable increase
in conductivity was observed as a result of higher carrier mobilities due to
lateral constriction and strain. The strain effects, which include the reversal
splitting of light- and heavy- hole bands as well as the decrease of
conduction-band effective mass by reduced Si bandgap energy, are formulated in
our microscopic model for explaining the experimentally observed enhancements
in both conduction- and valence-band mobilities with reduced Si wall thickness.
The role of the biaxial strain buffing depth is elucidated and the
quasi-quantum effect for the saturation hole mobility at small wall thickness
is also found and explained. Specifically, the enhancements of the valence-band
and conduction-band mobilities are found to be associated with different
aspects of theoretical model.
