Characterization of carrier transport properties in strained crystalline Si wall-like structures as a function of scaling into the quasi-quantum regime

摘要

We report the transport characteristics of both electrons and holes throughnarrow constricted crystalline Si "wall-like" long-channels that weresurrounded by a thermally grown SiO2 layer. Importantly, as a result of theexistence of fixed oxide charges in the thermally grown SiO2 layer and theSi/SiO2 interface, the effective Si cross-sectional wall widths wereconsiderably narrower than the actual physical widths, due the formation ofdepletion regions from both sides. These nanostructures were configured into ametal-semiconductor-metal device configuration that was isolated from thesubstrate 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 increasein conductivity was observed as a result of higher carrier mobilities due tolateral constriction and strain. The strain effects, which include the reversalsplitting of light- and heavy- hole bands as well as the decrease ofconduction-band effective mass by reduced Si bandgap energy, are formulated inour microscopic model for explaining the experimentally observed enhancementsin both conduction- and valence-band mobilities with reduced Si wall thickness.The role of the biaxial strain buffing depth is elucidated and thequasi-quantum effect for the saturation hole mobility at small wall thicknessis also found and explained. Specifically, the enhancements of the valence-bandand conduction-band mobilities are found to be associated with differentaspects of theoretical model.