Bandstructure Effects in Silicon Nanowire Hole Transport
Date of this Version
2008Acknowledgements
This work was funded by the Semiconductor Research Corporation (SRC). The computational resources for this work were provided through nanoHUB.org by the Network for Computational Nanotechnology (NCN). The authors would like to acknowledge Prof. Timothy Boykin of University of Alabama at Huntsville for tight-binding discussions.
This document has been peer-reviewed.
Abstract
Bandstructure effects in PMOS transport of strongly quantized silicon nanowire field-effect-transistors (FET) in various transport orientations are examined. A 20-band sp3d5s*-SO semi-empirical atomistic tight-binding model coupled to a self consistent Poisson solver is used for the valence band dispersion calculation. A semi-classical, ballistic FET model is used to evaluate the current-voltage characteristics. The dispersion shapes and curvatures are strong functions of device size, lattice orientation, and bias, and cannot be described within the effective mass approximation. The anisotropy of the confinement mass in the different quantization directions can cause the charge to preferably accumulate in the (110) and secondly on the (112) rather than (100) surfaces. The total gate capacitance of the nanowire FET devices is, however, very similar for all wires in all the transport orientations investigated ([100], [110], [111]), and is degraded from the oxide capacitance by ~30%. The [111] and secondly the [110] oriented nanowires indicate highest carrier velocities and better ON-current performance cmpared to [100] wires. The dispersion features and quantization behavior, although a complicated function of physical and electrostatic confinement, can be explained at first order by looking at the anisotropic shape of the heavy-hole valence band.
Keywords
nanowire, bandstructure, tight binding, transistors, PMOS, hole, valence band, MOSFETs, non-parabolicity, effective mass, injection velocity, quantum capacitance, anisotropy.
Discipline(s)
Nanoscience and Nanotechnology
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