Strain effects on the band structure for Si nanowires

The present paper discusses the strain effects on the conduction and valence bands for Si nanowires using k.p Hamiltonian, where, in addition to the usual radial symmetric strains, the torsional strain, being unique to axial symmetric devices, is also studied. The radial compression/expansion, analogous with the biaxial strain in planar devices, gives linear increase/decrease in the conduction band energy whereas for valence bands, multiband-specific edge shifts and effective mass changes are discussed with effective mass ellipsoid. The torsional strain only lowers the four-fold conduction subband for [110] nanowire, which is associated with normal strain in crystal coordinate. The torsion also raises the valence band energy with no substantial changes in effective masses. For the valence band, it is also suggested that the diagonal sum for inverted effective mass nearly unchanged under strain application.