Electronic properties of a strained ⟨100⟩ silicon nanowire

The effects of uniaxial strain on the electronic properties of silicon nanowires grown in < 100 > direction are studied using a tight binding sp(3)d(5)s(*) orbital basis quantum simulation. Calculations are performed using both Harrison and Boykin formalisms (discussed in Sec. II). The energy difference between the fourfold (Delta(4)) and the twofold (Delta(2)) degenerate valleys of conduction bands reduces with compressive strain and the nanowire becomes an indirect band gap material when the compressive strain exceeds a certain value. With tensile strain, this energy difference increases and the nanowire band structures remain direct. The conduction band edge is downshifted with compressive strain and is upshifted with tensile strain. However, the valence band edge is upshifted with both types of strain that results in band gap reduction with strain. The four-valley degeneracy of conduction band at the center of one dimensional wire Brillouin zone is slightly lifted with both types of strain. The energy difference between the top two valence bands is insensitive to tensile strain and is significantly changed with compressive strain. The strain has no effect on conduction band effective mass but changes the valence band effective mass significantly. A 1% strain can change the hole effective mass by approximate to 53%. Harrison and Boykin formalisms produce very similar valence band edge and hole and electron effective masses and significantly different conduction band edge and band gap. In Boykin formalism, strain affects the energy levels of both the Delta(4) and Delta(2) valleys of conduction band while the energy level of only Delta(2) valleys is affected by strain in Harrison calculations. The direct to indirect transition occurs at a slightly higher compressive strain in Boykin formalism.