Department of Applied Sciences and Mathematics, Arizona State University, Mesa, AZ 85212, USA.
J Phys Condens Matter. 2011 Mar 23;23(11):115502. doi: 10.1088/0953-8984/23/11/115502. Epub 2011 Mar 1.
Strain modulated electronic properties of Si/Ge core-shell nanowires along the [110] direction were reported, on the basis of first principles density-functional theory calculations. In particular, the energy dispersion relationship of the conduction/valence band was explored in detail. At the Γ point, the energy levels of both bands are significantly altered by applied uniaxial strain, which results in an evident change of the band gap. In contrast, for the K vectors far away from Γ, the variation of the conduction/valence band with strain is much reduced. In addition, with a sufficient tensile strain (∼1%), the valence band edge shifts away from Γ, which indicates that the band gap of the Si/Ge core-shell nanowires experiences a transition from direct to indirect. Our studies further showed that effective masses of charge carriers can also be tuned using the external uniaxial strain. The effective mass of the hole increases dramatically with tensile strain, while strain shows a minimal effect on tuning the effective mass of the electron. Finally, the relation between strain and the conduction/valence band edge is discussed thoroughly in terms of site-projected wavefunction characters.
基于第一性原理密度泛函理论计算，我们研究了[110]方向上 Si/Ge 核壳纳米线的应变调制电子性质。具体来说，我们详细探讨了导带/价带的能谱关系。在 Γ 点处，施加单轴应变会显著改变两个能带的能级，从而导致带隙明显变化。相比之下，对于远离 Γ 的 K 向量，导带/价带随应变的变化要小得多。此外，在足够大的拉伸应变（约 1%）下，价带边缘会远离 Γ，这表明 Si/Ge 核壳纳米线的带隙经历了从直接带隙到间接带隙的转变。我们的研究还表明，通过外部单轴应变可以调节载流子的有效质量。随着拉伸应变的增加，空穴的有效质量急剧增加，而应变对调节电子的有效质量影响很小。最后，根据局域波函数特征，我们详细讨论了应变与导带/价带边缘的关系。
