“Deep Ultra-Strength”-Induced Band Structure Evolution in Silicon Nanowires

Recently we experimentally demonstrated that vapor-liquid-solid (VLS) grown silicon (Si) nanowires can be stretched to above 10% elastic strain through in situ nanomechanical strategies (Zhang et al. Sci. Adv. 2016, 2 (8), e1501382). Here, based on first-principles calculation, the geometric and electric properties of <110>-oriented Si nanowires with diameter ∼1.5 nm under ultralarge strain are comparatively investigated. The anisotropic Poisson effect was observed in the silicon nanowire that the change of diameter along the (100) orientation decreases dramatically while that along the (110) orientation shows only minor influence. For the purpose of obtaining a thorough understanding of the influence of applied strain on the electronic properties, the electronic band structure, effective mass of electron, and work function are systematically studied. Direct-to-indirect band gap transformation occurs for hydrogen terminated nanowires when the applied strain is larger than 4%. When the applied strain is more than 19% (may vary depending on different chemical modifications), the Si nanowires could even transform from semiconductor to metallic behavior, with no band gap! Our results show the possibility of tuning Si nanowires' electronic properties through mechanical straining, which may offer a new route in Si-based optoelectronics applications.