| In the past decades, the nanostructures of semiconductors have drawn intensive attention, because their quantum-confinemnet effect gives rise to novel and anomalous properties which can satisfy the requirement of new device application. Although there have been long-term study on many nanostructures (e.g., nanowire, nanoplane, nanobelt, etc) of semiconductors such as the group VIA semiconductors C, Si, Ge. However, there are shortcomings in the properties and performance of these materials, so it is still necessary to design and study new semiconductor nanostructures. Therefore, the current study is focused on the nanostructures of two single-element and narrow-band-gap semiconductors.Using the first-principles calculations, we investigate band structure dependence of 2-dimensional arsenic layers with puckered honeycomb structure on the layer thickness and in-plane strains. We find that an indirect-direct transition of band gap will emerge when the number of layers and in-plane strains are changed. The indirect-direct transition stems from the distinct response of the direct band edge and indirect band edge states to quantum-confinement effect and in-plane strains:valence band edge state of the indirect gap comes from As-As bonds parallel to the layers, while that of the direct gap comes from the bonds perpendicular to the layers.We also study the surface and optical properties of tellurium by first-principles calculations. We find that its surfaces with different miller index have much lower surface energy than those of group IVA semiconductors C, Si, Ge, and the nanostructures surrounded by these surfaces have clean band gap with no surface electronic states. The analysis of optical properties shows that absorption peak in the 0-3 eV range stems from electronic transition between the two bands close to the gap; the absorption peaks of the tellurium nanowires and nanobelts have a blue shift and their band gaps increase obvioulsy with the decrease of size. |
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