In the ongoing development of novel nanoelectronic devices, silicon nanowires are of great interest due to the prevalence of silicon-based technologies. Recent experimental advances have enabled the growth of nanowires along controlled directions, and with thicknesses as small as 1.3 nm¹. To utilize these developments in transistors, sensors, or other devices, electronic device simulations will be necessary. The aim of the present work is to obtain rigorous, ab initio structural and electronic property information of nanowires for subsequent use in device simulations. We have studied pristine silicon nanowires oriented along the [100], [110], [111], and [112] directions, with several different cross-sectional geometries, and with thicknesses of up to 3.5 nm. All nanowires exhibit smaller band gaps than unrelaxed structures based on bulk silicon, indicating the importance of surface reconstruction. The effect is most pronounced in nanowires with diameters less than 2 nm, some of which are metallic. In addition to thickness, band gap is shown to depend on the growth direction, as well as the facet arrangement of the cross-section. Lastly, we discuss the implementation of these results in device simulations of silicon nanowire transistors.

¹ Ma, D. D. D., C. S. Lee, et al. (2003). "Small-diameter silicon nanowire surfaces." Science 299(5614): 1874-1877.