Doping of Nanowires and Atomic Films

摘要

Recent breakthroughs in the growth of freestanding one-dimensional (1D) semiconductor nanowires and two-dimensional (2D) atomic films have opened up great opportunities to revolutionize technologies in nanoscale electronics, optoelectronics, spintronics, and sensors. Doping, an essential element for manipulation of electronic transport in traditional semiconductor industry, is widely expected to play important role as well in control of transport properties in nanostructures. However, traditional theory of electronic disorder predicts that doping in 1D and 2D systems leads to carrier localization, limiting practical applications of doping in nanostructures because of poor carrier mobility. We proposed a novel concept, namely, confined doping in nanostructures, to significantly increase carrier mobility [1, 2]. In our approach, distribution of dopants in a nanostructure is confined within a particular region in the nanostructure so that the doped nanostructure becomes a coupled system comprising a doped subsystem and a perfect crystalline subsystem. We showed that carrier mobility in a 1D nanowire and in a 2D atomic film with confined doping exhibits rather counterintuitive behavior in the regime of heavy doping, namely, the larger the concentration of dopants the higher the carrier mobility. A nanowire with confined doping undergoes a quasi-metal/insulator transition while a 2D atomic film with confined doping exhibits a true metal-insulator transition. We have also conducted first-principles and molecular dynamics studies for the stable surface structures of silicon nanowires [3, 4]. One of our main findings is the existence of magic numbers for silicon nanowires. We also found that Si nanowires with diameters smaller than 1.7 nm prefer a shape that has a square cross section with sharp corners. These findings are important for guiding the syntheses of Si nanowires and for tailoring their transport properties through doping.