First-principles Investigation On Core-shell Silicon Nanowires Doped With3D Transition-metal Atoms

Silicon nanowires (SiNWs) exhibit novel characteristics, because of their largesurface to volume ratio, high anisotropy, special structures, comparing with traditionalbulk silicon materials. It obtained great concern from researchers due to itscompatible with current silicon technology. Doping and defect creating are twoimportant methods for the study of SiNWs. The one-dimensional structures can bemodified by doping different elements and by choosing different positions. Thedensity of carriers and geometrical structures can be changed and thus resulting novelphysical properties. Therefore, they have potential applications in the aspects ofnano-electron and spintronic devices.In this paper, we systematically investigated the stability of geo metric structures,electrical properties and magnetic moment of3d transition-metal (TM)(Mn, Fe, Co,Ni) atoms doped in core-shell SiNWs with eclipsed pentagonal and hexagonal incross-section using extensive first-principles calculations based on density functionaltheory (DFT). The results of energy calculation show that, all the structures with threedifferent doping methods including edge doping, core doping, and shell doping can beexist stably. Among the same type doped SiNWs, the stability of core doped structuresis highest. The analysis of the energy bands indicate that all the doped systems exhibitmetallic behavior, and become stronger with the concentration of TM atomsincreasing. The number of electronic bands crossing the Fermi level determine s thenumber of conductance channels. Our study shows that the number of conductancechannels is increased with the number of dopant atoms increasing. At the same time,the metallic behavior is stronger with the increasing of dopant concentration. Throughthe spin-polarized calculations, we found the different number of bands crossing atthe Fermi level in the band structures of spin-up and spin-down components,indicating the ferromagnetic behavior of doped systems. Through the Bader Chargeanalysis, the electrons are found transferred from silicon atoms to transition metalatoms and there also existing the transfer of electron from4s orbital to3d/4p orbital ina transition metal atom. The reduce of number of unpaired electrons in3d orbital andthe electrons transferred from majority spin to minority spin in each orbital (4s,3d,4p)cause the decrease of magnetic moment of TM atoms. The magnetic moment of singleTM atom in TM-shell SiNWs is largest when compared with that in other two kindsof structures doped with same TM atoms. Our computational results are significance for further research on the doped silicon nanowires and will provide guidance for theapplication in mirco-nano decices.