Doping and electrical characterization of individual silicon nanowire

As the drive to use silicon nanowires in nano-electronic devices and circuits is getting stronger, a clear understanding of the incorporation mechanism and electrical behavior of dopants in the nanowires is becoming more important. Owing to the quasi-one-dimensional structure of the nanowires leading to their high surface to volume ratio, the surface effects are expected to play a stronger role on the dopants in a nanowire than in planar silicon devices. We doped silicon nanowires of diameter ~ 100 nm uniformly - 1) in-situ with boron during growth by molecular beam epitaxy (MBE), and 2) ex-situ separately with boron, phosphorus and arsenic by ion implantation. In addition, the in-situ boron doping was combined with phosphorus ion implantation to fabricate an intra-nanowire p-n junction. Electrical current-voltage measurements of individual nanowires with a micro-manipulator revealed that - 1) for the uniformly implanted nanowires the electrical conductivity increases in accordance with the expected dopant concentration, and 2) the p-n junction nanowires show excellent diode characteristics. In order to understand the surface effects, profiling of electrically active dopants in individual nanowires was performed by scanning spreading resistance microscopy (SSRM). It revealed a ‘higher doped core-lower doped shell’ type of structure confirming the surface segregation of dopants. This effect was most pronounced in phosphorus-doped nanowires.