title: Distribution of active impurities in single silicon nanowires.
abstract: The distribution of electrically active B concentration in single SiNWs (nanowires) grown by a vapor-liquid-solid (VLS) process was studied by analyzing Fano resonance in Raman spectra. We found a gradient of active B concentration along the growth direction; the B concentration was the largest at the substrate side and the smallest at the catalyst side. The observed concentration gradient suggests the conformal growth of a high B concentration layer during a VLS process. To confirm this effect, we grew SiNWs with controlled impurity profiles, that is, p-type/intrinsic ( p-i) and intrinsic/ p-type ( i-p) SiNWs, by controlling the supply of B source during SiNWs growth. We found that p-i SiNWs can be grown by just stopping the supply of B source in the middle of the growth, while i-p SiNWs were not realized; that is, the whole region of nominal " i-p" SiNWs was B-doped even if we started the supply of B source in the middle of the growth. These results confirm the above doping model. We also found that the distribution of active B concentration was significantly modified by high temperature annealing. By annealing at 1,100 degrees C for 1 min, B concentration became almost uniform along 10 microm long SiNWs irrespective of initial B profiles. This suggests very efficient diffusion of B atoms in a defective high B concentration surface layer of SiNWs.
authors.affiliation: Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan.
authors.forename: Go
authors.initials: G
authors.lastname: Imamura
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kawashima
authors.forename: Minoru
authors.initials: M
authors.lastname: Fujii
authors.forename: Chiharu
authors.initials: C
authors.lastname: Nishimura
authors.forename: Tohru
authors.initials: T
authors.lastname: Saitoh
authors.forename: Shinji
authors.initials: S
authors.lastname: Hayashi