title: Dramatic reduction of surface recombination by in situ surface passivation of silicon nanowires.
abstract: Nanowires have unique optical properties and are considered as important building blocks for energy harvesting applications such as solar cells. However, due to their large surface-to-volume ratios, the recombination of charge carriers through surface states reduces the carrier diffusion lengths in nanowires a few orders of magnitude, often resulting in the low efficiency (a few percent or less) of nanowire-based solar cells. Reducing the recombination by surface passivation is crucial for the realization of high-performance nanosized optoelectronic devices but remains largely unexplored. Here we show that a thin layer of amorphous silicon (a-Si) coated on a single-crystalline silicon nanowire, forming a core-shell structure in situ in the vapor-liquid-solid process, reduces the surface recombination nearly 2 orders of magnitude. Under illumination of modulated light, we measure a greater than 90-fold improvement in the photosensitivity of individual core-shell nanowires, compared to regular nanowires without shell. Simulations of the optical absorption of the nanowires indicate that the strong absorption of the a-Si shell contributes to this effect, but we conclude that the effect is mainly due to the enhanced carrier lifetime by surface passivation.
authors: School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States.
authors: Yaping
authors: Y
authors: Dan
authors: Kwanyong
authors: K
authors: Seo
authors: Kuniharu
authors: K
authors: Takei
authors: Jhim H
authors: JH
authors: Meza
authors: Ali
authors: A
authors: Javey
authors: Kenneth B
authors: KB
authors: Crozier