Strongly enhanced minority lifetimes in single silicon nanowires by surface passivation

Nanosized materials, especially nanowires, have unique optical properties [1] and have been widely investigated as important building blocks for energy harvesting applications such as solar cells. [2] However, due to the large surface-to-volume ratio, recombination of charge carriers through the surface states of nanowires has been found to reduce the carrier diffusion lengths in nanowires a few orders of magnitude [3], often resulting in low efficiency. [4] Reducing the recombination by surface passivation is crucial to develop high performance nanosized optoelectronic devices, but remains largely unexplored. [5] Here we show that a thin layer of amorphous silicon (a-Si) coated on a single-crystalline silicon nanowire (sc-SiNW), forming a core-shell structure in-situ in the vapor-liquid-solid (VLS) process, reduces the density of surface states nearly 2 orders of magnitude and thereby increases the minority carrier lifetime ~100 times. We found that individual core-shell nanowire devices have a strongly enhanced sensitivity to modulated light, compared to nanowire without shells, mainly due to surface passivation effects.