Dramatic reduction of surface recombination by in-situ surface passivation of silicon nanowires

TL;DR

This paper demonstrates that in-situ surface passivation of silicon nanowires with an amorphous silicon shell significantly reduces surface recombination, greatly enhancing their photosensitivity for energy harvesting applications.

Contribution

The study introduces a novel in-situ passivation method during VLS growth, achieving nearly two orders of magnitude reduction in surface recombination of silicon nanowires.

Findings

Surface recombination reduced by nearly 100 times

Photosensitivity improved over 90-fold

Enhanced carrier lifetime due to surface passivation

Abstract

Nanowires have unique optical properties [1-4] and are considered as important building blocks for energy harvesting applications such as solar cells. [2, 5-8] 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,[9] often resulting in the low efficiency (a few percent or less) of nanowire-based solar cells. [7, 8, 10, 11] Reducing the recombination by surface passivation is crucial for the realization of high performance nanosized optoelectronic devices, but remains largely unexplored. [7, 12-14] 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 surface recombination nearly two 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.