Effects of the ambient medium and structure parameter on the optical properties of tapered silicon nanowire

Tapered silicon nanowire (T-SiNW) is expected to have a wider application than a cylindrical one in optical sensors, photovoltaics, etc. due to its broadband light-trapping. However, there is little research on the effect of ambient medium and structure parameters on the optical properties of T-SiNW. First, based on numerical simulations it is found that, compared with that in air, when a T-SiNW is embedded in ambient medium with refraction index of 1.284: the absorbed light by it under given irradiation becomes much less; the scattered light by it shows a wider angular distribution; the nearfield light around it becomes stronger in a wider area. These mean that T-SiNW is more desirable for light-trapping in the ambient medium. Then, as the bottom diameter of T-SiNW increases, its light-collecting waveband red-shifts; at the same time, its scattered light shows a broadened angular distribution range. Hence, T-SiNW with larger bottom diameter is more desirable for light-trapping, especially for longwave light which is sometimes difficult to be utilized in photovoltaic devices. Besides, we found that the light-collecting and -absorption multiples of T-SiNW are both proportional to its length approximatively, which provides a very convenient way to regulate its light-trapping performance. The insights in this work are helpful to the design of devices using T-SiNW as the main block.