Optical absorption of silicon nanowires

TL;DR

This study combines simulations and experiments to analyze how silicon nanowire diameter influences optical absorption, demonstrating tunable absorption properties from UV to visible light.

Contribution

It introduces combined Green function and FDTD simulation methods for silicon nanowires and experimentally validates the diameter-dependent absorption shift.

Findings

Absorption onset energy increases with nanowire diameter.

Photocurrent peak shifts to lower energies with larger diameters.

Absorption can be tuned from UV to visible spectrum.

Abstract

We report on simulations and measurements of the optical absorption of silicon nanowires (NWs) versus their diameter. We first address the simulation of the optical absorption based on two different theoretical methods : the first one, based on the Green function formalism, is useful to calculate the scattering and absorption properties of a single or a finite set of NWs. The second one, based on the Finite Difference Time Domain (FDTD) method is well-adapted to deal with a periodic set of NWs. In both cases, an increase of the onset energy for the absorption is found with increasing diameter. Such effect is experimentally illustrated, when photoconductivity measurements are performed on single tapered Si nanowires connected between a set of several electrodes. An increase of the nanowire diameter reveals a spectral shift of the photocurrent intensity peak towards lower photon energies, that allows to tune the absorption onset from the ultraviolet radiations to the visible light spectrum.