We have investigated optical characteristics of silicon nanowire (Si NW) on Al disk arrays using the finite-difference
time-domain (FDTD) simulations. Without the Al disk, the Si NW arrays alone exhibit strong absorption peaks,
originated from guided mode resonance. The arrays of SiNW with Al disk possess additional broad peaks, at slightly
larger wavelengths than those of the resonant guided mode peaks. The FDTD simulations show formation of
concentrated electromagnetic field at the Si NW/Al interface, indicating excitation of localized surface plasmons. These
results suggest that bottom-contact electrodes can work as means to enhance the optical absorption of the Si NWs as well
as to collect carriers in Si NW-based optoelectronic devices.
The optical properties of the silicon naniwires (SiNWs) fabricated by a method of metal-assisted
electroless etching have been investigated. The optical parameters of both SiNWs and the Si wafer,
including dielectric function (ε (ω) ) and the effective refractive index ( N(ω) ), could be obtained from
the light-absorption theory and Kramers-Kronig relation. From the comparation of calculated
characteristics, we can observe that the refractive index of the SiNWs is reduced to 1.26 while that of
Si wafer is changing from 2.4 to 6.2 in the range of 1.5-4eV, and the imaginary part of complex
dielectric constant of Si NWs is about two orders of magnitude lower than that of Si wafer. There are
two peak positions in the curve of Si wafer, while just one broad peak position in that of Si NWs.
These differences could be considered as the reasons for the special characteristic of the Si NWs.