  Vertically aligned silicon micro/nanowire arrays of different sizes have been
synthesized by combining the modified metal-assisted chemical etching (MACE)
and reactive ion etching (RIE) methods. This is a novel lithography-free method
to fabricate silicon micro/nanowire arrays. The size of micro/nanowire arrays
is controlled by controlling the etching rate and diameter of silica particles.
The silicon micro/nanowire geometry can utilize for efficient collection of
photo-generated charge carriers from impure silicon wafers, which have a short
minority carrier diffusion length also act as a self-antireflection coating
layer. For micro/nanowire having average diameters of 40 nm, 330 nm and 950 nm
and their corresponding average length 1.12 micron, 1.1 micron, and 1 micron,
respectively, the observed average reflectance was 0.22, 0.6 and 0.33 percent
at 45-degree incident angle, while the average reflectance was increased up to
4.2, 9.2, and 11 percent, respectively at 75-degree incident angle in the broad
range of 300 - 1200 nm of the solar spectrum. The measured average reflectance
for these samples is quite low compared to the planar silicon wafer. Thus this
geometry is a promising candidate for fabricating low-cost and highly efficient
radial junction silicon micro/nanowire arrays based solar cells.
