Anti-Reflecting Nanostructures - Biomimetic Architectures by Plasma Processing - page 66

The superior AR performance over broadband, for both the
nanotip structures [73,90], is attributed to the gradient index
achieved in the tapered structure. Considering the low absorption
coefficient (

-1 -1

for crystalline silicon at
600 nm and 1100 nm, respectively, the AR performance of the SMDE
produced 16

a

) of 5200 cm and 70 cm

m-long SiNTs is commendable [73]. This, however,
implies a better AR performance from longer (say > 30

µ

m) SiNTs.
More interestingly, it remains to be seen whether it would be feasible
to fabricate amorphous silicon NTs having higher

µ

a

and even lower

reflectance than these SiNTs.

Figure 2.18 (a-c) ZnO NRs array (NRA): (a) SEM image of a highly tapered

NRA. (b) Schematic representation of the corresponding
NRs parameters extracted via software analysis. (c) Front
reflectance spectra of flat top NRA (red), tapered NRA
(orange), sol-gel film (green), optimised SiN SLARC on Si
PV cell with metallic contact (blue), and highly tapered NRA
(black) . Reprinted with permission from Ref. [89]. Copyright
2008 American Chemical Society. (d, e) Si NTS: SEM image of
the high-density, high-aspect ratio corkscrew-like SiNTs (d).
(e) Total hemispherical reflectance from SiNTs samples etched
for different times. Reprinted with permission from Ref. [90].
Copyright 2005 American Chemical Society.