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structures is an effective way to reduce parasitic absorption in the passive layers of
devices [10, 11].
To fabricate these nanostructures, many different techniques were explored.
They can be categorized as top-down, bottom-up, and their combination. Among
these approaches, top-down method has the highest accuracy and controllability of
nanostructure geometries (aspect ratio and ordering) [12].
Figure 1a–d show the schematic of NP, double-NP, multiple-NP, and NC arrays
of germanium (Ge). As seen, the geometry of nanostructures can be tuned by applying various parameters during the growth step. It is noteworthy that the reflectance
Fig. 1 Schematics of Germanium nanostructure arrays with different shapes, (a) Single-NP array,
(b) Double-NP array, multiple-NP array, and nanocone (NC). (e) Broadband-integrated absorption
of 1000  nm pitch Ge multiple-NP array versus number of pillar. Red-dashed line indicates the
broadband-integrated absorption of 1000 nm pitch Ge NC array. (f) Broadband-integrated absorption of Ge NC array at 1000 nm pitch [2]
Efficient Light Harvesting in the Nanotextured Thin Film Solar Cells