Browsing by Author "Yu, Chen-Chieh"

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Broadband and wide angle antireflection of sub-20 nm GaAs nanograss
(2012-06-01)
Ravipati, Srikanth
;
Shieh, Jiann
;
Ko, Fu-Hsiang
;
Yu, Chen-Chieh
;
Chen, Hsuen-Li
GaAs nanograss with diameters of less than 20 nm has been fabricated using a simple, one-step, maskless plasma etching-based approach. GaAs nanograss exhibits remarkable broadband antireflection properties, which arise from the graded refractive index between air and the GaAs substrate by the nanograss layer. Moreover, GaAs nanograss shows less sensitivity to transverse electric polarized light and transverse magnetic polarized light over a wide range of incident angles compared to the strong variation in a bare GaAs substrate. These effects show that sub-20 nm GaAs nanograss with lengths of approximately 200 nm has an enhanced absorption of 98-100% when the incident energy is larger than the GaAs bandgap (lambda = 240-873 nm) and an enhanced absorption of 72-98% when the incident energy is less than the bandgap (lambda = 873-2400 nm). Our simple, one-step, and maskless plasma etching method opens a promising approach for the direct implementation of broad omnidirectional antireflective surfaces on solar cells and various optoelectronic devices to improve device performance.
Ultralow Reflection from a-Si Nanograss/Si Nanofrustum Double Layers
(2013-03-25)
Ravipati, Srikanth
;
Shieh, Jiann
;
Ko, Fu-Hsiang
;
Yu, Chen-Chieh
;
Chen, Hsuen-Li
A double-layer nanostructure comprising amorphous Si nanograss on top of Si nanofrustums (NFs) with a total height of 680 nm exhibits ultralow reflection. Almost near-unity absorption and near-zero reflectance result in this layered nanostructure, over a broad range of wavelengths and a wide range of angles of incidence, due to the low packing density of a-Si and the smooth transition of the refractive index from the air to the Si substrate across both the nanograss and NF layers.