The periodic bullet-like and cone-like submicron grating (SMG) structures on germanium (Ge) substrates were fabricated by dry etching processes via laser interference lithography. Their optical reflectance characteristics as well as the wettability of the surface were investigated. The wide cone-like Ge SMG structure exhibited a lower reflectance than that of the narrow bullet-like Ge SMG structure at wavelengths of 300-1100 nm due to its relatively high volume fraction and the more linearly graded effective refractive index distribution between air and the Ge substrate. As the period of cone-like Ge SMGs was increased, the low reflectance band of <10% was shifted toward the longer-wavelength region and its minimum value became slightly higher. The fabricated Ge SMG structures showed a hydrophobic surface property with contact angles of 90.7-102.5°. For theoretical analysis, the reflectance calculations were also performed by a rigorous coupled-wave analysis simulation, which indicated a similar trend to the experimental results.

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We reported the light-extraction properties of InGaN/GaN multiple quantum wells blue light-emitting diodes (LEDs) with ZnO nanorod arrays (NRAs) on Ni/Al-doped ZnO (AZO) films as a current spreading layer (CSL). The Ni/AZO bilayer exhibited a high optical transmittance of ∼80% at λ∼460 nm. The electrical property of AZO films was improved by inserting a thin Ni layer, which leads to the better current–voltage characteristics of LEDs. The ZnO nanorods can be easily grown on the AZO surface of Ni/AZO CBL as the same materials by a simple wet chemical growth. For 450 ×450 µm2 LED with Ni/AZO CSL, the incorporation of ZnO NRAs into the AZO surface improved the light output power by ∼14% at 100 mA without causing any electrical degradation compared to the conventional LED without ZnO NRAs.