The fabrication process of photonic crystals in a p-GaN layer was established to improve the light extraction efficiency of light-emitting diodes (LEDs) by using nanoimprint lithography and inductively coupled plasma (ICP) etching process. Due to low etch selectivity of imprinted pattern, Cr mask patterns were lifted-off from the p-GaN surface and ICP etch process was followed using SiCl4-based plasma. As a result, two-dimensional pillar array patterns were uniformly fabricated on the p-GaN layer and the photoluminescence intensity of the photonic crystal patterned LED was increased by 2.6 fold compared to that of the same LED sample without photonic crystal patterns.
A novel ultraviolet (UV)-assisted imprinting procedure that employs photosensitive tin(II) 2-ethylhexanoate is presented for the facile size-tunable fabrication of functional tin dioxide (SnO(2)) nanostructures by varying annealing temperatures. These imprinted SnO(2) nanostructures were also used as new masters for size reduction lithography. SnO(2) lines down to 40 nm wide were obtained from a silicon master with 200 nm wide lines by simply performing size reduction lithography twice. This leads to 80 and 87.5% reduction in the width and height of imprinted lines, respectively. An imprinted pattern annealed at 400 °C demonstrated transmittance greater than 90% over the range of 350-700 nm, which is high enough to make the pattern useful as a transparent SnO(2) mold. This demonstrated approach allows the accessibility to size-tunable molds, eliminating the need for conventional expensive imprinting masters with very fine structures, as well as functional SnO(2) nanostructures, potentially useful in applications where ordered surface nanostructures are required, such as photonic crystals, biological sensors, and model catalysts.
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