SiNx-based photonic crystal (PhC) patterns were fabricated on the ITO electrode layer of a GaN-based light-emitting diode (LED) device on a patterned sapphire substrate (PSS) by a UV nanoimprint lithography process in order to improve the light extraction of the device. A three-dimensional finite-difference time-domain simulation confirmed that the light extraction of a GaN LED structure on a PSS is enhanced when SiNx PhC patterns are formed on the ITO top layer. From the I-V characteristics, the electrical properties of patterned LED devices with SiNx-based PhC were not degraded compared to the unpatterned LED device, since plasma etching of the p-GaN or the ITO layers was not involved in the patterning process. Additionally, the patterned LED devices with SiNx-based PhCs showed 19%-increased electroluminescence intensity compared with the unpatterned LED device at 445 nm wavelength when a 20 mA current is driven.

In this study, a patterned ZnO nanorod array was formed on the ITO layer of GaN-based light-emitting diodes (LEDs), to increase the light extraction efficiency of the LED. The bi-layer imprinted resin pattern was used for selective growth of the ZnO nanorod array on the ITO layer. Compared to conventional LEDs grown on patterned sapphire substrate (PSS), the deposition of the blanket ZnO layer on the ITO layer increased the light extraction efficiency of the LED by about 10%. Further growth of the ZnO nanorod layer on the blanket ZnO layer increased the light extraction efficiency of the LED by about 23%. In the case that a patterned ZnO nanorod layer was formed on a blanket ZnO layer, the light extraction efficiency increased by about 34%. These enhancements of the device were caused by modulation of the refractive-index in ZnO layers and the surface roughening effects because of the unique design of the pattern, which was nanostructure-in-nanopattern, resulting in the formation of many escape cones on the LED surface.

In situ nanolithography is realized based on warm spin-casting of block copolymer solutions. This advancement is based on Si-containing block copolymers with an appropriate thermodynamic driving force for spontaneous phase-separation combined with the thermal assistance provided by slight temperature elevations during the spin-casting. Sub-10 nm half-pitch nanoscale patterns are produced within 30 s without a separate annealing process.

An optical scattering layer, consisting of a Si3N4 nano-pillar array and a spin-coated hydrogen silsesquioxane (HSQ) planarization layer, was introduced to an organic light-emitting diode (OLED) substrate to increase the out-coupling efficiency. After plasma enhanced chemical vapor deposition (PECVD) of the Si3N4 layer, the nano-pillar array was created using nanoimprint lithography and reactive ion etching. As the Si3N4 pillar array has a refractive index of 2.0, photons generated in the organic layer are scattered by the Si3N4 structures and thus have a higher chance of being emitted from the device. The spin-coated HSQ planarization layer produces a flat substrate, which is essential for depositing a uniform organic material layer and assuring the electric conductivity of the transparent conducting oxide (TCO) layer. In this study, Si3N4 nano-structures with a height of 100 or 300 nm were used to enhance the out-coupling efficiency of the OLED devices. Although the electrical conductivity of the TCO layer deposited on the light scattering layer was slightly degraded, the OLED devices formed with the light scattering layer exhibited a higher luminous power at given electrical power. Consequently, the use of a planarized 300-nm-thick Si3N4 layer increased the external quantum efficiency of the OLED device by 50% at 10,000 cd/m2 compared to the reference OLED device fabricated on a flat glass substrate.

Distributed antireflection (AR) layers with different composition ratios of ITO and SiO(2) formed on an ITO electrode of GaN-based LEDs provide substantial enhancement in light-extraction efficiency. By using the coradio frequency magnetron sputtering deposition, four 50 nm thick AR layers with graduated refractive indices were fabricated. The effect of the AR layers on enhancing the efficiency of the LED device was analyzed by electroluminescence (EL) and I-V measurements. As a result, the EL intensity of the LED device grown on the patterned sapphire substrate with AR layers was increased by up to 13% compared to the conventional patterned sapphire substrate-applied LED device without AR layers at a drive current of 20 mA. The AR layers on top of the LED device gradually changed the refractive indices between ITO (n=2.1) and air (n=1.0), which minimized the total internal reflection of generated light. And no degradation in the electrical characteristic of the LEDs was observed according to the I-V measurements.

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We fabricated moth-eye structures on photovoltaic (PV) protective glass, a hybrid nano-imprint lithography technique. The efficiency of the PV module with PV protective glass patterned on both sides was enhanced.

A micro- and nanoscale complex structure made of a high refractive index polymer (n = 2.08) was formed on the ITO electrode layer of an edge-emitting type GaN blue light-emitting diode (LED), in order to improve the photon extraction efficiency by suppressing total internal reflection of photons. The nanoimprint lithography process was used to form the micro- and nanoscale complex structures, using a polymer resin with dispersed TiO2 nano-particles as an imprint resin. Plasma processing, such as reactive ion etching, was used to form the micro- and nano-scale complex structure; thus, plasma-induced damage to the LED device can be avoided. Due to the high refractive index polymeric micro- and nanostructure on the ITO layer, the electroluminescence emission was increased up to 20%, compared to an identical LED that was grown on a patterned sapphire substrate to improve photon extraction efficiency.