[Show abstract][Hide abstract] ABSTRACT: Various sized nano-patterns, ranging from 0.8 μm × 0.4 μm to 2.0 μm × 1.0 μm were formed on the p-GaN top cladding layer of green LED, in order to increase photon extraction efficiency by suppressing total internal reflection. Fabrication of nano-patterns was done by UV nanoimprint lithography and reactive ion etching of p-GaN using SiCl4 and Ar gases using SiO2 as an etch mask. The effect of various nano-patterns on top p-GaN layer was investigated by photoluminescence. Compared to LED structure without nano-patterns on top cladding layer, the LED structures with sub-micron sized nano-patterns exhibit up to four times stronger emission intensity. This implies that the photon extraction efficiency of LED structures was increased by nano-patterns on top p-GaN layer. However, the luminescence intensity of LED structures with patterns greater than a micron, was less increased.
No preview · Article · Oct 2009 · Solid-State Electronics
[Show abstract][Hide abstract] ABSTRACT: Moth-eye structures were produced on a p-GaN top cladding layer by UV imprint and inductively coupled plasma (ICP) etch processes in order to improve the light extraction efficiency of GaN-based green light-emitting diodes (LEDs). The height and shape of moth-eye structures were adjusted by controlling the thickness of Cr mask layer and ICP etching time. The transmittance of LED device stacks with moth-eye structure was increased up to 1.5–2.5 times, compared to identical LED sample without moth-eye structure and the intensity of photoluminescence from the InGaN multi-quantum well layer of LED sample with moth-eye structure was 5–7 times higher than that of the LED sample without the moth-eye structure.
No preview · Article · Jul 2009 · Materials Science and Engineering B
[Show abstract][Hide abstract] ABSTRACT: Since polymer is flexible, lightweight, reliable and transparent and its material properties can easily be modified, it is a suitable substrate material for organic electronic devices, biomedical devices, and especially for flexible displays. To build a nano-device on a polymer substrate, nano to microsized patterning must be done. However, conventional photolithography cannot be used to fabricate patterns on flexible polymer substrate, due to the focusing and substrate handling issue associated with flexibility of polymer substrate and potential interaction between polymer and developer or other organic solvents used in photolithography. Degradation of polymer substrate during resist baking process over 120 ° C can be another problem. In this study, 100 nm sized resist patterns were made on flexible polyethylene-terephthalate (PET) film using newly developed monomer based UV curing imprinting lithography. Compared to conventional imprint lithography, UV curing imprint lithography uses monomer based liquid phase resin and thus patterns can be fabricated without residual layer at room temperature and at much lower pressure (≪3–5 atm ) with UV illumination. No degradation of PET film was observed due to the imprint process and, as a result, 100 nm sized Ti – Au metal patterns were successfully formed on PET film using UV curing imprint lithography and lift-off process.
Full-text · Article · May 2006 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: Due to polymer's excellent flexibility, transparency, reliability and light weight, it is a good candidate material for substrate of devices including organic electronic devices, biomedical devices, and flexible displays (LCD and OLED). In order to build such devices on polymer, nano- to micron-sized patterning must be accomplished. Since polymer materials reacts with organic solvents or developer solutions which are inevitably used in photolithography and cannot bear high temperature (similar to 140 degrees C process for photoresist baking, conventional photolithography cannot be used to polymer substrate. In this research, monomer based thermal curing imprinting lithography was used to make as small as 100 nm dense line and space patterns on flexible PET (polyethylene-terephthalate) film. Compared to hot embossing lithography, monomer based thermal curing imprint lithography uses monomer based imprint resin which consists of base monomer and thermal initiator. Since it is liquid phase at room temperature and polymerization can be initiated at 85 degrees C, which is much lower than glass temperature of polymer resin, the pattern transfer can be done at much lower temperature and pressure. Hence, patterns as small as 100 nm were successfully fabricated on flexible PET film substrate by monomer based thermal curing imprinting lithography at 85 degrees C and 5 atm without any noticeable degradation of PET substrate. (c) 2005 Elsevier B.V. All rights reserved.
Full-text · Article · Feb 2006 · Microelectronic Engineering