Papers by Kyeongjae Byeon
Thin Solid Films, 2012
The light extraction efficiency of light emitting diode (LED) devices was improved by embedding n... more The light extraction efficiency of light emitting diode (LED) devices was improved by embedding nano-sized two-dimensional, air cavity photonic crystal (PC) structure on the indium tin oxide (ITO) layer of GaN-based LEDs. The embedded air cavity PC structure was fabricated using a reversal imprint lithography technique. The nano-cavity patterns had a width of 560 nm, a space of 240 nm and a height of 280 nm. According to current-voltage characterization, the electrical performance of the LED devices was not degraded by the fabrication process of air cavity PC structure. The optical output power of the LED device was increased by up to 10% at a drive current of 20 mA by forming the nano-cavity PC structure on the transparent electrode of the blue LED device, which was grown on a patterned sapphire substrate, to maximize the photon extraction. Since photons are scattered with cavities and are unaffected by the packaging process, which is the encapsulation of a LED device with epoxy resin, this enhancement in light extraction efficiency will not be decreased after the packaging process.
2007 Digest of papers Microprocesses and Nanotechnology, 2007
This work reports on the economical and effective fabrication process of photonic crystal pattern... more This work reports on the economical and effective fabrication process of photonic crystal patterns on GaN-based light emitting diode (LED) structures using nanoimprint lithography (NIL) and inductively coupled plasma (ICP) etching process. Results reveal the capability of using NIL to fabricate sub-micron sized, photonic crystal patterns at reduced cost for high brightness LEDs.
IEEE Photonics Journal, 2013
A high-brightness GaN-based vertical light-emitting diode (VLED) was demonstrated by introducing ... more A high-brightness GaN-based vertical light-emitting diode (VLED) was demonstrated by introducing a large-area low-cost direct printing process. A hexagonally closepacked micrometer convex array was fabricated on the n-GaN top layer of the VLED by direct printing using a hydrogen silsesquioxane solution and subsequent inductively coupled plasma etching. To confirm that the enhancement of light extraction by this structure, a conventional wet-chemical-etched structure was also fabricated on the n-GaN top layer of the VLED, yielding randomly oriented pyramid structures on the layer. Both VLEDs showed much stronger electroluminescence emission than an unpatterned VLED. However, the micrometer convex array improved the light extraction significantly more than the random pyramid structure owing to its greater ability to enlarge the light escape cone, attributed to its 50-tapered profile and large extraction area. After chip packaging with silicone encapsulation, the light output power of the micropatterned VLED was 11.4% and 106% greater than those of the wet-etched and unpatterned VLEDs, respectively, under a 350-mA drive current.
Materials Science in Semiconductor Processing, 2010
Journal of Nanoscience and Nanotechnology, 2009
A highly durable imprint template is essential for the industrialization of nanoimprint lithograp... more A highly durable imprint template is essential for the industrialization of nanoimprint lithography (NIL). Conventionally, Si-based materials were used for the fabrication of imprint templates. However, their fabrication is very expensive and they can be easily damaged during repeated imprint processes due to their brittleness and poor mechanical properties. The Ni template has excellent mechanical strength and can be easily and cheaply duplicated by the electroforming process. It has the potential for application to the NIL process if its poor antistiction property, which causes serious detaching issues, is improved. In this study, thin Au and Ti layers were deposited on a Ni template and a thiol-based, hydrophobic, self-assembled monolayer (SAM) layer was stably formed on the Au coated Ni template. Thus, the antistiction property of the Ni template was drastically elevated. Using the prepolymer-based, thermal imprint process and the thiol-based, SAM-coated Ni template, sub-micron sized patterns were successfully formed on the Si substrate.
Journal of The Electrochemical Society, 2010
ABSTRACT
Current Applied Physics, 2011
Hexagonal arrays of submicron polymer patterns with a high refractive index were fabricated on a ... more Hexagonal arrays of submicron polymer patterns with a high refractive index were fabricated on a vertical light-emitting diode (LED) device by means of nanoimprint lithography (NIL) to improve the light extraction efficiency. An organic-inorganic hybrid resin containing a polymeric titanium dioxide precursor was spin-coated on the n-GaN top layer of a vertical LED wafer. The coated layer was then imprinted for 10 min with an elastomeric polydimethylsiloxane stamp at 200 C and 5 atm. The NIL process formed pillar patterns on the n-GaN layer of the vertical LED wafer. The pillar patterns have a high refractive index (n z 2.0) in the visible wavelength range; they also have a diameter of 200 nm and a pitch of 700 nm. The light output power of the patterned vertical LED device is 28% greater than that of a non-patterned vertical LED device with a driving current of 350 mA. The IeV characteristics of the vertical LED device confirm that the patterning process induces no electric degradation.
Materials Science Forum, 2007
Embossing or imprint lithography is the key-technology for the mass production of nanosized struc... more Embossing or imprint lithography is the key-technology for the mass production of nanosized structures with low cost. Currently Si or quartz template which is produced by e-beam or DUV lithography and reactive ion etching, is used. However they are very expensive and easily damaged due to their brittleness. On the other hand, Ni template has high mechanical durability and can be fabricated with low cost by electroplating. However, one of the key obstacles of Ni template is poor antistiction property, when it is used with sticky thermoset polymer. Due to its poor antistiction property, detachment of Ni template from epoxy substrate is one of the key obstacles. In this experiment, quartz template with 150nm to 1μm sized surface protrusion was fabricated and used to emboss the PMMA coated Si wafer. Then the imprinted PMMA layer was coated with metal seed layer and electroplating of Ni was followed to fabricate Ni template with 150nm to 1μm sized patterns. In order to form antistiction ...
Thin Solid Films, 2011
A UV-imprinting process for a full wafer was developed to enhance the light extraction of GaN-bas... more A UV-imprinting process for a full wafer was developed to enhance the light extraction of GaN-based green light-emitting diodes (LEDs). A polyvinyl chloride flexible stamp was used in the imprinting process to compensate for the poor flatness of the LED wafer. Two-dimensional photonic crystal patterns with pitches ranging from 600 to 900 nm were formed on the p-GaN top cladding layer of a 2 inch diameter wafer using nanoimprint and reactive ion etching processes. As a result, the optical output power of the patterned LED device was increased by up to 44% at a driving current of 20 mA by suppressing the total internal reflection and enhancing the irregular scattering of photons at the patterned p-GaN surface.
Applied Surface Science, 2015
We fabricated high-brightness GaN-based light-emitting diodes (LEDs) with highly refractive patte... more We fabricated high-brightness GaN-based light-emitting diodes (LEDs) with highly refractive patterned structures by using a thermal nanoimprint lithography (NIL). A highly refractive ZnO-nanoparticledispersed resin (ZNDR) was used in NIL, and a submicron hole, a submicron high-aspect-ratio pillar, and microconvex arrays were fabricated on the indium tin oxide (ITO) top electrode of GaN-based LED devices. We analyzed the light extraction mechanism for each of the three types of patterns by using a finite element method simulation, and found that the high-aspect-ratio pillar had a great ability to improve light extraction owing to its waveguide effect and prominent scattering effect. As a result, the light output power, which was measured in an integrating sphere, of the LED device was enhanced by up to 19.6% when the high-aspect-ratio pillar array was formed on the top ITO electrode of the device. Further, the electrical properties of none of the patterned LED devices fabricated using ZNDR degraded in comparison to those of bare LED devices.
Electronic Materials Letters, 2012
ABSTRACT This paper presents a new simple metal patterning technique, which is based on soft nano... more ABSTRACT This paper presents a new simple metal patterning technique, which is based on soft nanoimprint lithography. By using this method with a commercial Ag nano particle ink, a nano-sized metal pattern was successfully fabricated. The problem of the residual layer of patterned Ag layer was minimized by controlling the con-centration of the solution and the process conditions. By using this method, we could easily fabricate various patterns without reference to any shape. Furthermore, we fabricated an Ag mesh type pattern for the application of conducting transparent glass.
Optics express, Jan 7, 2012
SiNx-based photonic crystal (PhC) patterns were fabricated on the ITO electrode layer of a GaN-ba... more 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.
Small (Weinheim an der Bergstrasse, Germany), Jan 29, 2014
Negative-tone block copolymer (BCP) lithography based on in situ surface chemical modification is... more Negative-tone block copolymer (BCP) lithography based on in situ surface chemical modification is introduced as a highly efficient, versatile self-assembled nanopatterning. BCP blends films consisting of end-functionalized low molecular weight poly(styrene-ran-methyl methacrylate) and polystyrene-block-Poly(methyl methacylate) can produce surface vertical BCP nanodomains on various substrates without prior surface chemical treatment. Simple oxygen plasma treatment is employed to activate surface functional group formation at various substrates, where the end-functionalized polymers can be covalently bonded during the thermal annealing of BCP thin films. The covalently bonded brush layer mediates neutral interfacial condition for vertical BCP nanodomain alignment. This straightforward approach for high aspect ratio, vertical self-assembled nanodomain formation facilitates single step, site-specific BCP nanopatterning widely useful for various substrates. Moreover, this approach is co...
2008 Conference on Lasers and Electro-Optics, 2008
ABSTRACT
Solid State Phenomena, 2007
Embossing lithography is one of the most promising technologies for mass production of nano-scale... more Embossing lithography is one of the most promising technologies for mass production of nano-scale structures. To advance the industrialization of embossing lithography, fabrication of low cost, high mechanical strength embossing template is essential. Electroformed Ni template can be used as an embossing template if its poor anti-adhesive property is fixed by proper releasing layer treatment, especially, when it is used with sticky thermoset polymer. In this experiment, quartz master template with 200nm to 2um sized surface protrusions was fabricated and used to emboss the PMMA coated Si wafer. Then the embossed PMMA layer was coated with metal seed layer (Ni) and electroplating of Ni was followed to fabricate Ni template. To apply anti-stiction SAM layer, SiO2 and Si layer was coated on Ni template. With proper anti-stiction treatment of Ni template, sub-micron patterns were successfully transferred to sticky thermoset polymers such as epoxy resin using Ni template without any degr...
Solid-State Electronics, 2010
TiO2 nano-patterns were formed on the indium-tin-oxide (ITO) layer of GaN based light emitting di... more TiO2 nano-patterns were formed on the indium-tin-oxide (ITO) layer of GaN based light emitting diodes (LEDs) without a residual layer using a sol-imprinting process. A polydimethylsiloxane mold replicated from a Si master was used as the imprint stamp for the sol-imprinting process. The light extraction efficiency of LEDs was enhanced by the TiO2 nano-patterns formed on the ITO layer because
Solid-State Electronics, 2009
Various sized nano-patterns, ranging from 0.8μm×0.4μm to 2.0μm×1.0μm were formed on the p-GaN top... more Various sized nano-patterns, ranging from 0.8μm×0.4μm to 2.0μm×1.0μm 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
Semiconductor Science and Technology, 2009
ABSTRACT The indium tin oxide (ITO) transparent electrode layer on green and blue light-emitting ... more ABSTRACT The indium tin oxide (ITO) transparent electrode layer on green and blue light-emitting diodes (LEDs) was patterned with various-sized periodic hole arrays, size ranging from 300 nm to 380 nm, using thermal nanoimprint lithography and inductively coupled plasma (ICP) etching processes. The imprinted resin was used as a mask layer and etch resistance of the imprinted resin was adjusted in order to control the tapered and enlarged etch profile of the ITO layer, since the tapered etch profile can improve the light extraction efficiency of the LED by prominent scatterings. Photoluminescence intensity from InGaN multi-quantum wells for the green LED structure showed that up to 4.6 times stronger emission was exhibited with the patterned ITO electrode, compared to the identical sample with an un-patterned blanket ITO electrode layer. An electroluminescence (EL) intensity of a blue LED sample witha patterned ITO electrode layer was increased up to 23% compared to that of the identical sample with an un-patterned blanket ITO electrode layer.
Semiconductor Science and Technology, 2010
A vertical light-emitting diode (LED) with a chip size of 500 × 500 μm 2 was fabricated by the la... more A vertical light-emitting diode (LED) with a chip size of 500 × 500 μm 2 was fabricated by the laser lift-off (LLO) process of an InGaN-based blue LED wafer. After the LLO process, photonic crystal patterns by UV nano-imprint lithography were formed on the n-GaN top layer of the vertical LED over the entire area with a diameter of 2 inches. As the result of n-GaN patterning, light output power of the vertical LED with photonic crystals was increased by up to 44% compared to that of the vertical LED without a photonic crystal at a driving current of 1000 mA.
physica status solidi (a), 2010
ABSTRACT Wafer-scale UV nanoimprint and dry etching processes were used to fabricate photonic cry... more ABSTRACT Wafer-scale UV nanoimprint and dry etching processes were used to fabricate photonic crystal patterns on an indium tin oxide (ITO) top electrode of GaN-based green light-emitting diodes (LEDs). Photonic crystal patterns with pitches ranging from 600 to 900 nm were transferred to the entire 2-inch LED wafer. Plasma damage in the GaN crystal of the LED device was avoided because the GaN was covered by ITO layer and was not exposed to the etching plasma during the ITO dry etching process. Consequently, the electroluminescence intensity of the patterned LED devices was enhanced up to 25% at 20 mA of driving current, compared to the nonpatterned LED device, while the forward voltage was similar.
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Papers by Kyeongjae Byeon