Changmin Yun

Eunkyo Ju

Seon Kyeong Kim

Hoki Son

Yeong-Hoon Cho

Seungjae Baek

MinJi Kim

Serin Min

Kang Bin Bae

SangBum Kim

Taehwan Kim

Gyucheol Kim

Jinwoo Jo

KiHo Song

Chi Yeop Kim

The Laboratory for Optoelectronic Materials is located in Room 604 of the Engineering Building at Korea University. The lab is part of the Department of Materials Science and Engineering.

고려대학교 공과대학 604호에 위치한 광전소재 연구실. 소재공학과 소속.

Enhanced short-circuit current density in epitaxial InGaP/GaAs/Si trip…

Tuning Properties of II-IV-Nitrides for Optoelectronic Applications

Revolutionizing red micro-LEDs: Harnessing surface plasmons for enhanc…

Deep traps in GaN-based structures as affecting the performance of GaN devices

Au@ NiO core-shell nanoparticles as a p-type gas sensor: Novel synthesis, characterization, and their gas sensing properties with sensing mechanism

Dry etch damage in n -type GaN and its recovery by treatment with an plasma

Au@ Cu 2 O core–shell nanoparticles as chemiresistors for gas sensor applications: effect of potential barrier modulation on the sensing performance

Highly efficient degradation of dyes by carbon quantum dots/N-doped zinc oxide (CQD/N-ZnO) photocatalyst and its compatibility on three different commercial dyes under daylight

Evolution of stress relaxation and yellow luminescence in GaN/sapphire by Si incorporation

Understanding nonpolar GaN growth through kinetic Wulff plots

Glucose-assisted synthesis of Cu2O shuriken-like nanostructures and their application as nonenzymatic glucose biosensors

Electronic structure reconfiguration of nickel–cobalt layered double hydroxide nanoflakes via engineered heteroatom and oxygen-vacancies defect for efficient electrochemical …

Band-gap narrowing and potential fluctuation in Si-doped GaN

Low-Temperature Solution-Processed SnO 2 Nanoparticles as a Cathode Buffer Layer for Inverted Organic Solar Cells

Effect of annealing temperature on optical band-gap of amorphous indium zinc oxide film

Stress relaxation in Si-doped GaN studied by Raman spectroscopy

Hydrothermal synthesis of In2O3 nanocubes for highly responsive and selective ethanol gas sensing

Nitrogen-polar GaN growth evolution on c-plane sapphire

Fast neutron irradiation effects in n-GaN

Insightful understanding of hot-carrier generation and transfer in plasmonic Au@ CeO2 core–shell photocatalysts for light-driven hydrogen evolution improvement

Investigation of Optical and Structural Stability of Localized Surface Plasmon Mediated Light‐Emitting Diodes by Ag and Ag/SiO 2 Nanoparticles

Fabrication of flexible sheets of Cu/CuO/Cu2O heterojunction nanodisks: A dominant performance of multiple photocatalytic sheets under natural sunlight

Carbon quantum dots decorated N-doped ZnO: synthesis and enhanced photocatalytic activity on UV, visible and daylight sources with suppressed photocorrosion

N.B. Smirnov

Stephen Pearton

A.P. Uthirakumar

Jin-Hyeon Yun

Jin-Kyu Yang

Trilochan Sahoo

Hilmi Volkan Demir

Seong-Ju Park

Jung Han

Prabhakar Rai

Andrej Kuznetsov

DONG WOOK KIM

Sedat Nizamoglu

Emre SARI, Ph.D.

Hyung Koun Cho

Sang-Woo KIM

Sudarsan Raj

Suraj Kumar Tripathy

Joon Seop Kwak

Fan Ren

In-Hwan Lee

New developments in theoretical studies of defects and impurities in III-Nitrides as pertinent to compensation and recombination in these materials are discussed. New results on experimental studies on defect states of Si, O, Mg, C, Fe in GaN, InGaN, and AlGaN are surveyed. Deep electron and hole traps data reported for GaN and AlGaN are critically assessed. The role of deep defects in trapping in AlGaN/GaN, InAlN/GaN structures and transistors and in degradation of transistor parameters during electrical stress tests and after irradiation is discussed. The recent data on deep traps influence on luminescent efficiency and degradation of characteristics of III-Nitride light emitting devices and laser diodes are reviewed.

In this work, Au@NiO core-shell nanoparticles (C-S NPs) as a p-type gas sensing material was synthesized by a facile wet-chemical method, and evaluated their gas sensing properties as compared to the pristine NiO NPs gas sensors. Transmission electron microscope (TEM) results exhibited the well-dispersed formation of Au@NiO C-S NPs having the total size of 70–120 nm and NiO shells having 30–50 nm thickness. The C-S morphology as well as the overall particle sizes are unchanged even at 500 °C. The gas sensing result reveals that the response of Au@NiO C-S NPs gas sensor is higher than pristine NiO NPs gas sensor for 100 ppm of ethanol at 200 °C operating temperature. The baseline resistance in the air for Au@NiO C-S NPs sensor is lowered as compared to pristine NiO NPs, which is due to the increased number of holes as charge carriers in Au@NiO C-S NPs. The high response of Au …

We report on etch-induced damage in n -type GaN caused by an inductively coupled plasma, and damage recovery by means of treatment with an plasma. As the plasma dc bias was increased by increasing the rf table power during etching, the optical and electrical properties of the etched GaN films deteriorated as the result of etch-induced damage. However, an plasma treatment for the etched samples effectively removed the etch-induced defects and damage on the surface, leading to improved surface morphology, photoluminescence, and ohmic contact in n -type GaN.

Au@Cu2O core–shell nanoparticles (NPs) were synthesized by a solution method at room temperature and applied for gas sensor applications. Transmission electron microscopy (TEM) images showed the formation of Au@Cu2O core–shell NPs, where 12–15 nm Au NPs were covered with 60–30 nm Cu2O shell layers. The surface plasmon resonance (SPR) peak of Au NPs was red-shifted (520–598 nm) after Cu2O shell formation. The response of Au@Cu2O core–shell NPs was higher than that of bare Cu2O NPs to CO at different temperatures and concentrations. Similarly, the response of Au@Cu2O core–shell NPs was higher than that of bare Cu2O NPs for NO2 gas at low temperature. The improved performance of Au@Cu2O core–shell NPs was attributed to the pronounced electronic sensitization, high thermal stability and low screening effect of Au NPs.

Eco-friendly carbon quantum dots/nitrogen-doped ZnO (CQD/N-ZnO) composites were successfully prepared by a facile one-step method. The various techniques were employed to characterize the phase structure, morphology and optical properties of CQD/N-ZnO composites. The nitrogen doping was confirmed by Raman and X-ray photoelectron spectroscopy. Three commercial dyes, such as malachite green, methylene blue and fluorescein dyes were chosen to investigate the photocatalytic performance of CQD/N-ZnO under daylight irradiation. It was found that the CQD/N-ZnO photocatalyst established a high compatibility to degrade all three commercial dyes within 30–45 min, under daylight irradiation. Also, it remains capable of reusing the CQD/N-ZnO photocatalyst for repeated photocatalytic performance due to anti-photocorrosion offered by CQDs. The synergetic effect of N-doping and CQDs is key to …

We report a systematic study accomplished with a series of undoped and Si-doped GaN epilayers grown on sapphire (0001) with the carrier concentration of in order to investigate the evolution of stress relaxation and yellow luminescence by Si incorporation. As the Si doping becomes higher, the bound exciton peaks are gradually shifted to lower energy due to relaxation of the thermal residual stress with the linear coefficient of The present results show that both the full width at half maximum of double-crystal x-ray diffractometry and the photoluminescence intensity ratio of the yellow luminescence to edge emission gradually increase as the Si incorporation becomes heavier. We suggest that the Si doping in GaN epilayers induces overall defects and gives rise to stress relaxation during the cool-down process, and the yellow luminescence may be originated from a complex of …

In this paper we provide explanations to the complex growth phenomena of GaN heteroepitaxy on nonpolar orientations using the concept of kinetic Wulff plots (or v-plots). Quantitative mapping of kinetic Wulff plots in polar, semipolar, and nonpolar angles are achieved using a differential measurement technique from selective area growth. An accurate knowledge of the topography of kinetic Wulff plots serves as an important stepping stone toward model-based control of nonpolar GaN growth. Examples are illustrated to correlate growth dynamics based on the kinetic Wulff plots with commonly observed features, including anisotropic nucleation islands, highly striated surfaces, and pentagonal or triangular pits.

We have successfully synthesized high quality cuprous oxide shuriken-like nanostructures by low temperature hydrothermal process, using glucose as reducing agent. The resulting nanostructures were further characterized for the fabrication of nonenzymatic glucose biosensors. The glucose sensors exhibited excellent performances, giving a wide linear detection range (from 0.01 μM to 11.0 mM), an ultra-low detection limit (0.035 μM) and a high sensitivity (0.933 mA/mM cm 2 ). Furthermore, the proposed biosensor showed high selectivity and favorable reproducibility along with long-term performance stability.

The development of earth-abundant and high-efficiency bifunctional electrocatalysts is extremely desirable for electrochemical water splitting, but there are some critical challenges that need to be addressed. The coordinated tailoring of electronic structure and Bader charge transference by heteroatom doping and oxygen vacancy defects are one of the strongest tactics to enhance the oxygen and hydrogen evolution reactions (OER and HER) of catalysts. Herein, a novel Mo-decorated nickel–cobalt layered double hydroxides 3D honeycomb nanoflake on Ni foam (labeled as Mo-NiCo LDHs (Vo) ) as bifunctional electrode materials with enriched oxygen vacancy defects, excellent geometric stability, and enriched active sites was successfully fabricated through a facile hydrothermal reaction strategy. Density functional theory computations and experimental results confirmed that the electrocatalytic intrinsic activity of …

We investigate the optical properties of two sets of Si-doped GaN epitaxial layers with different degree of compensation. The electron concentration dependence of the band-gap energy measured by photoluminescence is interpreted as band-gap narrowing effect and evaluated by a simple relation. The photoluminescence peak positions of heavily compensated samples are shifted downward with respect to those of moderately compensated samples, and the down shift becomes larger at higher electron density. Based on analysis of photoluminescence spectra, these prominent behaviors are accounted for by band-edge potential fluctuation associated with inhomogeneous residual impurities.

SnO 2 recently has attracted particular attention as a powerful buffer layer for organic optoelectronic devices due to its outstanding properties such as high electron mobility, suitable band alignment, and high optical transparency. Here, we report on facile low-temperature solution-processed SnO 2 nanoparticles (NPs) in applications for a cathode buffer layer (CBL) of inverted organic solar cells (iOSCs). The conduction band energy of SnO 2 NPs estimated by ultraviolet photoelectron spectroscopy was 4.01 eV, a salient feature that is necessary for an appropriate CBL. Using SnO 2 NPs as CBL derived from a 0.1 M precursor concentration, P3HT:PC 60 BM-based iOSCs showed the best power conversion efficiency (PCE) of 2.9%. The iOSC devices using SnO 2 NPs as CBL revealed excellent long-term device stabilities, and the PCE was retained at ∼95% of its initial value after 10 weeks in ambient air. These solution …

The effect of annealing temperature on the electrical and optical properties of indium zinc oxide (IZO) (In 2 O 3 :ZnO=90:10wt.%) thin films has been investigated. The IZO thin films were deposited on glass substrates by radio frequency magnetron sputtering and then subjected to annealing in a mixed ambient of air and oxygen at 100, 200 and 300°C. All the IZO films were found to have amorphous structure. With the increase of the annealing temperature, the carrier concentration decreased and the resistivity increased. The average transmittance of IZO thin films decreased slightly with annealing temperature. Interestingly, a systematic reduction of the optical band-gap from 3.79eV to 3.67eV was observed with annealing temperature. The change in optical band-gap was observed to be caused predominantly by Burstein-Moss band-gap widening effect suggesting unusual absence of band narrowing effect. The effects …

We report the Si-doping-induced relaxation of residual stress in GaN epitaxial layers grown on (0001) sapphire substrate by the metalorganic vapor phase epitaxy technique. Micro-Raman spectroscopy is used to assess stress situation in the films with systematically modulated doping concentration from up to As the Si-doping concentration increases, a monotonic decrease of the phonon frequency is observed, which signifies gradual relaxation of the stress in the film. The layers are fully relaxed when electron concentration exceeds The linear coefficient of shift in Raman frequency (ω) induced by the in-plane biaxial compressive stress is estimated to be We suggest that Si doping increases density of misfit dislocation, judging from linewidth of x-ray rocking curve.

Indium oxide nanocubes (NCs) were prepared via a simple, template-free hydrothermal method at low temperature; the so-obtained structures exhibited large surface area (47.67 m 2 /g) and Barrett−Joyner−Halenda (BJH) adsorption average pore diameter (11.92 nm), both higher than for commercial In 2 O 3 nanoparticles. At the optimal temperature of 300 °C, the In 2 O 3 NCs-based sensor showed a superior response of 85–100 ppm ethanol, 3.4 times higher than that of the commercial one based on In 2 O 3 NPs, and also faster response time (15 s) than the commercial device (60 s). The better sensing performance of the synthesized In 2 O 3 NCs can be attributed to its unique properties that include large BET surface area and BJH adsorption average pore diameter as well as abundance of sharp edges and tips, which result in high surface to volume ratios for the gas adsorption and diffusion processes, facilitating the …

This letter presents a study on N-polar GaN growth evolution on sapphire using a low-temperature GaN buffer, which is distinctly different from the two-step growth of Ga-polar GaN according to both in situ reflectance and ex situ microscopy. Annealed N-polar GaN buffer exhibits densely packed tiny grains, serving as a template for the subsequent high-temperature GaN growth, which starts in a quasi-two-dimensional mode without any roughening-recovery process. Atomically smooth N-polar GaN has been achieved with no stacking fault or inversion domain observed. The mosaic microstructure, electrical, and optical properties of N-polar GaN are compared with those of Ga-polar GaN.

The electrical properties and deep level spectra in undoped n-Ga N films irradiated by fast neutrons are reported. The electron removal rate was∼ 5 cm− 1⁠, and the dominant deep states introduced by neutron damage were electron traps with activation energy of 0.75 eV⁠. For high doses of 1.7× 10 17–10 18 cm− 2 the material becomes semi-insulating n-type with the Fermi level pinned near E c− 0.85 eV⁠. Deep level spectra are dominated by electron traps with activation energy of 0.75 eV⁠, close to the energy of the Fermi level pinning in heavily irradiated material. Neutron irradiation also introduces a high density of centers giving rise to strong persistent photocapacitance. The observed phenomena are explained under the assumption that the dominant defects in neutron irradiated GaN are disordered regions produced by high-energy recoil atoms.

Plasmonic metal@semiconductor core–shell nanoparticles (CSNPs) are considered as promising candidates for artificial photosynthesis. Herein, Au@CeO 2 CSNPs are hydrothermally fabricated for photocatalytic hydrogen evolution reaction (HER). CSNPs deliver superior HER performance compared to free CeO 2 . In particular, Au@CeO 2 -18 model (shell thickness of 18 nm) produces an HER rate of 4.05 μmol mg –1 h –1 , which is ∼10 times higher than that of pure CeO 2 (0.40 μmol mg –1 h –1 ) under visible-light. Additionally, Au@CeO 2 -18 photocatalyst demonstrates long-term stability after five repetitive runs, at which point it only loses approximately 5% of the activity, while core-free CeO 2 decreases by 37.5 %. Such improvements are attributed to the electronic interactions between Au and CeO 2 , which not only enriches Ce 3+ active sites to narrow bandgap of ceria toward visible, but also increases the affinity …

Localized surface plasmon (LSP) effects due to Ag and Ag/SiO 2 nanoparticles (NPs) deposited on GaN/InGaN multiquantum well (MQW) light‐emitting diode (LED) structures are studied. The colloidal NPs are synthesized by a sol‐gel method and drop‐cased on the LED structures. The surface density of NPs its controlled by the concentration of the NP solution. Theoretical modeling is performed for the emission spectrum and the electric field distribution of LSP resonance for Ag/SiO 2 NPs. Enhanced photoluminescence (PL) efficiency is observed in the LED structures and the amount of PL enhancement increases with increasing the surface density of Ag and Ag/SiO 2 NPs. These effects are attributed to resonance coupling between the MQW and LSP in the NPs. It is also shown that the PL enhancement attainable with Ag NPs and Ag/SiO 2 NPs is comparable, but the latter displays a much higher stability with …

Development of immobilized photocatalyst on a flexible sheet is an urgent need for wastewater treatment in industry. A facile method is established to fabricate flexible Cu/CuO/Cu 2 O heterojunction nanodisks. The existence of both phases of CuO and Cu 2 O are identified by XRD, XPS and Raman spectroscopy. The combined CuO and Cu 2 O phases having different bandgaps are responsible for an improved photodegradation due to increased charge separation efficiency and an extended range of photoexcitation while decreasing recombination of photogenerated electrons and holes. For the first time, a single to several sheets of Cu/CuO/Cu 2 O heterojunction nanodisk are introduced to investigate the performance of photodegradation and continued to maximum of eight sheets. The superior photocatalytic performance of Cu/CuO/Cu 2 O heterojunction on rhodamine dye solution is observed and compared with …

Carbon quantum dots decorated N-doped ZnO (CQD/N-ZnO) composites were prepared by a simple one step method. The existence of CQD and ZnO phases in the CQD/N-ZnO composite was confirmed by XRD, Raman, XPS and HRTEM techniques. The CQD/N-ZnO composite exhibited an enhanced photocatalytic performance on aqueous malachite green dye, irrespective to the light sources of UV, visible and daylight. The dye degradation of ∼38% and 99% was noticed for N-doped ZnO and CQD/N-ZnO photocatalyst, respectively after 15 min of daylight irradiation and it required just 30 min to degrade an entire dye. Repeated photocatalytic experiment was carried out to investigate the reusing capability of CQD/N-ZnO photocatalyst and it was found that the suppressed photocorrosion offered by CQDs coverage on the ZnO crystals.

Ultrafast Fiber-Optic Networks Research Center

School of Advanced Materials Science and Engineering

Department of Electrical Engineering (supported by LG Yeonam Foundation)

Department of Materials Science and Engineering

Laboratory for Optoelectronic Materials

교수님 소개

이인환

연구실 소개

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Enhanced short-circuit current density in epitaxial InGaP/GaAs/Si trip…

Tuning Properties of II-IV-Nitrides for Optoelectronic Applications

Revolutionizing red micro-LEDs: Harnessing surface plasmons for enhanc…

연구실 보유 특허

대학별 입시끈

우리 연구실 모집

교수님 소개

이인환

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Enhanced short-circuit current density in epitaxial InGaP/GaAs/Si trip…

Tuning Properties of II-IV-Nitrides for Optoelectronic Applications

Revolutionizing red micro-LEDs: Harnessing surface plasmons for enhanc…

연구실 보유 특허

최근 3년간 연구실적 높은 연구실

대학별 입시끈

우리 연구실 모집