• Membrane Journal
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• v.33 no.4
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• pp.233-233
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• 2023

• Journal of the Korean Vacuum Society
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• v.15 no.1
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• pp.81-88
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• 2006

Laterally self-aligned InGaAs/GaAs quantum-dots (QDs) have been fabricated by using a multilayer stacking technique. For the growth optimization, we vary the number of stacks and the growth temperature in the ranges of 1-15 periods and $500-540^{\circ}C$. respectively, Atomic force microscope (AFM) images and photoluminescence (PL) spectra reveal that the lateral alignment of QDs is enhanced in extended length by an increased stack period, but severely degrades into film-like wires above a critical growth temperature. The morphological and the photoluminescence characteristics of laterally self-aligned InGaAs QDs have been analyzed through mutual comparisons among four samples with different parameters. An anisotropic arrangement develops with increasing number of stacks, and high-temperature capping allows isolated QDs to be spontaneously organized into a one-dimensionally aligned chain-like shape over a few ${\mu}m$, Moreover, the migration time allowed by growth interruption plays an additional important role in the chain arrangement of QDs. The QD chains capped at high temperature exhibit blue shifts in the emission energy, which may be attributed to a slight outdiffusion of In from the InGaAs QDs.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.6
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• pp.663-668
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• 2021

For the development of highly efficient quantum dot-sensitized solar cells (QDSCs), it is important to enhance the electrocatalytic activity of the counter electrodes (CEs). Herein, a fabrication process of Cu₂S CEs are optimized for the development highly efficient QDSCs. The surface of brass film is treated with HCl solution to prepare the Cu₂S CEs, and the concentraion as well as the temperature of HCl solution are controlled. It is found that the uniformity for the thickness of prepared Cu₂S CEs is enhanced when the diluted HCl solution is used, compared to the HCl solution of standard concentration. In addition, the electrocatalytic activity of the Cu₂S CEs is also increased with the modificed process, which is confirmed by impedance data and Tafel polarization curves. As a result, the photoconversion efficiency of QDSCs is improved from 4.49% up to 5.73%, when the concentraion and temperature of the HCl treatment are efficiently optimized.

• Advances in nano research
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• v.2 no.3
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• pp.173-177
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• 2014

This study is aimed to the numerical modeling of the surface plasmon-polariton excitation by a layer of active (electrically pumped) quantum dots embedded in a semiconductor, covered with a metal. It is shown that this excitation becomes much more efficient if the metal has a form of a thin (with thickness of several nanometers) film. The cause of this enhancement in comparison with a thick covering metal film is the partial surface plasmon-polariton localized at the metal-semiconductor interface penetration into air. In result the real part of the metal+air half-space effective dielectric function becomes closer (in absolute value) to the real part of the semiconductor dielectric function than in the case of a thick covering metal film. This leads to approaching the point of the surface plasmon-polariton resonance (where absolute values of these parts coincide) and, therefore, the enhancement of the surface plasmon-polariton excitation. The calculations were made for a particular example of InAs quantum dot layer embedded in GaAs matrix covered with an Au film. Its results indicate that for the 10 nm Au film the rate of this excitation becomes by 2.5 times, and for the 5 nm Au film - by 6-7 times larger than in the case of a thick (40 nm or more) Au film.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.110-110
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• 2010

본 실험에서는 Silicon (001) 기판을 사용하여 silicon 기판상에 modified Stranski-Krastanow(S-K) 방식으로 InAs quantum dot (QD) 을 성장하고 그 위에 InSb layer를 형성하였다. 기판온도 $390^{\circ}$에서 In injection period를 4번 반복하여 제작된 InAs quantum dot layer를 buffer로 사용하였으며, QD layer의 밀도는 $1{\mu}m^2$ 당 600개, height가 $6.2\;{\pm}\;2.0\;nm$, width가 $36.1\;{\pm}\;9.2\;nm$ 정도이다. 성장된 $2.8{\mu}m$ 두께의 InSb film의 특성을 분석해 보면 AFM 상에서의 root mean square (rms) roughness는 5.142nm정도이며, electron mobility는 340 K 에서 $41,352cm^2/Vs$, 1.8 K에서는 $4,215cm^2/Vs$ 정도를 나타내었다. 본 실험에서는 다른 실험과는 달리 InAs QD 을 buffer layer로 사용하였으며, silicon기판도 아무런 처리가 되지 않은 (001)기판을 사용하였으므로 기존의 다른 연구 결과와는 차별성을 가진다. 또한 buffer로 사용된 InAs quantum dot layer의 종류를 한 가지로 고정하고 실험을 하였지만 추후 더욱 다양한 밀도와 크기의 quantum dot layer를 적용시키고, 기존의 다른 논문에서 적용된 방법들을 추가로 적용시켜 본다면 mobility값은 더욱 증가할 것으로 생각된다. 이러한 연구를 통해 값이 싸고 구하기 쉬운 silicon기판상에 silicon에 비하여 더 좋은 특성을 갖는 III-V족 화합물 반도체 소자를 구현 할 수 있을 것으로 생각된다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.341-341
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• 2016

The discovery of light emission in nanostructured silicon has opened up new avenues of research in nano-silicon based devices. One such pathway is the application of silicon quantum dots in advanced photovoltaic and light emitting devices. Recently, there is increasing interest on the silicon quantum dots (c-Si QDs) films embedded in amorphous hydrogenated silicon-nitride dielectric matrix (a-SiNx: H), which are familiar as c-Si/a-SiNx:H QDs thin films. However, due to the limitation of the requirement of a very high deposition temperature along with post annealing and a low growth rate, extensive research are being undertaken to elevate these issues, for the point of view of applications, using plasma assisted deposition methods by using different plasma concepts. This work addresses about rapid growth and single step development of c-Si/a-SiNx:H QDs thin films deposited by RF (13.56 MHz) and ultra-high frequency (UHF ~ 320 MHz) low-pressure plasma processing of a mixture of silane (SiH4) and ammonia (NH3) gases diluted in hydrogen (H2) at a low growth temperature ($230^{\circ}C$). In the films the c-Si QDs of varying size, with an overall crystallinity of 60-80 %, are embedded in an a-SiNx: H matrix. The important result includes the formation of the tunable QD size of ~ 5-20 nm, having a thermodynamically favorable <220> crystallographic orientation, along with distinct signatures of the growth of ${\alpha}$-Si3N4 and ${\beta}$-Si3N4 components. Also, the roles of different plasma characteristics on the film properties are investigated using various plasma diagnostics and film analysis tools.

• Journal of Sensor Science and Technology
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• v.31 no.4
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• pp.249-254
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• 2022

To achieve high-performance colloidal quantum dot light-emitting diodes (QD-LEDs), the use of a densely packed QD film is crucial to prevent the formation of leakage current pathways and increase in interface resistance. Spin coating is the most common method to deposit QDs; however, this method often produces pinholes that can act as short-circuit paths within devices. Since state-of-the-art QD-LEDs typically employ mono- or bi-layer QDs as an emissive layer because of their low conductivities, the use of a densely packed and pinhole-free QD film is essential. Herein, we introduce the Langmuir-Blodgett (LB) technique as a deposition method for the fabricate densely packed QD films in QD-LEDs. The LB technique successfully transfers a highly dense monolayer of QDs onto the substrate, and multilayer deposition is performed by repeating the transfer process. To validate the comparability of the LB technique with the standard QD-LED fabrication process, we fabricate and compare the performance of LB-based QD-LEDs to that of the spin-coating-based device. Owing to the non-destructiveness of the LB technique, the electroluminescence efficiency of the LB-based QD-LEDs is similar to that of the standard spin coating-based device. Thus, the LB technique is promising for use in optoelectronic applications.

• Bulletin of the Korean Chemical Society
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• v.35 no.10
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• pp.2895-2900
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• 2014

We fabricated quantum dot-sensitized solar cells (QDSSCs) using cadmium sulfide (CdS) and cadmium telluride (CdTe) quantum dots (QDs) as sensitizers. A spin coated $TiO_2$ nanoparticle (NP) film on tin-doped indium oxide glass and sputtered Au on fluorine-doped tin oxide glass were used as photo-anode and counter electrode, respectively. CdS QDs were deposited onto the mesoporous $TiO_2$ layer by a successive ionic layer adsorption and reaction method. Pre-synthesized CdTe QDs were deposited onto a layer of CdS QDs using a direct adsorption technique. CdS/CdTe QDSSCs had high light harvesting ability compared with CdS or CdTe QDSSCs. QDSSCs incorporating single-walled carbon nanotubes (SWNTs), sprayed onto the substrate before deposition of the next layer or mixed with $TiO_2$ NPs, mostly exhibited enhanced photo cell efficiency compared with the pristine cell. In particular, a maximum rate increase of 24% was obtained with the solar cell containing a $TiO_2$ layer mixed with SWNTs.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.49-53
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• 2022

In this study, quantum dot light-emitting diodes (QLEDs) of the optimized EL performance with a radio frequency (RF) sputtered Zn_0.85Mg_0.15O thin film as an electron transport layer (ETL). In typical QLEDs, ZnO nanoparticles (NPs) are widely used materials for ETL layer due to their advantages of high electron mobility, suitable energy level and easy capable of solution processing. However, the instability problem of solution-type ZnO NPs has not yet been resolved. To solve this problem, ZnMgO thin film doped with 15% Mg of ZnO was fabricated by RF sputtering and optimized for the device applied as an ETL. The QLEDs of optimized ZnMgO thin film exhibited a maximum luminance of 15,972 cd/m² and a current efficiency of 7.9 cd/A. Efficient QLEDs using sputtering ZnMgO thin film show the promising results for the future display technology.

• Korean Journal of Optics and Photonics
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• v.32 no.5
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• pp.220-229
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• 2021

The optical characteristics of high-power direct-lit white light-emitting diode (LED) lighting were investigated, where a quantum dot (QD) film was adopted to enhance the color-rendering index (CRI). The transmittance of the diffuser plate and the concentration of the QD film were varied in this study. The color coordinates and the correlated color temperature (CCT) did not show any appreciable change, while the CRI values increased slightly as the transmittance of the diffuser plate decreased. The investigated optical properties were nearly independent of the viewing angle, and the luminance distribution was close to Lambertian. The CCT decreased from approximately 6000 K to approximately 4000 K as the concentration of the QD film increased from 0 to 7.5 wt%, which was due to the enhanced red component in the emission spectrum. The CRI increased to approximately 95 for some optical configurations of the lighting. These results demonstrate that glare-free, color-changeable, high-rendering LED lighting can be realized by using a combination of a diffuser plate of appropriate transmittance and a red QD film.