• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.400-400
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• 2011

습식 식각과 RIE (reactive ion etching) 텍스처링 된 다결정 실리콘 태양전지의 라미네이팅 공정 전 후에 양자 효율과 광학적 특성 및 전기적 특성의 변화를 관찰 하였다. 두 식각 방법을 이용해 라미네이팅 공정 전 습식 식각의 표면 텍스처 태양전지에 비해 RIE 표면 텍스처태양전지에서 높은 양자 효율이 관측 되었지만, 라미네이팅 공정 후에 두 셀을 비교해 보면 RIE 텍스처링 된 것의 양자 효율이 더 낮아지는 것을 확인 할 수 있었다. 300~1,100 nm의 파장 범위에서 10 nm의 간격으로 양자효율, 반사율, 투과율, 흡수율 및 변환 효율을 측정하였다. 또한, 공정 전 후의 셀의 dark current를 측정하였다. 위 연구 결과를 통해 라미네이팅 공정에 따른 다결정 실리콘 태양전지의 특성 변화를 분석 하였다.

• Journal of the Korean Vacuum Society
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• v.19 no.4
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• pp.314-318
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• 2010

We fabricated a plasma texturing for multi-crystalline silicon cells using reactive ion etching (RIE). Multi-crystalline Si cells have not benefited from the cost-effective wet-chemical texturing processes that reduce front surface reflectance on single-crystal wafers. Elimination of plasma damage has been achieved while keeping front reflectance to extremely low levels. We will discuss reflectance, quantum efficiency and conversion efficiency for multi-crystalline Si solar cell by each RIE process conditions.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.422-428
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• 2023

Ultrafast ultrasound imaging has been applied to various imaging approaches, including shear wave elastography, ultrafast Doppler, and super-resolution imaging. However, these methods are still challenging in real-time implementation for three Dimension (3D) or portable applications because of their massive data rate required. In this paper, we proposed an adaptive quantization method that effectively reduces the data rate of large Radio Frequency (RF) data. In soft tissue, ultrasound backscatter signals require a high dynamic range, and thus typical quantization used in the current systems uses the quantization level of 10 bits to 14 bits. To alleviate the quantization level to expand the application of ultrafast ultrasound imaging, this study proposed a depth-sectional quantization approach that reduces the quantization errors. For quantitative evaluation, Field II simulations, phantom experiments, and in vivo imaging were conducted and CNR, spatial resolution, and SSIM values were compared with the proposed method and fixed quantization method. We demonstrated that our proposed method is capable of effectively reducing the quantization level down to 3-bit while minimizing the image quality degradation.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.315.1-315.1
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• 2013

표면 조직화의 목적은 태양전지 표면에서의 입사되는 빛의 반사율을 감소 시키고, 웨이퍼 내에서 빛의 통과 길이를 길게 하며, 흡수되는 빛의 양을 증가시키는 것이다. 본 연구에는 습식, 건식 표면조직화 방법에 따른 표면 형상과 표면 반사도를 분석 하였으며, 셀을 제작하여 전기적 특성과 광학적 특성의 상관관계를 분석하였다. 표면 조직화 공정은 염기성 용액인 KOH를 이용한 식각 방법과 Ag를 이용한 metal-assisted 식각, 산증기를 이용한 식각, 플라즈마를 이용한 반응성 이온식각을 적용하여 제작하였다. 표면 반사율을 400~1000 nm 사이의 파장에서 측정하였으며 KOH를 이용하여 식각한 샘플이 9.11%의 표면 반사율을 가졌으며 KOH를 이용하여 식각한 표면에 추가로 metal-assisted 식각을 한 샘플이 2%로 가장 낮은 표면 반사율을 보였다. 표면 조직화 후 동일 조건으로 셀을 제작 하여 효율 측정 결과 Ag를 이용한 2단계 metal-assisted chemical 식각이 15.83%의 가장 낮은 광변환 효율을 보였으며 RIE를 이용한 2단계 반응성 이온 식각공정이 17.78%로 가장 높은 광변환 효율을 보였다. 이 결과는 반사도 결과와 일치 하지 않았다. 표면 조직화 모양에 따른 셀 효율의 변화는 도핑 프로파일과 표면 재결합 속도의 변화 때문이라 생각되며 더 명확한 분석을 위해 양자 효율을 측정하여 분석을 시도하였다. 측정 결과 단파장 대역에서 낮은 응답특성을 가지는 것을 확인 할 수 있었는데 그 이유는 낮은 반사도를 가지는 표면조직화 공정의 경우 나노사이즈의 구조를 갖기 때문에 균일한 도핑 프로파일을 얻지 못해 전자 정공의 분리가 제대로 이루어지지 못하였고 표면 재결합 속도증가의 원인으로 단락전류와 개방전압이 낮아져 효율이 떨어진 것으로 판단된다. 실험 결과 도핑 프로파일의 균일성은 셀 효율 개선을 위해 낮은 표면 반사율 만큼 중요하다는 점을 알게되었다. 낮은 반사율을 갖는 표면조직화 공정도 중요하지만 표면에 따른 균일한 도핑 프로파일을 갖는 공정을 개발한다면 단파장 응답도가 향상되어 단락전류밀도의 상승효과를 얻을 수 있을 것이라 판단된다.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2005.11a
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• pp.301-306
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• 2005

The possibility and limitation of one dimensional nano scale electron shielder is briefly discussed. A Nano scale electron shielder will reduce the weight and size of shielding materials. However, practical application still requires further research. In this work, we discuss general problems related to nano scale electron shielder, by taking an arbitrary one dimensional potential barrier as an example.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1B
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• pp.120-127
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• 2000

In this paper, we propose multispectral image compression using classified interband prediction and vector quantization in wavelet domain. This method classifies each region considering reflection characteristics of each band in image data. In wavelet domain, we perform the classified intraband VQ to remove intraband redundancy for a reference band image that has the lowest spatial variance and the best correlation with other band. And in wavelet domain, we perform the classifled interband prediction to remove interband redundancy for the remaining bands. Then error wavelet coefficients between original image and predicted image are intraband vector quantized to reduce prediction error. Experiments on remotely sensed satellite image show that coding efficiency of theproposed method is better than that of the conventional method.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.9
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• pp.23-30
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• 2000

The performance of two types of surface reflecting all-optical switches with InGaAs/InAlAs multiple quantum wells are investigated. The absorption spectra and the refractive index changes of the quantum well are calculated for various pump and probe beam intensities and device conditions. From theses results, on ON/OFF ratio and switching speed of the two switches are compared. It is shown that the switch using DBR has higher ON/OFF ratio and higher switching speed than the switch without DBR.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.7
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• pp.31-36
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• 2004

In comparison with in-plane lasers, predicting the output power and differential quantum efficiency of Vertical-Cavity Surface-Emitting Lasers(VCSELs) is very difficult due to the distributed Bragg reflector(DBR) layers. Therefore, effective cavity model and transfer matrix method have been adapted in order to calculate the output power and differential quantum efficiency The effective cavity model is inappropriate to calculate output power and differential quantum efficiency while it is practically adequate to calculate the threshold gain and threshold current density The reason is that the effective cavity model can not take account of the absorption in GaAs stack layer right below the metal aperture. In this paper, we have compared the threshold current and differential quantum efficiency calculated by using transfer matrix method with effective cavity model and we have made a study of the validity of the effective cavity model. Finally, we have confirmed the versatility of the transfer matrix method with these studies.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.40 no.2
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• pp.11-19
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• 2003

This paper proposes an algorithm to reduce the estimation error of surface spectral-reflectance(SR) using a conventional 3-band RGB camera. In the proposed method, estimation error can be reduced by using adaptive principal components(PCs) for each color region. In order to build adaptive set of PCs, n SR populations are organized for n PC sets by using Lloyd quantizer design algorithm. Macbetch ColorCheckcer is utilized as initial representative SR values for 1485 Munsell color chips of total color population and the Munsell chips arc divided subsets and a set of corresponding adaptive PCs per each subset is organized. As a result of experiments, the proposed method showed advanced estimation performance compared to both the two 3-band PCA methods and the 5-band wiener method.

• Journal of the Korean Vacuum Society
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• v.20 no.3
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• pp.225-232
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• 2011

Reactive ion etching (RIE) technique for maskless surface texturing of mc-silicon solar wafers has been applied and succeed in fabricating a grass-like black-silicon with an average reflectance of $4{\pm}1%$ in a wavelength range of 300~1,200 nm. In order to investigate the optimized texturing conditions for mass production of high quantum efficiency solar cell Surface characteristics such as the spatial distribution of average reflectance, micrscopic surface morphology and minority carrier lifetime were monitored for samples from saw-damaged $15.6{\times}15.6\;cm^2$ bare wafer to key-processed wafers as well as the mc-Si solar cells. We observed that RIE textured wafers reveal lower average reflectance along from center to edges by 1% and referred the origin to the non-uniform surface structures with a depth of 2 times deeper and half-maximum width of 3 times. Samples with anti-reflection coating after forming emitter layer also revealed longer minority carrier lifetime by 40% for the edge compared to wafer center due to size effects. As results, mc-Si solar cells with RIE-textured surface also revealed higher efficiency by 2% and better external quantum efficiency by 15% for edge positions with higher height.