• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
• /
• pp.172-173
• /
• 2012

Currently GaN based LED is known to show high internal or external efficiency at low current range. However, this LED operation occurs at high current range and in this range, a significant performance degradation known as 'efficiency droop' occurs. Auger process, carrier leakage process, field effect due to lattice mismatch and thermal effects have been discussed as the causes of loss of efficiency, and these phenomena are major hindrance in LED performance. In order to investigate the main effects of efficiency loss and overcome such effects, it is essential to obtain relative proportion of measurements of internal quantum efficiency (IQE) and various radiative and nonradiative recombination processes. Also, it is very important to obtain radiative and non-radiative recombination times in LEDs. In this research, we measured the IQE of InGaN/GaN multiple quantum wells (MQWs) LEDs with PSS and Planar substrate using modified ABC equation, and investigated the physical mechanism behind by analyzing the emission energy, full-width half maximum (FWHM) of the emission spectra, and carrier recombination dynamic by time-resolved electroluminescence (TREL) measurement using pulse current generator. The LED layer structures were grown on a c-plane sapphire substrate and the active region consists of five 30 ${\AA}$ thick In0.15Ga0.85N QWs. The dimension of the fabricated LED chip was $800um{\times}300um$. Fig. 1. is shown external quantum efficiency (EQE) of both samples. Peak efficiency of LED with PSS is 92% and peak efficiency of LED with planar substrate is 82%. We also confirm that droop of PSS sample is slightly larger than planar substrate sample. Fig. 2 is shown that analysis of relation between IQE and decay time with increasing current using TREL method.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2009년도 제38회 동계학술대회 초록집
• /
• pp.121-121
• /
• 2010

ZnO is a promising material for the application of high efficiency light emitting diodes with short wavelength region for its large bandgap energy of 3.37 eV which is similar to GaN (3.39 eV) at room temperature. The large exciton binding energy of 60 meV in ZnO provide provides higher efficiency of emission for optoelectronic device applications. Several ZnO/ZnMgO multiple quantum well (MQW) structures have been grown on various substrates such as sapphire, GaN, Si, and so on. However, the achievement of high quality ZnO/ZnMgO MQW structures has been somehow limited by the use of lattice-mismatched substrates. Therefore, we propose the optical properties of ZnO/ZnMgO multiple quantum well (MQW) structures with different well widths grown on lattice-matched ZnO substrates by molecular beam epitaxy. Photoluminescence (PL) spectra show MQW emissions at 3.387 and 3.369 eV for the ZnO/ZnMgO MQW samples with well widths of 2 and 5 nm, respectively, due to the quantum confinement effect. Time-resolved PL results show an efficient photo-generated carrier transfer from the barrier to the MQWs, which leads to an increased intensity ratio of the well to barrier emissions for the ZnO/ZnMgO MQW sample with the wider width. From the power-dependent PL spectra, we observed no PL peak shift of MQW emission in both samples, indicating a negligible built-in electric field effect in the ZnO/$Zn_{0.9}Mg_{0.1}O$ MQWs grown on lattice-matched ZnO substrates.

• 천문학회보
• /
• 제40권1호
• /
• pp.51.4-52
• /
• 2015

From 2010 to 2014, CQUEAN (Camera for QUasars in EArly uNiverse) has been operated for the observation at the 82 inch Otto Struve Telescope of the McDonald Observatory, US. This camera is optimized at wavelength range of 0.7 - 1.1 um with seven (g', r', I', z', Y, Iz and Is) broad-band filters for the survey of high redshift (z > 5) quasars in the early universe. We are upgrading this system to identify more details of SED (Spectral Energy Distribution) of quasar candidates and other astronomical sources. The SQUEAN is comprised of a focal reducer, a CCD camera, a new filter wheel, new auto guiding system and new control software. The new filter wheel consists of interchangeable cartridges for various wavelength and size of filters. 50 nm medium bandwidth filters from 600 - 1050 nm, seven SDSS (Sloan Digital Sky Survey) filters and Johnson-Cousin BVRI filters are installed for now. We also have a plan to use narrow band interference filters to classify high redshift quasars or to obtain SEDs of interesting astronomical sources in details more efficiently. We also developed KAP82 (Kyung Hee University Auto guiding Package for 82 inch telescope) for auto guiding software. CQUEAN and SQUEAN have been developed by CEOU (Center for the Exploration of the Origin of the Universe).

• 과학교육연구지
• /
• 제44권1호
• /
• pp.38-49
• /
• 2020

본 연구의 목적은 고등학교 물리 I '시공간과 우주' 단원의 지필평가 문항과 교과서 목표가 인지영역과 내용영역에서 어느 정도 유사한지를 분석하기 위한 것이었다. 9개의 고등학교에서 출제한 지필고사 문제지와 평가원에서 출제한 문항 중에서 물리 I의 첫번째 단원인 '시공간과 우주'에 해당하는 문항들을 분석하였다. 문항의 분석기준으로 교육과정 성취기준에 제시된 내용영역들과 교과서에 진술된 목표들을 사용하여 살펴보기 위해 성취기준에 따라 내용영역을 11개로 분류하였고, 인지영역 수준은 지식, 이해, 적용의 틀로 각각 분류하였다. 결론적으로 학교에서 출제된 문항에서는 적용능력을 평가하는 문항의 비율이 낮았으며, 내용영역간 분포에도 불균형이 나타났다. 비율차 지수를 통한 비교에서는 교과서에 제시된 학습목표와 학교 출제 문항은 유사성이 매우 높았지만, 교과서 목표와 평가원 출제 문항을 비교하였을 때는 유사성이 낮았다. 이상을 바탕으로 평가문항의 타당성을 높이기 위한 몇 가지 제언을 하였다.

• 한국의학물리학회:학술대회논문집
• /
• 한국의학물리학회 2006년도 제33회 추계학술대회 발표논문집
• /
• pp.102-102
• /
• 2006

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권1호
• /
• pp.853-856
• /
• 2007

We report on the alignment properties of new cellulose based photopolymer. The LC alignment quality and image sticking property of the TN and IPS cells made by using the photopolymer were investigated. Thermal and UV stability of those properties were also investigated. Excellent LC alignment quality and stability were obtained particularly in IPS mode.

• 한국자기학회:학술대회 개요집
• /
• 한국자기학회 2008년도 Asian Magnetics Conference
• /
• pp.26.2-26.2
• /
• 2008

• Journal of Korean Vacuum Science & Technology
• /
• 제6권3호
• /
• pp.116-119
• /
• 2002

A performance of a new positron polarimeter is investigated by simulation using a charged-particle trajectory program. The results of the ray tracing are presented along with the details of the design parameters and projected system performance. A ray tracing analysis indicates that this design is capable of effectively transmitting positrons at beam energies varying from 0.1 to 30 keV within the beam diameter of 2-6mm. However, the observed reflection of the positrons(lower than 2 keV) at 12 kGauss indicated that further refinement of beam design is needed to produce a better positron polarimeter.

• 한국과학교육학회지
• /
• 제10권2호
• /
• pp.49-54
• /
• 1990

The purpose of this paper is to promote the physics study of high school students with computer. A computer simulation for falling motion is used to provide the students a chance to study by themselves viewing the concrete motion pictures of computer. By this simulation program, the students can observe various movements of a falling body with calculated distance according to falling time.

• 한국과학교육학회지
• /
• 제23권2호
• /
• pp.176-188
• /
• 2003

자체 유도 현상은 고등학교의 모든 물리II 교과서에서 다뤄지고 있는 중요한 개념이다. 자체 유도 현상에 대한 설문 조사 결과, 코일로 구성된 회로에서 스위치를 열기만 하면 고압의 유도기전력이 발생한다는 과 일반화된 사고는 일반고등학교 학생뿐만 아니라 과학고등학교 학생들에서도 심각할 정도로 많이 나타난다. 자체 유도 현상에 대한 학생들의 일반화된 사고의 원인을 현행 물리II 교과서 분석을 통해 찾아볼 수 있었다. 그 결과, 특정 회로에서의 네온 전구의 점등 현상을 바탕으로 학생들의 직관적 사고에 의존한 막연한 설명이 주된 원인으로 나타났다. 자체 유도 현상에 대한 과학자적 이해를 돕기 위하여 정량적 해석을 시도 하였으며, 이를 바탕으로 학생들에게 자체 유도 현상을 효과적으로 이해시킬 수 있는 정상적인 접근 방법을 찾아보았다.