• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.10
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• pp.852-858
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• 2007

The dependence of substrate on the Ag photodoping phenomenon into amonhous $({\alpha}-)$ GeSe thin film has been investigated using holographic method. A 442 nm HeCd laser was utilized as a light source for the holographic exposure and a 632.8 nm HeNe laser to measure the variation of diffraction efficiency $(\eta)$ in real time. The films (Ag and ${\alpha}-GeSe$) were thermally deposited on the substrates, i.e. p-type Si(100), n-type Si(100) and slide glass. The sample structures prepared were two types: type I (Ag/${\alpha}$-SeGe/substrate) and type II (${\alpha}$-SeGe/Ag/substrate). The $\eta$ kinetics comprised to be three steps in which $\eta$ initially increases, is saturated to be maximized $(\eta_M)$, and then decreases relatively gradually. For the same substrate, the $\eta_M$ values of the type II were higher than those of type I. In addition, the type II exhibited the highest $\eta_M$ for p-type Si substrate, while that in type I was observed for n-type Si substrate. These tendency is explained by the diffusion of minority carrier in the films and the change of magnitude and direction in internal fields generated at the film interfaces. Atomic-force-microscope (AFM) was used to observe relief-type grating patterns.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.355-356
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• 2008

In this work, ZnO films doped with different contents of Indium (0.1at.%, 0.3at.%, 0.6at.%, respectively) were deposited on Si (111) substrate that has 1~20 $\Omega$cm by pulsed laser deposition (PLD) at $600^{\circ}C$ for 30min. The thickness of the films are about 250 nm. The structural, optical and electrical properties of the films were investigated using X-ray Diffraction (XRD), Atomic force microscope (AFM), Photoluminescence (PL) and Hall measurement. It has been found that RMS of the films is decreased and grain size is increased with increasing the contents of doped Indium. The results of the Photoluminescence properties were indicated that the films have UV emission about 380nm and shows a little red shitf with increasing contents of doped indium. The result of the Hall measurement shows that the concentration and resisitivity in doped ZnO are as changing as one order, respectively ${\sim}10^{18}/cm^2$, ${\sim}10^{-2}cm{\Omega}cm$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.112-112
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• 2008

박막형 태양전지에 관한 연구는 1954년 D.C. Reynolds 가 단결정 CdS 에서 광기전력을 발견하면서부터 시작되었다. 고효율 단결정 규소 태양전지가 간편하게 제작되고 박막형 태양전지의 수명문제가 대두되어 한때는 연구가 중단되어지기도 하였으나, 에너지 문제가 심각해지면서 값이 저렴하고 넓은 면적에 쉽게 실용화 할 수 있는 박막형 태양전지에 많은 관심을 가지게 되었다. 박막형 태양전지에 사용되는 CdS는 II-VI 족 화합물 반도체로서 에너지금지대폭이 2.42eV인 직접천이형 n-type 반도체로서 대부분의 태양광을 통과시킬 수 있으며 가시광선을 잘 투과시키고 낮은 비저항으로서 광흡수층인 CdTe/$CuInSe_2$ 등과 같이 태양전지의 광투과층(윈도레이어)으로 널리 사용되고 있다. 이러한 이종접합 박막형 태양전지의 효율을 높이기 위해선 윈도레이어 재료인 CdS 박막의 낮은 전기 비저항치와 높은 광 투과도 값이 요구되어지고 있다. CdS 박막의 제작방법으로는 spray pyrolysis법, 스크린프린팅, 소결법, puttering법, 전착법, CBD(chemical bath deposition)법 및 진공증착법 등의 여러 가지 방법들이 보고되었다. 이 중 sputtering의 경우, 다른 방법들에서는 얻기 어려운 매우 얇은 두께의 박막 증착이 가능하며, 균일성 또한 우수하다. 또한 대면적화가 용이하여 양산화 기술로는 다른 제조 방법들에 비해 많은 장점을 가지고 있다. 따라서 본 연구에서는 sputtering에 의해 증착한 CdS의 박막에 광투과도 등의 향상을 위하여 CMP( chemical mechanical polishing) 공정을 적용하여 표면 특성을 개선하고자 하였다. 그 기초적인 자료로서 CdS 박막의 CMP 공정 조건에 따른 연마율과 비균일도, 표면 특성 등을 ellipsometer, AFM(atomic force microscopy) 및 SEM(scanning electron microscope) 등을 활용 하여 분석하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.79-79
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• 2008

We report the growth of $Ba_{0.5}Sr_{0.5}TiO_3$(BST) thin films and their substrate-dependent electrical characteristics. BST thin films were deposited on alumina(non-single crystal), $Al_2O_3$(100) substrates by Nd:YAG Pulsed Laser Deposition(PLD) with a 355nm wavelength at substrate temperature of $700^{\circ}C$ and post-deposition annealing at $750^{\circ}C$ in flowing $O_2$ atmosphere for 1hours. BST materials had been chosen due to high dielectric permittivity and tunability for high frequency applications, To analyze the oxygen partial pressure effects, deposited films at 1, 10, 50, 100, 150, 200, 300 mTorr. The effects of oxygen pressure on structural properties of the deposited films have been investigated by X-ray diffraction(XRD) and atomic force microscope(AFM), respectively. Then we manufactured a inter-digital capacitor(IDC) patterns twenty fingers and $10{\mu}m$ gap, $700{\mu}m$ length and electrical properties were characterized. The results provide a basis for understanding the growth mechanisms and basic structural and electrical properties of BST thin films as required for tunable microwave devices applications such as varactors and tunable filters.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.208-208
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• 2010

Zinc oxide (ZnO) is a functional material with interesting optical and electrical properties, a wide band gap (more than 3.3 eV), a high transmittance in the visible light region, piezoelectric properties, and a high n-type conductivity. This material has been investigated for use in many applications, such as transparent electrodes, blue light-emitting diodes, and ultra-violet detector. ZnO films grown under low oxygen pressure by thin film deposition methods show low resistivity and large free electron concentration. Therefore, reducing the background carrier concentration in ZnO films is one of the major challenges ahead of realizing high-performance ZnO-based optoelectronic devices. In this study, we deposited ZnO thin films on sapphire substrates by pulsed laser deposition (PLD) with employing an oxygen plasma source to decrease the background free-electron concentration and enhance the crystalline quality. Then, the substrate temperature was varied between 200 'C to 900 'C The vacuum chamber was initially evacuated to a pressure of $10^{-6}$ Torr, and then a pure $O_2$ gas was introduced into the chamber and the pressure during deposition was maintained at $10^{-2}$ Torr. Crystallinity and orientation of ZnO films were investigated by X-ray diffraction (XRD). The film surface was analyzed with atomic force microscope (AFM). And electrical properties were measured at room temperature by Hall measurement.

• Korean Journal of Materials Research
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• v.15 no.6
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• pp.361-369
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• 2005

InP(100) crystal surface was irradiated by ion beams with low energy $(180\~225\;eV)$ and high flux $(\~10^{15}/cm^2/s)$, Self-organization process induced by ion beam was investigated by examining nano structures formed during ion beam sputtering. As an ion source, an electrostatic closed electron Hall drift thruster with a broad beam size was used. While the incident angle $(\theta)$, ion flux (J), and ion fluence $(\phi)$ were changed and InP crystal was rotated, cone-like, ripple, and anistropic nanostrucuture formed on the surface were analyzed by an atomic force microscope. The wavelength of the ripple is about 40 nm smaller than ever reported values and depends on the ion flux as $\lambda{\propto}J^{-1/2}$, which is coincident with the B-H model. As the incident angle is varied, the root mean square of the surface roughness slightly increases up to the critical angle but suddenly decreases due to the decrease of sputtering yield. By the rotation of the sample, the formation of nano dots with the size of $95\~260\;nm$ is clearly observed.

• Design & Manufacturing
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• v.13 no.4
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• pp.57-62
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• 2019

In this study, we investigated the halo surface defection of various phenomenon occurred during the injection molding process which is caused by the thinning of the product thickness and the importance of the appearance. Surface analysis was performed to observe the difference between the surface where defects appeared and the surface which did not appear. Based on these results, we analyzed the phenomenon of halo surface defects was caused by unstable flow of resin generated in injection molding and velocity change of flow front. Furthermore, we will conduct a clear analysis of halo surface defects through observations through optical microscopy and subsequent observations with atomic force microscope. It has been analyzed that halo in PP is due to the rheological difference between the crystalline and amorphous regions while that in PC/ABS is due to shear separation of PC and ABS.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.297-297
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• 2012

양자점은 공간적으로 세 방향 모두 전하의 운동을 제한하는 0차원 구조로 불연속적인 상태 밀도를 가진다. 이런 양자점의 특성은 광통신용 소자, 레이저 다이오드 등과 같은 광학 및 전자 장치에 응용될 수 있기 때문에 많은 주목을 받아 활발히 연구되어 왔다. 본 연구에서는 MBE 장비를 이용하여 GaAs 기판위에 InAs 양자점을 성장시키는 동안 As의 공급을 임의로 차단시켜 양자점 형성 조건을 변화시킨 시료들의 광학적 특성을 Photoluminescence (PL) 와 Time-resolved PL (TRPL) 실험을 이용하여 분석하였다. GaAs (001) 기판 위에 GaAs buffer layer를 $610^{\circ}C$에서 성장한 후, $470^{\circ}C$에서 As 공급 조건 변화에 따른 InAs 양자점을 성장하였다. 양자점을 성장한 후 GaAs cap layer를 $610^{\circ}C$에서 성장하였다. InAs 양자점 시료들은 In을 20초 공급하는 동안 As의 공급과 차단을 각각 1초, 2초, 3초의 일정한 간격으로 반복하였다. 10 K에서 각각의 시료들의 PL을 측정한 결과 As 공급과 차단을 2초씩 반복한 T2시료에서 PL 세기가 가장 좋게 나타났으며, 3초씩 반복한 T3시료에서 가장 나쁘게 나타났다. PL 피크는 공급과 차단을 1초씩 반복한 T1 시료가 1.23 eV, T2 시료가 1.24 eV, T3 시료가 1.26 eV에 나타났으며, As의 차단시간이 증가함에 따라 PL 피크가 높은 에너지로 이동함을 보였다. 발광파장에 따른 PL 소멸은 파장이 증가함에 따라 점차 느려지다가 PL 피크 근처에서 가장 느린 소멸곡선을 보이고, 파장이 더 증가하였을 때 점차 빠르게 소멸하였다. As 공급 조건의 변화에 따라 InAs 양자점의 크기와 밀도, 모양 등이 변하는 것을 Atomic Force Microscope (AFM) image를 통하여 확인하였으며, PL과 TRPL을 이용하여 InAs 양자점의 광학적 특성을 분석하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.185-185
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• 2011

ZnTe semiconductor is very attractive materials for optoelectronic devices in the visible green spectral region because of it has direct bandgap of 2.26 eV. The prototypes of ZnTe light emitting diodes (LEDs) have been reported [1], showing that their green emission peak closely matches the most sensitive region of the human eye. Another application to photovoltaics proved that ZnTe is useful for the production of high-efficiency multi-junction solar cells [2,3]. By using the pulse laser deposition system, ZnTe thin films were deposited on ZnO thin layer, which is grown on (0001) Al2O3substrates. To produce the plasma plume from an ablated ZnO and ZnTe target, a pulsed (10 Hz) YGA:Nd laser with energy density of 95 mJ/$cm^2$ and wavelength of 266 nm by a nonlinear fourth harmonic generator was used. The laser spot focused on the surface of the ZnO and ZnTe target by using an optical lens was approximately 1 mm2. The base pressure of the chamber was kept at a pressure around $10^{-6}$ Torr by using a turbo molecular pump. The oxygen gas flow was controlled around 3 sccm by using a mass flow controller system. During the ZnTe deposition, the substrate temperature was $400^{\circ}C$ and the ambient gas pressure was $10^{-2}$ Torr. The structural properties of the samples were analyzed by XRD measurement. The optical properties were investigated by using the photoluminescence spectra obtained with a 325 nm wavelength He-Cd laser. The film surface and carrier concentration were analyzed by an atomic force microscope and Hall measurement system.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.332-332
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• 2012

분자선 에피탁시(molecular beam epitaxy)를 이용하여 GaAs 기판에 성장한 InAs 양자점(QDs: quantum dots)은 성장 온도, 압력, As/In의 공급비 등의 성장 조건에 따라 다른 변수(parameter)를 갖는다. 따라서 성장변수에 따라 양자점의 모양과 크기, 밀도가 달라져 균일한 양자점 형성에 어려움이 있어 많은 연구가 진행되고 있다. 예를 들면 In-interruption 법으로 성장한 양자점의 특성이 S-K mode (Stranski-Krastanov mode)로 성장한 양자점에 비해 광학적 특성이 향상되었다. 본 연구에서는 In pre-deposition (IPD) 법으로 성장한 InAs/GaAs 양자점의 광학적 특성을 PL(photoluminescence)와 TRPL (time-resolved PL)을 이용하여 분석하였다. InAs QDs 시료들은 In과 As 공급시간을 각각 1초와 19초 (QD1), 2초와 18초 (QD2), 3초와 17초 (QD3)로 조절하여 성장하였으며, In이 공급되는 시간 동안 As shutter를 차단하여 As 공급을 중단하였다. In과 As의 차단 없이 S-K mode로 성장한 시료를 기준시료로 사용하였다 (QD0). AFM (atomic force microscope) 측정결과, In 공급시간이 1초에서 2초로 증가할 때, 양자점의 밀도와 종횡비(aspect ratio)가 증가하였고, 양자점의 균일도가 증가하였다. 그러나 QD3 시료는 QD1 시료에 비해 밀도와 종횡비, 균일도가 감소하였다. 10 K에서 PL 피크는 In 공급 시간이 증가할 때, 970 nm에서 1020 nm로 적색편이 하였고 반치폭 (FWHM: full width at half maximum)은 75 meV에서 85 meV로 증가하였다. QD2 시료의 PL 피크 에너지가 가장 낮았고, 가장 강한 PL 세기를 보였다. IPD 시간이 증가함에 따라 PL 피크에서 측정한 PL 소멸은 점차 빨라졌다. IPD 기법으로 성장한 양자점의 빠른 PL 소멸은 양자점 밀도와 종횡비 향상에 의한 파동함수 중첩의 증가와 구속 에너지 증가에 의한 것으로 설명된다.