• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.112.1-112.1
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• 2011

The back contact solar cell (BCSC) has several advantages compared to the conventional solar cell since it can reduce grid shadowing loss and contact resistance between the electrode and the silicon substrate. This paper presents the effect of the surface texturing of the silicon BCSC by varying the texturing depth or the texturing gap in the commercially available simulation software, ATHENA and ATLAS of the company SILVACO. The texturing depth was varied from $5{\mu}m$ to $150{\mu}m$ and the texturing gap was varied from $1{\mu}m$ to $100{\mu}m$ in the simulation. The resulting efficiency of the silicon BCSC was evaluated depending on the texturing condition. The quantum efficiency and the I-V curve of the designed silicon BCSC was also obtained for the analysis since they are closely related with the solar cell efficiency. Other parameters of the simulated silicon BCSC are as follows. The substrate was an n-type silicon, which was doped with phosphorous at $6{\times}10^{15}cm^{-3}$, and its thickness was $180{\mu}m$, a typical thickness of commercial solar cell substrate thickness. The back surface field (BSF) was $1{\times}10^{20}\;cm^{-3}$ and the doping concentration of a boron doped emitter was $8.5{\times}10^{19}\;cm^{-3}$. The pitch of the silicon BCSC was $1250{\mu}m$ and the anti-reflection coating (ARC) SiN thickness was $0.079{\mu}m$. It was assumed that the texturing was anisotropic etching of crystalline silicon, resulting in texturing angle of 54.7 degrees. The best efficiency was 25.6264% when texturing depth was $50{\mu}m$ with zero texturing gap in case of low texturing depth (< $100{\mu}m$).

• Journal of Sensor Science and Technology
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• v.13 no.2
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• pp.128-132
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• 2004

Short wave infrared (SWIR) photovoltaic devices have been fabricated from metal organic vapour phase epitaxy (MOVPE) grown n- on p- HgCdTe films on GaAs substrates. The MOVPE grown films were processed into mesa type discrete devices with wet chemical etching employed for meas delineation and ZnS surface passivatlon. ZnS was thermally evaporated from effusion cell in an ultra high vacuum (UHV) chamber. The main features of the ZnS deposited from effusion cell in UHV chamber are low fixed surface charge density, and small hysteresis. It was found that a negative flat band voltage with -0.6 V has been obtained for Metal Insulator Semiconductor (MIS) capacitor which was evaporated at $910^{\circ}C$ for 90 min. Current-Voltage (I-V) and temperature dependence of the I-V characteristics were measured in the temperature range 80 - 300 K. The Zero bias dynamic resistance-area product ($R_{0}A$) was about $7500{\Omega}-cm^{2}$ at room temperature. The physical mechanisms that dominate dark current properties in the HgCdTe photodiodes are examined by the dependence of the $R_{0}A$ product upon reciprocal temperature. From theoretical considerations and known current expressions for thermal and tunnelling process, the device is shown to be diffusion limited up to 180 K and g-r limited at temperature below this.

• Tribology and Lubricants
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• v.24 no.6
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• pp.374-377
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• 2008

Due to the environmental concerns, especially the greenhouse effect and GWP (Global Warming Potential), the carbon dioxide was investigated as an alternative natural refrigerant to replace HFCs (HydroFluoroCarbons) in refrigerator or air conditioning systems. Because new compressor with carbon dioxide is going to be operated under the high pressure, the tribology of sliding surfaces in the compressor becomes very important. To improve of wear resistance in compressor parts, especially rotary type, the friction and wear characteristics of improved sliding surfaces between vane and flange were evaluated in this paper. The method of reformed sliding surface, such as micro-dimple processes, was applied on surfaces in order to improve the tribological characteristics, and their performances were evaluated experimentally. The vane-on-flange type lubricated sliding tests were performed with a high pressure wear tester using carbon dioxide. Test results showed that the reformed surfaces were very effective to reduce the friction and the wear amounts of vane surfaces. The method of improved surfaces showed good tribological properties at vane and flange.

• Journal of the Korean Vacuum Society
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• v.6 no.1
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• pp.91-96
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• 1997

The electrical characteristics and the plasma parameters of planar inductively coupled plasmas (ICP) have been measured. The resistance of the total load including the coil and the plasma varied from 1 to 4 W and the inductance from 1.5 m to 2 mH when the power was changed from 100 to 1000 W and the pressure from 1 to 10 mTorr. The density of electron measured by Langmuir probe was over $10^{11}/\textrm{cm}^3$ and the temperature varied between 3 and 5 eV as the process conditions were changed. Bias modulation was adopted as a new method to improve the selectivity of $SiO_2$on Si in $C_4F_8$ (octafluorocyclobutane) plasma. The selectivity was improved as the duty ratio decreased, but the etch rate of $SiO_2$decreased below 400$\AA$/min. $H_2$addition to $C_4F_8$ plasma showed that the etch selectivity could be higher than 50 and the etch rate of $SiO_2$over 2000$\AA$/min when 60% $H_2$was added.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.373-375
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• 2011

최근 태양전지 연구에서 저가격화를 실현하는 방법 중 하나로 폐 실리콘 웨이퍼를 재생하는 방법에 관하여 많은 연구가 진행되고 있다. 그러나 기존 웨이퍼 재생공정은 높은 재처리 비용과 복잡한 공정등의 많은 단점을 가지고 있다. 결정형 태양전지에서 저가격화 및 고효율은 태양전지를 제작하는데 있어 필수 요소 이다. 그 중 결정질 태양전지 고효율을 위한 여러 연구 방법 중 표면 텍스쳐링(texturing)에 관한 연구가 활발하다. 텍스쳐링은 표면반사에 의한 광 손실을 최소화 하여 효율을 증가시키기 위한 방법으로 습식 식각과 건식 식각을 사용하여 태양전지 표면 위에 요철 및 피라미드구조를 형성하여 반사율을 최소화 시킨다. 건식식각은 습식식각과 다른 환경적 오염이 적은 것과 소량의 가스만으로 표면 텍스쳐링이 가능하여 많은 연구가 진행중이다. 건식 식각 중 하나인 RIE(reactive ion etching)는 고주파를 이용하여 플라즈마의 이온과 silicon을 반응 시킨다. 실험은 RIE를 이용하여 SF6/02가스를 혼합하여 비등방성 에칭 및 피라미드 구조를 구현하였다. RIE 공정 중 SF6/02가스는 높은 식각 율을 갖으며 self-masking mechanism을 통해 표면이 검게 변화되고 반사율이 감소하게 된다. 이 과정을 통해 블랙 실리콘을 형성하게 된다. 블랙 실리콘은 반사율 10% 이하로 self-masking mechanism으로 바늘모양의 구조를 형성되는 게 특징이며 표면이 검은색으로 반사율이 낮아 효율증가로 예상되지만 실제 바늘 모양의 블랙 실리콘은 태양전지 제작에 있어 후속 공정 인 전극 형성 시 Ag Paste의 사이즈와 표면 구조를 감안할 때 태양 전지 제작 시 Series resistance를 증가로 효율 저하를 가져온다. 본 연구는 SF6/02가스를 혼합하여 기존 RIE로 형성된 바늘모양의 구조의 블랙 실리콘이 아닌 RIE 내부에 metal-mesh를 장착하여 단결정(100)실리콘 웨이퍼 표면을 텍스쳐링 하였고 SF6/02 가스 1:1 비율로 공정을 진행 하였다. metal-mesh 홀의 크기는 100um로 RIE 내부에 장착하여 공정 시간 및 Pressure를 변경하여 실험을 진행하였다. 공정 시간이 변경됨에 따라 단결정(100) 실리콘 웨이퍼 표면에 피라미드 구조의 균일한 1um 크기의 블랙 실리콘을 구현하였다. 바늘모양의 블랙 실리콘을 피라미드 구조로 구현함으로써 바늘 모양의 단점을 보완하여 태양전지 전기적 특성을 분석하여 태양전지 제작시 변환 효율을 증가시킬 것으로 예상된다.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.444-444
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• 2011

Recently, patterned magnetic films and elements attract a wide interest due to their technological potentials in ultrahigh-density magnetic recording and spintronic devices. Among those patterned magnetic structures, magnetic anti-dot patterning induces a strong shape anisotropy in the film, which can control the magnetic properties such as coercivity, permeability, magnetization reversal process, and magneto-resistance. While majority of the previous works have been concentrated on anti-dot arrays with a single magnetic layer, there has been little work on multilayered anti-dot arrays. In this work, we report on study of the magnetic properties of bilayered anti-dot system consisting of upper perforated Co layer of 40 nm and lower continuous Ni layer of 5 nm thick, fabricated by photolithography and wet-etching processes. The magnetic hysteresis (M-H) loops were measured with a superconducting-quantum-interference-device (SQUID) magnetometer (Quantum Design: MPMS). For comparison, investigations on continuous Co thin film and single-layer Co anti-dot arrays were also performed. The magnetic-domain configuration has been measured by using a magnetic force microscope (PSIA: XE-100) equipped with magnetic tips (Nanosensors). An external electromagnet was employed while obtaining the MFM images. The MFM images revealed well-defined periodic domain networks which arise owing to the anisotropies such as magnetic uniaxial anisotropy, configurational anisotropy, etc. The inclusion of holes in a uniform magnetic film and the insertion of a uniform thin Ni layer, drastically affected the coercivity as compared with single Co anti-dot array, without severely affecting the saturation magnetization ($M_s$). The observed changes in the magnetic properties are closely related to the patterning that hinders the domain-wall motion as well as to the magneto-anisotropic bilayer structure.

• Journal of the Korean Solar Energy Society
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• v.31 no.1
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• pp.37-43
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• 2011

In this paper, the optimized doping condition of crystalline silicon solar cells with $156{\times}156\;mm^2$ area was studied. To optimize the drive-in temperature in the doping process, the other conditions except variable drive-in temperature were fixed. These conditions were obtained in previous studies. After etching$7\;{\mu}m$ of the surface to form the pyramidal structure, the silicon nitride deposited by the PECVD had 75~80nm thickness and 2 to 2.1 for a refractive index. The silver and aluminium electrodes for front and back sheet, respectively, were formed by screen-printing method, followed by firing in 400-425-450-550-$850^{\circ}C$ five-zone temperature conditions to make the ohmic contact. Drive-in temperature was changed in range of $830^{\circ}C$ to $890^{\circ}C$to obtain the sheet resistance $30{\sim}70\;{\Omega}/{\box}$ with $10\;\Omega}/{\box}$ intervals. Solar cell made in $890^{\circ}C$ as the drive-in temperature revealed 17.1% conversion efficiency which is best in this study. This solar cells showed $34.4\;mA/cm^2$ of the current density, 627 mV of the open circuit voltage and 79.3% of the fill factor.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.30A no.12
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• pp.51-59
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• 1993

A 4${\times}10^{19}cm^{3}$ carbon-doped base AlGaAs/GaAs HBY was grown using carbontetracholoride(CCl$_4$) by atmospheric pressure MOCVD. Abruptness of emitter-base junction was characterized by SIMS(secondary ion mass spectorscopy) and the doping concentration of base layer was confirmed by DXRD(double crystal X-ray diffractometry). Mesa-type HBTs were fabricated using wet etching and lift-off technique. The base sheet resistance of R$_{sheet}$=550${\Omega}$/square was measured using TLM(transmission line model) method. The fabricated transistor achieved a collector-base junction breakdown voltage of BV$_{CBO}$=25V and a critical collector current density of J$_{O}$=40kA/cm$^2$ at V$_{CE}$=2V. The 50$\times$100$\mu$$^2$ emitter transistor showed a common emitter DC current gain of h$_{FE}$=30 at a collector current density of JS1CT=5kA/cm$^2$ and a base current ideality factor of ηS1EBT=1.4. The high frequency characterization of 5$\times$50$\mu$m$^2$ emitter transistor was carried out by on-wafer S-parameter measurement at 0.1~18.1GHz. Current gain cutoff frequency of f$_{T}$=27GHz and maximum oscillation frequency of f$_{max}$=16GHz were obtained from the measured Sparameter and device parameters of small-signal lumped-element equivalent network were extracted using Libra software. The fabricated HBT was proved to be useful to high speed and power spplications.

• Journal of the Korean Magnetics Society
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• v.13 no.4
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• pp.160-164
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• 2003

The external magnetic field dependency of the impedance, resistance, and inductance of the meander pattern fabricated by using Co-base amorphous ribbon has been investigated in the frequency range of 300 ㎑∼1 ㎓. The amorphous ribbon was patterned to the meander pattern through conventional photolithography and wet etching process. The extremely high sensitivity in impedance changing ratio by external magnetic field was observed. This is due to the transverse magnetic anisotropy the pattern which was induced by magnetic field annealing. The impedance had peak value at the external field of -13 Oe and the impedance changing ratio 100 ${\times}$ (Z$\_$13/-Z$\_$0/)/Z$\_$0/) was about 210％ at the frequency of 50 MHz.

• Journal of the Korean Vacuum Society
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• v.20 no.3
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• pp.182-188
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• 2011

Polysilazane and polymethylsilazane based precursor films were deposited on Si-substrate by spin-coating, subsequently annealed at $150{\sim}850^{\circ}C$, and characterized. Structural analysis, shrink, compositional change, etch rate, and gap-filling were observed. Annealing the precursor films led to formation of spin-on dielectric films. C-containing precursor films showed that less loss of N, H, and C while less gain of O than that of C-free precursor films at $400^{\circ}C$, but more loss of N, H, and C while more gain of O at $850^{\circ}C$. Thus polysilazane based precursor films exhibited less reduction in thickness of 14.5% than silazane based one of 15.6% at $400^{\circ}C$ but more 37.4% than 19.4% at $850^{\circ}C$. FTIR indicated that C induced smaller amount of Si-O bond, non-uniform property, and lower resistance to chemical etching.