• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.356.1-356.1
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• 2014

The Isolation of few-layered transition metal dichalcogenides has mainly been performed by mechanical and chemical exfoliation with very low yields. in particular, the two-dimensional layer of molybdenum disulfide (MoS2) has recently attracted much interest due to its direct-gap property and potential application in optoelectronics and energy harvesting. However, the synthetic approach to obtain high-quality and large-area MoS2 atomic thin layers is still rare. In this account, a controlled thermal reduction-sulfurization method is used to synthesize large-MoOx thin films are first deposited on Si/SiO2 substrates, which are then sulfurized (under vacuum) at high temperatures. Samples with different thicknesses have been analyzed by Raman spectroscopy and TEM, and their photoluminescence properties have been evaluated. We demonstrated the presence of mono-, bi-, and few-layered MoS2 on as-grown samples. It is well known that the electronic structure of these materials is very sensitive to the number of layer, ranging from indirect band gap semiconductor in the bulk phase to direct band gap semiconductor in monolayers. This synthetic approach is simple, scalable, and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS2 films are transferable to arbitrary substrates, providing great opportunities to make layered composites by stacking various atomically thin layers.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.398.1-398.1
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• 2014

The $Cu_2ZnSnSe_4$ (CZTSe) thin films solar cell is one of the next generation candidates for photovoltaic materials as the absorber of thin film solar cells because it has optimal bandgap (Eg=1.0eV) and high absorption coefficient of $10^4cm^{-1}$ in the visible length region. More importantly, CZTSe consists of abundant and non-toxic elements, so researches on CZTSe thin film solar cells have been increasing significantly in recent years. CZTSe thin film has very similar structure and properties with the CIGS thin film by substituting In with Zn and Ga with Sn. In this study, As-deposited CZTSe thin films have been deposited onto soda lime glass (SLG) substrates at different deposition condition using Pulsed Laser Deposition (PLD) technique without post-annealing process. The effects of deposition conditions (deposition time, deposition temperature) onto the structural, compositional and optical properties of CZTSe thin films have been investigated, without experiencing selenization process. The XRD pattern shows that quaternary CZTSe films with a stannite single phase. The existence of (112), (204), (312), (008), (316) peaks indicates all films grew and crystallized as a stannite-type structure, which is in a good agreement with the diffraction pattern of CZTSe single crystal. All the films were observed to be polycrystalline in nature with a high (112) predominant orientation at $2{\theta}{\sim}26.8^{\circ}$. The carrier concentration, mobility, resistivity and optical band gap of CZTSe thin films depending on the deposition conditions. Average energy band gap of the CZTSe thin films is about 1.3 eV.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.203-203
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• 2014

Due to the electrical properties such as narrow bandgap and high carrier mobility, indium antimonide (InSb) has attracted a lot of attention recently. For the fabrication of electronic or photonic devices, an etching process is required. However, during etching process, enegetic ions can induce structural damages on the bombarded surface. Especially, InSb has a very weak binding energy between In atom and Sb stom, it can be easily damaged by impingement of ions. In the previous work, to evaluate the surface properties after Ar ion beam etching, the plasma-induced structural damage on the etched InSb(100) surface had been examined by resonant Raman spectroscopy. As a result, we demonstrated the relation between the enhanced transverse optical(TO) peak in the Raman spectrum and the ion-induced structral damage near the InSb surface. In this work, the annealing effect on the etched InSb(100) surface has investigated. Annealing process was performed at $450^{\circ}C$ for 10 minute under antimony ambient. As-etched InSb(100) surface had shown a strongly enhanced TO scattering intensity in the Raman spectrum. However, the annealing process with antimony flowing caused the intensity to recover due to the structural reordering and the reduction of antimony vacancies. It proves that the origin of enhanced TO scattering is Sb vacancies. Furthermore, it shows that etching-induced damage can be cured effectively by the following annealing process under Sb ambient.

• 한국재료학회지
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• 제23권6호
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• pp.304-308
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• 2013

The effect of a sputter deposition sequence of Cu, Zn, and Sn metal layers on the properties of $Cu_2ZnSnS_4$ (CZTS) was systematically studied for solar cell applications. The set of Cu/Sn/Zn/Cu multi metal films was deposited on a Mo/$SiO_2$/Si wafer using dc sputtering. CZTS films were prepared through a sulfurization process of the Cu/Sn/Zn/Cu metal layers at $500^{\circ}C$ in a $H_2S$ gas environment. $H_2S$ (0.1%) gas of 200 standard cubic centimeters per minute was supplied in the cold-wall sulfurization reactor. The metal film prepared by one-cycle deposition of Cu(360 nm)/Sn(400 nm)/Zn(400 nm)/Cu(440 nm) had a relatively rough surface due to a well-developed columnar structure growth. A dense and smooth metal surface was achieved for two- or three-cycle deposition of Cu/Sn/Zn/Cu, in which each metal layer thickness was decreased to 200 nm. Moreover, the three-cycle deposition sample showed the best CZTS kesterite structures after 5 hr sulfurization treatment. The two- and three-cycle Cu/Sn/Zn/Cu samples showed high-efficient photoluminescence (PL) spectra after a 3 hr sulfurization treatment, wheres the one-cycle sample yielded poor PL efficiency. The PL spectra of the three-cycle sample showed a broad peak in the range of 700-1000 nm, peaked at 870 nm (1.425 eV). This result is in good agreement with the reported bandgap energy of CZTS.

• 멤브레인
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• 제29권6호
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• pp.299-307
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• 2019

광촉매는 물에서 유기 염료를 분해하는 친환경적 기술이다. 산화 텅스텐은 이산화 티타늄에 비해 더 작은 밴드갭을 지니고 있어 광촉매 나노물질로서 활발히 연구되고 있다. 계층적 구조의 합성, 백금 도핑, 나노 복합물 또는 다른 반도체와의 결합 등이 광촉매 분해 효율을 향상시키는 방법들로 연구되고 있다. 이들 방법들은 광 파장의 적색편이를 유도하여 전자 이동, 전자-정공 쌍의 형성과 재결합에 영향을 미친다. 산화 텅스텐의 형태 개질을 통해 앞서 언급한 광촉매 분해 효율을 향상시키는 방법들과 합성에 대해 분석하였으며 금속 산화물과 탄소 복합재를 결합하는 방법이 새로운 물질의 합성이 필요없으며 가장 효율적인 방법으로 조사되었다. 이러한 광촉매 기술은 수처리 분리막기술과 모듈화하여 정수처리 목적으로 사용될 수 있다.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2012년도 추계학술대회
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• pp.838-841
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• 2012

본 논문에서는 온도변화에 따른 회로 손상이나 성능 저하를 피하기 위해서 회로 안에 내장할 수 있는 온도 센서 회로를 설계하였다. 일반적인 PTAT회로를 사용하여 온도감지를 하고, 스위치를 내장시켜 회로 동작이 불가능할 정도로 IC 내부 온도가 높을 때는 절전모드로 동작하게 하였다. 또한, 전류미러 및 캐스코드회로를 사용함으로서 전류 정합특성을 향상시켰다. 시뮬레이션 결과 $75^{\circ}C$일 경우 약 1V, $130^{\circ}C$일 경우 1.75V를 출력전압을 발생하였으며, 절전모드의 경우 0V~7uV까지 즉 거의 0V에 가까운 출력전압을 발생함을 확인 할 수 있었다.

• 한국정보통신학회논문지
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• 제21권5호
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• pp.861-868
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• 2017

도핑 되지 않은 반 절연 LEC GaAs내의 EL2와 얕은 준위 분포를 영상화하기 위해 대역단 적외선 영상 기법을 활용했다. 대역단 적외선 투사 매핑에 근거한 본 기법은 분석 속도가 빠르고 비파괴적인 방법이다. EL2 흡수 영상이 콘트라스트 반전되는 대역단 부근에 대한 정량적인 해석은 아직 보고되지 않고 있다. 본 논문은 대역단 부근에서 영상의 특정 부분(cell, wall)에 대한 포토퀀칭 메커니즘의 스펙트럼-, 공간- 및 온도- 종속성을 논하고 있다. 결함 부분별(EL2w, EL2b)로 포토퀀칭 개시점이 다른 것은 불순물 종류의 차이로 인한 서로 다른 전기적 작용에 기인한 것으로 해석할 수 있다. 전위(dislocation) 밀도가 높은 곳에서는 EL2b 밀도는 약간 적은 반면 EL2w 밀도는 보다 많다는 것을 정량적 해석으로부터 확인 했다.

• 한국통신학회논문지
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• 제40권8호
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• pp.1622-1630
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• 2015

본 연구에서는 원형편파를 양방향으로 복사하는 등각 스파이럴 안테나에 EBG(electromagnetic bandgap) 반사판을 사용하여 단일 방향으로 복사가 발생하게 하였다. EBG 반사판에서 스파이럴 암 까지의 높이가 가장 낮은 동작 주파수의 0.07 파장 높이로 한 경우, 원형편파의 축비가 손상되는 것이 발생하였다. 본 논문에서는, +z 방향에서의 동일 편파인 우선 원형 편파를 발생시키는 $E_{\theta},E_{\phi}$의 크기와 시간 위상차를 해석하여, 전 주파수 영역에서 축비를 개선하는 조건을 제시하였다. 그 결과, 3 ~ 10[dB] 주파수 범위에서 축비는 3[dB] 이하이고, 이득은 자유공간에서의 양방향 복사와 비교해서 약 3[dB] 정도 개선되었고, $S_{11}$은 전 주파수 영역에서 -10[dB]이하를 얻었다.

• 한국표면공학회지
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• 제51권2호
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• pp.126-132
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• 2018

SnS thin films with different substrate temperatures ($150 {\sim}300^{\circ}C$) as process parameters were grown on soda-lime glass substrates by RF magnetron sputtering. The effects of substrate temperature on the structural and optical properties of SnS thin films were investigated by X-ray diffraction (XRD), Raman spectroscopy (Raman), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and Ultraviolet-visible-near infrared spectrophotometer (UV-Vis-NIR). All of the SnS thin films prepared at various substrate temperatures were polycrystalline orthorhombic structures with (111) planes preferentially oriented. The diffraction intensity of the (111) plane and the crystallite size were improved with increasing substrate temperature. The three major peaks (189, 222, $289cm^{-1}$) identified in Raman were exactly the same as the Raman spectra of monocrystalline SnS. From the XRD and Raman results, it was confirmed that all of the SnS thin films were formed into a single SnS phase without impurity phases such as $SnS_2$ and $Sn_2S_3$. In the optical transmittance spectrum, the critical wavelength of the absorption edge shifted to the long wavelength region as the substrate temperature increased. The optical bandgap was 1.67 eV at the substrate temperature of $150^{\circ}C$, 1.57 eV at $200^{\circ}C$, 1.50 eV at $250^{\circ}C$, and 1.44 eV at $300^{\circ}C$.

• Current Photovoltaic Research
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• 제4권4호
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• pp.150-154
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• 2016

Mg and In co-doped ZnO (MIZO) thin films with transparent conducting characteristics were successfully prepared on glass substrates by RF magnetron sputtering technique. The Influence of different substrate temperature (from RT to $400^{\circ}C$) on the structural, morphological, electrical, and optical properties of MIZO thin films were investigated. The MIZO thin film prepared at the substrate temperature of $350^{\circ}C$ showed the best electrical characteristics in terms of the carrier concentration ($4.24{\times}10^{20}cm^{-3}$), charge carrier mobility ($5.01cm^2V^{-1}S^{-1}$), and a minimum resistivity ($1.24{\times}10^{-4}{\Omega}{\cdot}cm$). The average transmission of MIZO thin films in the visible range was over 80% and the absorption edges of MIZO thin films were very sharp. The bandgap energy of MIZO thin films becomes wider from 3.44 eV to 3.6 eV as the substrate temperature increased from RT to $350^{\circ}C$. However, Band gap energy of MIZO thin film was narrow at substrate temperature of $400^{\circ}C$.