• Korean Journal of Materials Research
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• v.33 no.11
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• pp.491-496
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• 2023

As the demand for p-type semiconductors increases, much effort is being put into developing new p-type materials. This demand has led to the development of novel new p-type semiconductors that go beyond existing p-type semiconductors. Copper iodide (CuI) has recently received much attention due to its wide band gap, excellent optical and electrical properties, and low temperature synthesis. However, there are limits to its use as a semiconductor material for thin film transistor devices due to the uncontrolled generation of copper vacancies and excessive hole doping. In this work, p-type CuI semiconductors were fabricated using the chemical vapor deposition (CVD) process for thin-film transistor (TFT) applications. The vacuum process has advantages over conventional solution processes, including conformal coating, large area uniformity, easy thickness control and so on. CuI thin films were fabricated at various deposition temperatures from 150 to 250 ℃ The surface roughness root mean square (RMS) value, which is related to carrier transport, decreases with increasing deposition temperature. Hall effect measurements showed that all fabricated CuI films had p-type behavior and that the Hall mobility decreased with increasing deposition temperature. The CuI TFTs showed no clear on/off because of the high concentration of carriers. By adopting a Zn capping layer, carrier concentrations decreased, leading to clear on and off behavior. Finally, stability tests of the PBS and NBS showed a threshold voltage shift within ±1 V.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.69-70
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• 2012

본 발표에서는 최근 과학계에서 대두되어 전 세계적으로 폭발적인 연구가 수행되고 있는 신소재 그래핀에 대한 전반적인 소개와 현재 동향 및 미래 응용가능성에 대해 언급하고자 한다. 그래핀 연구관련 다양한 분야가 있으나, 본 세미나에서는 CVD로 합성하는 방법에 대한 개념 그리고 합성한 대면적 그래핀의 다양한 응용 분야들과 본인이 수행했던 연구결과물들을 몇 가지 소개하고자 한다. 구체적인 내용으로는 CVD에 의한 대면적 그래핀의 합성, 합성된 그래핀의 전사 및 패터닝 공정, CVD 그래핀의 도핑 및 다양한 물성분석, 그리고 그래핀 파이버, 히터 및 태양전지 응용 연구 등이다. 특히, 그래핀의 연구에 있어서 가장 중요한 이슈가 아주 품질이 좋은 그래핀 시료를 준비하는 것인데, 이는 좋은 그래핀을 합성해야 하는 것은 물론이고, 깨끗한 전사공정이 수반되어야 가능하다. 따라서 깨끗한 전사공정을 통해 품질 좋은 그래핀을 준비하는 상세한 과정들과 이에 대한 결과물들을 언급하겠다. 이어서 최근에는 CVD 방법에 의한 질소원자가 도핑된 그래핀의 직접 합성을 시도하였고, 이렇게 도핑된 그래핀 시료에 대해, 다양한 분석 장비들(Raman, STM, XPS & XAS)을 이용하여 기초물성들을 측정하고 비교 분석하였다. 끝으로 최근에 수행중인 그래핀과 기타 다른 나노소재(VO2, h-BN etc.)들과 접목된 hybrid 나노소재 연구에 대한 내용을 간략히 소개하고 발표를 마무리하겠다.

• Korean Journal of Materials Research
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• v.24 no.9
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• pp.451-457
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• 2014

We developed a high-performance methane gas sensor based on a $SnO_2$ hollow hemisphere array structure of nano-thickness. The sensor structures were fabricated by sputter deposition of Sn metal over an array of polystyrene spheres distributed on a planar substrate, followed by an oxidation process to oxidize the Sn to $SnO_2$ while removing the polystyrene template cores. The surface morphology and structural properties were examined by scanning electron microscopy. An optimization of the structure for methane sensing was also carried out. The effects of oxidation temperature, film thickness, gold doping, and morphology were examined. An impressive response of ~220% was observed for a 200 ppm concentration of $CH_4$ gas at an operating temperature of $400^{\circ}C$ for a sample fabricated by 30 sec sputtering of Sn, and oxidation at $800^{\circ}C$ for 2 hr in air. This high response was enabled by the open structure of the hemisphere array thin films.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.87.2-87.2
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• 2015

Transparent conductors are commonly used in photoelectric devices, where the electric energy converts to light energy or vice versa. Energy consumption devices, such as LEDs, Displays, Lighting devices use the electrical energy to generate light by carrier recombination. Meanwhile, solar cell is the only device to generate electric energy from the incident photon. Most photoelectric devices require a transparent electrode to pass the light in or out from a device. Beyond the passive role, transparent conductors can be employed to form Schottky junction or heterojunction to establish a rectifying current flow. Transparent conductor-embedded heterojunction device provides significant advantages of transparent electrode formation, no need for intentional doping process, and enhanced light-reactive surface area. Herein, we present versatile applications of transparent conductors, such as NiO, ZnO, ITO in photoelectric devices of solar cells and photodetectors for high-performing UV or IR detection. Moreover, we also introduce the growth of transparent ITO nanowires by sputtering methods for large scale application.

• Korean Journal of Materials Research
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• v.19 no.2
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• pp.95-101
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• 2009

Glass ceramics were made from coal bottom ash by adding CaO and $Li_2O$ as glass modifiers and $TiO_2$ as a nucleating agent in a process of melting and quenching followed by a thermal treatment. The surface of the glass ceramics has 1.6 times more $Li_2O$ compared to the inner matrix. When $TiO_2$ was not added or when only 2 wt% was added, the surface parts of the glass ceramics were crystalline with a thickness close to $130{\mu}m$. In addition, the matrixes showed only the glass phase and not the crystalline phase. However, doping of $TiO_2$ from 4 wt% to 10 wt% began to create small crystalline phases in the matrix with an increase in the quantity of the crystalline. The matrix microstructure of glass ceramics containing $TiO_2$ in excess of 8 wt% was a mixture of dark-gray crystalline and white crystalline parts. These two parts had no considerable difference in terms of composition. It was thought that the crystallization mechanism affects the crystal growth, direction and shape and rather than the existence of two types of crystals.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.115-115
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• 2009

Current sensing in power semiconductors involves sensing of over-current in order to protect the device from harsh conditions. This technique is one of the most important functions in stabilizing power semiconductor device modules. The Power MOSFET is very efficient method with low power consumption, fast sensing speed and accuracy. In this paper, we have analyzed the characteristics of proposed sense FET and optimized its electrical characteristics to apply conventional 40 V power MOSFET by numerical and simulation analysis. The proposed sense FET has the n-drift doping concentration $1.5\times10^{14}\;cm^{-3}$, size of $600\;{\mu}m^2$ with $4.5\;{\Omega}$, and off-state leakage current below $50\;{\mu}A$. We offer the layout of the proposed Power MOSFET to process actually. The offerd design and optimization methods are meaningful, which the methods can be applied to the power devices having various breakdown voltages for protection.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.7
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• pp.611-617
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• 2006

We report the preparation of N doped, p-type ZnO films by post-annealing in $NH_3$ ambient. The properties were examined by XRD, Hall-effect measurement, PL, and SIMS. ZnO films showed better crystallinity and electron concentration of $10^{15}-10^{17}/cm^3$ with post-annealing in $NH_3$ ambient. These films were converted to p-type ZnO by activation thermal annealing process at $800^{\circ}C$ under $N_2$ ambient. The electrical properties of the p-type ZnO showed a hole concentration of $1.06\times10^{16}/cm^3$, a mobility of $15.8cm^2/V{\cdot}s$, and a resistivity of $40.18\Omega{\cdot}cm$. The N doped ZnO films showed a strong photoluminescence peak at 3.306 eV at 13 K, which is closely related to neutral acceptor bound excitons of the p-type ZnO:N. In the SIMS spectra, the incorporation of nitrogen was confirmed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.8
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• pp.1719-1724
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• 2004

In this paper, we have proposed a new structure of LDMOST, which has been expected as a next generation RF power device, to improve the BV(Breakdown Voltage) characteristics. The proposed structure, named external field ring, is formed around a drift region by the three dimensional structure. The external field ring relieves the electric field in the drift region and improves the BV characteristics. By the three dimensional TCAD simulations, it was found that the BV of LDMOST was increased by the increase of the junction depth and doping concentration of the external field ring. Therefore, the BV characteristics of the LDMOST can be remarkably improved by addition of external field ring using an existing p+ sinker process.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.107-109
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• 2010

화석연료 사용으로 발생한 환경 문제와 에너지원 고갈로 생성된 새로운 청정에너지에 대한 중요성은 시간이 지나면서 더욱더 증가해 가고 있다. 청정에너지로 알려져 있는 많은 에너지원 중에 태양의 빛에너지를 전기적 에너지로 변환하여 활용하기 위한 연구는 상당히 많이 이루어지고 있다. 태양전지는 공해가 적고, 자원이 무한적이며 반영구적인 수명을 가지고 있어 일부 에너지 문제에 도움을 줄 수 있는 에너지원으로 평가받고 있다. 태양전지 기술 개발 방향은 전지의 변환효율을 높이는 방향과 공정 개발 원가를 줄이는방향의 연구들로 진행되어 오고 있다. 태양전지의 변환 효율은 새로운 물질의 개발과 공정 개발을 통하여 연구가 진행되고 있으며, 발전해온 많은 반도체 기술을 통하여 많은 부분 향상되어 오고 있다. 하지만, 반도체 기술 중에 도핑 기술은 많은 부분을 연구되어 왔지만, 아직도 쉽지만은 않은 기술이다. 이러한 기술이 안정화되지 않고서는 높은 효율의 태양전지의 개발은 어려운 일이다. 본 연구에서는 태양전지 제작하는 공정을 단순화 하고 그 공정 중에 어려운 공정으로 알려진 도핑공정에 대한 연구를 진행하였다. 대양한 공정 조건으로 연구가 이루어 졌으며, 그 변화에 따른 온도변화와 소스의 농도 변화에 따른 면저항 값을 분석하였다.

• Advances in environmental research
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• v.3 no.1
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• pp.11-28
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• 2014

Advanced oxidation processes using UV and catalysts like $TiO_2$ and ZnO have been recently applied for the photocatalytic degradation of MTBE in water. Attempts have been made to replace the UV radiation by the solar spectrum. This review intends to shed more light on the work that has been done so far in this area of research. The information provided will help in crystallizing the ideas required to shift the trend from UV photocatalysis to sunlight photocatalysis. The careful optimization of the reaction parameters and the type of the dopant employed are greatly responsible for any enhancement in the degradation process. The advantage of shifting from UV photocatalysts to visible light photocatalysts can be observed when catalysts like $TiO_2$ and ZnO are doped with suitable metals. Therefore, it is expected that in the near future, the visible light photocatalysis will be the main technique applied for the remediation of water contaminated with MTBE.