• 한국전기전자재료학회논문지
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• 제31권3호
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• pp.129-134
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• 2018

Herein, we report the manufacture of high-performance, ambipolar organic field-effect transistors (OFETs) and complementary-like electronic circuitry based on a blended, polymeric, semiconducting film. Relatively high and well-balanced electron and hole mobilities were achieved by incorporating a small amount of ionic additives. The equivalent P-channel and N-channel properties of the ambipolar OFETs enabled the manufacture of complementary-like inverter circuits with a near-ideal switching point, high gain, and good noise margins, via a simple blanket spin-coating process with no additional patterning of each active P-type and N-type semiconductor layer.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.305-305
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• 2010

It is known that a pulse of electrons of high kinetic energy (1-3 eV) in metals can be generated with the deposition of external energy to the surface such as in the absorption of light or in exothermic chemical processes. These energetic electrons are not in thermal equilibrium with the metal atoms and are called "hot electrons" The concept of photon energy conversion to hot electron flow was suggested by Eric McFarland and Tang who directly measured the photocurrent on gold thin film of metal-semiconductor ($TiO_2$) Schottky diodes [1]. In order to utilize this scheme, we have fabricated metal-semiconductor Schottky diodes that are made of Pt or Au as a metallic layer, Si or $TiO_2$ as a semiconducting substrate. The Pt/$TiO_2$ and Pt/Si Schottky diodes are made by PECVD (Plasma Enhanced Chemical Vapor Deposition) for $SiO_2$, magnetron sputtering process for $TiO_2$, e-beam evaporation for metallic layers. Metal shadow mask is made for device alignment in device fabrication process. We measured photocurrent on Pt/n-Si diodes under AM1.5G. The incident photon to current conversion efficiency (IPCE) at different wavelengths was measured on the diodes. We also show that the steady-state flow of hot electrons generated from photon absorption can be directly probed with $Pt/TiO_2$ Schottky diodes [2]. We will discuss possible approaches to improve the efficiency of photon energy conversion.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.207-207
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• 2012

Si quantum dot (QD) imbedded in a $SiO_2$ matrix is a promising material for the next generation optoelectronic devices, such as solar cells and light emission diodes (LEDs). However, low conductivity of the Si quantum dot layer is a great hindrance for the performance of the Si QD-based optoelectronic devices. The effective doping of the Si QDs by semiconducting elements is one of the most important factors for the improvement of conductivity. High dielectric constant of the matrix material $SiO_2$ is an additional source of the low conductivity. Active doping of B was observed in nanometer silicon layers confined in $SiO_2$ layers by secondary ion mass spectrometry (SIMS) depth profiling analysis and confirmed by Hall effect measurements. The uniformly distributed boron atoms in the B-doped silicon layers of $[SiO_2(8nm)/B-doped\;Si(10nm)]_5$ films turned out to be segregated into the $Si/SiO_2$ interfaces and the Si bulk, forming a distinct bimodal distribution by annealing at high temperature. B atoms in the Si layers were found to preferentially substitute inactive three-fold Si atoms in the grain boundaries and then substitute the four-fold Si atoms to achieve electrically active doping. As a result, active doping of B is initiated at high doping concentrations above $1.1{\times}10^{20}atoms/cm^3$ and high active doping of $3{\times}10^{20}atoms/cm^3$ could be achieved. The active doping in ultra-thin Si layers were implemented to silicon quantum dots (QDs) to realize a Si QD solar cell. A high energy conversion efficiency of 13.4% was realized from a p-type Si QD solar cell with B concentration of $4{\times}1^{20}atoms/cm^3$. We will present the diffusion behaviors of the various dopants in silicon nanostructures and the performance of the Si quantum dot solar cell with the optimized structures.

• Bulletin of the Korean Chemical Society
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• 제30권10호
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• pp.2371-2376
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• 2009

Three phenoxazine-based conjugated polymers, namely, the aryl substituted phenoxazine homopolymer (P1) as well as the dimeric phenoxazine-fluorene (P2) and phenoxazine-bithiophene (P3) copolymers, were synthesized via the Ni(0) mediated Yamamoto reaction and the palladium-catalyzed Suzuki coupling reaction. The weight-averaged molecular weights ($M_w$) of P1, P2, and P3 were found to be 27,000, 22,000, and 15,000, respectively, and their polydispersity indices were 3.6, 1.8, and 2.1. All the polymers were soluble in common organic solvents such as chloroform, toluene, and so on. The UV-visible absorption maxima for P1, P2, and P3 in the film state were located at 421, 415 and 426 nm, respectively, and the ionization potentials of the polymers ranged between 4.90 and 5.12 eV. All the studied phenoxazine-based polymers exhibited amorphous behavior, as confirmed by X-ray diffraction (XRD) and atomic force microscopy (AFM) studies. Thin film transistors were fabricated using the top-contact geometry. P1 showed much better thin-film-transistor performance than P2 or P3: A thin film of P1 gave a saturation mobility of 0.81 ${\times}\;10^{-3}\;cm^2V^{-1}s^{-1}$ and an on/off ratio of about $10^2$.

• 한국재료학회지
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• 제24권8호
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• pp.434-442
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• 2014

Serious environmental problems have been caused by the greenhouse effect due to carbon dioxide($CO_2$) or nitrogen oxides($NO_x$) generated by the use of fossil fuels, including oil and liquefied natural gas. Many countries, including our own, the United States, those of the European Union and other developed countries around the world; have shown growing interest in clean energy, and have been concentrating on the development of new energy-saving materials and devices. Typical non-fossil-fuel sources include solar cells, wind power, tidal power, nuclear power, and fuel cells. In particular, organic solar cells(OSCs) have relatively low power-conversion efficiency(PCE) in comparison with inorganic(silicon) based solar cells, compound semiconductor solar cells and the CIGS [$Cu(In_{1-x}Ga_x)Se_2$] thin film solar cells. Recently, organic cell efficiencies greater than 10 % have been obtained by means of the development of new organic semiconducting materials, which feature improvements in crystalline properties, as well as in the quantum-dot nano-structure of the active layers. In this paper, a brief overview of solar cells in general is presented. In particular, the current development status of the next-generation OSCs including their operation principle, device-manufacturing processes, and improvements in the PCE are described.

• 한국분말재료학회지
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• 제22권5호
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• pp.321-325
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• 2015

The triboelectric property of a material is important to improve an efficiency of triboelectric generator (TEG) in energy harvesting from an ambient energy. In this study, we have studied the TEG property of a semiconducting $SnO_2$ which has yet to be explored so far. As a counter triboelectric material, PET and glass are used. Vertical contact mode is utilized to evaluate the TEG efficiency. $SnO_2$ thin film is deposited by atomic layer deposition on bare Si wafer for various thicknesses from 5.2 nm to 34.6 nm, where the TEG output is increased from 13.9V to 73.5V. Triboelectric series are determined by comparing the polarity of output voltage of 2 samples among $SnO_2$, PET, and glass. In conclusion, $SnO_2$, as an intrinsic n-type material, has the most strong tendency to be positive side to lose the electron and PET has the most strong tendency to be negative side to get the electron, and glass to be between them. Therefore, the $SnO_2$-PET combination shows the highest TEG efficiency.

• 공업화학
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• 제3권1호
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• pp.88-99
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• 1992

광 전기분해시 양극으로 사용되는 산화티타늄 반도체 전극의 안정성을 증대시키고 효율향상을 위해서 순수한 티타늄 전극을 양극 산화법, 전기로 산화법, 불꽃 산화법으로 산화 피막을 제조하였으며 In을 Ti와 $TiO_2$소지에 전기도금을 한 후 전기로 산화법으로 혼합 산화물을 제조하였다. 또한 $Al_2O_3$ 와 NiO는 진공증착 방법을 이용하여 Ti 소지위에 증착시킨 후 전기로 산화법을 이용하여 혼합 산화물을 제조하였다. 에너지변환 효율(${\eta}$)은 인가전위에 따라서 다른 값을 갖는데 0.6V로 계산하여 보면 $1200^{\circ}C$의 불꽃으로 2분간 산화시킨 전극이 0.98%로 가장 큰 값을 가졌으며 양극 산화법으로 제조한 전극의 ${\eta}$는 0.14%로 작은 값을 보여 주었다. 한편 $800^{\circ}C$ 전기로에서 10분간 산화시킨 전극의 ${\eta}$는 0.57%로 띠간 에너지는 2.9eV로 나타났다. 한편 In을 Ti 및 $TiO_2$ 소지위에 전기도금시킨 전극의 ${\eta}$는 0.8%였으며 인가전위가 증가함에 따라서 ${\eta}$는 증가하였다. 그러나 $Al_2O_3$와 NiO를 Ti소지위에 진공증착시킨 전극의 ${\eta}$는 다른 전극들에 비해서 가장 낮은 값을 나타내었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.289-289
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• 2013

While there are plenty of studies on synthesizing semiconducting germanium nanowires (Ge NWs) by vapor-liquid-solid (VLS) process, it is difficult to inject dopants into them with uniform dopants distribution due to vapor-solid (VS) deposition. In particular, as precursors and dopants such as germane ($GeH_4$), phosphine ($PH_3$) or diborane ($B_2H_6$) incorporate through sidewall of nanowire, it is hard to obtain the structural and electrical uniformity of Ge NWs. Moreover, the drastic tapered structure of Ge NWs is observed when it is synthesized at high temperature over $400^{\circ}C$ because of excessive VS deposition. In 2006, Emanuel Tutuc et al. demonstrated Ge NW pn junction using p-type shell as depleted layer. However, it could not be prevented from undesirable VS deposition and it still kept the tapered structures of Ge NWs as a result. Herein, we adopt $C_2H_2$ gas in order to passivate Ge NWs with carbon sheath, which makes the entire Ge NWs uniform at even higher temperature over $450^{\circ}C$. We can also synthesize non-tapered and uniformly doped Ge NWs, restricting incorporation of excess germanium on the surface. The Ge NWs with carbon sheath are grown via VLS process on a $Si/SiO_2$ substrate coated 2 nm Au film. Thin Au film is thermally evaporated on a $Si/SiO_2$ substrate. The NW is grown flowing $GeH_4$, HCl, $C_2H_2$ and PH3 for n-type, $B_2H_6$ for p-type at a total pressure of 15 Torr and temperatures of $480{\sim}500^{\circ}C$. Scanning electron microscopy (SEM) reveals clear surface of the Ge NWs synthesized at $500^{\circ}C$. Raman spectroscopy peaked at about ~300 $cm^{-1}$ indicates it is comprised of single crystalline germanium in the core of Ge NWs and it is proved to be covered by thin amorphous carbon by two peaks of 1330 $cm^{-1}$ (D-band) and 1590 $cm^{-1}$ (G-band). Furthermore, the electrical performances of Ge NWs doped with boron and phosphorus are measured by field effect transistor (FET) and they shows typical curves of p-type and n-type FET. It is expected to have general potentials for development of logic devices and solar cells using p-type and n-type Ge NWs with carbon sheath.

• 접착 및 계면
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• 제24권2호
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• pp.64-68
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• 2023

유기 전계효과 트랜지스터(OFETs)는 유기 반도체를 채널층으로 하여 유연한 기판에서 제작할 수 있어 차세대 전자 소자 분야에서 각광받고 있다. 특히 diketopyrrolopyrrole (DPP) 계열 고분자 반도체는 다른 유기 반도체에 비하여 전하 이동도가 높아 활발하게 활용되고 있지만 여전히 무기 반도체에 비하여 낮아, 유기반도체의 전하 이동도를 향상시키기 위한 여러 연구가 진행되고 있다. 본 연구에서는 절연체와 고분자 반도체사이에 자가 조립 단층 박막을 형성하여 표면 에너지를 제어함으로써 고분자 반도체의 결정성을 향상시키고자 하였다. 이를 통해 고분자 박막의 결정성을 성공적으로 제어할 수 있었고, 유기 반도체의 전하 이동도를 3.57×10^-3 cm²V^-1s^-1에서 5.12×10^-2 cm²V^-1s^-1로 약 14배 향상시킬 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.174-174
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• 2000

A strong antiferromagnetic coupling in Fe/Si multilayered films (MLF) had been recently discovered and much consideration has been given to whether the coupling in the Fe/Si MLF system has the same origin as the metal/metal MLF. Nevertheless, the nature of the interfacial ron silicide is still controversial. On one hand, a metal/ semiconductor structure was suggested with a narrow band-gap semiconducting $\varepsilon$-FeSi spacer that mediates the coupling. However, some features show that the nature of coupling can be well understood in terms of the conventional metal/metal multilayered system. It is well known that both magneto-optical (MO) and optical properties of a metal depend strongly on their electronic structure that is also correlated with the atomic and chemical ordering. In this study, the nature of the interfacial regions is the Fe/Si multilayers has been investigated by the experimental and computer-simulated MO and optical spectroscopies. The Fe/Si MLF were prepared by rf-sputtering onto glass substrates at room temperature with the number of repetition N=50. The thickness of Fe sublayer was fixed at 3.0nm while the Si sublayer thickness was varied from 1.0 to 2.0 nm. The topmost layer of all the Fe/Si MLF is Fe. In order to carry out the computer simulations, the information on the MO and optical parameters of the materials that may constitute a real multilayered structure should be known in advance. For this purpose, we also prepared Fe, Si, FeSi2 and FeSi samples. The structural characterization of Fe/Si MLF was performed by low- and high -angle x-ray diffraction with a Cu-K$\alpha$ radiation and by transmission electron microscopy. A bulk $\varepsilon$-FeSi was also investigated. The MO and optical properties were measured at room temperature in the 1.0-4.7 eV energy range. The theoretical simulations of MO and optical properties for the Fe/Si MLF were performed by solving exactly a multireflection problem using the scattering matrix approach assuming various stoichiometries of a nonmagnetic spacer separating the antiferromagnetically coupled Fe layers. The simulated spectra of a model structure of FeSi2 or $\varepsilon$-FeSi as the spacer turned out to fail in explaining the experimental spectra of the Fe/Si MLF in both intensity and shape. Thus, the decisive disagreement between experimental and simulated MO and optical properties ruled out the hypothesis of FeSi2 and $\varepsilon$-FeSi as the nonmagnetic spacer. By supposing the spontaneous formation of a metallic ζ-FeSi, a reasonable agreement between experimental and simulated MO and optical spectra was obtained.