• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.351.1-351.1
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• 2014

In this study, we prepared the solution-based In-Ga-Zn oxide thin film transistors (IGZO TFTs) of multistacked active layer and characterized the gate bias instability by measuring the change in threshold voltage caused by stacking. The solutions for IGZO active layer were prepared by In:Zn=1:1 mole ratio and the ratio of Ga was changed from 20% to 30%. The TFTs with multistacked active layer was fabricated by stacking single, double and triple layers from the prepared solutions. As the number of active layer increases, the saturation mobility shows the value of 1.2, 0.8 and 0.6 (). The electrical properties have the tendency such as decreasing. However when gate bias VG=10 V is forced to gate electrode for 3000 s, the threshold voltage shift was decreased from 4.74 V to 1.27 V. Because the interface is formed between the each layers and this affected the current path to reduce the electrical performances. But the uniformity of active layer was improved by stacking active layer with filling the hole formed during pre-baking so the stability of device was improved. These results suggest that the deposition of multistacked active layer improve the stability of the device.

• Journal of the Korean Chemical Society
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• v.60 no.3
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• pp.194-202
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• 2016

Two conjugated semiconducting copolymers consisting of 4,7-bis(4-(2-ethylhexyl)-2-thiophene)-2,1,3-benzothiadiazole (DTBT) and benzo[1,2-b:4,5-b']dithiophene with 5-(2-ethylhexyl)-2,2'-bithiophene (BDTBT) or 5-(2-ethylhexylthio)- 2,2'-bithiophene (BDTBT-S) were designed and synthesized as donor materials for organic photovoltaic cells (OPVs). Alkylthio-substituted PBDTBT-S-DTBT showed a higher hole mobility and lower highest occupied molecular orbital (HOMO) energy level (by 0.08 eV) than the corresponding alkyl-substituted PBDTBT-DTBT. An OPV fabricated using PBDTBT-S-DTBT showed higher V_OC and J_SC values of 0.83 V and 7.56 mA/cm², respectively, than those of a device fabricated using PBDTBT-DTBT (0.74 V) leading to a power conversion efficiency of 2.05% under AM 1.5G 100 mW/cm² illumination.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.12
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• pp.847-851
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• 2015

The effects of Al-substitution on thermoelectric and charge transport properties of BiCuOSe compounds were investigated. The compounds were prepared by a solid-state reaction and consolidated by SPS (spark plasma sintering). In spite of the increase in the hole concentration with increasing Al amounts in BiCuOSe compound, the electrical conductivity at room temperature was kept constant due to the reduction of mobility. However, electrical conductivities of Al-substituted BiCuOSe compounds at elevated temperature (> 600 K) were higher than those of BiCuOSe, and this result was discussed in terms of it's the band gap energy. The Seebeck coefficient was drastically reduced when Al was substituted in Bi site, which indicated that the electronic structure was influenced by the Al-substitution into Bi-site.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.11-11
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• 2008

ZnO has a very large exciton binding energy (60 meV) as well as thermal and chemical stability, which are expected to allow efficient excitonic emission, even at room temperature. ZnO based electronic devices have attracted increasing interest as the backplanes for applications in the next-generation displays, such as active-matrix liquid crystal displays (AMLCDs) and active-matrix organic light emitting diodes (AMOLEDs), and in solid state lighting systems as a substitution for GaN based light emitting diodes (LEDs). Most of these electronic devices employ the electrical behavior of n-type semiconducting active oxides due to the difficulty in obtaining a p-type film with long-term stability and high performance. p-type ZnO films can be produced by substituting group V elements (N, P, and As) for the O sites or group I elements (Li, Na, and K) for Zn sites. However, the achievement of p-type ZnO is a difficult task due to self-compensation induced from intrinsic donor defects, such as O vacancies (Vo) and Zn interstitials ($Zn_i$), or an unintentional extrinsic donor such as H. Phosphorus (P) doped ZnO thin films were grown on c-sapphire substrates by radio frequency magnetron sputtering with various Ar/ $O_2$ gas ratios. Control of the electrical types in the P-doped ZnO films was achieved by varying the gas ratio with out post-annealing. The P-doped ZnO films grown at a Ar/ $O_2$ ratio of 3/1 showed p-type conductivity with a hole concentration and hole mobility of $10^{-17}cm^{-3}$ and $2.5cm^2/V{\cdot}s$, respectively. X-ray diffraction showed that the ZnO (0002) peak shifted to lower angle due to the positioning of $p^{3-}$ ions with a smaller ionic radius in the $O^{2-}$ sites. This indicates that a p-type mechanism was due to the substitutional Po. The low-temperature photoluminescence of the p-type ZnO films showed p-type related neutral acceptor-bound exciton emission. The p-ZnO/n-Si heterojunction LEO showed typical rectification behavior, which confirmed the p-type characteristics of the ZnO films in the as-deposited status, despite the deep-level related electroluminescence emission.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.2
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• pp.9-14
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• 2009

The effects of post-annealing temperature on the optical and electrical properties of P-doped ZnO thin films grown on sapphire substrate have been investigated under oxygen ambient. The XRD shows that regardless of the post-annealing temperature, all P-doped ZnO thin films indicate the c-axis orientation. The results of hall effect measurements indicate the P-doped ZnO thin film annealed at $850^{\circ}C$ exhibits p-type behavior with hole concentration of $1.18{\times}1016cm^{-3}$ and hole mobility of $0.96cm^2/Vs$. The low-temperature (10K) Photoluminescence results reveal that the peak related to the neutral-acceptor exciton (A0X), free electrons to neutral acceptor (FA) and donor acceptor pair (DAP) at 3.351ev, 3.283eV and 3.201eV are observed in the films showing p-type behavior with acceptor. The optimization of deposition and post-annealing conditions will certainly make the P-doped ZnO thin films promising materials for the application to the next generation of optical devices.

• Journal of Adhesion and Interface
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• v.21 no.3
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• pp.107-112
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• 2020

Recently, the atomically thin transition-metal dichalcogenide (TMD) semiconductors have attracted much attention owing to their remarkable properties such as tunable bandgap with high carrier mobility, flexibility, transparency, etc. However, because these TMD materials have a significant drawback that they are easily degraded in an ambient environment, various attempts have been made to improve chemical stability. In this research article, I report a method to improve the air stability of WSe₂ one of the TMD materials via surface passivation with an h-BN insulator, and its application to field-effect transistors (FETs). With a modified hot pick-up transfer technique, a vertical heterostructure of h-BN/WSe₂ was successfully made, and then the structure was used to fabricate the top-gate bottom-contact FETs. The fabricated WSe₂-based FET exhibited not only excellent air stability, but also high hole mobility of 150 ㎠/Vs at room temperature, on/off current ratios up to 3×10⁶, and 192 mV/decade of subthreshold swing.

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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• pp.1356-1364
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• 2014

A new conjugated copolymer, poly{4,8-bis(triisopropylsilylethynyl)benzo[1,2-b:4,5-b']dithiophene-alt-4,7- bis(5-thiophen-2-yl)-5,6-difluoro-2-(heptadecan-9-yl)-2H-benzo[d][1,2,3]triazole} (PTIPSBDT-DFDTBTz), is synthesized by Stille coupling polycondensation. The synthesized polymer has a band gap energy of 1.9 eV, and it absorbs light in the range 300-610 nm. The hole mobility of a solution-processed organic thin-film transistor fabricated using PTIPSBDT-DFDTBTz is $3.8{\times}10^{-3}cm^2V^{-1}s^{-1}$. Bulk heterojunction photovoltaic cells are fabricated, with a conventional device structure of ITO/PEDOT:PSS/polymer:$PC_{71}BM$/Ca/Al ($PC_{71}BM$ = [6,6]-phenyl-$C_{71}$-butyric acid methyl ester); the device shows a power conversion efficiency (PCE) of 2.86% with an open-circuit voltage ($V_{oc}$) of 0.85 V, a short-circuit current density ($J_{sc}$) of 7.60 mA $cm^{-2}$, and a fill factor (FF) of 0.44. Inverted photovoltaic cells with the structure ITO/ethoxylated polyethlyenimine/ polymer:$PC_{71}BM/MoO_3$/Ag are also fabricated; the device exhibits a maximum PCE of 2.92%, with a $V_{oc}$ of 0.89 V, a $J_{sc}$ of 6.81 mA $cm^{-2}$, and an FF of 0.48.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.6
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• pp.574-579
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• 1999

A counter-flow type horizontal reactor of metal organic chemical vapor deposition was designed with the Reynolds and the Rayleigh numbers of Re = 4.5 and Ra = 215.8, respectively. The GaN thin films were grown and characterized by Hall measurement, double crystal X-ray diffraction analysis and photoluminescence measurement. The Si and Mg were also used for doping of GaN films. The dislocation density of $2.6{\times}10^8/\textrm {cm}^2$ was included in GaN films representing the geometrical lattice mismatch between sapphire substrates and GaN films. The Si doped n-GaN films provide the electron carrier density and mobility in the regions of $10^{17}~10^{18}/\textrm{cm}^3$ and 200~400 $\textrm{cm}^2$/V .sec, respectively. Mg doped p-GaN films were post-annealed and activated with the hole carrier density of $8{\times}10^{17}/{\textrm}{cm}^3$.

• Journal of the Korean Vacuum Society
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• v.13 no.1
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• pp.9-13
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• 2004

Perylene is an interesting material known to have P-type and N-type characteristics at the same time. We prepared perylene thin-films in ultrahigh vacuum with two different deposition rates of 0.1 $\AA$/s and 1.0 $\AA$/s in order to study the dependence of film characteristics on the growth condition. The smaller average grain size with larger surface coverage as well as the better crystallinity were observed on the perylene film prepared under 1.0 $\AA$/s deposition rate in x-ray diffraction (XRD) and atomic force microscopy (AFM) study. For studying electrical property of the film, perylene organic thin-film transistor (OTFT) with gold contacts was fabricated on $SiO_2$/Si surface in UHV condition. The prepared perylene OTFT device shows P-type characteristic. The obtained hole mobility in the current-voltage characteristic curve was$2.23\times10^{-5}\textrm{cm}^2$/Vs.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.35T no.2
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• pp.6-12
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• 1998

Thin film SOI(Silicon-on-insulator) device offer unique advantages such as reduction in short channel effects, improvement of subthreshold slope, higher mobility, latch-up free nature, and so on. But these devices exhibit floating-body effet such as current kink which inhibits the proper device operation. In this paper, the SOI NMOSFET with a T-type gate structure is proposed to solve the above problem. To simulate the proposed device with TSUPREM-4, the part of gate oxide was considered to be 30nm thicker than the normal gate oxide. The I-V characteristics were simulated with 2D MEDICI. Since part of gate oxide has different oxide thickness, the gate electric field strength is not same throughout the gate and hence the impact ionization current is reduced. The current kink effect will be reduced as the impact ionization current drop. The reduction of current kink effect for the proposed device structure were shown using MEDICI by the simulation of impact ionization current, I-V characteristics, and hole current distribution.