• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.413-413
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• 2012

Lead sulfide (PbS) Colloidal quantum dots (CQDs) are promising material for the photovoltaic device due to its various outstanding properties such as tunable band-gap, solution processability, and infrared absorption. More importantly, PbS CQDs have large exciton Bohr radius of 20 nm due to the uniquely large dielectric constants that result in the strong quantum confinement. To exploit desirable properties in photovoltaic device, it is essential to fabricate a device exhibiting stable performance. Unfortunately, the performance of PbS NQDs based Schottky solar cell is considerably degraded according to the exposure in the air. The air-exposed degradation originates on the oxidation of interface between PbS NQDS layer and metal electrode. Therefore, it is necessary to enhance the stability of Schottky junction device by inserting a passivation layer. We investigate the effect of insertion of passivation layer on the performance of Schottky junction solar cells using PbS NQDs with band-gap of 1.3 eV. Schottky solar cell is the simple photovoltaic device with junction between semiconducting layer and metal electrode which a significant built-in-potential is established due to the workfunction difference between two materials. Although the device without passivation layer significantly degraded in several hours, considerable enhancement of stability can be obtained by inserting the very thin LiF layer (<1 nm) as a passivation layer. In this study, LiF layer is inserted between PbS NQDs layer and metal as an interface passivation layer. From the results, we can conclude that employment of very thin LiF layer is effective to enhance the stability of Schottky junction solar cells. We believe that this passivation layer is applicable not only to the PbS NQDs based solar cell, but also the various NQDs materials in order to enhance the stability of the device.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.148-148
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• 2015

Over the past several years, Colloidal core/shell type quantum dots lighting-emitting diodes (QDLEDs) have been developed for the future of optoelectronic applications. An inverted-type quantum-dot light-emitting-diode (QDLED), employing low work function organic material polyethylenimine ethoxylated(PEIE) (<10 nm)[1] modified ZnO nanoparticles (NPs) as electron injection and transport layer, was fabricated by all solution processing method, instead of electrode in the device. The PEIE surface modifier incorporated on the top of the ZnO NPs film, facilitates the enhancement of both electorn injection into the CdSe-ZnS QD emissive layer by lowering the workfunction of ZnO from 3.58eV to 2.87eV and charge balance on the QD emitter. In this inverted QDLEDs, blend of poly (9,9-di-n-octyl-fluorene-alt-benzothiadiazolo) and poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] are used as hole transporting layer (HTL) to improve hole transporting property. At the operating voltage of 7.5 V, the QDLED device emitted spectrally orange color lights with high luminance up to 11110 cd/m2, and showed current efficiency of 2.27 cd/A.[2]

• Journal of Advanced Navigation Technology
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• v.7 no.2
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• pp.211-216
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• 2003

In this paper, characteristics of Ta-Ti alloy was studied as a gate electrode for NMOS devices to replace the widely used polysilicon. Ta-Ti alloy was deposited directly on $SiO_2$ by a co-sputtering method using two of Ta and Ti targets. The sputtering power of each metal target was 100W. To compare with Ta-Ti, Ta deposited with a 100W sputtering power was fabricated as well. In order to investigate the thermal/chemical stability of the Ta-Ti alloy gate, the alloy was annealed at $600^{\circ}C$ with rapid thermal annealer. No appreciable degradation of the device was observed. Also the results of electrical analysis showed that the work function of Ta-Ti metal alloy was about 4.1eV which was suitable for NMOS devices and sheet resistance of alloy was lower than that of polysilicon.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2007.06a
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• pp.193-198
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• 2007

The NiSi is very promising candidate for the metallization in 60nm CMOS process such as FUSI(fully silicided) gate and source/drain contact because it exhibits non-size dependent resistance, low silicon consumption and mid-gap workfunction. Ni film was first deposited by using ALD (atomic layer deposition) technique with Bis-Ni precursor and $H_2$ reactant gas at $220^{\circ}C$ with deposition rate of $1.25{\AA}/cycle$. The as-deposited Ni film exhibited a sheet resistance of $5{\Omega}/{\square}$. RTP (repaid thermal process) was then performed by varying temperature from $400^{\circ}C$ to $900^{\circ}C$ in $N_2$ ambient for the formation of NiSi. The process window temperature for the formation of low-resistance NiSi was estimated from $600^{\circ}C$ to $800^{\circ}C$ and from $700^{\circ}C$ to $800^{\circ}C$ with and without Ti capping layer. The respective sheet resistance of the films was changed to $2.5{\Omega}/{\square}$ and $3{\Omega}/{\square}$ after silicidation. This is because Ti capping layer increases reaction between Ni and Si and suppresses the oxidation and impurity incorporation into Ni film during silicidation process. The NiSi films were treated by additional thermal stress in a resistively heated furnace for test of thermal stability, showing that the film heat-treated at $800^{\circ}C$ was more stable than that at $700^{\circ}C$ due to better crystallinity.

• Journal of the Korean Institute of Telematics and Electronics
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• v.22 no.4
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• pp.76-83
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• 1985

Mo2N/Mo double layer which is to be used for gate of the RMOS (refractory metal oxide semiconductor) and interconnection material has been formed by means of low temperature r.f. reactive sputtering in Ar and N2 mixture. The sheet .esistance of 1 000$\AA$Mo2 N/4000$\AA$Mofilm was about 1.20-1.28 ohms/square, which is about an order of magnitude lower than that of polysilicon film. The workfunction difference naE between MO2N/MO layer and (100) p-Si with 6-9 ohm'cm resistivity obtained from C-V plots was about -0.30ev, and the fixed charge density Qss/q in the oxide was about 2. Ix1011/cm2. To evaluate the signal transfer delay time per inverter stage, an integrated ring oscillator circuit consisting of 45-stage inverters was fabricated using the polysilicon gate NMOS process. The signal transfer delay time per inverter stage obtained in this experiment was about 0.8 nsec

• JSTS:Journal of Semiconductor Technology and Science
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• v.6 no.1
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• pp.22-29
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• 2006

We demonstrate highly manufacturable Multi-channel Field Effect Transistor (McFET) on bulk Si wafer. McFET shows excellent transistor characteristics, such as $5{\sim}6 times higher drive current than planar MOSFET, ideal subthreshold swing, low drain induced barrier lowering (DIBL) without pocket implantation and negligible body bias dependency, maintaining the same source/drain resistance as that of a planar transistor due to the unique feature of McFET. And suitable threshold voltage ($V_T$) for SRAM operation and high static noise margin (SNM) are achieved by using TiN metal gate electrode.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.207.1-207.1
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• 2014

High-mobility and two dimensional conduction at the interface between two band insulators, LaAlO3 (LAO) and SrTiO3 (STO), have attracted considerable research interest for both applications and fundamental understanding. Several groups have reported the photoconductivity of LAO/STO, which give us lots of potential development of optoelectronic applications using the oxide interface. Recently, a giant photo response of Pd nano particles/LAO/STO is observed in UV illumination compared with LAO/STO sample. These phenomena have been suggested that the correlation between the interface and the surface states significantly affect local charge modification and resulting electrical transport. Water and gas adsorption/desorption can alter the band alignment and surface workfunction. Therefore, characterizing and manipulating the electric charges in these materials (electrons and ions) are crucial for investigating the physics of metal oxide. Proposed mechanism do not well explain the experimental data in various ambient and there has been no quantitative work to confirm these mechanism. Here, we have investigated UV photo response in various ambient by performing transport and Kelvin probe force microscopy measurements simultaneously. We found that Pd nano particles on LAO can form Schottky contact, it cause interface carrier density and characteristics of persistence photo conductance depending on gas environment. Our studies will help to improve our understanding on the intriguing physical properties providing an important role in many enhanced light sensing and gas sensing applications as a catalytic material in different kinds of metal oxide systems.

• Korean Chemical Engineering Research
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• v.51 no.5
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• pp.634-639
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• 2013

We investigated the effects of a cathode underlayer on the electroluminescence (EL) characteristics of organic light-emitting diodes (OLEDs) using various metal acetates (M-acetate, M = Li, Na, K, Cs) as a cathode underlayer. When 1 nm thick M-acetate layers were used as a cathode underlayer, the OLEDs with M-acetate showed better EL performance than the device with the conventional LiF electron injection layer except the device with Cs-acetate. More enhanced current density and improved EL characteristics were obtained when lower work function metal acetate was employed. In addition, the optimum M-acetate layer thickness that gives the best device performance proved to be 0.7 and 2.0 nm for Li-acetate and Cs-acetate, respectively, probably depending on the molecular size of M-acetate. The OLEDs with the M-acetate layers of optimized thickness demonstrated more than 60% enhanced current efficiency compared with that of the device using an LiF layer at the same applied voltage.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.189-189
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• 2012

Lead sulfide (PbS) nanocrystal quantum dots (NQDs) are promising materials for various optoelectronic devices, especially solar cells, because of their tunability of the optical band-gap controlled by adjusting the diameter of NQDs. PbS is a IV-VI semiconductor enabling infrared-absorption and it can be synthesized using solution process methods. A wide choice of the diameter of PbS NQDs is also a benefit to achieve the quantum confinement regime due to its large Bohr exciton radius (20 nm). To exploit these desirable properties, many research groups have intensively studied to apply for the photovoltaic devices. There are several essential requirements to fabricate the efficient NQDs-based solar cell. First of all, highly confined PbS QDs should be synthesized resulting in a narrow peak with a small full width-half maximum value at the first exciton transition observed in UV-Vis absorbance and photoluminescence spectra. In other words, the size-uniformity of NQDs ought to secure under 5%. Second, PbS NQDs should be assembled carefully in order to enhance the electronic coupling between adjacent NQDs by controlling the inter-QDs distance. Finally, appropriate structure for the photovoltaic device is the key issue to extract the photo-generated carriers from light-absorbing layer in solar cell. In this step, workfunction and Fermi energy difference could be precisely considered for Schottky and hetero junction device, respectively. In this presentation, we introduce the strategy to obtain high performance solar cell fabricated using PbS NQDs below the size of the Bohr radius. The PbS NQDs with various diameters were synthesized using methods established by Hines with a few modifications. PbS NQDs solids were assembled using layer-by-layer spin-coating method. Subsequent ligand-exchange was carried out using 1,2-ethanedithiol (EDT) to reduce inter-NQDs distance. Finally, Schottky junction solar cells were fabricated on ITO-coated glass and 150 nm-thick Al was deposited on the top of PbS NQDs solids as a top electrode using thermal evaporation technique. To evaluate the solar cell performance, current-voltage (I-V) measurement were performed under AM 1.5G solar spectrum at 1 sun intensity. As a result, we could achieve the power conversion efficiency of 3.33% at Schottky junction solar cell. This result indicates that high performance solar cell is successfully fabricated by optimizing the all steps as mentioned above in this work.

• Journal of the Korean Vacuum Society
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• v.16 no.3
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• pp.197-204
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• 2007

Ultra thin Er-silicide layers formed by Er deposition on the clean p-silicon and in situ post annealing technique were investigated with respect to change of the Schottky barrier height. The formation of Er silicides was confirmed by XPS results. UPS measurements revealed that the workfunction of the silicide decreased and was saturated as the deposited Er thickness increased up to $10{\AA}$. We found that the silicides were mainly composed of Er5Si3 phase through the XRD experiments. After Schottky diodes were fabricated with the Er silicide/p-Si junctions, the Schottky barrier heights were calculated $0.44{\sim}0.78eV$ from the I-V measurements of the Schottky diodes. There was large discrepancy in the Schottky barrier heights deduced from the UPS with the ideal junction condition and the real I-V measurements, so that we attributed the discrepancy to the $Er_5Si_3$ phase in the Er-silicides and the large interfacial density of trap state of it.