• Transactions on Electrical and Electronic Materials
• /
• v.10 no.6
• /
• pp.203-207
• /
• 2009

We have investigated the effect of ambient gases on the structural, electrical, and optical characteristics of ITO thin films intended for use as anode contacts in OLED (organic light emitting diodes) devices. These ITO thin films are deposited by radio frequency (RF) magnetron sputtering under different ambient gases (Ar, Ar+$O_2$, and Ar+$H_2$) at $300{^{\circ}C}$. In order to investigate the influences of the oxygen and hydrogen, the flow rate of oxygen and hydrogen in argon mixing gas has been changed from 0.5 sccm to 5 sccm and from 0.01 sccm to 0.25 sccm, respectively. The intensity of the (400) peak in the ITO thin films increased with increasing $O_2$, flow rate whilst the (400) peak was nearly invisible in an atmosphere of Ar+$H_2$. The electrical resistivity of the ITO thin films increased with increasing $O_2$ flow rate, whereas the electrical resistivity decreased sharply under an Ar+$H_2$ atmosphere and was nearly similar regardless of the $H_2$ flow rate. The change of electrical resistivity with changes in the ambient gas composition was mainly interpreted in terms of the charge carrier mobility rather than the charge carrier concentration. All the films showed an average transmittance of over 80% in the visible range. The OLED device was fabricated with different ITO substrates made with the configuration of ITO/$\alpha$-NPD/DPVB/$Alq_3$/LiF/Al in order to elucidate the performance of the ITO substrate. Current density and luminance of OLED devices with ITO thin films deposited in Ar+$H_2$ ambient gas is the highest among all the ITO thin films.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.28 no.4
• /
• pp.244-248
• /
• 2015

We proposed and demonstrated the double layered metallic nano-hole structure using polystyrene beads process to enhance the sensitivity of surface plasmon resonance (SPR). The double layered SPR structures are calculated using the finite-difference time-domain (FDTD) method for the width, thickness, and period of the metallic nano-hole structures. The thickness of the metal film and the metallic nano-hole is 30 and 20 nm in the 214 nm wide nano-hole size, respectively. The double layered SPR structures are fabricated with monolayer polystyrene beads of 420 nm wide. The sensitivities of the conventional SPR sensor and the double layered SPR sensor are obtained to 42.2 and 52.1 degree/RIU, respectively.

• Journal of Convergence for Information Technology
• /
• v.7 no.5
• /
• pp.53-58
• /
• 2017

In the age of oil exhaustion, low cost, semi-transparent solar cell, the dye-sensitized solar cell (DSC) has attracted significant attention since 1991 of $Gr{\ddot{a}}tzel$ report. To enhance the light-harvest capability of the photoelectric electrode, and efficiency of photoelectric transformation of the DSC, scattering layer of various structure have been proposed to photoelectric electrode materials. The scattering center of scattering layer needs the large titanium dioxide nanoparticles of 250 - 300 nm in diameter. In this study, the large sized $TiO_2$ nanocyrstals of around 300 nm were synthesized using the modified sol-gel process. According to the analysis of XRD and TEM, the synthesized $TiO_2$ nanoparticles exhibit single crystals of anatase phase. The optical transmittance of the synthesized titanium dioxide film prepared by spin coating is around 50% at 550 nm. It is suitable for scattering layer as a scattering center, and expected to enhance the efficiency of photoelectric transformation of the DSC.

• Journal of Convergence for Information Technology
• /
• v.10 no.8
• /
• pp.137-143
• /
• 2020

This study examined the effects of rapid thermal annealing (RTA) on the physical and chemical characteristics of thin silver (Ag) layers on SiO2 coated metal foils. Ag layers were annealed at various temperatures of the range between 150 ℃ and 550 ℃ for 20 min. The surface roughness and resistivity are increased at the annealing temperatures of 550 ℃. We also found that oxygen (O) and silicon (Si) atoms exist at the Ag film surface by using compositional analysis in the annealing temperatures of 550 ℃. The total reflectance is decreased with increasing temperature. These phenomena are due to an out-diffusion of Si atoms from SiO2 layers during the RTA annealing. The results offer the possibility of using it as a substrate for various flexible optoelectronic devices.

• Korean Journal of Optics and Photonics
• /
• v.16 no.4
• /
• pp.340-344
• /
• 2005

Microlens cells of Ge-doped BPSG (Boro-Phospho-Silicate Glass) are fabricated by dicing the film produced by FHD (Flame Hydrolysis Deposition). Microlens arrays of $53.4{\mu}m$ square unit are produced by the thermal reflow of the diced unit cells at $1200^{\circ}C$. The gap between the microlenses was about $70{\mu}m,$ and the thickness of the produced lens was about $28.4{\mu}m$. We analyzed the reflowed shape of the microlens cell by an image-process technique, and the focal length was about $62.2{\mu}m$. This method of fabricating a microlens is simple and inexpensive compared to the conventional method using the photolithographic process. Also, the control of the radius of curvature of the microlens is easier and a more precise microlens way of various types can be fabricated using this method.

• Korean Journal of Optics and Photonics
• /
• v.18 no.2
• /
• pp.155-161
• /
• 2007

A new and simple method of 3-dimensional circuit modeling and analysis is proposed and verified experimentally for the first time by determining 3-dimensional current flow and 2-dimensional light distribution in blue InGaN/GaN multi-quantum well (MQW) light emitting diode (LED) devices. Circuit parameters of the LED consist of the resistance of the metallic film and epitaxial layer, and the intrinsic diode which represents the active region emitting the light. The circuit parameters are extracted from the transmission line model (TLM) and current-voltage relation. We applied the >> proposed method and extracted circuit parameters to obtain the light emission pattern in a top-surface emitting-type LED. The current spreading effect is analyzed theoretically and quantitatively with a variation of the resistance of metallic and epitaxial layers. The emitting-light distribution of the fabricated blue LED showed a good agreement with the analyzed result, which shows the dark emission intensity at the corner of the p-electrode.

• Journal of the Microelectronics and Packaging Society
• /
• v.26 no.4
• /
• pp.113-118
• /
• 2019

In this study, we investigated the growth of single-crystallinity α-Ga₂O₃ thin films on c-plane sapphire substrates using halide vapor pressure epitaxy. We also found the optimal growth conditions to suppress the phase transition of α-Ga₂O₃. Our results confirmed that the growth temperature and partial pressure of the reactive gas greatly influenced the crystallinity. The optimal growth temperature range was about 460~510℃, and the α-Ga₂O₃ thin films with the highest crystallinity were obtained at a III/VI ratio of 4. The thickness and surface morphology of the thin films was observed by scanning electron microscopy. The film thickness was 6.938 ㎛, and the full width at half maximum of the ω-2θ scan rocking curve was as small as 178 arcsec. The optical band gap energy obtained was 5.21 eV, and the films were almost completely transparent in the near-ultraviolet and visible regions. The etch pit density was found to be as low as about 6.0 × 10⁴ cm^-2.

• Bulletin of the Korean Chemical Society
• /
• v.30 no.3
• /
• pp.661-666
• /
• 2009

1-{2,4-Di-(2-hydroxyethoxy)phenyl}-2-(2-thienyl)ethene (5) was prepared and condensed with terephthaloyl chloride to yield polyester (6). Polymer 6 was reacted with tetracyanoethylene to give novel Y-type polyester (7) containing 1-(2,4-dioxyethoxy)phenyl-2-{5-(2,2,3-tricyanovinyl)-2-thienyl)}ethenyl groups as NLO-chromophores, which are parts the polymer backbones. Polymer 7 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It showed thermal stability up to 300 ${^{\circ}C}$ in thermogravimetric analysis with glasstransition temperature obtained from differential scanning calorimetry near 134 ${^{\circ}C}$. The second harmonic generation (SHG) coefficient ($d_33$) of poled polymer film at the 1560 nm fundamental wavelength was around 6.74 x $10^{-9}$ esu. The dipole alignment exhibited high thermal stability up to the glass-transition temperature ($Tg$), and there was no SHG decay below 135 ${^{\circ}C}$ because of the partial main-chain character of polymer structure, which is acceptable for NLO device applications.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.1
• /
• pp.95-98
• /
• 2013

The photoluminescence (PT) properties of Al-doped ZnO thin films grown by the sol-gel dip-coating method have been investigated. At 12 K, nine distinct PL peaks were observed at 2.037, 2.592, 2.832, 3.027, 3.177, 3.216, 3.260, 3.303, and 3.354 eV. The deep-level emissions (2.037, 2.592, 2.832, and 3.027 eV) were attributed to native defects. The near-band-edge (NBE) emission peaks at 3.354, 3.303, 3.260, 3.216, and 3.177 eV were attributed to the emission of the neutral-donor-bound excitons ($D^0X$), two-electron satellite (TES), free-to-neutral-acceptors (e,$A^0$), donor-acceptor pairs (DAP), and second-order longitudinal optical (2LO) phonon replicas of the TES (TES-2LO), respectively. According to Haynes' empirical rule, we calculated the energy of a free exciton (FX) to be 3.374 eV. The thermal activation energy for $D^0X$ in the nanocrystalline ZnO thin film was found to be ~25 meV, corresponding to the thermal dissociation energy required for $D^0X$ transitions.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.52 no.5
• /
• pp.201-205
• /
• 2003

We synthesized dendrimers containing light switchable units, azobenzene group. And the dendrimer containing 48 pyridinepropanol functional end group, which could form a complex structure with metal ions was synthesized. To apply to the molecular level devices or data storage system using Langmuir-Blodgett(LB) film, we firstly investigated the monolayer behavior using the surface pressure-area($\pi$-A) isotherms at air-water interface. And then the surface pressure shift of monolayer by light irradiation was also measured to the dendrimer with azobezene group. As a result, the monolayer of dendrimer with azobenzene group showed the reversible photo-switching behavior by the isomerization of azobenzene group in their periphery. The samples for electrical measurement were fabricated to two types which were pure dendrimer with pyridinepropanol group and its complexes with $Pt^4+$ ions by LB method. We have studied the electrical properties of the ultra thin dendrimer LB films investigated by the current-voltage(I-V) characteristics of Metal/Dendrimer LB films/Metal(MIM) structure. And we have investigated different results in the surface activity at the air-water interface as well as the electrical properties for the monolayers of pure dendrimer with pyridinevopanol group and its complex with $Pt^4+$ ions. In conclusion, it is demonstrated that the metal ion around dendrimer with pyri야nepropanol group can contribute to make formation of network structure among dendrimers and it result from the change of electrical properties. This results suggest that the dendrimers with azobenzene group and pvridinedropanol group can be applied to high efficient nano-device of molecular level.