• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.99-100
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• 2007

ZnO films on $Al_2O_3$ substrates were grown using a pulsed laser deposition method. Through photoluminescence (PL) and X-ray diffraction (XRD) measurements, the optimum growth conditions for the ZnO growth were established. The results of the XRD measurements indicate that ZnO films were strongly oriented to the c-axis of the hexagonal structure and epitaxially crystallized under constraints created by the substrate. The full width half maximum for a theta curve of the (0002) peak was $0.201^{\circ}$. Also, from the PL measurements, the grown ZnO films were observed to give free exciton behaviour, which indicates a high quality of the epilayer. The Hall mobility and carrier density of the ZnO films at 293 K were estimated to be $299\;cm^2/V\;s$ and $8.27\;{\times}\;10^{16}\;cm^{-3}$, respectively. The absorption spectra revealed that the temperature dependance of the optical band gap on the ZnO films was $E_g(T)\;=\;3.439\;eV\;-\;(5.30\;{\times}\;10^{-4}\;ev/K)T^2(367\;+\;T)$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.125-128
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• 1998

The electro-optical properties of PDLCs ( Polymer Dispersed Liquid Crystals ) that have been interested for applications to projection display devices lately are significantly improved. For this improvement, we optimized not only the material parameters of liquid crystal and polymer but also the process conditions. Using TL series liquid crystals and polymer PN393 provided from Merck, we obtained the optimized process conditions such as cell gap, LC concentration, curing temperature and curing time. Under these conditions, we have achieved PDLC cells of threshold voltage 2.6V. contrast ratio 260 and negligible hysteresis.

• Journal of Korean Vacuum Science & Technology
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• v.3 no.2
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• pp.116-120
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• 1999

Possible role of hydrogen atoms on the formation of microcrystalline silicon films was schematically investigated using a plasma enhanced chemical vapor deposition system. A layer-by-layer technique that can alternate deposition of ${\alpha}$-Si thin film and then exposure of H2 plasma was used for this end. The experimental process was extensively carried out under different hydrogen plasma times (t2) at a fixed number of 20 cycles in the deposition. structural properties, such as crystalline volume fractions and grain shapes were analyzed by using a Raman spectroscopy and a scanning electron microscopy. Electrical transports were characterized by the temperature dependence of the dark conductivity that gives rise to the calculation of activation energy (Ea). Optical absorption was measured using an ultra violet spectrophotometer, resulting in the optical energy gap (Eopt). Our experimental results indicate that both of the hydrogen etching and the structural relaxation effects on the film surface seem to be responsible for the growth mechanism of the crystallites in the ${\mu}$c-si films.

• Korean Journal of Materials Research
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• v.20 no.6
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• pp.289-293
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• 2010

Silicon quantum dots (Si QDs) in a superlattice for high efficiency tandem solar cells were fabricated by magnetron rf sputtering and their characteristics were investigated. SiC/$Si_{1-x}C_x$ superlattices were deposited by co-sputtering of Si and C targets and annealed at $1000^{\circ}C$ for 20 minutes in a nitrogen atmosphere. The Si QDs in Si-rich layers were verified by transmission electron microscopy (TEM) and X-ray diffraction. The size of the QDs was observed to be 3-6 nm through high resolution TEM. Some crystal Si and -SiC peaks were clearly observed in the grazing incident X-ray diffractogram. Raman spectroscopy in the annealed sample showed a sharp peak at $516\;cm^{-1}$ which is an indication of Si QDs. Based on the Raman shift the size of the QD was estimated to be 4-6 nm. The volume fraction of Si crystals was calculated to be about 33%. The change of the FT-IR absorption spectrum from a Gaussian shape to a Lorentzian shape also confirmed the phase transition from an amorphous phase before annealing to a crystalline phase after annealing. The optical absorption coefficient also decreased, but the optical band gap increased from 1.5 eV to 2.1 eV after annealing. Therefore, it is expected that the optical energy gap of the QDs can be controlled with growth and annealing conditions.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.314-314
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• 2016

In this paper, the effects of carrier concentration on dielectric constant of ITO films were investigated by spectroscopic ellipsometry. From SE results, we find the pronounced shift of the ${\varepsilon}1$ peaks toward high energy with concentration; while contrarily, the ${\varepsilon}2$ values at low energy region increases with decreasing concentration. These shifts are attributed to the Burstein-Moss and free-carrier absorption effects within ITO films. With increases carrier concentration, the values of extinction coefficients show quite different behaviors in range of wavelength from 200 to 1200 nm. The reduction in k at ${\lambda}{\leq}500nm$, while increasing at ${\lambda}{\geq}500nm$ was observed. The QE of HJ solar cells behaviors can be roughly classified into two regions: short-wavelengths (${\leq}650nm$) and long-wavelengths region (${\geq}650nm$). With increasing carrier concentration as well as energy band gap, QE shows improvement at short-wavelength, while at long-wavelength QE shows opposite trend. Widening band gap energy due to Burstein-Moss shift is the key to improve QE in short-wavelength; simultaneously FCA effect due to optical scattering is attributed to the reduction in QE at long-wavelength. In spite of band gap extension, Jsc calculated from QE decreases from 34.7 mA/cm2 to 33.2 mA/cm2 with increasing carrier concentration. It demonstrated that FCA effect may more govern Jsc in the HJ solar cells.

• Electrical & Electronic Materials
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• v.10 no.5
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• pp.467-472
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• 1997

In this study, we investigated the thickness dependence of thermal bleaching(TB) effect as well as photo-induced scalar phenomena, such as photodrakening(PD) effect and photorefraction(PR) change, in chalcogenide A $s_{40}$ G $e_{10}$S $e_{15}$ $S_{35}$ thin films. We found that when these films were exposed for 15 minutes using blue-pass filtered Hg lamp(~4300$\AA$) after annealing for 30 minutes around the glass transition temperature Tg(20$0^{\circ}C$), the refractive index change ($\Delta$n) was varied up to 0.02~0.46 according to each thickness condition and the optical energy gap ($\Delta$ $E_{op}$ ) was shifted to a longer wavelength of approximately 0.67eV, especially for 1000$\AA$-thickness. Also, the TB PD effects have been understood by the results related to optical absorption characteristics. The TB effect could be estimated as increasing the stabilization of amorphous chalcogenide films since absorption slope of extended regions(U) was not changed by annealing. On the other hand, the PD effect could be understood as due to the enhancement of disorder since U and the slope of Urbachs tail(1/F) around an absorption edge were decreased by exposing.ing.n edge were decreased by exposing.

• Applied Chemistry for Engineering
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• v.10 no.1
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• pp.98-104
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• 1999

In this work, we investigated hydrogen content, bond structure, and electrical properties of a-Si:H films prepared by ECR plasma CVD as a function of pressure. In general, the photo sensitivity of a-Si:H films prepared by CVD method decreases as the deposition rate increases, but the photo sensitivity of a-Si:H films prepared by ECR plasma deposition method increases as the deposition rate increases. In the same condition of microwave power, the ratio of $SiH_4/H_2$, and pressure, though film thickness increases linearly with deposition time and hydrogen content in the film is constant, photo conductivity can be decreased because $SiH_2$ bond is made more than SiH bond in the short reaction time. According to increase pressure in the chamber, SiH bond in the film increase and optical energy gap decrease. So, photo conductivity can be increased. But photo sensitivity decreased as dark conductivity increase. It must be grown in the condition of low pressure and hydrogen gas for taking the a-Si:H film of high quality.

• Journal of the Semiconductor & Display Technology
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• v.12 no.4
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• pp.49-54
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• 2013

In this study, we have investigated the effect of the substrate temperature and oxygen flow rate on the characteristics of IZO thin films for the OLED (organic light emitting diodes) devices. For this purpose, IZO thin films were deposited by RF magnetron sputtering at room temperature and $300^{\circ}C$ with various $O_2$ flow rate. In order to investigate the influences of the oxygen, the flow rate of oxygen in argon mixing gas has been changed from 0.1sccm to 0.5sccm. IZO thin films deposited at room temperature show amorphous structure, whereas IZO thin films deposited at $300^{\circ}C$ show crystalline structure having an (222) preferential orientation regardless of $O_2$ flow rate. The electrical resistivity of IZO film increased with increasing flow rate of $O_2$ under Ar+$O_2$. The change of electrical resistivity with increasing flow rate of $O_2$ was mainly interpreted in terms of the charge carrier concentration rather than the charge carrier mobility. The electrical resistivity of the amorphous-IZO films deposited at R.T. was lower than that of the crystalline-IZO thin films deposited at $300^{\circ}C$. The change of electrical resistivity with increasing substrate temperature was mainly interpreted in terms of the charge carrier mobility rather than the charge carrier concentration. All the films showed the average transmittance over 85% in the visible range. The current density and the luminance of OLED devices with IZO thin films deposited at room temperature in 0.1sccm $O_2$ ambient gas are the highest amongst all other films. The optical band gap energy of IZO thin films plays a major role in OLED device performance, especially the current density and luminance.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.420-423
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• 2003

[ $TiO_2$ ] thin films were fabricated by DC magnetron sputtering system at by controlling deposition times, ratios of $Ar:O_2$ partial presser ratio and substrate conditions. And the surface, cross-section morphology, microstructure, and composition ratio of the films were analyzed by FE-SEM, TEM and XPS. Besides, the optical absorption and transmittance of the $TiO_2$ films were measured by a UV-VIS-NIR Spectrophotometer, and photocatalytic properties were studied by G C Analyzer & Data Analysis system. As the result, when $TiO_2$ thin film was made at deposition time of 120[min] and $Ar:O_2$ ratio of 60:40, the best structural and optical properties among many thin films could be accepted. The best results of properties were as follows: thickness; $360{\sim}370[nm]$, grain size; 40[m], gap between two peak binding energy, $5.8{\pm}0.05[eV]$ ($2p_{3/2}$ peak and $2p_{1/2}$ peak of Ti was show at $458.3{\pm}0.05[eV]$ and $464.1{\pm}0.05[eV]$ respectively), binding energy; $530{\pm}0.05\;[eV]$, opticalenergy band gap; 3.4[eV].

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.193-196
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• 2001

Single phase $CuInS_2$ thin film with the highest diffraction peak (112) at diffraction angle $(2\theta)$ of $27.7^{\circ}$ and the second highest diffraction peak (220) at diffraction angle $(2\theta)$ of $46.25^{\circ}$ was well made with chalcopyrite structure at substrate temperature of $70^{\circ}C$, annealing temperature of $250^{\circ}C$, annealing time of 60 min. The $CuInS_2$ thin film had the greatest grain size of $1.2{\mu}m$ and Cu/In composition ratio of 1.03. Lattice constant of a and c of that $CuInS_2$ thin film was 5.60 A and 11.12 A respectively. Single phase $CuInS_2$ thin films were accepted from Cu/In composition ratio of 0.84 to 1.3. P-type $CuInS_2$ thin films were appeared at over Cu/In composition ratio of 0.99. Under Cu/In composition ratio of 0.96, conduction types of $CuInS_2$ thin films were n-type. Also, fundamental absorption wavelength, the absorption coefficient and optical energy band gap of p-type $CuInS_2$ thin film with Cu/In composition ratio of 1.3 was 837 nm, $3.0{\times}104cm^{-1}$ and 1.48 eV respectively. When Cu/In composition ratio was 0.84, fundamental absorption wavelength, the absorption coefficient and optical energy band gap of n-type $CuInS_2$ thin film was 821 nm, $6.0{\times}10^4cm^{-1}$ and 1.51 eV respectively.