Nae-Man Park

Electronics and Telecommunications Research Institute, Sŏul, Seoul, South Korea

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Publications (63)117 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated the electrical properties of indium tin oxide (ITO) thin films deposited on chemically strengthened glass (CSG) substrate by room-temperature ionized physical vapor deposition (IPVD). The ITO thin film on the CSG substrate shows a higher sheet resistance after high-temperature anneal process (>200 °C) possibly due to the out-diffusion of potassium ions (K+) from the CSG. We have improved the electrical properties of the ITO thin film by inserting Nb2O5/SiO2 buffer layers between the ITO layer and the CSG substrate. As a result, a protected and index-matched 30-nm-thick ITO thin film with sheet resistance less than 120 Ω/sq and optical transmittance higher than 90% (at 550 nm) has been achieved.
    Japanese Journal of Applied Physics 07/2014; 53(8S3):08NG01. · 1.06 Impact Factor
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  • Nae-Man Park, Chel-Jong Choi
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    ABSTRACT: A new method for growing silicon nanowires is presented. They were grown in an aqueous solution at a temperature of 85 °C under atmospheric pressure by using sodium methylsiliconate as a water-soluble silicon precursor. The structure, morphology, and composition of the as-grown nanowires were characterized by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectrometry. It was also confirmed by X-ray powder diffraction and Raman spectroscopy that the silicon nanowire has a hexagonal structure. It was possible to grow the crystalline silicon nanowires at low temperature under atmospheric pressure because potassium iodide, which was used as a gold etchant, sufficiently increased the surface energy and reactivity of gold as a metal catalyst for the reaction of the Si precursor even at low temperature.
    Nano Research 06/2014; 7(6). · 6.96 Impact Factor
  • Jeha Kim, Ho-Sub Lee, Nae-Man Park
    Current Applied Physics 02/2014; 14. · 2.03 Impact Factor
  • Jeha Kim, Nae-Man Park
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    ABSTRACT: Using reactive sputtering, we fabricated stoichiometric CuIn1- x Ga x Se2 (CIGS) thin films. Both Cu0.6Ga0.4 (CuGa) and Cu0.4In0.6 (CuIn) alloy targets were simultaneously sputtered under the delivery of elemental Se produced from a thermal cracker. By changing the sputtering rates of the CuGa and the CuIn, we were able to obtain the composition ratios of Cu/(Ga+In) and Ga/(Ga+In) in the range of 0.71-0.95 and 0.10-0.30, respectively. Both the grain size and the surface roughness of the CIGS film increased as the Cu/(Ga+In) ratio increased. In the X-ray diffraction analysis on CIGS films of 0.9 m, preferential growth with a [112] orientation was found, and reflections from the (211), (220)/(204), (301), (312)/(116), (400)/(008), and (332)/(316) planes were observed. The CIGS films showed the existence of Cu2- x Se phases in the Cu-rich samples and ordered defect compound (ODC) phases in the Cu-poor films, as confirmed in the Raman measurements. A best device performance of η = 8.1%, V oc = 0.442 V, J sc = 34.3 mA/cm2, and FF = 53.4% was obtained from a cell fabricated with a CIGS layer (t = 0.9 µm) with the Cu/(Ga+In) ratio = 0.71 and the Ga/(Ga+In) ratio = 0.10.
    Journal- Korean Physical Society 01/2014; 64(3). · 0.43 Impact Factor
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    ABSTRACT: Index-matched indium tin oxide (ITO) electrodes for capacitive touch screen panels have been fabricated to improve optical transmittance and reduce the difference of reflectance (deltaR) between the etched and un-etched regions. 8.5 nm Nb2O5 and 49 nm SiO2 thin films were deposited by magnetron sputtering as index-matching layers between an ITO electrode and a glass substrate. In case of 30 nm ITO electrode, a 4.3% improvement in the optical transmittance and a deltaR of less than 1% were achieved, along with a low sheet resistance of 90 omega/.
    Journal of Nanoscience and Nanotechnology 11/2013; 13(11):7756-9. · 1.34 Impact Factor
  • Jeha Kim, Ho-Sub Lee, Nae-Man Park
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    ABSTRACT: The reactive co-sputtering was developed as a new way of preparing high quality CuInGaSe2(CIGS) films from two sets of targets; Cu0.6Ga 0.4 and Cu0.4In0.6 alloy and Cu and (In0.7Ga0.3)2Se3 compound targets. During sputtering, Cu, In, Ga metallic elements as well as the compound materials were reacted to form CIGS simultaneously in highly reactive elemental Se atmosphere generated by a thermal cracker. CIGS layer had been grown on Mo/soda-lime glass(SLG) at 500°C. For both sets of targets, we controlled the composition of CIGS thin film by changing the RF power for target components. All the films showed a preferential (112) orientation as observed from X-ray diffraction analysis. The composition ratios of CIGS were easily set to 0.71-0.95, 0.10-0.30 for [Cu]/[III] and [Ga]/[III], respectively. The grain size and the surface roughness of a CIGS film increased as the [Cu]/[III] ratios increased. The solar cells were fabricated using a standard base line process in the device structure of grid/ITO/i-ZnO/CdS/CIGS/Mo/ SLG. The best performance was obtained the performance of Voc = 0.45 V, Jsc =35.6, FF = 0.535, η = 8.6% with a 0.9 μm-CIGS solar cell from alloy targets while Voc = 0.54 V, Jsc =30.8, FF = 0.509, η = 8.5% with a 0.8 μm-CIGS solar cell from Cu and (In0.7Ga0.3)2Se3.
    SPIE Solar Energy + Technology; 09/2013
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    ABSTRACT: A transparent non-volatile memory device was fabricated using silicon quantum dots in silicon nitride film as a gate insulator. A silicon quantum dots were grown in-situ in the film by plasma-enhanced chemical vapor deposition. The silicon quantum dot film had a high optical transmittance of over 95% at 550 nm with a thickness of 50 nm. A large hysteresis curve was observed in a current-voltage measurement. When we increased the voltage sweep range, electrons were charged into the silicon quantum dots because of the electrical n-type channel in an oxide thin film transistor.
    Electronic Materials Letters 07/2013; 9(4). · 3.98 Impact Factor
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    Thin Solid Films 07/2013; · 1.87 Impact Factor
  • 223th ECS Meeting; 05/2013
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    ABSTRACT: Silicon nanocrystals (Si-NCs) were grown in situ in carbide-based film using a plasma-enhanced chemical vapor deposition method. High-resolution transmission electron microscopy indicates that these nanocrystallites were embedded in an amorphous silicon carbide-based matrix. Electron diffraction pattern analyses revealed that the crystallites have a hexagonal-wurtzite silicon phase structure. The peak position of the photoluminescence can be controlled within a wavelength of 500 to 650 nm by adjusting the flow rate of the silane gas. We suggest that this phenomenon is attributed to the quantum confinement effect of hexagonal Si-NCs in silicon carbide-based film with a change in the sizes and emission states of the NCs.
    Nanoscale Research Letters 11/2012; 7(1):634. · 2.48 Impact Factor
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    ABSTRACT: Cu(In1−x Gax )Se2 (CIGS) thin-film solar cells have been fabricated using the CIGS compound prepared with a two-step selenization process at 400 °C followed by successive thermal annealing at 550 °C. The compositions of the Cu-In-Ga precursors were controlled by changing the thickness ratio of the Cu-In and the Cu-Ga films. After the selenization, the thickness of the CIGS film was approximately three times that of the precursor layer. X-ray diffraction peaks showed that the CIGS had the chalcopyrite structure with a preferential orientation in the (112) direction. The composition analysis using X-ray fluorescence revealed that the Cu/[III] and the Ga/[III] ratios of CIGS changed in ranges of 0.66 ∼ 0.80 and 0.11 ∼ 0.20, respectively, with variations in the precursor thickness. We obtained a power conversion efficiency of 3.91% from the fabricated CIGS solar cell.
    Journal- Korean Physical Society 05/2012; 60(10). · 0.43 Impact Factor
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    ABSTRACT: We have studied the influence of growth temperature (TG) in the deposition of an indium tin oxide (ITO) transparent conducting oxide layer on Cu(In,Ga)Se2 (CIGS) thin-film solar cells. The ITO films were deposited on i-ZnO/glass and i-ZnO/CdS/CIGS/Mo/glass substrates using radio-frequency magnetron sputtering at various TG up to 350°C. Both the resistivity of ITO and the interface quality of CdS/CIGS strongly depend on TG. For a TG≤200°C, a reduction in the series resistance enhanced the solar cell performance, while the p–n interface of the device was found to become deteriorated severely at TG>200°C. CIGS solar cells with ITO deposited at TG=200°C showed the best performance in terms of efficiency.
    Thin Solid Films 01/2012; · 1.87 Impact Factor
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    Nae-Man Park, Ho Sub Lee, Jeha Kim
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    ABSTRACT: (CIGS) thin films are grown on Mo/soda lime glass using a reactive sputtering process in which a Se cracker is used to deliver reactive Se molecules. The Cu and targets are simultaneously sputtered under the delivery of reactive Se. The effects of Se flux on film composition are investigated. The Cu/(In+Ga) composition ratio increases as the Se flux increases at a plasma power of less than 30 W for the Cu target. The (112) crystal orientation becomes dominant, and crystal grain size is larger with Se flux. The power conversion efficiency of a solar cell fabricated using an 800-nm CIGS film is 8.5%.
    Etri Journal 01/2012; 34(5). · 0.95 Impact Factor
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    ABSTRACT: In the current study, chemical bath deposition (CBD) was used to grow CdS thin films on a Cu(In,Ga)Se2 (CIGS) absorption layer, in order to examine the effects of CdS deposition conditions on the properties of CIGS solar cell devices. The dip time leading up to the start of CdS synthesis is thought to be an important process variable determining the concentration of Cd ions diffused into the CIGS as well as the condition of the CIGS surface. Accordingly, the behavior of the CIGS solar cell efficiency variation was observed while different dip times were applied, at 4, 15 and 30 minutes, respectively. When the dip time was extended, the series resistance (Rs) of the device fell by a substantial margin, leading to improved photoelectric conversion efficiency and enhanced uniformity in device properties. This can be attributed to the effect of CIGS surface cleaning by the NH4OH contained in the reaction solution.
    Molecular Crystals and Liquid Crystals 11/2011; 551(1). · 0.49 Impact Factor
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    ABSTRACT: Cd2SnO4(CTO) thin film was made using RF magnetron sputtering and a single (CTO) target. Among various deposition variables, the effect of changes in plasma power on the electrical and optical properties of the film was investigated. It was observed, as plasma power grows, specific resistivity of the thin film increases while transmittance considerably decreases. It was found that such a phenomenon occurred because of the density of the thin film reduced by increased deposition speed. Another noteworthy result obtained through the X-ray photoelectron spectroscopy analysis is that Sn has metallic bond in the case of the thin film deposited under high power. It seems that existence of such metal was another cause of the reduced transmittance of the thin film.
    Molecular Crystals and Liquid Crystals 11/2011; 551(1):123-129. · 0.49 Impact Factor
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    ABSTRACT: Electrical properties of the Silicon quantum dots (Si-QD) light-emitting diodes (LEDs), in its dependence on the nitrogen source used in the silicon nitride (SiNx) matrix growth, have been studied. Si-QDs are formed in-situ during the SiNx film growth, and no post-annealing process for crystallization was applied. To confirm the electrical properties of the Si-QD devices, we manufacture the Si-QD LED. Both p-type and p+-type Si substrate were tested in role of hole tunneling in the LED performance. The high-resolution transmission electron microscopy (HRTEM) analyses and the current--voltage (I--V) measurement show that the Si-QDs embedded in the SiNx grown with ammonia (NH3) are located at the interface between the SiNx film and the Si substrate. This is related to the observed increase in the forward current by considering a decrease in the hole tunneling barrier width between the Si substrate and the Si-QDs.
    Japanese Journal of Applied Physics 04/2011; 50. · 1.06 Impact Factor
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    ABSTRACT: We have investigated the effect of annealing thin-film CdS/Cu(In,Ga)Se2 (CIGS) on solar cell performance. CdS/CIGS/Mo and CdS deposited on glass substrates were annealed on a hot plate in an air environment. Both the transmittance of the CdS layer at short wavelength and the X-ray diffraction (XRD) intensity of its (200)H peak increased after annealing. The quantum efficiency of the fabricated solar cells with annealed CdS buffer layer was also enhanced at short wavelength. A CIGS solar cell with a CdS buffer annealed at 200 °C for 1 min showed an efficiency of 16.47% (Jsc = 34.18 mA/cm2, Voc = 0.642 V and Fill Factor = 75.0%) which is higher than that of an un-annealed solar cell by about 0.6%. We believe that annealing increases the optical transmittance and eliminates recombination centers at the p–n junction. This leads to the improved performance of CIGS solar cells.
    Current Applied Physics 01/2011; 11(1):S65–S67. · 2.03 Impact Factor
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    ABSTRACT: We analyze the current density - voltage (J - V) curve of a Cu(In,Ga) $Se_2$ (CIGS) thin-film solar cell measured at different irradiation power densities. For the solar-cell sample investigated in this study, the fill factor and power conversion efficiency decreased as the irradiation power density (IPD) increased in the range of 2 to 5 sun. Characteristic parameters of solar cell including the series resistance ( $r_s$ ), the shunt resistance ( $r_{sh}$ ), the photocurrent density ( $J_L$ ), the saturation current density ( $J_s$ ) of an ideal diode, and the coefficient ( $C_s$ ) of the diode current due to electron-hole recombination via ionized traps at the p-n interface are determined from a theoretical fit to the experimental data of the J - V curve using a two-diode model. As IPD increased, both $r_s$ and $r_{sh}$ decreased, but $C_s$ increased.
    Journal of the Optical Society of Korea 12/2010; 14(4). · 0.96 Impact Factor
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    Journal- Korean Physical Society 12/2010; 57(61). · 0.43 Impact Factor

Publication Stats

796 Citations
117.00 Total Impact Points

Institutions

  • 2002–2012
    • Electronics and Telecommunications Research Institute
      • • Department of Intelligent Convergence Technology Research
      • • Department of Future Technology Research
      Sŏul, Seoul, South Korea
  • 2004
    • Gwangju Institute of Science and Technology
      • School of Materials Science and Engineering
      Kwangju, Gwangju, South Korea