Yong-Tae Moon

LG Electronics, Sŏul, Seoul, South Korea

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Publications (19)27.77 Total impact

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    ABSTRACT: Indium predeposition prior to the growth of InGaN well layers was found to significantly improve the optical properties of InGaN/GaN multiple quantum wells (MQWs). Photoluminescence and ultraviolet-visible absorption spectroscopy measurements showed a remarkable decrease in the Stokes shift with increasing indium predeposition time. High resolution x-ray diffraction measurements revealed a significant improvement in the interface quality of the MQWs. These results indicate that indium predeposition improves the uniformity of the indium composition in InGaN well layers, resulting in the formation of nearly perfect square potential wells in MQWs.
    Journal of Physics D Applied Physics 01/2008; 41(16). · 2.53 Impact Factor
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    ABSTRACT: Nanoindentation studies have been carried out on undoped and doped epitaxial GaN thin films with different thickness (1–4 μm) were grown epitaxially on c-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD). Multiple discontinuities (so-called ‘pop-in’ events) were observed in the load–indentation depth curve irrespective of the thickness as well as the doping condition. Atomic force microscopy (AFM) studies on the residual indentation impression revealed no micro-cracks even after the indentation beyond the critical depth. The physical mechanism responsible for the ‘pop-in’ was explained by the interaction of the deformed region, produced by the indenter tip, with the pre-existing threading dislocation in the epitaxial GaN thin films.
    Materials Chemistry and Physics 01/2006; 99:410-413. · 2.07 Impact Factor
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    ABSTRACT: The enhancement of phase separation in the InGaN layer grown on a GaN layer with a rough surface was investigated for the formation of self-assembled In-rich quantum dots (QDs) in the InGaN layer. Transmission electron microscopy images showed that In-rich QDs with a size of 2–5 nm were formed even in an InGaN layer with a low indium content, and a layer thickness less than the critical thickness. The room-temperature photoluminescence (PL) spectrum of this layer showed emission peaks corresponding to In-rich QDs. The temperature-dependent PL spectra showed dominant peak shifts to the lower energy side, indicating that the self-assembled In-rich QDs are formed in the InGaN layer grown on a rough GaN surface and that the carriers are localized in In-rich QDs.
    Applied Physics Letters 08/2005; 87(6):061906-061906-3. · 3.79 Impact Factor
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    ABSTRACT: We report that NH 3 ambient thermal annealing is a promising method for recovering the dry-etch-induced damage on Mg-doped GaN surfaces. The surface electrical properties of dry-etched Mg-doped GaN can be fully recovered by thermal annealing using NH 3 as an ambient gas at temperatures above 900 °C. The complete recovery of sheet hole concentration in dry-etched Mg-doped GaN can be attributed to a reduction in excess nitrogen vacancies in the damaged surface region by reactive nitrogen atoms supplied during NH 3 ambient thermal annealing. © 2004 American Vacuum Society.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2004; 22(2). · 1.27 Impact Factor
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    ABSTRACT: The effects of the growth temperature for GaN barrier layers on the characteristics of InGaN/GaN multiple quantum wells (MQWs) grown by using metalorganic chemical vapor deposition were investigated. The improvement in the electrical properties of MQW light-e1mitting diodes with increasing barrier growth temperature from 700 to 840 • C is attributed to a decrease in the number of deep-level-related defects in the barrier layers. The interface flatness and the structural properties in the MQWs were significantly improved with increasing barrier-layer growth temperature and are attributed to an increase in the in-plane domain size and to the atomic stacking order in GaN barrier layers.
    Journal- Korean Physical Society 05/2003; 42. · 0.51 Impact Factor
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    ABSTRACT: We report on the growth and photoluminescence of InGaN/GaN multiple quantum wells (MQWs) grown on GaN nanocrystals embedded in amorphous SiN x ; grown on a p-type Si(1 0 0) substrate. p-Type Si(1 0 0) was thermally nitridated using NH 3 to form an amorphous SiN x layer in a metalorganic vapor phase epitaxy system. GaN nanocrystals were then grown on the SiN x layer, followed by the growth of InGaN/GaN MQWs on the GaN nanocrystals. These nanosize MQWs were capped with amorphous SiN x in a plasma enhanced chemical vapor deposition system. The findings show that nanosize InGaN/GaN MQWs can be embedded in amorphous SiN x grown on p-type Si(1 0 0) and that these self-assembled nanostructures may be used as new nanosize light-emitting sources as evidenced by photoluminescence from nanosize MQWs. r 2002 Elsevier Science B.V. All rights reserved.
    Journal of Crystal Growth 01/2003; 248(78). · 1.55 Impact Factor
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    ABSTRACT: The electrical and optical characteristics of GaN:Mg irradiated by a pulsed KrF 248 nm excimer laser have been studied. When an as-grown Mg-doped GaN film was irradiated by an excimer laser at an energy density of 590 mJ/cm 2 in a nitrogen atmosphere, the hole concentration was drastically increased up to 4.4210 17 cm 3 . Furthermore, a GaN:Mg thin film, which was treated by laser irradiation following a conventional rapid thermal annealing process, showed a very high hole concentration of 9.4210 17 cm 3 . The GaN:Mg samples, which were activated in a nitrogen ambient by the KrF excimer laser irradiation, showed two photoluminescence peaks at 2.95 eV and 2.7 eV. The intensities of both photoluminescence peaks were increased with increasing laser energy density and number of pulses. The changes in photoluminescence peaks depending on the laser energy density further suggest that the pulsed KrF excimer laser irradiation dissociates the Mg–H complexes and allows the hydrogens to diffuse out, thus significantly enhancing the p-type conductivity of GaN:Mg. © 2003 American Vacuum Society.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2003; 21(2).
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    ABSTRACT: We fabricated the white light-emitting diodes without phosphor materials using phase-separated InGaN active layers. The white luminescence was attributed to the broad distributions of indium composition and size of quantum dot- like In-rich regions in the phase-separated InGaN Ternary alloys.
    Proc SPIE 12/2001;
  • physica status solidi (b) 11/2001; · 1.49 Impact Factor
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    ABSTRACT: The effects of indium segregation and hydrogen on the optical and structural properties of InGaN/GaN multiple quantum wells, grown by metalorganic chemical vapor deposition were investigated. Photoluminescence and high-resolution transmission electron microscopy analysis showed that two types of indium-rich regions can be formed in the InGaN well layers. Self-assembled quantum dot-like indium-rich regions were found in the well layer grown at a normal growth temperature. These regions behaved as luminescent centers, showing a maximum indium content at the center of indium-rich region. However, randomly-distributed indium-segregated regions, which formed near the upper interface of the InGaN well layers during the subsequent high-temperature annealing process led to the degradation of the optical properties by generating defects such as misfit dislocations. The use of hydrogen during the growth interruption was found to be very effective in suppressing the formation of indium-segregated regions in the InGaN well layers. © 2001 American Institute of Physics.
    Journal of Applied Physics 05/2001; 89(11):6514-6518. · 2.21 Impact Factor
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    ABSTRACT: We investigated the effect of barrier thickness on the interfacial and optical properties of the InGaN/GaN multiple quantum wells (MQWs) grown in a low-pressure metalorganic chemical vapor deposition system. The GaN barrier thickness in the InGaN/GaN MQWs was found to play a key role to determine the interfacial structural and optical characteristics of the MQWs. As the thickness of the GaN barrier layer was increased, the abruptness of the interface between InGaN and GaN layers deteriorated, probably due to the generation of defects induced by the strain accumulation in the MQWs. Accordingly, the intensity and the line-width of the photoluminescence taken from the MQWs were reduced and broadened, respectively with the increase of the GaN barrier thickness. The InGaN/GaN MQWs grown with an optimized barrier thickness showed an intense room-temperature photoluminescence at the wavelength of 479.5 nm with a very narrow full width at half maximum of 40.82 meV.
    Japanese Journal of Applied Physics 04/2001; 40(1):3085-3088. · 1.07 Impact Factor
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    ABSTRACT: The effect of the growth pressure on the In incorporation in InGaN thin films, grown by metalorganic chemical vapor deposition (MOCVD) have been investigated. The InGaN thin films were grown by varying the growth pressures, while maintaining all other growth parameters constant. Photoluminescence and high resolution x-ray diffraction (XRD) measurements showed that the In incorporation in the InGaN thin film was drastically increased with decreasing growth pressures. XRD analysis also revealed that the In concentration in the films was increased by 7.5% as the growth pressure was decreased from 250 torr to 150 torr. This can be attributed to the enhanced mass transportation of precursor gases through the boundary-layer on the substrate in the MOCVD system.
    Journal of Electronic Materials 01/2001; 30(2):99-102. · 1.64 Impact Factor
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    ABSTRACT: The temperature dependence of the photoluminescence (PL) of InGaN films, grown by metalorganic chemical vapor deposition, has been investigated. A strained InGaN thin film which contains composition-fluctuated regions shows the so-called S-shaped temperature dependence of the dominant PL peak energy. However, an InGaN thick film which contains quantum dot-like In-rich regions shows a sigmoidal temperature dependence of the dominant PL peak energy, as the result of a transfer of carriers from the band-edge related luminescent centers to quantum dot-like In-rich regions. It is also found that the activation energy for the thermal quenching of PL intensity in the InGaN thick film which contains quantum dot-like In-rich regions is larger than that in the strained InGaN thin film which contains composition-fluctuated regions.
    Applied Physics Letters 01/2001; 79. · 3.79 Impact Factor
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    ABSTRACT: Metalorganic chemical vapor deposition growth of GaN films using trimetylgallium (TMGa) and triethylgallium (TEGa) sources exhibited the different growth mechanisms and properties of GaN films. In situ normal incidence reflectance measurements during the growth of GaN with TEGa showed an increased coalescence time and a lower growth rate compared with TMGa, resulting in defect free columnar domains, a lower density of dislocation at the domain boundary, a rough surface, and good electrical properties. These results indicate that the growth mode for TEGa-grown GaN slowly changes from three-dimensional to quasi-two dimensional lateral growth via a coalescence stage and that the roughening and coalescence processes are repeated with increasing film thickness. A broad yellow emission peak was also observed at around 550nm, in the case of the TEG-grown GaN. This yellow emission can be attributed to an increase in the concentration of nitrogen vacancy-related complexes or extended defects in the TEGa-grown GaN. This situation led also to an increase in the background electron concentration and a rough surface, compared with those of TMG-grown GaN.
    Journal of Crystal Growth 01/2001; 233(3):439-445. · 1.55 Impact Factor
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    ABSTRACT: A two-step rapid thermal annealing (RTA) process is proposed in order to improve the electrical properties, the crystal quality, and the surface roughness of Mg-doped p-type GaN films. In the two-step RTA process, the first low temperature step (600 °C) with a long annealing time (5 min) was followed by the second high temperature (950 °C) step with a short annealing time. These results show that the two-step RTA process significantly improves electrical properties and reduces the surface roughness of p-GaN compared to the one-step RTA process. © 2001 American Vacuum Society.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2001; 19(1):215-218. · 1.27 Impact Factor
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    ABSTRACT: The e!ect of the number of InGaN/GaN quantum well (QW) pairs on the interfacial structural and optical properties of InGaN/GaN multiple quantum wells (MQWs), as grown by low-pressure metalorganic vapor-phase epitaxy was examined. As the number of QW pairs increased, In-rich InGaN precipitates were more readily detected in the InGaN/GaN MQWs by cross-sectional transmission electron microscope. The intensity of the photoluminescence (PL) peak was decreased and the PL peak was red-shifted with an increase in the number of QW pairs. X-ray di!raction measurements revealed that the interfacial structure between InGaN and GaN were also deteriorated with the increasing number of QW pairs. These results can be attributed to the relaxation of an accumulated strain through the dislocations induced by an increase in the total thickness of the MQWs with an increase in the number of QW pairs. These results suggest that the defects such as dislocations facilitate the formation of In-rich phases in the InGaN layers in the MQWs. 2000 Elsevier Science B.V. All rights reserved.
    Journal of Crystal Growth 01/2000; 22120(61). · 1.55 Impact Factor
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    ABSTRACT: The effects of the growth interruption and the introduction of H2 during interruption time on the optical and structural properties of InGaN/GaN multiquantum wells (MQWs), grown by metalorganic chemical vapor deposition, were investigated. When the growth was interrupted during the formation of interfaces in the MQWs, the intensity of photoluminescence (PL) was greatly increased and the formation of InN-rich regions near the surface of the InGaN well layer was suppressed. As the interruption time increased, however, the PL intensity decreased and the average In composition of InGaN/GaN MQWs decreased. When H2 was introduced during the growth interruption, the intensity of the PL was significantly enhanced by eliminating the impurities at the interface and the PL peaks were blueshifted due to the reduction in the thickness of the InGaN well layers, as a result of H2 etching of well and barrier layers. © 2000 American Vacuum Society.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2000; 18(6):2631-2634.
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    ABSTRACT: The effect of the growth rate of the nucleation layer on the growth of a high temperature GaN layer has been studied by observing the in situ normal incidence reflectance during the growth of GaN by metalorganic chemical vapor deposition. This study revealed that the lateral growth and coalescence of a high temperature GaN layer was enhanced as the growth rate of the nucleation layer was increased. However, the measurement of (102) hk-circle scan using x-ray diffraction showed that the in-plane structural qualities of GaN were found to be deteriorated by increasing the growth rate of the nucleation layer. The electron mobility was also decreased by increasing the growth rate of the nucleation layer. These results suggest that the nucleation sites are well oriented on the sapphire substrate at a low growth rate of the nucleation layer but that the lateral growth and coalescence of the GaN layer is hindered due to the limited surface diffusion of adatoms at a fast growth rate of the nucleation layer. © 2000 American Vacuum Society.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2000; 18(1):140-143.
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    ABSTRACT: We have studied the effects of growth temperature, film thickness, and Si doping on the phase separation in InGaN films grown by metalorganic chemical vapor deposition. As the growth tem-perature decreased, the band-edge photoluminescence peak became splitted due to the In compo-sition fluctuation in the InGaN film and finally separated into two discrete peaks corresponding to the epitaxial InGaN and InN-rich phase. The size and the In content of the spinodally-formed InN-rich regions increased with increasing InGaN film thickness. The Si doping was found to sup-press the composition fluctuation and the In incorporation in InGaN films.
    physica status solidi (b) 01/1999; 216(68). · 1.49 Impact Factor

Publication Stats

97 Citations
27.77 Total Impact Points

Institutions

  • 2008
    • LG Electronics
      Sŏul, Seoul, South Korea
  • 2006
    • Gwangju Institute of Science and Technology
      • School of Materials Science and Engineering
      Gwangju, Gwangju, South Korea
  • 2005
    • Virginia Commonwealth University
      • Electrical Engineering
      Richmond, VA, United States