Publications (13)38.56 Total impact
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Article: Enhanced electroluminescence of a-plane InGaN light emitting diodes grown on oxide-patterned r-plane sapphire substrates.
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ABSTRACT: We report on the new fabrication method of a-plane InGaN light emitting diodes (LEDs) using the epitaxy on patterned insulator on sapphire substrate (EPISS). Cathodoluminescence spectrum of the fully coalesced a-plane GaN template showed that band edge emission intensity of the wing region was four times higher than that of the window region. Threading dislocations and basal stacking faults densities in wing region were ~1×10⁷ cm⁻² and ~5☓10⁴ cm⁻¹, respectively. Blue-emitting (443.4 nm) a-plane InGaN LED employing EPISS showed the optical power of 3.1 mW and the EL FWHM of 25.2 nm at the injection current of 20 mA.Optics Express 11/2011; 19(23):23036-41. · 3.59 Impact Factor -
Article: Characteristics of a-GaN films and a-AlGaN/GaN heterojunctions prepared on r-sapphire by two-stage growth process
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ABSTRACT: The electrical properties, presence of deep electron and hole traps and photoluminescence spectra were measured for undoped a-GaN films grown by metal-organic chemical vapor deposition (MOCVD) in a two-stage process using a high V/III ratio at the first stage and low V/III ratio at the second stage. Growth was performed on r-sapphire substrates with a high temperature GaN nucleation layer. The films showed a full width at half maximum of 450-470 arcseconds for the (11-20) x-ray rocking curve with little anisotropy with respect to the sample rotation around the growth direction. The stacking fault (SF) density determined by selective etching was ∼5 × 104 cm−1. The residual donor concentration was 1014–1015 cm−3, with a very low density (2.5 × 1013 cm−3) of electron traps located at Ec − 0.6 eV, which are believed to be one of the major non-radiative recombination centers in nonpolar GaN. Consequently, the films showed a high intensity of bandedge luminescence with negligible contribution from defect bands associated with SFs. In contrast to previously studied nonpolar GaN films, the a-GaN layers showed a high concentration of gallium-vacancy-related acceptors near Ev + 1 eV and a strong yellow luminescence band, both indicating that growth conditions were effectively N-rich. a-AlGaN/GaN heterojunctions with thin heavily Si doped AlGaN barriers made on a-GaN substrates showed two-dimensional electron gas (2DEG) concentrations of 1.2 × 1013 cm−3, with 2DEG mobility of 80 cm2/Vs. Capacitance-voltage profiling of Schottky diodes on these HJs suggest that the 2DEG is fully depleted by the built-in voltage of the Schottky diode.Journal of Applied Physics 11/2011; 110(9):093709-093709-6. · 2.17 Impact Factor -
Article: Design and fabrication of vertical-injection GaN-based light-emitting diodes.
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ABSTRACT: The fabrication process and design issues for the fabrication of vertical-injection GaN-based light-emitting diodes were investigated. The process yield was reduced according to the adhesion of reflective p-electrodes, the exposure of electroplated metal in plasma, and wet-etching induced surface textures. The chip design utilizing current blocking layer and branched n-electrode was found to significantly affect the power efficiency of LEDs.Optics Express 07/2011; 19 Suppl 4:A937-42. · 3.59 Impact Factor -
Article: Orange a-plane InGaN/GaN light-emitting diodes grown on r-plane sapphire substrates.
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ABSTRACT: We report on orange a-plane light-emitting diodes (LEDs) with InGaN single quantum well (SQW) grown on r-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD). The peak wavelength and the full-width at half maximum (FWHM) at a drive current of 20mA were 612.2 nm and 72 nm, respectively. The device demonstrated a blue shift in emission wavelength from 614.6 nm at 10 mA to 607.5 nm at 100 mA, representing a net shift of 7.1 nm over a 90 mA range, which is the longest wavelength compared with reported values in nonpolar LEDs. The polarization ratio values obtained from the orange LED varied between 0.36 and 0.44 from 10 to 100mA and a weak dependence of the polarization ratio on the injection current was observed.Optics Express 07/2011; 19(14):12919-24. · 3.59 Impact Factor -
Article: Large-area transparent conductive few-layer graphene electrode in GaN-based ultra-violet light-emitting diodes Related Articles
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ABSTRACT: Metal-assisted electroless fabrication of nanoporous p-GaN for increasing the light extraction efficiency of light emitting diodes AIP Advances 2, 012109 (2012) Work-function-tuned multilayer graphene as current spreading electrode in blue light-emitting diodes Appl. Phys. Lett. 100, 023502 (2012) Effect of strain and barrier composition on the polarization of light emission from AlGaN/AlN quantum wells Appl. Phys. Lett. 100, 021101 (2012) Spectroscopic study of white organic light-emitting devices with various thicknesses of emissive layer J. Appl. Phys. 111, 014507 (2012) Barrierless hole injection through sub-bandgap occupied states in organic light emitting diodes using substoichiometric MoOx anode interfacial layer Appl.Applied Physics Letters 04/2011; 99:143101. · 3.84 Impact Factor -
Article: Opposite carrier dynamics and optical absorption characteristics under external electric field in nonpolar vs. polar InGaN/GaN based quantum heterostructures.
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ABSTRACT: We report on the electric field dependent carrier dynamics and optical absorption in nonpolar a-plane GaN-based quantum heterostructures grown on r-plane sapphire, which are surprisingly observed to be opposite to those polar ones of the same materials system and similar structure grown on c-plane. Confirmed by their time-resolved photoluminescence measurements and numerical analyses, we show that carrier lifetimes increase with increasing external electric field in nonpolar InGaN/GaN heterostructure epitaxy, whereas exactly the opposite occurs for the polar epitaxy. Moreover, we observe blue-shifting absorption spectra with increasing external electric field as a result of reversed quantum confined Stark effect in these polar structures, while we observe red-shifting absorption spectra with increasing external electric field because of standard quantum confined Stark effect in the nonpolar structures. We explain these opposite behaviors of external electric field dependence with the changing overlap of electron and hole wavefunctions in the context of Fermi's golden rule.Optics Express 03/2011; 19(6):5442-50. · 3.59 Impact Factor -
Article: Ohmic contact properties of non-polar a-plane GaN films on r-plane sapphire substrates
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ABSTRACT: The properties of Ti/Al/Ni/Au Ohmic contacts on n-type a-plane GaN epitaxial layers directly grown on r-plane sapphire substrates are reported. The minimum specific contact resistance of ~10−5 Ω cm2 was achieved after annealing at 650–700 °C. Ohmic contact properties were measured using transmission line method patterns oriented in both the m- and c-axis directions of a-plane GaN. The sheet resistance of a-plane GaN along the c-axis was two times higher than that along the m-axis, which shows significant electric anisotropy in the two orientations.Journal of Physics D Applied Physics 07/2010; 43(29):295102. · 2.54 Impact Factor -
Article: Effects of Basal Stacking Faults on Electrical Anisotropy of Nonpolar a-Plane ( ) GaN Light-Emitting Diodes on Sapphire Substrate
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ABSTRACT: We report on the effects of basal stacking faults (BSFs) on the electrical anisotropy and the device characteristics of nonpolar a-plane GaN (1120) light-emitting diodes (LEDs) on r-plane (1102 ) sapphire substrates. The sheet resistance in the direction parallel to the c-axis [0001] is 18%-70% higher than the one in the direction parallel to the m-axis [1100 ]. The anisotropic conductivity of faulted a-plane GaN films can be explained by carrier scatterings from BSFs. It is also shown that the output power of nonpolar a-plane GaN LEDs are significantly influenced by the presence of BSFs, which laterally hampers the carrier transport in the n-GaN layer, especially in the direction parallel to the c-axis in faulted nonpolar nitride films.IEEE Photonics Technology Letters 06/2010; · 2.19 Impact Factor -
Article: Effects of Photoelectrochemical Etching of N-Polar and Ga-Polar Gallium Nitride on Sapphire Substrates
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ABSTRACT: We studied the effects of photo electrochemical (PEC) etching by using various concentrations (1, 2, and 4 M) of KOH solutions on both Ga- and N-face GaN layers on sapphire substrates. The Ga-face was chemically stable for KOH solutions, while by sharp contrast the KOH could etch the N-face, where the 6-fold symmetry was observed after the PEC etching. Surface texturing of GaN-based light emitting diodes and solar cells by KOH-based PEC etch could enhance the efficiency of GaN-based photonic devices by increasing the number of the scattering events and randomly changing the angles of the light.Journal of The Electrochemical Society. 05/2010; 157(6):H676-H678. -
Article: Enhanced light extraction of nonpolar a-plane (11-20) GaN light emitting diodes on sapphire substrates by photo-enhanced chemical wet etching.
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ABSTRACT: The extraction efficiency of nonpolar a-plane (11-20) GaN LEDs on sapphire substrates has been enhanced by selectively etching the mesa sidewall faces and the n-type GaN surfaces with photoenhanced chemical wet etching. Submicron-sized trigonal prisms having prismatic planes of {1-100} were clearly displayed on the n-type GaN surfaces as well as the sidewall face after 5 min etching at 60 degrees C. The radiation patterns have shown that more light is extracted in all directions and the output powers of surface textured a-plane GaN LEDs have increased by 25% compared with control samples. PEC wet etching produced unique feature of etching morphology on the mesa sidewall faces and the n-type GaN surface.Optics Express 04/2010; 18(9):9728-32. · 3.59 Impact Factor -
Article: Demonstration of nonpolar a-plane InGaN/GaN light emitting diode on r-plane sapphire substrate
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ABSTRACT: High crystalline a-plane (110) GaN epitaxial layers with smooth surface morphology were grown on r-plane (102) sapphire substrate by metalorganic chemical vapor deposition. The full width at half maximum of x-ray rocking curve was measured as 407 arc sec along c-axis direction, and the root mean square roughness was 1.23 nm. Nonpolar a-plane InGaN/GaN light emitting diodes were subsequently grown on a-plane GaN template, and the optical output power of 0.72 mW was obtained at drive current of 20 mA (3.36 V) and 2.84 mW at 100 mA (4.62 V) with the peak emission wavelength of 477 nm.Applied Physics Letters 08/2009; 95(7):071101-071101-3. · 3.84 Impact Factor -
Article: Design of high-efficiency GaN-based light emitting diodes with vertical injection geometry
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ABSTRACT: The authors report on the design and fabrication of high-efficiency GaN-based light emitting diodes (LEDs) with vertical-injection geometry. Based on the analyses of LED test patterns fabricated with various n -electrode dimensions, a design rule for vertical LEDs is proposed. It is found that the suppression of the vertical current under n electrodes and the efficient injection of the spreading current across the n layers are essential to fabricate high-efficiency LEDs. Introduction of the current blocking layer along with well-designed branched n electrodes results in a large enhancement of power efficiency by a factor of 1.9, compared with that of reference LEDs.Applied Physics Letters 08/2007; · 3.84 Impact Factor -
Article: High-Reflectance and Thermally Stable AgCu Alloy p-Type Reflectors for GaN-Based Light-Emitting Diodes
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ABSTRACT: We report on the formation of high-quality AgCu alloy p-type reflectors for GaN-based light-emitting diodes (LEDs). Compared with Ag contacts, the AgCu alloy reflectors produce lower specific contact resistance (7.5times10<sup>-5</sup> Omegamiddotcm<sup>2</sup>), higher light reflectance (89.5% at 400 nm), and better thermal stability (absence of interfacial voids), when annealed at 400 degC in N<sub>2 </sub> : O<sub>2</sub>(=1:1) ambient. LEDs fabricated with the AgCu reflectors show light output power better than that of LEDs with the Ag reflectors. The ohmic mechanism for the AgCu alloy reflectors is explained in terms of the formation of Ag-Ga solid solution and the presence of Cu-oxide nano-particles at the contact/GaN interfaceIEEE Photonics Technology Letters 04/2007; · 2.19 Impact Factor
Top co-authors
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Institutions
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2011
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Chonbuk National University
Seoul, Seoul, South Korea
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2009–2011
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Korea Electronics Technology Institute
Seongnam, Gyeonggi, South Korea
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2010
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Korea University
- Department of Chemical and Biological Engineering
Seoul, Seoul, South Korea
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