Kyu-Chul Lee

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Visible-color-tunable light-emitting diodes (LEDs) with electroluminescent color that changes continuously from red to blue by adjusting the external electric bias are fabricated using multifacetted GaN nanorods with anisotropically formed 3D InGaN multiple-quantum wells. Monolithically integrated red, green, and blue LEDs on a single substrate, operating at a fixed drive current, are also demonstrated for inorganic full-color LED display applications.

Flexible inorganic nanostructure light-emitting diodes (LEDs) are fabricated using high-quality GaN/ZnO coaxial nanorod heterostructures grown directly on large graphene films. The nanostructure LEDs fabricated on graphene films are readily transferred onto flexible plastic substrates, which operated reliably in a flexible form without significant degradation of the LED performance.

The photocatalytic activity of GaN nanowires was investigated for the use of GaN nanowires as photocatalysts in harsh environments. GaN nanowires with diameters of 20-50 nm and lengths of 4-6 microm were prepared by Ni catalyst-assisted metal-organic chemical vapor deposition. Comparisons of GaN nanowires with GaN submicron dot arrays and thin films showed that GaN nanowires exhibit much better photocatalytic activity, resulting from a high surface-to-volume ratio. In addition, GaN nanowires exh

We report the growth of high-quality GaN films on large-size graphene films for visible light-emitting diodes (LEDs). The graphene films were synthesized by chemical vapor deposition and then transferred onto amorphous silica (SiO2) substrates that do not have an epitaxial relationship with GaN. Before growing the high-quality GaN thin films, ZnO nanowalls were grown on the graphene films as an intermediate layer. The structural and optical characteristics of the GaN films were investigated, and

Direct epitaxial growth of inorganic compound semiconductors on lattice-matched single-crystal substrates has provided an important way to fabricate light sources for various applications including lighting, displays and optical communications. Nevertheless, unconventional substrates such as silicon, amorphous glass, plastics, and metals must be used for emerging optoelectronic applications, such as high-speed photonic circuitry and flexible displays. However, high-quality film growth requires g

This paper reports on the controlled fabrication of a highly sensitive piezoresistive sensor by using Si nanorod (NR) arrays. An efficient, large-area, scalable strategy was adopted to fabricate the pressure sensors by incorporating chemically etched, high-aspect-ratio, vertical Si NR arrays between two thin Au layers. The piezoresistive properties corresponding to dimension- and position-controlled and randomly etched, closely packed, and thin Si NR arrays were exploited to fabricate the small,

The epitaxial lateral overgrowth (ELOG) of GaN microdisks on graphene microdots and the fabrication of flexible light-emitting diodes (LEDs) using these microdisks is reported. An ELOG technique with only patterned graphene microdots is used, without any growth mask. The discrete micro-LED arrays are transferred onto Cu foil by a simple lift-off technique, which works reliably under various bending conditions.

This article presents a review of current research activities on the hybrid heterostructures of inorganic nanostructures grown directly on graphene layers, which can be categorized primarily as zero-dimensional nanoparticles; one-dimensional nanorods, nanowires, and nanotubes; and two-dimensional nanowalls. For the hybrid structures, the nanostructures exhibit excellent material characteristics including high carrier mobility and radiative recombination rate as well as long-term stability while

Plan-view and cross-sectional transmission electron microscopy images show the microstructural properties of GaN thin films grown on graphene layers, including dislocation types and density, crystalline orientation and grain boundaries. The roles of ZnO nanowalls and GaN intermediate layers in the heteroepitaxial growth of GaN on graphene, revealed by cross-sectional transmission electron microscopy, are also discussed.

Position- and morphology-controlled ZnO nanostructures are grown on an oxygen plasma-treated selective area of graphene layers using metal-organic vapor-phase epitaxy. The structural and optical characteristics examined by electron microscopy, cathodoluminescence and photoluminescence techniques indicate that high-quality nanostructures are prepared on graphene layers. This approach to grow the controlled ZnO nanostructures selectively on graphene layers enables us to fabricate various nanodevic

We report on photoluminescent properties of ZnO/Zn 0.8 Mg 0.2 O nanorod single-quantum-well structures (SQWs). Catalyst-free metalorganic vapor-phase epitaxy (MOVPE) was employed for precise controls of well widths and compositions of the nanorod SQWs. Both time-integrated and time-resolved photoluminescence (PL) spectra of ZnO/Zn 0.8 Mg 0.2 O nanorod SQWs were measured at various temperatures between 10 and 300 K. From the PL spectra of the nanorod SQWs measured at 10 K, a PL peak blue-shift de

Deep level defects in n-type epitaxial GaN compensated with Mg were measured using photocapacitance spectroscopy on Schottky barrier diodes. The doped GaN was prepared by atmospheric pressure metalorganic vapor phase epitaxy using bis(cyclopentadienyl)magnesium as the dopant source. The Mg-doped GaN films were n type as determined by Hall-effect measurements. Addition of magnesium resulted in the formation of a series of deep centers with optical threshold energies of 1.0, 1.2, 1.8, and 3.1 eV.