Gyu‐Chul Yi

This paper presents a review of current research activities on ZnO nanorods (or nanowires). We begin this paper with a variety of physical and chemical methods that have been used to synthesize ZnO nanorods (or nanowires). There follows a discussion of techniques for fabricating aligned arrays, heterostructures and doping of ZnO nanorods. At the end of this paper, we discuss a wide range of interesting properties such as luminescence, field emission, gas sensing and electron transport, associate

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.

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. As a service to our authors and readers, this journal provides supporting information

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,

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

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.

Carbon–hydrogen complexes in undoped and Mg-doped epitaxial GaN films have been investigated using Fourier transform infrared spectroscopy. Infrared absorption peaks in the Mg-doped material were observed at 2853, 2923, and 2956 cm−1. The absorption peaks are attributed to the symmetric and asymmetric vibrational stretching modes of C–H in CHn (n=1–3) defect complexes. The carbon–hydrogen complexes were unintentionally incorporated during the Mg-doped GaN film growth. The absorbances of the vibr

A novel method for shaping and positioning ZnO nanoarchitectures using conventional lithography and catalyst-free metal organic vapor-phase epitaxy is demonstrated. Nanowalls and nanotubes of desired shapes and arrangements can be grown heteroepitaxially on Si substrates, and their electron-emission characteristics were optimized by changing their diameter and spacing. This method can be readily expanded to create many artificial 1D and 2D structures, as required for various device applications.

Compensation in Se-doped n-type GaN prepared by atmospheric pressure metalorganic vapor phase epitaxy was studied. Hydrogen selenide was the dopant source. The carrier concentration is linearly proportional to the H2Se pressure for low partial pressures and proportional to the cube root at high partial pressures. Carrier concentrations as high as 6×1019 cm−3 at 295 K were achieved. From Hall-effect measurements, the Se-doped GaN was shown to be highly compensated even for heavily n-type material

Abstract A facile and novel technique for the fabrication of pressure sensors is reported based on the hybridization of one-dimensional nanomaterials and two-dimensional graphene film. In particular, piezoelectric pressure sensors are fabricated by using vertically aligned and position- and dimension-controlled ZnO nanotube arrays grown on graphene layers. Graphene layers act not only as substrates for catalyst-free growth of high-quality ZnO nanotubes but also as flexible conduction channels co

A combined experimental and theoretical investigation has clarified the nanometre-scale vapour-phase epitaxial growth of ZnO nanostructures on different crystal planes of GaN substrates. Under typical growth conditions, ZnO nanorods grow perpendicular to the GaN(0001) plane, but thin flat films form on GaN(101), (100) and (110). High-resolution X-ray diffraction data and transmission electron microscopy confirm the heteroepitaxial relationship between the ZnO nanostructures and GaN substrates. T

Microdonut-shaped GaN/Inx Ga1-x N light-emitting diode (LED) microarrays are fabricated for variable-color emitters. The figure shows clearly donut-shaped light emission from all the individual microdonut LEDs. Furthermore, microdonut LEDs exhibit spatially-resolved blue and green EL colors, which can be tuned by either controlling the external bias voltage or changing the size of the microdonut LED.

Fine art: Ultrafine ZnO nanowires selectively grown parallel to the substrate only on Au patterns allow the integration of large numbers of nanowire field-effect transistor arrays (see picture).