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We present a strong non-Ohmic transport characteristic of the exfoliated La0.7Ca0.3MnO3 thin film obtained by growing a water-soluble sacrificial layer of Sr3Al2O6 between the SrTiO3 substrate and the La0.7Ca0.3MnO3 film. The non-Ohmic conduction manifests itself as a significant amount of electroresistance over a wide range of temperatures. The resistance shows a plateaulike feature at low temperatures, and the electroresistance reaches ∼50 000% at 10 K for input currents varying from 1024 nA to 125 pA. The structural characterization of the exfoliated film reveals the existence of antiphase boundaries, the tunneling through which appears to cause the non-Ohmic feature. Our results provide an avenue into colossal tunneling electroresistance mediated by crystallographic defects.

This study investigates the influence of voids on the electroluminescence (EL) emission color of ZnO microdisk/p-GaN heterojunction light-emitting diodes (LEDs). For this study, position-controlled microdisk arrays were fabricated on patterned p-GaN via wet chemical epitaxy of ZnO, and specifically, the use of trisodium citrate dihydrate (TCD) yielded high-density voids at the bottom of the microdisk. Greenish yellow or whitish blue EL was emitted from the microdisk LEDs formed with or without TCD, respectively, at reverse-bias voltages. Such different EL colors were found to be responsible for the relative EL intensity ratio between indigo and yellow emission peaks, which were originated from radiative recombination at p-GaN and ZnO, respectively. The relative EL intensity between dichromatic emissions is discussed in terms of (i) junction edge effect provoked by interfacial voids and (ii) electron tunneling probability depending on the depletion layer geometry.

We report on heteroepitaxial fabrication and structural characterizations of ultrafine GaN/ZnO coaxial nanorod heterostructures. The coaxial nanorod heterostructures were fabricated by epitaxial growth of a GaN layer on ultrafine ZnO nanorods. Epitaxial growth and precise control of GaN overlayer thickness were obtained by low pressure metalorganic vapor-phase epitaxy. ZnO nanorods grown on Si and sapphire substrates using catalyst-free metalorganic chemical vapor deposition exhibited diameters as small as 7 nm. Furthermore, structural properties of the coaxial nanorod heterostructures were investigated using both synchrotron-radiation x-ray diffraction and high resolution transmission electron microscopy.

Position-controlled n-ZnO microwire (MW) and nanowire-bundle (NW-B) arrays were fabricated using hydrothermal growth of ZnO on a patterned p-GaN film. Both the wire/film p–n heterojunctions showed electrical rectification features at reverse-bias (rb) voltages, analogous to backward diodes. Dichromatic electroluminescence (EL) emissions with 445- and 560-nm-wavelength peaks displayed whitish-blue and greenish-yellow light from MW- and NW-B-based heterojunctions at rb voltages, respectively. The different dichromatic EL emission colors were studied based on photoluminescence spectra and the dichromatic EL peak intensity ratios as a function of the rb voltage. The different EL colors are discussed with respect to depletion thickness and electron tunneling probability determined by wire/film junction geometry and size.

We report the vertical growth of ZnO nanostructures on graphene layers and their photoluminescence (PL) characteristics. ZnO nanostructures were grown vertically on the graphene layers using catalyst-free metal-organic vapor-phase epitaxy. The surface morphology of the ZnO nanostructures on the graphene layers depended strongly on the growth temperature. Further, interesting growth behavior leading to the formation of aligned ZnO nanoneedles in a row and vertically aligned nanowalls was also observed and explained in terms of enhanced nucleation on graphene step edges and kinks. Additionally, the optical characteristics and carbon incorporation into ZnO were investigated using variable-temperature PL spectroscopy.

We studied the fabrication and electroluminescent (EL) characteristics of GaN/In1−xGaxN/GaN/ZnO nanoarchitecture light emitting diode (LED) microarrays consisting of position-controlled GaN/ZnO coaxial nanotube heterostructures. For the fabrication of nanoarchitecture LED arrays, n-GaN, GaN/In0.24Ga0.76N multiquantum well (MQW) structures and p-GaN layers were deposited coaxially over the entire surface of position-controlled ZnO nanotube arrays grown vertically on c-plane sapphire substrates. The nanoarchitecture LEDs exhibited strong green and blue emission from the GaN/GaN/In0.24Ga0.76N MQWs at room temperature. Furthermore, the origins of dominant EL peaks are also discussed.

The use of a wet chemical method to selectively grow ZnO microrod and nanorod arrays on Si substrates is described. To control the size and position of the ZnO microrods and nanorods, polymethylmethacrylate (PMMA) submicron patterns were prepared on the Si substrates with an intermediate ZnO layer using e-beam lithography. Selective growth of the ZnO structures was achieved by the absence of ZnO nucleation sites on the PMMA mask, resulting in position-controlled growth of ZnO structures only on patterned holes where the ZnO layer was exposed. In addition, the diameters of the ZnO microrods were determined by the patterned hole size, and the diameters as small as 250nm were obtained when a hole diameter of 250nm was employed. The structural and optical characteristics of the ZnO microrods were further investigated using x-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy.

Hexagonal nanodisks of ZnO were fabricated by a solution process using ZnO nanoparticles and their cathodoluminescence characteristics were investigated. Monochromatic cathodoluminescence images showed that luminescence was spatially localized near the boundary of the nanodisk and spectral analysis in conjunction with the intensity profile consistently ascribed the spatial localization of luminescence to whispering-gallery-modelike-enhanced emission.