We fabricated transferable gallium nitride (GaN) thin films and light-emitting diodes (LEDs) using graphene-layered sheets. Heteroepitaxial nitride thin films were grown on graphene layers by using high-density, vertically aligned zinc oxide nanowalls as an intermediate layer. The nitride thin films on graphene layers show excellent optical characteristics at room temperature, such as stimulated emission. As one of the examples for device applications, LEDs that emit strong electroluminescence emission under room illumination were fabricated. Furthermore, the layered structure of a graphene substrate made it possible to easily transfer GaN thin films and GaN-based LEDs onto foreign substrates such as glass, metal, or plastic.

method reported previously [20]. In a typical procedure to synthesize the MWCNT/CdS core±shell nanowires, 14 mg purified MWCNTs were added into dry tetrahydrofuran (THF), which contained 0.1± 0.4 mmol S (99.999 %) powder and an identical stoichiometric amount of anhydrous CdCl 2 . After ultrasonical dispersion for 30 min, excess KBH 4 was slowly added to the flask under vigorous stirring at room temperature. The S was reduced to S 2± and the suspension gradually turned light yellow. After the mixture was stirred for 12 h, a dark yellow precipitate was produced. The dark yellow powder was filtered and washed thoroughly with dry THF, deionized water, and absolute ethanol several times to remove the impurities.The Electroluminescence in n-ZnO Nanorod Arrays Vertically Grown on p-GaN** By Won Il Park and Gyu-Chul Yi* ZnO is a promising material for short-wavelength photonic device applications due to its characteristic direct and wide bandgap with a large exciton binding energy of 60 meV.[1] Recently, both ZnO epitaxial films and single crystalline nanorods have shown excellent optical characteristics.[2±5] Further research on ZnMgO alloys has enabled the control of the bandgap energy in ZnO-based materials and the fabrication of ZnO/ZnMgO nanorod quantum structures.[6] Despite significant progress on ZnO films and nanostructures, the difficulty of p-type doping in ZnO has impeded the fabrication of ZnO p±n homojunction devices. As an alternative approach to homojunction, an n-ZnO/p-GaN heterojunction has been suggested as a strong candidate for device applications, [7,8] since these materials have a similar fundamental bandgap energy (~3.4 eV), the same wurtzite crystal structure, and a low lattice constant misfit of 1.9 %. In general, however, p±n heterojunction devices show a lower efficiency than homojunction devices, [9] because an energy barrier formed at the junction interface decreases carrier injection efficiency for heterojunction devices with a large band offset. [10] This problem may be solved by increasing the carrier injection efficiency by making nanosized junctions, since, as previously reported, the carrier injection rate significantly increases for nanocontacts in Schottky diodes. [11,12] Here, we report on the fabrication of n-ZnO/p-GaN nanorod electroluminescent (EL) devices and their EL characteristics. A schematic of n-ZnO/p-GaN nanorod heterojunction arrays is shown in Figure 1a. For EL device fabrication, vertically well-aligned n-type ZnO nanorod arrays were epitaxially grown on p-GaN(0001) substrates employing catalyst-free metal-organic vapor phase epitaxy (MOVPE). The growth parameters of ZnO nanorods on GaN(0001) substrates were similar to those on Al 2 O 3 (0001) substrates.[13] The synthesis of ZnO nanorods resulted in a preferential growth direction along the c-axis of ZnO normal to the substrate surface. As shown in Figure 1b, field-emission scanning electron micros-COMMUNICATIONS

Recently, there has been considerable interest in oxide semiconductors for photocatalyst applications. This is due to their high photocatalytic activity and excellent chemical and mechanical stability. [1,2] Many oxide materials including TiO 2and ZnO have been prepared as thin films as well as fine powders. [2] In particular, tremendous attention has been paid to fine powders since high photocatalytic efficiency can be achieved by increasing the effective surface area of the materials. However, these powders have generally been used in a suspended state in water, which limits their practical use, due to problems in their separation and recovery. Such difficulty is more serious with nanometer-scale ultrafine powders. Supporting photocatalytic materials on a rigid substrate can solve this problem. Many thin film deposition techniques have been widely used for the immobilization of photocatalytic materials. [3,4] Among the numerous thin film deposition techniques, metal-organic chemical vapor deposition (MOCVD) has many advantages: excellent crystallinity, mechanical stability, good adhesion of films, and easy mass production. Meanwhile, since photocatalytic activity generally increases with effective surface area, a rough film surface with a high surface-tovolume (S/V) ratio is beneficial. From this point of view, onedimensional (1D) semiconductor nanomaterials with extremely high S/V ratios are good candidates for photocatalytic and photovoltaic applications. [5,6] Nevertheless, photocatalytic applications of oxide nanostructures have rarely been reported. In this communication, we report on the photocatalytic activity of ZnO thin films and nanoneedle arrays grown using MOCVD. We prepared both ZnO thin films and nanoneedle arrays using the same MOCVD growth system, in order to compare photocatalytic characteristics of these materials. The substrates used in this study were Si wafers and glass plates. These materials are suitable for mass production because of their low cost and availability in large sizes. Additionally, MOCVD enables us to deposit the materials on cheap and large substrates. For MOCVD of ZnO thin films and nanoneedle arrays, deposition temperatures were as low as 400 C. [7,8] Low growth temperature is essential for the use of cheap glass substrates. Meanwhile, ZnO nanoneedle arrays were prepared without using any metal catalysts that are generally employed for the one-dimensional growth of semiconductor nanowires. This catalyst-free method excludes possible incorporation of metal impurities into the nanomaterials and the formation of metal nanoparticles on the nanoneedle tips. [7,9] Hence, sharp or flat tips of nanomaterials can be easily made by changing only growth parameters such as deposition pressure and temperature, without any post-treatment. [7,10] As previously reported, both ZnO thin films and nanoneedle arrays exhibited excellent crystallinity and optical properties. [7,9] Photocatalytic activity of ZnO thin films grown by MOCVD was determined by measuring the photoinduced decoloration...

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.

We report on fabrication and electrical characteristics of ZnO nanorod Schottky diode arrays. High quality ZnO nanorods were grown for the fabrication of the Schottky diodes using noncatalytic metalorganic vapor phase epitaxy and Au was evaporated on the tips of the vertically well-aligned ZnO nanorods. I–V characteristics of both bare ZnO and Au/ZnO heterostructure nanorod arrays were measured using current-sensing atomic force microscopy. Although both nanorods exhibited nonlinear and asymmetric I–V characteristic curves, Au/ZnO heterostructure nanorods demonstrated much improved electrical characteristics: the reverse-bias breakdown voltage was improved from −3 to −8 V by capping a Au layer on the nanorod tips. The origin of the enhanced electrical characteristics for the heterostructure nanorods is suggested.