Electroluminescence in n‐ZnO Nanorod Arrays Vertically Grown on p‐GaN

Abstract

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

Flexible Piezotronic Strain Sensor

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