Ultraviolet-light-emitting materials are a key to the future of optoelectronics. They can be used in laser diodes, for lithography processes, for large-capacity memories, and as a sterilizing light source. [1±3] (0001)-oriented ZnO is a realistic candidate for a room-temperature ultraviolet-light-emitting material, because of its wide bandgap energy of 3.3 eV and high exciton binding energy of 59 meV. (0001)-oriented ZnO layers have been prepared by heteroepitaxial growth onto GaN and single-crystal aluminum oxide (sapphire) substrates with a lattice mismatch of 2.4 % for the (0001) ZnO/(0001) GaN and 18.3 % for the (0001) ZnO/(0001) Al 2 O 3 systems, respectively. Because of the advantages of Si wafers in conventional integrated circuit technology, Si wafers have also been employed as a substrate in ultraviolet-light-emitting devices for industrial applications. Since the lattice mismatch between the (0001) ZnO plane and the (001) or (111) Si planes is very large, an interlayer, such as CaF 2 , is indispensable for growing heteroepitaxial ZnO on Si wafers. [4] (0001)-oriented ZnO layers have been prepared with gas-phase deposition techniques such as sputtering molecular beam epitaxy (MBE) and laser ablation, in which heating above 673 K during and/or after the film deposition is necessary. [5±8] If low-temperature preparation could be achieved by a simple process, ZnO could be used for a greater number of applications in optoelectronics, e.g., in circuit boards with embedded devices. [9] Electrodeposition of ZnO films, which has several advantages over gas-phase deposition techniques, has been demonstrated by Izaki and Omi [10] and by Peulon and Lincot. [11] Het-eroepitaxial electrodeposition of a (0001)-oriented ZnO was reported on a single-crystalline Au substrate by Switzer and co-workers [12] and on a (0001)-GaN-coated (0001) sapphire substrate by Pauporte and Lincot. [13] Although much research has been carried out, room-temperature ultraviolet-lightemission from electrodeposited (0001)-oriented ZnO has not been realized to date. Here we report on the low-temperature electrodeposition of a high-quality, (0001)-oriented ZnO layer that emits ultraviolet light due to bound excitons at photon energies of 3.25±3.30 eV and visible light at 2.38±2.70 eV at room temperature. We used an electrodeposition technique with a nitrate reduction reaction in aqueous solution and a (111) Au-coated (100) Si wafer as the substrate for depositing the (0001)-oriented ZnO layer. Figure 1 shows an X-ray diffraction (XRD) spectrum and pole figures of (101 Å 1) ZnO and (111) Au planes for a ZnO layer electrodeposited onto a Au-coated Si substrate at ±0.6 V. Only two peaks, assigned to the Au (111) and ZnO (0001) planes, could be observed. The Au layer with a face-centered cubic lattice had a (111) out-of-plane orientation with a random inplane orientation, because the peaks at 0 and 65.9 on the (111) pole figure (Fig. 1b) could be assigned to equivalent planes of (111) orientation, and the intensity is distributed homogeneously al...

High-quality (0001)-oriented zinc oxide (ZnO) micropatterns, 5-μm-wide microlines and 5-μm-diam microdot arrays, have been prepared on (111) Au-coated (100) Si wafer substrates by electrodeposition at 333 K in zinc nitrate aqueous solution and industrially employed positive type photoresist techniques. The ZnO micropatterns emitted ultraviolet light at photon energy of 3.25 eV due to recombination of bound excitons and visible light at 2.37 and 2.80 eV at room temperature.

A low-temperature method for growing (0001)-oriented one-dimensional ZnO nanopillars using electrodeposition in a simple zinc nitrate aqueous solution without any template is presented. The 20–100 nm diameter ZnO nanopillars emitted ultraviolet light at around 3.30 eV due to the recombination of the bound excitons and visible light at 2.30–2.55 eV at room temperature. Since the diameter and length can be controlled easily, some applications for use in ultraviolet light lasing diode and organic solar cells will be made.

By the catalytic action of Cu on DMAB, ZnO crystals grow directly on various Cu substrates immersed in an aqueous solution containing zinc nitrate and dimethylamine borane at 80 °C under an ambient atmosphere.

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