No abstract

The direct electrodeposition of Ag2O films was discovered for the first time using a new strategy termed “oxides synthesis induced by electrogenerated acid”. The Ag2O film with a bandgap energy of 1.46 eV is suited to a light absorption layer in photovoltaic cells.

A p-type semiconductor CuO film with a bandgap energy of 1.4 eV has been prepared by anodic electrodeposition in a basic aqueous solution containing copper nitrate hydrate and ammonium nitrate at 297 K, and the structural, optical, and electrical characterizations were carried out. The randomly-oriented CuO film prepared on a transparent conductive glass substrate showed electrical characteristics of a 1.26 × 103 Ω cm in resistivity, 2.11 × 1016 cm−3 in carrier concentration, and 0.234 cm2 V−1 s−1 in mobility, and a slight photocurrent generation could be observed during light irradiation. The (002)-oriented CuO film could be prepared on the (111)-oriented Au/Si wafer substrate and possessed an excellent photoactivity of a large photocurrent density and quick response compared to those for the randomly oriented CuO film.

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...