RESUMO
A Ag:AZO electrode was used as an electrode for a self-powered solar-blind ultraviolet photodetector based on a Ag2O/ß-Ga2O3 heterojunction. The Ag:AZO electrode was fabricated by co-sputtering Ag and AZO heterogeneous targets using the structural characteristics of a Facing Targets Sputtering (FTS) system with two-facing targets, and the electrical, crystallographic, structural, and optical properties of the fabricated thin film were evaluated. A photodetector was fabricated and evaluated based on the research results that the surface roughness of the electrode can reduce the light energy loss by reducing the scattering and reflectance of incident light energy and improving the trapping phenomenon between interfaces. The thickness of the electrodes was varied from 20 nm to 50 nm depending on the sputtering time. The optoelectronic properties were measured under 254 nm UV-C light, the on/off ratio of the 20 nm Ag:AZO electrode with the lowest surface roughness was 2.01 × 108, and the responsivity and detectivity were 56 mA/W and 6.99 × 1011 Jones, respectively. The Ag2O/ß-Ga2O3-based solar-blind photodetector with a newly fabricated top electrode exhibited improved response with self-powered characteristics.
RESUMO
Controlling built-in potential can enhance the photoresponse performance of self-powered photodetectors. Among the methods for controlling the built-in potential of self-powered devices, postannealing is simpler, more efficient, and less expensive than ion doping and alternative material research. In this study, a CuO film was deposited on a ß-Ga2O3 epitaxial layer via reactive sputtering with an FTS system, and a self-powered solar-blind photodetector was fabricated through a CuO/ß-Ga2O3 heterojunction and postannealed at different temperatures. The postannealing process reduced the defects and dislocations at the interface between each layer and affected the electrical and structural properties of the CuO film. After postannealing at 300 °C, the carrier concentration of the CuO film increased from 4.24 × 1018 to 1.36 × 1020 cm-3, bringing the Fermi level toward the valence band of the CuO film and increasing the built-in potential of the CuO/ß-Ga2O3 heterojunction. Thus, the photogenerated carriers were rapidly separated, increasing the sensitivity and response speed of the photodetector. The as-fabricated photodetector with 300 °C postannealing exhibited a photo-to-dark current ratio of 1.07 × 103; responsivity and detectivity of 30.3 mA/W and 1.10 × 1012 Jones, respectively; and fast rise and decay times of 12 ms and 14 ms, respectively. After three months of storage in an open-air space, the photocurrent density of the photodetector was maintained, indicating good stability with aging. These results suggest that the photocharacteristics of CuO/ß-Ga2O3 heterojunction self-powered solar-blind photodetectors can be improved through built-in potential control using a postannealing process.
RESUMO
In the photo-Fenton reaction, highly reactive oxygen species are generated on UV irradiation of ß-FeOOH, which contributes significantly to hydrogen production. The production process was performed by adjusting the pH of the solution. The effect of acid concentration on hydrogen production was analyzed in this study, and the difference in the amount of hydrogen gas produced in each sample with different pH values was determined. X-ray powder diffraction (XRD) measurements of the samples corresponding to the peaks of ß-FeOOH were compared with the reference data, and crystallite sizes were calculated by the Scherrer equation using XRD patterns. The rod-like structure of the sample particles was revealed by scanning electron microscopy. A higher amount of hydrogen was produced at lower pH, and these results confirmed that pH plays an important role in hydrogen production.
RESUMO
Renewable energy is spotlighted as a resource to replace fossil fuels, and among the resources, active research on hydrogen energy is ongoing. Various methods have been developed to produce hydrogen energy using photoreduction processes. In this study, we synthesized ß-phase iron oxyhydroxide (ß-FeOOH) using a hydrothermal method with an optimal synthesis time and investigated its photofunctional properties, including hydrogen production. The obtained samples were characterized and compared with reference data. X-ray powder diffraction results corresponded to the peaks of the reference data. A rod structure was confirmed by scanning electron microscopy, and no impurities were observed. The band-gap energy of ß-FeOOH was calculated as 1.8-2.6 eV. A photoreduction process was performed based on a photo-Fenton reaction to produce hydrogen by irradiating ultraviolet (UV) on ß-FeOOH. The synthesized ß-FeOOH was subjected to UV irradiation for 24 h to produce hydrogen, and we confirmed that hydrogen was successfully produced. The properties of ß-FeOOH were evaluated after UV irradiation.
