碩士 / 國立成功大學 / 光電科學與工程研究所 / 98 / Working electrodes of photoelectrolytic cells were built using the Gallium Nitride (GaN) to generate hydrogen gas through water splitting. To clarify the mechanism of water splitting reaction and promote the efficiency of hydrogen generation, we varied the carrier concentrations of GaN, the light intensities of the Xe lamp, the crystal structures of GaN, and the processes of ohmic contacts of the GaN working electrodes. Furthermore, the results were analyzed under different conditions.
First, the photoelectrochemical reactions of n-GaN samples, which had different carrier concentrations, were observed. The photocurrent densities were enhanced as the carrier concentrations increased because of the resistivity of n-GaN. High resistivity of the materials can lead to low photocurrent densities. The light densities of the Xe lamp were also varied, and the photocurrent densities were enhanced as the light densities increased. By AC resistance analysis, we found that the flat-bend potential shifted to positive when the light intensities increased. Furthermore, different growing conditions were used to grow n-GaN samples with naturally roughened and flat surfaces. Although the reflectance of the naturally roughened n-GaN was lower than that of the flat n-GaN, and the working area of the naturally roughened n-GaN was larger than that of the flat n-GaN, the performance of the naturally roughened n-GaN was better than that of flat n-GaN. Because of the inferior electrical properties and crystal qualities of the naturally roughened n-GaN samples, flat n-GaN performed better. Furthermore, GaN working electrodes that were immersed in metal ohmic electrodes, which had different spaces on the GaN surfaces, were built. Experimental results indicate that the photocurrent densities increased as the spaces of immersed metal ohmic electrodes decreased. The decrease can be attributed to the samples with smaller ohmic electrode spaces, which can have higher electron collection efficiencies. Finally, because we preferred to use simpler processes to build immersed ohmic electrodes, we used ITO materials instead of metal materials to immerse ohmic electrodes. With this method, building SiO2 protection layers on the metal ohmic electrodes is unnecessary. In addition, the life span of ITO-immersed ohmic electrodes are longer than that of metal-immersed ohmic electrodes.
| Identifer | oai:union.ndltd.org:TW/098NCKU5614020 |
| Date | January 2010 |
| Creators | Jhao-ChengYe, 葉昭呈 |
| Contributors | Jinn-Kong Sheu, 許進恭 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 86 |
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