本論文主要是利用三五族氮化鎵材料製作光電解電池之工作電極光電解水產生氫氣。實驗設計上我們分別針對氮化鎵電極的載子濃度、氙燈的照光強度、氮化鎵材料的磊晶結構、氮化鎵電極的外部製程方面做不同的變化，分析在各種情況下的實驗結果，釐清氮化鎵材料光電解水產氫的反應機制，進而改善光電化學產氫的效率。
首先，我們觀察不同載子濃度之n型氮化鎵的光電化學反應，發現光電流隨著載子濃度的增加而上升，推測主要原因來自於電阻率的影響，我們也改變氙燈的照光強度，發現光電流明顯隨著照光強度的增加而上升，同時藉由交流阻抗的分析發現，隨著照光強度的增加，其平帶電位有往正電位偏移之趨勢。此外，我們也改變氮化鎵的磊晶條件，分別做出自然粗化表面跟平坦表面這兩種氮化鎵，發現自然粗化結構的氮化鎵在吸收波段的反射率比平坦氮化鎵小且反應面積較大，但由於其電特性與晶體品質較差的關係，使得平坦氮化鎵的表現較佳。另外，我們也在氮化鎵電極表面上製作出不同間距的金屬浸入式歐姆電極設計，發現光電流隨著電極間距減少而上升，這是由於較密的金屬電極其載子汲取能力較好。最後我們希望能用較簡易的製程來做浸入式電極，因此將金屬電極材料換成氧化銦錫材料，如此便可省下在金屬電極上製作二氧化矽保護層的步驟，且氧化銦錫浸入式電極的壽命較長。

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.

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