人類大量使用石化燃料，造成溫室效應愈趨嚴重，產生極端氣候變遷。能源的議題浮上檯面，我們應該正視能源的使用，並尋求乾淨能源。其中，氫能舉有潛力取代石化燃料，避免石化燃料急速消耗。透過太陽光及海水搭配半導體材料，我們以光電解水，促使水電解產氫氣，同時轉化二氧化碳產生甲酸，為地球永續發展及潔淨能源創造一個新的領域。
本論文實驗應用三五族半導體氮化鎵，做為光電化學電解水之工作電極相關特性研究。透過製程在氮化鎵表面形成奈米柱狀結構，量測表面形貌、光電化學反應的光電流大小，並收集分析對電極端生成的氫氣和甲酸。目的是希望增強工作電極的化學穩定性，以及提升照光時分解水產生氫氣，以及二氧化碳還原為甲酸的效率。
氮化鎵擁有穩定的化學特性、良好的抗酸鹼及腐蝕特性，且具有轉換二氧化碳的寬能隙。然而寬能隙也使得氮化鎵僅能吸收紫外光波段的能量(365nm以下)，占太陽能光譜5%而已，故我們希望提升其使用比率。我們在元件上利用奈米金屬粒子，作為乾式電漿蝕刻時的遮罩，使我們的元件表面形成高深寬比的奈米柱，希望增加其光子的吸收，提升元件效能。
實驗中我們調整其表面上的覆蓋比率，去比較不同參數下的元件其光電化反應表現，整體實驗光電流密度上升，產氫氣和甲酸的能力改善，觀察長時間光電化學反應，進一步提升氮化鎵工作電極的效能。
後面實驗我們希望能夠減緩奈米柱的蝕刻速率，在奈米柱表面濺一層氧化鎳。由於氧化鎳能夠幫助光生電洞的排出，使氮化鎵表面能夠減緩反應，以達到更高效的產氫反應。

SUMMARY
Humans use a lot of fossil fuels, and we should look for clean energy, in which hydrogen have the potential to replace fossil fuels. We use electrolysis of water to produce hydrogen, while converting carbon dioxide to produce formic acid. Gallium Nitride materials are used as the working electrode. Nanorods structure is formed on the surface of GaN, and the photocurrent of the photoelectrochemical reaction is measured. Hydrogen and formic acid are generated and collected at the counter electrode side. The aim is to increase the efficiency of hydrogen generation and the reduction of carbon dioxide to formic acid. Nano metal particles are utilized as a mask for plasma etching to form nanorods on the surface of GaN. In the photoelectrochemical reaction, the overall experimental photocurrent density increased, the ability to produce hydrogen and formic acid improved. To slow down the etch rate, we sputter a layer of nickel oxide. Since NiO can help the discharge of photogenerated holes, and GaN can retard the reaction to achieve a more efficient hydrogen production reaction.
Keywords: Gallium Nitride, Hydrogen, Formic Acid, Nanorods, Nickel Oxide

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