本論文將pn接面應用於GaN光陽極，n-GaN和pn-GaN光陽極在二電極系統下(外加偏壓1V)的起始電流分別為Jn = 0.17 mA/cm2及 Jpn = 0.22 mA/cm2。我們利用EIS電化學阻抗譜法和Mott-Schottky plot證實了pn接面的存在。由於pn接面具有內建電場可有效分離光生載子，pn接面延長了GaN光陽極本身與電解液的空間電荷層，增加載子分離的機會而使GaN光陽極的電流密度獲得提升。
不過，GaN光陽極在進行PEC水分解時腐蝕現象嚴重，導致p-GaN被侵蝕，最終失去pn接面的功能。經過一小時穩定性測試後，電流密度分別下降為Jn = 0.091 mA/cm2及Jpn = 0.105 mA/cm2。
為了解決GaN光陽極的腐蝕問題，我們利用電子束蒸鍍方法將金屬鎳Ni鍍在GaN表面，再透過爐管加熱方法將Ni轉化為氧化鎳NiO。表面具有氧化鎳的GaN光陽極，其穩定性得到有效提升。經過一小時測試後，pn-GaN/NiO的光電流只下降了17%，從初始的Jpn-GaN/NiO = 0.225 mA/cm2下降至Jpn-GaN/NiO = 0.187 mA/cm2; 而n-GaN/NiO則從Jn-GaN/NiO = 0.174 mA/cm2下降到Jn-GaN/NiO = 0.126 mA/cm2。
從SEM圖像來看，無論是俯視圖或是截面圖，鍍上NiO的GaN光陽極表面沒有被侵蝕的現象。說明NiO能夠有效保護GaN光陽極，抵抗光腐蝕問題。另外，EIS電化學阻抗譜法和MS plot亦證實了pn-GaN/NiO光陽極的pn接面，經歷穩定性測試後仍然存在。
除此之外，我們發現pn-GaN/NiO的onset potential比pn-GaN往負電位偏移了約-0.2 VRHE，證明NiO除具有抗腐蝕功能，亦有催化水氧化反應的作用。

The pn junction was adopted on the GaN photoanode, the extension of the depletion region is beneficial to the charge separation. However, the GaN photoanodes are easily corroded and hence the pn junction will disappear. We deposited a NiO thin film on the GaN photoanodes as the anti-corrosion layer. The NiO film is highly transparent and has a sufficiently low charge transfer resistance. The pn-GaN/NiO photoanode has an excellent stability, and it can drive the water splitting reaction under the AM1.5 G illumination without any external bias. This is attributed to the catalytic effect of the NiO film and the modified flat band potential of the pn-GaN photoanode.

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