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不同極性氮化鎵電極的交流阻抗與光電流密度量測作分析，也在不同極性氮化鎵上增加一層氮化物層，藉此比較有無氮化物層對光電解水產氫的影響，經過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。
首先我們將不同極性的氮化鎵去做光電解水反應，同時藉由交流阻抗分析出其平帶電壓，而平帶電壓影響著光電流的產生與液半接面上能帶彎曲程度，透過光電解水反應發現光電流密度會因為極性的不同而有不同的表現，再加上平帶電壓的量測，因而推測主要原因來自於液半接面上能帶彎曲的影響。而我們在表面上增加未摻雜的氮化鎵，發現光電流密度卻沒有明顯增加，推斷是因為加了此層反倒沒有增加極化電場的強度，但發現未摻雜氮化鎵半極性面中有些面的極化電場較小，也因此產生的光電流密度較小。而我們也在表面上增加不同結構的氮化鋁鎵，對於一般結構的氮化鋁鎵本身對氮化鎵就晶格不匹配，所以再接面處會產生壓電極化效應，導致極化電場的產生。而我們也使用漸變結構的氮化鎵，使得能帶彎曲更劇烈，產生的內建電場越大，越有利於光電流的產生。

Hydrogen generation through direct photoelectrolysis of water was studied using photoelectronchemical cells made of different facets of free-standing polar GaN system. To build the fundamental understanding at the differences of surface photochemistry afforded by the GaN polar surfaces, we correlated the relationship between the band structure and photoelectrochemical performance on the different polar facets. The photoelectrochemical measurements clearly revealed that the Ga-polar surface had a more negative onset potential relative to the N-polar and semipolar surface due to the much negative flat-band potential. However,the flat-band potential depend on band bending at the semiconductor-liquid junction. We also use two typical layers of AlGaN/GaN heterostructures as working electrode on photoelectronchemical cells. For AlGaN/GaN heterostrucrtures, we use the bulk layer and the gradual changed layer on different facets of free-standing polar GaN system. The photoelectrochemical measurements exhibit the semipolar GaN with gradual changed AlGaN have the highest photocurrent than the other samples at bias zero voltage. Therefore, we simulate the band bending at bias zero voltage. Though the simulation, we think the photogenerated holes on the valence band are more than the others. Because the amount of the holes which spreads to the electrolyte determine the photocurrent on the photoelectronchemical cells. Therefore, the key parameter of the photoelectronchemical cells is the amount of the holes on the valence band by bending the band diagram.

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