近年來氮化鎵因具有寬的直接能隙與優異的光電特性等優點，而越來越受到重視，一般可應用於藍紫光發光二極體與高速元件等電子元件中，此外氮化鎵尚可作為一氫氣檢測器，因具有寬的直接能隙與穩定的化學性質，相較於以矽為主的氫氣檢測器，氮化鎵可於高溫、惡劣的環境中工作，然而也由於其穩定之化學性質，使其無法直接使用一般傳統的方法進行氧化，以製作出金屬／氧化物／半導體之氣體檢測器。於本論文中，以光電化學氧化法對氮化鎵直接進行氧化形成氧化鎵，並利用高溫爐對初成長之氧化鎵進行700oC、氧氣氛圍、2小時的熱處理，氧化層經熱處理後，出現-Ga2O3晶相，此氧化層具有穩定之化學性質且可與氫氣反應。最後於此熱處理後之氧化層上蒸鍍鉑金屬做為一催化金屬，製作出鉑／氧化鎵／氮化鎵（金屬／氧化物／半導體）氫氣檢測器，同時並製作一鉑／氮化鎵（金屬／半導體）氫氣檢測器作為比較。
當氫氣通入於腔體中，氫氣分子受鉑金屬催化分解為氫原子，並滲透到介面處形成偶極降低能障，進而改變元件之電流，相較於一般之金屬／半導體氫氣檢測器，金屬／氧化物／半導體氫氣檢測器之氧化物可於介面處提供更多位置給氫原子，產生更多的偶極造成更大的能障變化，且氧化鎵為一反應式之氧化層，可與氫氣產生反應進而降低薄膜之電阻，於10000 ppm氫氣／空氣混合氣中，鉑／氧化鎵／氮化鎵氫氣檢測器其能障與串聯電阻變化量分別為0.655V與191，而鉑／氮化鎵氫氣檢測器則為0.149V與2，相較之下金屬／氧化物／半導體氫氣檢測器具有更大之響應。最後進行量測並分析鉑／氧化鎵／氮化鎵於不同環境溫度下之穩態響應與暫態反應以探討其物理與化學吸附機制。藉由不同溫度與氫氣濃度下之穩態分析，氫氣吸附於鉑／氧化鎵介面與氫氣吸附於氧化鎵內之焓分別為8.5與7.65 千焦耳/莫爾，由於此氫氣吸附反應為一放熱反應，因此元件隨著工作溫度之上升，其檢測能力有隨之下降趨勢；此外由不同溫度暫態之分析，由阿瑞尼斯方程式可計算出其活化能為1.99千焦耳/莫爾，因此元件可快速反應偵測出環境中氫氣濃度之變化，提早做出預警。

In the recent years, GaN had attracted more and more attentions due to its direct wide band and superior optoelectronic characteristics. Different kinds of GaN-based light-emitting diodes and high speed devices had been studied. Besides, it could be used as a hydrogen gas sensor. The applications of hydrogen in modern technology include industry fabrication processes, hydrogen fueled cell and vehicles etc.. Due to the requirement of robust gas sensors for use at harsh environments, semiconductorbased hydrogen gas sensors have attracted much attention. However, the Si-based hydrogen sensors could not operated at high temperatures. Based on characteristics of high electron saturation velocity, high breakdown electric field, superior thermal and chemical stability, GaNbased hydrogen sensors have become a potential sensors to improve hydrogensensing performances. However, the GaN was difficult to oxidize directly due to its strong chemical bond. In this study, a photoelectrochemical oxidation was used to grow an oxide layer directly on the GaN layer.
The Pt/Ga2O3/GaN (metal/reactive insulator/semiconductor) MIStype hydrogen sensors were fabricated in which the Ga2O3 oxide layers were directly grown on GaN layer using a photoelectrochemical oxidation method and then annealed in O2 ambience at 700oC for 2 hours. The Pt/Ga2O3/GaN MIStype hydrogen sensors exhibited high hydrogen sensing ability than the Pt/GaN (metal/semiconductor) MStype hydrogen sensors. When the MIStype hydrogen sensors were exposed to dilute hydrogen ambience, the reactive oxide layer not only helped to increase the number of trapping sites for the hydrogen atoms at the Pt/Ga2O3 interface, but its associated series resistance could also be decreased as well. The barrier height change and series resistance change of MIStype hydrogen sensors exposure to the ambience of 10000 ppm H2/air were 0.655 V and 191, respectively. The corresponding values of the MStype hydrogen sensors were 0.149 V and 2, respectively. Therefore, more hydrogen diploes were performed at the Pt/Ga2O3 interface and resulted in larger barrier lowing.
An increase in current was observed when the MIStype hydrogen sensors were exposed to a dilute hydrogen ambience due to the changes in barrier height and series resistance. In addition, the physical and chemical hydrogen sensing mechanisms of the MIStype hydrogen sensors were investigated. Based on the steadystate analysis at different operating temperatures, the corresponding enthalpies for hydrogen adsorbed at the interface and also in the oxide layer were 8.5 and 7.65 kJ/mol, respectively. A negative enthalpy indicated that the kinetic reaction was exothermic in force. Therefore, the hydrogen response decreased in response to an increase in operating temperature. Furthermore, based on the kinetic analysis, the activation energy value was 1.99 kJ/mol. The small activation energy value indicated that the rapid hydrogen detection could be achieved with the Pt/Ga2O3/GaN MIStype hydrogen sensors. The experimental results demonstrated that the Ga2O3 layer played an important role in the MIStype hydrogen sensors.

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Chapter 3
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Chapter 4
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