在本論文中，我們研製一系列高性能化合物半導體式之氣體感測器，包含蕭特基二極體、異質場效電晶體及電阻式元件。由於鈀和鉑分別對氫氣和氨氣具有良好的觸媒活性，可用來當作感測金屬。氮化鎵和氮化鋁鎵具有比矽材料較大的能隙，可用來當作感測平台。此外，水熱法成長之一維結構氧化鋅奈米柱相較於氧化鋅薄膜具有高比表面積，有利於氣體吸附，並利用鈀奈米粒子修飾氧化鋅奈米柱，使其大幅提升感測能力。我們探討這些感測器在不同溫度下對不同濃度的氫氣和氨氣之相關感測電性、偵測效能和動態表現。
首先，我們研製一具電漿表面處理之鈀/氮化鎵蕭特基二極體式氫氣感測器。此元件展現良好的感測性能，包含高靈敏度、高選擇性、大蕭特基能障變化量、寬廣的溫度操作區間及快速響應時間。探討順向及反向電壓的感測特性比較，並提出一個簡單的模型來詮釋經由電將表面處理之元件的氫氣感測表現。從實驗結果得知，較粗糙的鈀表面對於氫氣吸附特性具有極大的影響。
其次，研究鉑/氮化鋁鎵/氮化鎵蕭特基二極體之氨氣感測特性。提出直接解離和三點接觸機制解釋氨氣分子解離、氫原子擴散、氨氣/氧/鉑接觸及電偶極層的形成造成蕭特基能障的有效減少。並在不同氨氣濃度與溫度之環境下，分析本感測器之氨氣感測行為；此元件適合在高溫下操作，因高溫有助於氨氣解離擴散，。
第三，利用氮化鋁鎵/氮化鎵異質結構及鉑觸媒閘極電極，研製場效電晶體來偵測氨氣靈敏度。對此元件而言，成長10 nm厚的鉑金屬層主要是通入氣體時，易使三點接觸位於金半接面處形成一極化層，使蕭特基能障降低飽和電流上升。我們探討並分析此感測元件在不同溫度下的電流–電壓特性，發現到截止區的氨氣偵測靈敏度具有劇烈的變化。最後針對氨氣誘導效應對於電晶體之電性參數諸如:門檻電壓、轉導、汲極電流之導通/截止比例做完整探討。
第四，提出以氧化鋅奈米柱製作成電阻式氨氣感測器，並討論氧化鋅材料在不同生長條件下所成長氧化鋅奈米柱的特性(水溶液濃度、種晶層厚度、酸鹼值和成長溫度)。利用指叉電極和氧化鋅奈米柱的結合製作一高靈敏度的氨氣感測器，探討指叉電極間距的改變對氨氣感測能力的影響。
最後，探討氧化鋅奈米柱經由鈀奈米粒子修飾的氨氣感測特性。因氧化鋅奈米柱有大比表面積，有利於氣體的吸附和奈米粒子的還原，使得提升其元件感測能力。氧化鋅奈米柱利用一低溫水熱法成長在一藍寶石基板上，並藉由含浸法將鈀奈米粒子還原在氧化鋅奈米柱上，可觀察到鈀奈米粒子均勻的分佈在氧化鋅奈米柱表面。溫度在250oC，暴露在1000 ppm的氨氣氛圍下，具有鈀奈米粒子修飾之元件的最高靈敏度約310.2倍，而未修飾的元件約87倍。我們探討並分析此感測元件在不同溫度下的氨氣感測特性。

In this dissertation, a series of high-performance compound semiconductor based hydrogen sensors, including Schottky diodes, heterostructure field-effect transistors, and resistors, are fabricated and studied. Pd and Pt are used as sensing metals due to their excellent catalytic activity towards hydrogen and ammonia gases, respectively. GaN and AlGaN materials are served as sensing platforms because of their larger band gap than that of Si-based materials. In addition, hydrothermal growth of one-dimensional (1-D) ZnO nanorods-based device possesses higher surface to volume ratio (SV) than thin film-based device. It is beneficial to the adsorption of gas. Moreover, Pd nanoparticles-decorated ZnO nanorods could significant enhance the sensing response. We present the related electric characteristics, detection performance, and dynamic behaviors of these sensors measured under different hydrogen and ammonia concentrations at different temperatures.
First, Pd/GaN Schottky diode-type hydrogen sensors with and without plasma surface treatment are studied and demonstrated. The studied device exhibits significant sensing performance, including high sensing response, large Schottky barrier height variation, widespread temperature operation regime, and fast transient response time. A comparative study between forward and reverse biases is presented. A simple detection model is proposed to elucidate the hydrogen sensing behavior of devices with plasma surface treatment. A rougher Pd surface exhibits considerable influences on the hydrogen adsorption properties.
Second, ammonia-sensing characteristics of a Pt/AlGaN/GaN-based Schottky diode are studied. The related ammonia-sensing mechanisms, direct dissociation of ammonia gas and triple-point model, are presented to explain the effects of dissociation of ammonia molecules, diffusion of hydrogen atoms, boundaries between NH3, O2, and Pt metal, and formation of dipolar layer, thus reducing the effective Schottky barrier height. The temperature-dependent NH3 sensing behaviors are investigated for the studied device. The studied device is suitable for high temperature operation because the temperature effect would facilitate dissociation and diffusion of gases.
Third, field-effect transistors based on AlGaN/GaN heterostructures are fabricated with catalytically active platinum (Pt) gate electrodes to induce the sensitivity of ammonia gas. For the studied device, a 10 nm-thick Pt metal grain is grown. When the target gas is introduced, a polarized layer is formed at Pt/AlGaN interface due to the triple-point contact (Pt, NH3, and O-, O2, or O2-), which leads to the reduction of Schottky barrier height and the increased of saturation current. Comprehensive analysis on the electrical properties at different temperatures is presented. A drastic change of ammonia detection sensitivity is observed in the cut-off region. Ammonia-induced effects on electrical parameters of a field-effect transistor (FET), such as threshold voltage, transconductance, and on-off current ratio are investigated.
Fourth, ZnO nanorods (NRs)-based resistance-type ammonia sensor are mentioned and studied. Different growth conditions of ZnO NRs are discussed, such as precursor concentration, thickness of ZnO seedlayer, pH value, and growth temperature. A combination of interdigitated electrodes and 1-D ZnO NRs has been used to make an ammonia sensor with a high degree of sensitivity. We are going to study the effect of varying the electrode spacing on the sensing performance.
Finally, the NH3 sensing properties of ZnO NRs decorated with Pd nanoparticles are investigated. The large surface-to-volume ratio of ZnO nanostructures is favorable for the adsorption of analytes and reduction of nanoparticles. This leads to the improved sensor performance. ZnO NRs were synthesized through a hydrothermal route on a sapphire substrate. Pd nanoparticles were reduced on the surface of ZnO NRs using an impregnation approach. It was observed that. the nano-sized Pd particles (~5 nm) were uniformly distributed on the surface of ZnO NRs. A maximum NH3 sensing response of 310.2 was found when the device was exposed to a 1000 ppm NH3/air gas at 250oC. The as-grown ZnO nanorods, however, illustrated the maximum sensing response only of 87. The temperature-dependent NH3 sensing properties of the studied device were also systematically investigated.

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