在本論文中，我們研製一系列三-五族化合物半導體蕭特基式氣體感測器，包含蕭特基二極體以及異質場效結構電晶體。三-五族化合物半導體材料如：氮化鋁鎵及砷化銦鋁系列材料，可用來當作感測平台。由於三-五族化合物半導體具有較寬之能隙，因此，使用其製作而得之元件可適用於高溫環境之應用。此外，鈀和鉑分別對氫氣與氨氣具有良好的觸媒活性，可用來當作感測金屬
。除了研究蕭特基式感測器在不同溫度下的感測效能外，也探討閘極絕緣層對感測器效能之影響。
本論文首先探討鈀/氮化鋁鎵（金屬-半導體）與鈀/二氧化矽/氮化鋁鎵（金屬-氧化物-半導體）蕭特基二極體之氫氣感測特性。我們利用熱離子發射方程式來描述感測器於氫氣之環境下之電流-電壓特性。經由熱離子發射方程式，可得到二極體之蕭特基位障高度、理想因子及串聯電阻，並且可以觀察到此些參數會隨著不同濃度之氫氣而改變。我們從感測器之二極體參數、感測響應、響應時間方面探討金屬-半導體及金屬-氧化物-半導體之氫氣感測行為。
其次，研究鉑/二氧化矽/氮化鋁鎵蕭特基二極體之氨氣感測特性。鉑金屬對於氨氣具有良好之觸媒活性。因此，可使用於檢測氨氣之感測金屬。根據三相接觸理論，我們藉由二氧化矽提升『觸媒金屬-氧化物-氨氣分子』接觸之機率，以提升氨氣分子之解離效率，並在不同氨氣濃度與溫度來之環境下，分析本感測器之氨氣感測行為。
接著，研製鈀/變晶式高速載子移動率電晶體式高效能氫氣感測器。針對氫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，並進一步分析感測元件之平衡吸附與動力吸附模型。此外，以熱氧化方式成長熱氧化層於蕭特基接觸層上，形成金屬/氧化物/變晶式高速載子移動率電晶體。實驗結果顯示金屬/熱氧化層/變晶式電晶體不論是電性與感測效能方面皆大幅提升。由於本論文所研製之元件呈現良好之感測效能，且製程方式與微機電系統製程相容，本研究之感測元件在高效能感測器與微機電系統整合方面極具潛力。

In this dissertation, a series of III-V compound semiconductor Schottky-type gas sensors, including Schottky diodes and heterostructure field-effect transistors, are fabricated and studied. III-V compound semiconductors, such as AlGaN- and InAlAs-based materials, are served as sensing platforms. The larger band gaps of those materials make the fabricated devices suitable for high-temperature operation. Pd and Pt are used as sensing metals due to their excellent catalytic activity toward hydrogen and ammonia gases, respectively. The electrical characteristics and gas-sensing performance of these sensors are investigated at different temperatures. Furthermore, the influence of gate insulator on the sensing performance of each sensing device is studied.
First, hydrogen-sensing characteristics of metal semiconductor (MS) Pd/AlGaN-based and metal-oxide-semiconductor (MOS) Pd/SiO2/AlGaN-based Schottky diode-type sensors are studied. Thermionic emission (TE) equation is employed to characterize the current-voltage (I-V) behaviors of the studied devices under exposing to hydrogen gas. Schottky barrier height, ideality factor, and series resistance extracted from TE equation, are found to be sensitive to hydrogen gases with different concentrations. Hydrogen sensing behaviors of MS and MOS devices are investigated in terms of those diode parameters, sensing response, and response time.
Second, ammonia-sensing characteristics of a Pt/AlGaN-based Schottky diode are studied. Pt metal shows high catalytic activity to ammonia gas. It is, therefore, used as the sensing metal for ammonia detection. Based on the “triple-point theorem”, SiO2 layer is employed to increase the “boundaries” between SiO2, Pt metal, and NH3 molecules, thus facilitating the dissociation of NH3 molecules. The temperature-dependent NH3 sensing behaviors are investigated for the studied device.
Third, metamorphic high electron mobility transistors (MHEMTs)-type hydrogen sensors with catalytically active palladium (Pd) gate electrodes are fabricated and studied. Hydrogen-induced effects on electrical parameters of a field-effect transistor (FET), such as threshold voltage, transconductance, and on-off current ratio are investigated. Equilibrium adsorption and kinetic adsorption are studied for the devices. In addition, an MHEMT with thermally-grown gate oxide are also fabricated to be compared with the metal-oxide (MS) Pd/MHEMTs. It is found that the electrical and sensing performance of the MHEMTs is significantly improved by the thermally-grown gate oxide. Based on the good results and compatibility of fabrication process of these devices, the studied devices show the promise for the integration of high-performance sensor and micro-electro-mechanical system (MEMS).

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