金屬基極電晶體由於有極薄的基極金屬，其基極阻抗低，而由射極發射出之高能熱電子在集極電壓的汲引下，甚至有可能發生彈道傳輸的現象，故於高速元件應用上有著極大的潛力。然於早期使用無機單晶矽做為射極與集極半導體材料，因物理條件之限制導致其熱電子傳輸效率極差，因此元件之電流增益比較不佳，加上製程之困難，使得針對此一元件開發之研究趨緩。雖然目前有許多材料被應用在射極與集極半導體材料上，包括有機材料與高分子材料，然主要的問題仍在製程上的困難及較低的電流增益。本論文中選用之半導體材料為氧化銦鎵鋅，其優點為電子於基極-集極接面之量子反射量低、製程過程較簡易且為室溫下製程與高載子遷移率與高穩定性等。
本論文旨在研製氧化銦鎵鋅形成蕭特基二極體與金屬基極電晶體以及其電特性探討。我們以鈦作為下電極金屬，並調變沉積氧化銦鎵鋅時製程氣體氧氣含量，於鈦金屬上方形成金半接面，藉此來完成下接觸式蕭特基二極體之製作，其元件電流整流比為10000，能障高度為0.71 eV。另外於改變蕭特基二極體整流方向之實驗中，於氧化銦鎵鋅上方沉積介面層氧化矽鉿8 nm與上電極金屬金，介面氧化層材料之導入得以減緩金屬離子之交互擴散避免造成不利於蕭特基接面產生之金屬化介面，藉此來完成上接觸式蕭特基二極體之製作，其元件電流整流比為1000，能障高度為0.68 eV。物性分析方面以化學分析電子儀(XPS)之縱深分佈分析其不同製程對於蕭特基接面之影響。
本研究利用良好整流特性之上接觸式與下接觸式不同方向性之氧化銦鎵鋅蕭特基二極體，以垂直整合的方式製作出金屬基極電晶體，並藉由調變其雙層金屬基極之厚度以改善元件特性，提升電流增益。製作出之氧化銦鎵鋅金屬基極電晶體在使用鈦(5 nm)/金(5 nm)之基極厚度下具備優異之電流增益特性，其共射極電流增益達2415及共基極電流增益極接近理想值(~0.999)，遠大於目前文獻中主流之有機材料與鈣鈦礦MBT。
氧化銦鎵鋅金屬基極電晶體為目前文獻中極少數應用無機材料製作之金屬基極電晶體。本研究結果顯示，以氧化銦鎵鋅為半導體材料搭配極薄的雙層金屬鈦/金之金屬基極電晶體，將有助於擴展高速元件與有機發光二極體面板之應用。

Metal-base transistor (MBT) was first proposed in 1962 and received much attention due to its potential as a high-speed device. MBT offers certain potential advantages such as low base resistance, high-speed operation due to ballistic transport in the thin base. In spite of this long history, two basic problems have imposed serious constraints on the development of MBTs, namely, poor emitter-collector transfer ratios and technological difficulties in fabrication. More important, the fundamental limitation of low current gain due to quantum-mechanical reflection exerts a challenging issue for the MBTs. Although different materials have been used as emitter and collector semiconductors, including organic materials and molecular, however, the major problems of MBTs are the difficulty of fabrication and low current gain. In this thesis, to overcome the problems mentioned above, indium gallium zinc oxide (InGaZnO, abbreviated as IGZO) are served as semiconductor material of Schottky diodes and metal-base transistors. The advantages of the amorphous type IGZO are the simplicity of fabrication, low thermal budget, high carrier mobility, and high stability as compared with the other amorphous materials. In this study, the top-contacted Au/HfSiO/IGZO Schottky diodes are fabricated successfully by inserting an HfSiO interlayer between the metal and the semiconductor, the bottom-contacted Ti/IGZO diodes are fabricated through Oxygen pressure adjustment during IGZO deposition. The metal-base transistors are fabricated by vertically stacking the two IGZO Schottky diodes: The emitter Au/HfSiO/IGZO and the collector Ti/IGZO diodes. High common emitter current gain (β) and common base current gain (α) are obtained from the proposed IGZO-based metal-base transistors.

The vertical InGaZnO metal-base transistors (MBTs) were fabricated by integrating top-contacted Au/HfSiO/InGaZnO and bottom-contacted Ti/InGaZnO Schottky diodes as emitter and collector of the MBT, respectively. The InGaZnO Schottky diodes (Ti/InGaZnO and Au/HfSiO/InGaZnO) were fabricated through oxygen doping and HfSiO interlayer insertion to eliminate Fermi level pinning and to enhance Schottky behavior, which could be attributed to the lowered oxygen vacancies, the widened depletion width at the junction, and the avoiding of inter-diffusion of the metal cations. Different metals (Ti and Au) were chosen for the fabrication of the uni-directional Schottky diodes depending on their reactivity to the oxygen atoms. To the best of our knowledge, reports of MBTs based on in-organic materials are very limited. In the present study, InGaZnO MBTs with high common-emitter current gain (β = 2415) and high common-base current gain (α = 0.999) were fabricated, which are much higher than the reported current gains in organic and perovoskite MBTs.

In conclusion, a-IGZO Schottky diodes are fabricated successfully through oxygen doping and HfSiO interlayer insertion for the bottom-contacted Ti/IGZO and top-contacted Au/HfSiO/IGZO Schottky diodes, respectively. The a-IGZO MBT with high current gains (α=0.999 and β=2415) is demonstrated by vertically integrating the Ti/IGZO and the Au/HfSiO/IGZO Schottky diodes as collector and emitter, respectively. The high current gains obtained could be attributed to the high electron transmission through base due to the alleviated electron scattering and the enhanced collector efficiency with the use of thin dual metal base and IGZO.

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