本篇論文主要為利用射頻磁控濺鍍法製備金屬氧化物薄膜，並探討其物理、光電特性及實際應用於光電元件之特性研究。研究主要可以分為三個部分，第一部分為單純以本質氧化鋅（intrinsic zinc oxide）製備薄膜電晶體以作為後續研究之特性基準參考。由於我們理解，氧化鋅作為一個經常被使用的寬能隙金屬半導體，它的晶格中普遍性地存在許多會造成元件特性退化或是降低元件性能表現的氧空缺（oxygen vacancies）及鋅間隙（zinc interstitials），因此，在不摻雜其他元素的情況之下，氧化鋅薄膜電晶體的電性並不好。

第二部份的重點則著重於兩種新穎的氧化鋅系列之氧化物半導體研究，氧化鋅鈦銦（indium titanium zinc oxide, InTiZnO）以及氧化鋅錫鎵（gallium tin zinc oxide, GaSnZnO）。這兩種半導體在過去學界中並無受矚目，於是我們詳細地刻畫其薄膜的特性，其中包含了表面結構、光學特性、以及元素組成等。在製作InTiZnO之光電元件時，我們系統性地討論氧流比（oxygen flow ratio）對於元件特性的影響，並提出如何透過操控氧流比來抑制氧空缺並達成電晶體性能提升的目標。於此同時，我們也研究絕緣層對於元件性能的重要性，並將常用的二氧化矽（SiO2）更換成具有較高介電常數的氧化鋁（Al2O3），結合理論提出載子遷移率大幅提升的原因。而最終製備而成的InTiZnO薄膜電晶體表現優異，擁有一個1.31 V的臨界電壓、載子遷移率為44.69 cm^2/Vs、開關電流比為 6.6×10^6、次臨界擺幅為0.34 V/dec。

另一方面，我們也同樣製備GaSnZnO的光電元件，利用共濺鍍製程（co-sputtering）的方式以薄膜當中不同金屬的含量做為實驗的變因，討論兩種不同含量的GaSnZnO薄膜電晶體特性的改變與原因。研究結果顯示，以單靶濺鍍製備而成的電晶體，其臨界電壓、載子遷移率、開關電流比、次臨界擺幅的表現，均落後於以共濺鍍製備之電晶體，共濺鍍製備之GaSnZnO薄膜電晶體的開關電流比大於單靶元件約三個數量級，而載子遷移率更是大於單靶元件50倍以上。除此之外，我們也製作了一批GaSnZnO光感測器，並討論了氧流比對光感能力的影響。在適當的調配下，GaSnZnO光感測器能夠有效區別可見光與紫外光，其拒斥比高達10^4。

最後，我們提出了以「無鎵無鋅」（Ga/Zn-free）的金屬氧化物製作光電元件的概念，我們詳盡地說明為何要捨棄這兩個常見的元素，轉而投入開發氧化銦系列金屬氧化物的原因及其優勢。結果顯示以InSiO為主動層製作而成的薄膜電晶體其效能表現良好，臨界電壓相較於先前研究中所實現之薄膜電晶體要來得低，遷移率在使用同樣氧流比與絕緣層材料之製程手法下也優於其他組，開關電流比也十分優秀。

In this dissertation, several metal oxides were synthesized through sputtering method, inclusive of intrinsic ZnO, indium titanium zinc oxide (InTiZnO), gallium tin zinc oxide (GaSnZnO), and indium silicon oxide (InSiO). Their material properties were explicitly characterized by quite a few analyses regarding to structure, morphology, transparency, chemical states, and so on. Confirmed by UV-vis spectrophotometer, these materials were all transparent in the visible light region, indicating that we could take the advantages from them and fabricate different kinds of optoelectronic devices with the assistance of these semiconducting metal oxides.

In the beginning, we first manufactured thin film transistors (TFTs) with intrinsic ZnO as active layer. The electrical performance was not impressive, which might stem from the innate defects, namely excess oxygen vacancies, in the ZnO film. It is known that the indigenous oxygen vacancies and zinc interstitials in ZnO lattice could cause deterioration to ZnO and ZnO-based electrical components. Hence, it is urgent that we look for a solution to cope with this matter. Fortunately, doping metals is one of the simplest and straightforward solutions. In this dissertation we reported that some metallic elements were promising and had potential of being a dopant, such as indium, titanium, gallium, and tin. We discussed the physical and chemical properties of these elements to elucidate the reasons why they were chosen as dopants.

Next, we fabricated InTiZnO TFTs with different oxygen flow ratios to investigate the effect of oxygen flow on device performance. It was found that appropriate amount of oxygen could fill the oxygen vacancies of the film, contributing to the optimal device performance. However, too much oxygen participating in sputtering was likely to form oxygen interstitials, in which we must be cautious when we regulated the reactive gas flow ratio. The superior InTiZnO TFT demonstrated a threshold voltage of 1.31 V, a mobility of 44.69 cm^2/Vs, and an on-off current ratio of 6.6×10^6, and a subthreshold swing of 0.34 V/dec. Since InTiZnO played a role of a wide-gap material, we also employed it to realize metal-semiconductor-metal (MSM) photodetectors (PDs). The UV-sensing ability was also related to the oxygen flow ratio. The results showed that the InTiZnO PDs could effectively reject the interference of the visible light.

After considering the availability of InTiZnO, we placed stress on GaSnZnO. In this part, we dealt with the constituents in GaSnZnO films. It was found the elemental content might also have impact on the device properties. Two kinds of GaSnZnO films were grown by different sputtering approaches; in other words, one was sputtering a single target, and the other was co-sputtering two targets to manipulate the content of Zn in the films. If we prudently engineered the ZnO content of the film, the device can operate more stably. The GaSnZnO TFT fabricated via sputtering one target demonstrated a threshold voltage of 3.76 V, a mobility of 0.06 cm^2/Vs, and an on-off current ratio of 3.2×10^3, and a subthreshold swing of 0.421 V/dec. Compared with the former one, the GaSnZnO TFT fabricated via co-sputtering method exhibited a threshold voltage of 2.98 V, a mobility of 3.86 cm^2/Vs, and an on-off current ratio of 1.5×10^6, and a subthreshold swing of 0.392 V/dec. On the other hand, the GaSnZnO PDs were made at various oxygen flow ratios, and the better one exhibited a responsivity of 9.12×10^-2 A/W and a UV-to-visible rejection ratio of about 10^4.

In the last part of our research, we were seeking the possibilities of not using Ga/Zn-contained metal oxides. We clearly pointed out what could happen when we utilized these two elements for semiconductor processing. Furthermore, the potential candidates to replace Ga/Zn-contained metal oxides were proposed. InSiO was selected and the consequent TFTs were fabricated. It tuned out that the Ga/Zn-free material InSiO also performed very well. The threshold voltage was 0.32 V, the mobility was 5.03 cm^2/Vs, the on-off current ratio was 2.9×10^5, and the subthreshold swing was 0.37 V/dec. The InSiO PDs with four different oxygen flow ratios were also realized. Despite the fact that InSiO possessed an energy gap around 3 eV, the fabricated PDs were not very sensitive to the UV light, showing a low rejection ratio of 10^2 and sensitivity of 10^2.

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