本論文是利用化學氣相沉積法將三氧化鉬硫化，形成二硫化鉬，並深入探討不同製程參數下對於二硫化鉬薄膜的影響。此外，將二硫化鉬薄膜製作為氣體感測器、光檢測器、延伸式閘極場效電晶體pH感測器，並分析元件特性。
實驗第一部分，我們在不同製程參數下利用化學氣相沉積法成長二硫化鉬薄膜。藉由結構分析、光學分析、元素分析，研究不同成長時間、二硫化鉬的層數、硫化氫壓力，以及基板所造成薄膜的差異。在原子力顯微鏡分析中，可以觀察到薄膜表面粗糙度隨著成長時間增加而減小。另外，層數愈多，薄膜表面粗糙度隨之減小。在掃描電子顯微鏡分析中，可以確認圖案藍寶石基板的規格。此外，隨著成長時間，二硫化鉬會經歷成核、聚集的階段，並逐漸形成薄膜。透過穿透式電子顯微鏡分析，確認在平坦藍寶石基板、圖案藍寶石基板，以及在具有200 nm二氧化矽的矽基板上，分別沉積5埃三氧化鉬，經硫化後，都形成2層二硫化鉬。藉由能量色散X射線譜分析，驗證二硫化鉬的元素組成，鉬與硫的原子含量接近33.33%和66.66%。根據X射線光電子能譜分析的結果可知，二硫化鉬的相態是2H半導體態。增加硫化氫壓力，相態也為2H半導體態，且Mo-O鍵結的峰消失，代表薄膜中此類型的缺陷減少。拉曼光譜研究在平坦藍寶石基板、圖案藍寶石基板，以及在具有200 nm二氧化矽的矽基板上分別沉積5、10、15埃的三氧化鉬，硫化後所形成的二硫化鉬。透過兩個特徵峰的頻率差距來判斷層數，對於平坦藍寶石基板和具有200 nm二氧化矽的矽基板，判斷為2、3、6層二硫化鉬。而對於圖案藍寶石基板，則判斷為2、3、4層二硫化鉬。另外，觀察到拉曼訊號偏移，是因為在高溫冷卻時，不同基板會給二硫化鉬不同的應力。其中，二硫化鉬在具有200 nm二氧化矽的矽基板上拉伸應力最大，其拉曼訊號紅移。然而，在圖案藍寶石基板上拉伸應力最小，其拉曼訊號藍移。最後，光致發光分析顯示，隨著層數愈少，二硫化鉬特徵峰訊號強度愈強。接著，提高硫化氫壓力製作2層二硫化鉬在不同基板上，其特徵峰的強度變大，推測改善薄膜結晶度。同時，觀察到特徵峰偏移，也是因為不同基板給予不同的應力所導致。此外，使用不同前驅物(鉬以及硫粉)來成長單層二硫化鉬，其主要特徵峰位於664.77 nm，經計算後，能隙約為1.87 eV。
實驗第二部分，我們研究二硫化鉬金半金感測器。在氣體感測器的部分，針對還原性氣體(異丙醇、乙醇、丙酮等等)討論其元件的特性和響應。我們發現層數和響應高度相關。當2層和3層時，其元件表現為n型半導體，響應高。而4層時，其元件表現為p型半導體，響應小。其中，3層二硫化鉬氣體感測器對於500ppm的異丙醇具有最大的響應，為148.31%。在光檢測器的部分，我們發現層數也和響應高度相關。當2層和3層時，元件響應較大。而4層時，其元件的響應小。其中，3層二硫化鉬光檢測器具有最大的響應，為3.23×10-6 A/W。在連續開關燈量測中，觀察到每一週期的電流都小於前一週期。
實驗第三部分，我們研究2層二硫化鉬延伸式閘極場效電晶體pH感測器在不同基板上的性能。敏感度和線性測量結果表明，2層二硫化鉬pH感測器在平坦藍寶石基板上表現較好，分別為37.0493 μA/pH和0.99716。接著，將感測器浸泡在pH值為2和12的緩衝溶液中連續測量，我們觀察到響應都非常快速且穩定，顯示出良好的可靠性。

In this thesis, molybdenum trioxide (MoO3) is deposited by electron beam evaporation, Then, molybdenum disulfide (MoS2) is formed by chemical vapor deposition (CVD). Subsequently, the effects of different process parameters on the properties of MoS2 thin films are discussed. In addition, MoS2 films are made into gas sensors, photodetectors, and extended gate field effect transistor (EGFET) pH sensors. Simultaneously, the performance of the devices is analyzed.
First, MoS2 films under different process parameters were grown by CVD. Through structural analysis, optical analysis, and elemental analysis, the film differences due to different growth times, different layers, different hydrogen sulfide (H2S) pressures, and different substrates were studied. In the AFM analysis, it could be observed that as the growth time increases, the surface roughness of the film decreases. Besides, as the number of layers increases, the surface roughness of the film tends to decrease. SEM is used to confirm the specifications of the patterned sapphire substrate (PSS). In addition, as the growth time increases, MoS2 would gradually form a thin film through nucleation and aggregation. 5 Å MoO3 was deposited on a flat sapphire substrate (FSS), a PSS and a silicon substrate with 200 nm silicon dioxide (SiO2). Then, MoS2 was formed by CVD. According to TEM analysis, it is confirmed that all MoS2 films are two layers. The elemental composition of the MoS2 films was verified by EDS. The atomic contents of molybdenum and sulfur are close to 33.33% and 66.66%. XPS analysis can confirm that the phase state of MoS2 is 2H semiconductor state. Increasing the pressure of H2S, the phase state of the grown MoS2 is also 2H semiconductor state. As well, the peak of the Mo-O bond disappeared, indicating that this type of defect in the film was reduced. After sulfidation, 5, 10, and 15 Å MoO3 on FSSs, PSSs, and silicon substrates with 200 nm SiO2 formed different thicknesses of MoS2. Their Raman analysis were studied. The number of MoS2 layers is determined by the frequency difference between the two characteristic peaks. For FSSs and silicon substrates with 200 nm SiO2, it is judged as 2, 3, and 6 layers of MoS2. For PSSs, it is determined to be 2, 3, and 4 layers of MoS2. Moreover, the Raman signal would shift because different substrates would exert different stresses on MoS2 during high-temperature cooling. Among them, MoS2 has the largest tensile stress on a silicon substrate with 200 nm SiO2, and its Raman signal is red-shifted. However, the tensile stress is the smallest on the PSS, and the Raman signal is blue-shifted. Finally, PL analysis shows that as the number of layers decreases, the intensity of MoS2 signal becomes larger. Next, the pressure of H2S is increased to fabricate two layers of MoS2 on different substrates. PL results show that the intensity of MoS2 signal becomes larger. It is speculated that the quality of the films is improved, and it is found that the peak position shift is also caused by the stress applied by different substrates. Furthermore, using different precursors (molybdenum and sulfur powder) to grow the MoS2 film, the main characteristic peak of the monolayer MoS2 is at 664.77 nm. After calculation, the energy gap is about 1.87 eV.
Secondly, MoS2 metal-semiconductor-metal sensors were fabricated. For gas sensors, the characteristics and response of devices used for reducing gases (isopropanol, ethanol, acetone, etc.) are discussed. However, it is found that the number of layers is highly correlated with the response. In the case of 2-layer and 3-layer MoS2, the devices behave as n-type semiconductors with high response. In the case of 4-layer MoS2, the device behaves as a p-type semiconductor with a small response. Among them, the 3-layer MoS2 gas sensor has the largest response to 500 ppm isopropanol, which is 148.31%. For photodetectors, it is found that the number of layers is also highly correlated with the response. In the case of 2-layer and 3-layer MoS2, the response of devices is larger. In the case of 4-layer MoS2, the response of the device is small. Among them, the 3-layer MoS2 photodetector has the largest response of 3.23×10-6 A/W. In continuous switching measurements, it is observed that the current in each cycle is less than the previous cycle.
Third, the performance of the 2-layer MoS2 EGFET pH sensors on FSS and Si substrate with 200nm SiO2 were studied. The sensitivity and linearity indicate that the 2-layer MoS2 EGFET pH sensor performs better on FSS, with 37.0493 μA/pH and 0.99716, respectively. Then, the sensors were immersed in buffer solutions with pH values of 2 and 12 for continuous measurement. It is observed that the response is very fast and stable, showing good reliability.

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Chapter 4
[1] Chen, Sung-Wen Huang, et al. "Enhanced wavelength-selective photoresponsivity with a MoS2 bilayer grown conformally on a patterned sapphire substrate." Journal of Materials Chemistry C 7.6 (2019): 1622-1629.
[2] Dolui, Kapildeb, Ivan Rungger, and Stefano Sanvito. "Origin of the n-type and p-type conductivity of MoS2 monolayers on a SiO2 substrate." Physical review B 87.16 (2013): 165402.
[3] Min, Sung-Wook, et al. "Charge-Transfer-Induced p-Type Channel in MoS2 Flake Field Effect Transistors." ACS applied materials & interfaces 10.4 (2018): 4206-4212.
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[5] Agrawal, Abhay V., et al. "Photoactivated mixed in-plane and edge-enriched p-Type MoS2 flake-based NO2 sensor working at room temperature." ACS sensors 3.5 (2018): 998-1004.
[6] Chen, Sung-Wen Huang, et al. "Enhanced wavelength-selective photoresponsivity with a MoS2 bilayer grown conformally on a patterned sapphire substrate." Journal of Materials Chemistry C 7.6 (2019): 1622-1629.