本論文中我們以石墨烯薄膜作為場效電晶體元件的薄膜作為主軸，利用乙烷 ( ethane, C2H6 ) 以化學氣相沉積技術在藍寶石基板上成長大面積的石墨烯薄膜，運用乙烷的解離能小於甲烷 ( methane, CH4 ) 的特性，使得碳的裂解情況比常見的甲烷更有效率，藉由調整成長壓力和時間來優化薄膜，再製作成上閘極結構以及平面式閘極結構來展示石墨烯薄膜之特性。由於在上閘極電晶體的結構裡必須要成長氧化層來隔絕閘極，但二維材料和氧化層的介面問題導致電晶體特性不理想，在氧化層中會有許多缺陷使得漏電流變大，元件容易穿透氧化層使元件崩潰，我們更改電晶體結構成平面式閘極，在平面式閘極電晶體中，汲極、源極和閘極皆位在同一平面上，此結構不需要氧化層來隔絕閘極和薄膜，解決了氧化層和二維材料之間的介面問題。在平面閘極電晶體的製程裡，運用電子束微影技術 ( EBL ) 使其元件尺寸可以更小，進而達到更好的電特性。在討論完石墨烯薄膜的各式電晶體結構後，在石墨烯薄膜上成長二硫化鉬作為保護層，避免在製程的中造成石墨烯薄膜的破壞以及其他製程步驟對通道薄膜的汙染，進而探討其元件特性，二硫化鉬的成長方式分別為濺鍍成長、熱蒸鍍成長。在石墨烯上濺鍍成長二硫化鉬，因為電漿射頻系統對於石墨烯薄膜的破壞導致無法成膜；因此我們選用熱蒸鍍的方法來成長二硫化鉬，在元件製備過程中，利用原子層蝕刻技術，將金屬電極底下作為保護層的的二硫化鉬蝕刻掉，之後再進行後續製程，發現載子遷移率可以有效的提升。

In this thesis, we have fabricated transistors with top and in-plane gates on bi-layer graphene films grown directly on sapphire substrates [1] by using photo-lithography and e-beam lithography, respectively. For top-gate graphene transistors, since there are no dangling bonds on graphene surfaces, it is difficult to achieve uniform precursor distribution on the graphene surface for the growth of dielectric layer by using the atomic layer deposition. In this case, the inferior dielectric layer would lead to a high leakage current and therefore, the breakdown of the device. On the other hand, since the channel is only of bi-layer graphene, strong carrier scatterings are observed on the Al2O3/graphene interface, which will degrade the field-effect mobilities of the top-gate graphene transistors. To avoid the influence of the dielectric layer to the graphene channel, graphene transistors with in-plane gates are fabricated. Since there is no dielectric layer for this device, compared with top-gate graphene transistors, significant field-effect mobility enhancement is observed for the device with in-plane gates. However, for this device architecture, the graphene channel is exposed to the atmospheric environment, we have deposited another MoS2 layer on top of the graphene channel by using the thermal evaporation. An even higher field-effect mobility value is observed for the MoS2-passivated graphene transistor with in-plane gates after the removal of MoS2 films underneath the source/drain electrodes. Besides the field-effect mobility enhancement, we have also observed large Dirac point shift under light irradiation, which suggests that the MoS2-passivated graphene transistor with in-plane gates can also act as a high-speed photo-transistors.

[1] Long M, Wang P, Fang H, Hu W. Progress, challenges, and opportunities for 2D material based photodetectors. Adv Funct Mater. 2018;1803807.
[2] Hu, C., Wang, X. & Song, B. High-performance position-sensitive detector based on the lateral photoelectrical effect of two-dimensional materials. Light Sci Appl 9, 88 (2020)
[3] Chin-Cheng Chiang, Vaibhav Ostwal, Peng Wu, Chin-Sheng Pang, Feng Zhang, Zhihong Chen, and Joerg Appenzeller , "Memory applications from 2D materials", Applied Physics Reviews 8, 021306 (2021)
[4] Choi, W., Lahiri, I., Seelaboyina, R., & Kang, Y. S. “Synthesis of graphene and its applications: a review”. Critical Reviews in Solid State and Materials Sciences, 35 (1), 52-71. (2010)
[5] Kim, K. S., Zhao, Y., Jang, H., Lee, S. Y., Kim, J. M., Kim, K. S., ... & Hong, B. H. “Large-scale pattern growth of graphene films for stretchable transparent electrodes”. Nature, 457 (7230), 706. (2009).
[6] Schwierz, F. “Graphene transistors”. Nature nanotechnology, 5 (7), 487, (2010).
[7] Iqbal, M. W., Iqbal, M. Z., Khan, M. F., Shehzad, M. A., Seo, Y., Park, J. H., ... & Eom, J. (2015). High-mobility and air-stable single-layer WS 2 field-effect transistors sandwiched between chemical vapor deposition-grown hexagonal BN films. Scientific reports, 5, 10699
[8] Ye, M., Winslow, D., Zhang, D., Pandey, R., & Yap, Y. K. (2015, March). Recent advancement on the optical properties of two-dimensional molybdenum disulfide (MoS2) thin films. In Photonics (Vol. 2, No. 1, pp. 288-307).
[9] Zahn, D. R., Tonndorf, P., Schmidt, R., Böttger, P., Zhang, X., Börner, J., ... & Bratschitsch, R. (2013). Photoluminescence emission and Raman response of monolayer MoS2, MoSe2, and WSe2.
[10] Li, H., Wu, J., Yin, Z., & Zhang, H. (2014). Preparation and applications of mechanically exfoliated single-layer and multilayer MoS2 and WSe2 nanosheets. Accounts of chemical research, 47(4), 1067-1075.
[11] Schmidt, H., Wang, S., Chu, L., Toh, M., Kumar, R., Zhao, W., ... & Eda, G. (2014). Transport properties of monolayer MoS2 grown by chemical vapor deposition. Nano letters, 14(4), 1909-1913.
[12] Calizo, I., Bejenari, I., Rahman, M., Liu, G., & Balandin, A. A. (2009). Ultraviolet Raman microscopy of single and multilayer graphene. Journal of Applied Physics, 106(4), 043509.
[13] Ferrari, A. C., Meyer, J. C., Scardaci, V., Casiraghi, C., Lazzeri, M., Mauri, F., ... & Geim, A. K. (2006). Raman spectrum of graphene and graphene layers. Physical review letters, 97(18), 187401.
[14] Sutter, P. W., Flege, J. I., & Sutter, E. A. (2008). Epitaxial graphene on ruthenium. Nature materials, 7(5), 406-411.
[15] Li, X., Zhang, G., Bai, X., Sun, X., Wang, X., Wang, E., & Dai, H. (2008). Highly conducting graphene sheets and Langmuir–Blodgett films. Nature nanotechnology, 3(9), 538-542
[16] Celebi, K., Cole, M. T., Choi, J. W., Wyczisk, F., Legagneux, P., Rupesinghe, N., ... & Park, H. G. (2013). Evolutionary kinetics of graphene formation on copper. Nano letters, 13(3), 967-974.
[17] Li, X., Cai, W., An, J., Kim, S., Nah, J., Yang, D., ... & Banerjee, S. K. (2009). Large-area synthesis of high-quality and uniform graphene films on copper foils. science, 324(5932), 1312-1314.
[18] Li, X., Cai, W., Colombo, L., & Ruoff, R. S. (2009). Evolution of graphene growth on Ni and Cu by carbon isotope labeling. Nano letters, 9(12), 4268-4272.
[19] Lee, J. H., Lee, E. K., Joo, W. J., Jang, Y., Kim, B. S., Lim, J. Y., ... & Yang, C. W. (2014). Wafer-scale growth of single-crystal monolayer graphene on reusable hydrogen-terminated germanium. Science, 344(6181), 286-289.
[20] Lin, M. Y., Su, C. F., Lee, S. C., & Lin, S. Y. (2014). The growth mechanisms of graphene directly on sapphire substrates by using the chemical vapor deposition. Journal of Applied Physics, 115(22), 223510.
[21] Kim, H., & Maeng, W. J. “Applications of atomic layer deposition to nanofabrication and emerging nanodevices”. Thin Solid Films 517.8, 2563-2580. (2009).
[22] Moura, C. C., Tare, R. S., Oreffo, R. O., & Mahajan, S. (2016). Raman spectroscopy and coherent anti-Stokes Raman scattering imaging: prospective tools for monitoring skeletal cells and skeletal regeneration. Journal of The Royal Society Interface, 13(118), 20160182
[23] F. T. Johra, J. W. Lee, W. G. Jung and F. Tuz, Facile and safe graphene preparation on solution based platform. J. Ind. Eng. Chem., 2014, 20, 2883
[24] Orlita, Milan, et al. "Approaching the Dirac point in high-mobility multilayer epitaxial graphene." Physical review letters 101.26 (2008): 267601.
[25] Mayorov, Alexander S., et al. "How close can one approach the Dirac point in graphene experimentally?." Nano letters 12.9 (2012): 4629-4634.
[26] Jiang, Zhigang, et al. "Quantum Hall states near the charge-neutral Dirac point in graphene." Physical review letters 99.10 (2007): 106802.
[27] Bardarson, Jens H., et al. "One-parameter scaling at the Dirac point in graphene." Physical review letters 99.10 (2007): 106801.
[28] Sui, Zhu-Yin, et al. "High surface area porous carbons produced by steam activation of graphene aerogels." Journal of Materials Chemistry A 2.25 (2014): 9891-9898.
[29] Park, Sul Ki, et al. "CNT branching of three-dimensional steam-activated graphene hybrid frameworks for excellent rate and cyclic capabilities to store lithium ions." Carbon 116 (2017): 500-509.
[30] Ebnonnasir, Abbas, et al. "Tunable MoS2 bandgap in MoS2-graphene heterostructures." Applied Physics Letters 105.3 (2014): 031603
[31] Simone Bertolazzi, Daria Krasnozh on, and Andras Kis, Nonvolatile Memory Cells Based on MoS2/Graphene Heterostructures. ACS Nano 2013 7 (4), 3246-3252DOI: 10.1021/nn3059136
[32] Haomin Wang, Yihong Wu, Chunxiao Cong, Jingzhi Shang, and Ting Yu, Hysteresis of Electronic Transport in Graphene Transistors ACS Nano 2010 4 (12), 7221-7228
[33] Kuan-Chao Chen et al 2017 2D Mater. 4 034001
[34] Daniel Gunlycke, Denis A. Areshkin, Junwen Li, John W. Mintmire, and Carter T. White Graphene Nanostrip Digital Memory Device Nano Letters 2007 7 (12), 3608-3611
[35] Malard, L. M., Pimenta, M. A. A., Dresselhaus, G., & Dresselhaus, M. S. (2009). Raman spectroscopy in graphene. Physics reports, 473(5-6), 51-87
[36] Lee, C., Yan, H., Brus, L. E., Heinz, T. F., Hone, J., & Ryu, S. (2010). Anomalous lattice vibrations of single-and few-layer MoS2. ACS nano, 4(5), 2695-2700.
[37] Jung, Y., Shen, J., & Cha, J. J. (2014). Surface effects on electronic transport of 2D chalcogenide thin films and nanostructures. Nano Convergence, 1(1), 1-8. [31]
[38] Kuc, A., Zibouche, N., & Heine, T. (2011). Influence of quantum confinement on the electronic structure of the transition metal sulfide T S 2. Physical Review B, 83(24), 245213