多年來，在半導工業上多以Si晶圓作為材料，其優點有成本低、取得容易、產能大，但近年來由於光纖通訊的迅速發展使得人們對於紅外光長波長的通訊波段有著極大的需求，而光電元件也相應設計可應用於紅外光波長。以光學設計之角度來看，Si的能帶約1.11 eV且其對1310~1550 nm的紅外光吸收係數非常的弱[1]，反觀Ge的能帶約0.67 eV且其對紅外光波長具良好的吸收係數，因此Ge材料更適用於紅外光通訊元件。
在紅外光光子偵測器的研究，已有許多文獻被提出，其中MSM架構下的光子偵測器具有速度快、製程簡單的優點，但由於金屬與鍺之間的蕭特基位障由費米能階釘位(Fermi level pinning)效應所影響，文獻指出通常在電洞端的位障較低，而此較低的位障易造成較大的暗電流，然而許多文獻也針對此問題來討論如何降低暗電流(dark curent)的影響，例如：摻雜(dopant)、非對稱金屬電極、表面鈍化(passivation)，而本論文利用結合快速熱熔再結晶法(rapid melting growth)、表面鈍化、不同退火(RTA)條件的方式來來達到降低暗電流的目的，另外在模擬上模擬出元件的吸光效率來計算對紅外光波長的吸收，最後在量測上比較各元件的暗電流、光電流、訊雜比、光響應度。

Over decades, silicon semiconductor industry grows rapidly due to advanced CMOS technology as well as relatively low cost for silicon and stable material properties. Silicon-based optoelectronics, benefited from the matured IC industry, receives a lot of attention recently. One of the key applications is high-speed photodetectors for optical communication or optical links. However, Si is transparent for infrared wavelength that is usually used in optical communication. Other materials should be integrated on the Si optoelectronic devices to detect infrared signals. Ge is an ideal material for long wavelength absorption; meanwhile, Ge process is usually CMOS-compatible, indicating the possibility of mass production.
Ge-based photodetectors on silicon substrate have been studied by several research groups. One of the key issues is difficult epitaxy of Ge on silicon due to lattice mismatch (4%). In this thesis, we propose using rapid melting growth method to grow high-quality monocrystal metal-semiconductor-metal Ge photodetectors on Si substrate with low thermal budget. By well selecting metal contact and Ge passivation, the device dark current was significant reduced by three orders of magnitude. Since the absorption layer is very thin, we propose back illumination or metallic grating couplers to enhance the responsivity.

[1] Streetman, Ben G, Sanjay Banerjee, “Solid State electronic Devices (5th ed.),” New Jersey: Prentice Hall. pp. 524, (2000)
[2] Xiaochen Sun, “Ge-on-Si Light-Emitting Materials and Devices for Silicon Phoonics,” B.S. Physics, Peking University, (2004)
[3] M. Oehme, “Photocurrent analysis of a fast Ge p-i-n detector on Si,” APPLIED PHYSICS LETTERS, vol. 91, (2007)
[4] R. Calarco, “Near-infrared metal semiconductor metal photodetector integrated on silicon,” Thin Solid Films, vol. 391, pp. 138-142, (2001)
[5] Shu-Lu Chen, “Design and process for three-dimensional heterogeneous integration,” (2010)
[6] Yaocheng Liu, Michael D. Deal, and James D. Plummer, “High-quality single-crystal Ge on insulator by liquid-phase epitaxy on Si substrates,” APPLIED PHYSICS LETTERS, vol. 84, (2004)
[7] J. D. Hwang, E. H. Zhang, “Effects of a a-Si:H layer on reducing the dark current of 1310 nm metal-germanium-metal photodetectors,” Thin Solid Films, vol. 519, pp. 3819-3821, (2011)
[8] M. Takenaka, “Ultralow-dark-current Ge photodetector with GeO2 passivation and gas-phase doped junction,” IEEE, vol. 978, pp. 4244-8339, (2011)
[9] Kah-Wee Ang, “Novel Silicon–Carbon (Si:C) Schottky Barrier Enhancement Layer for Dark-Current Suppression in Ge-on-SOI MSM Photodetectors,” IEEE ELECTRON DEVICE LETTERS, vol. 29, (2008)
[10] Jungwoo Oh, “Metal–Germanium–Metal Photodetectors on Heteroepitaxial Ge-on-Si With Amorphous Ge Schottky Barrier Enhancement Layers,” IEEE PHOTONICS TECHNOLOGY LETTERS, vol. 16, (2004)
[11] http://refractiveindex.info/
[12] H. Xiao, 羅正忠, 張鼎忠, “半導體製程技術導論,” 歐亞書局, (2009)
[13] D. S. Yu, H. L. Kao, A. Chin, and S. P. McAlister, “Performance and potential of germanium on insulator field-effect transistors,” J. Vac. Sci. Tech., vol. 24, pp. 690, (2006)
[14] A. S. Velasco, P. Amirfeiz, S. Bengtsson, and C. Colinge, “Room temperature wafer bonding using oxygen plasma treatment in reactive ion etchers with and without inductively coupled plasma,” J. Electrochem. Soc., vol. 150, pp. 155-162, (2003)
[15] Liu YC, Deal MD, and Plummer JD, “Rapid Melt Growth of Germanium Crystals with Self-Aligned Microcrucibles on Si Substrates,” JOURNAL OF THE ELECTROCHEMICAL SOCIETY, vol. 152, pp. 688-693, (2005)
[16] H.-Y. Serene Koh, Shu-Lu Chen, Peter B. Griffin, and James D. Plummer, “High Quality Single-Crystal Laterally Graded SiGe on Insulator by Rapid Melt Growth,” Electrochemical and Solid-State Letters., vol. 13, pp. 281-283, (2010)
[17] Douglas J. Tweet, Jong Jan Lee, Jer-Shen Maa, and Sheng Teng Hsu, “Characterization and reduction of twist in Ge on insulator produced by localized liquid phase epitaxy,” APPLIED PHYSICS LETTERS, vol. 87, (2005)
[18] S. Balakumar, M. M. Roy, and B. Ramamurthy, “Fabrication Aspects of Germanium on Insulator from Sputtered Ge on Si-Substrates,” Electrochemical and Solid-State Letters, vol. 9, pp. 158-160, (2006)
[19] Y. Ohta, T. Tanaka, K. Toko, T. Sadoh , and M. Miyao, “Growth-direction-dependent characteristics of Ge-on-insulator by Si–Ge mixing triggered melting growth,” Solid-State Electronics, vol. 60, pp. 18-21, (2011)
[20] T. Sakane, K. Toko, T. Tanaka, T. Sadoh , and M. Miyao, “Strained single-crystal GOI (Ge on Insulator) arrays by rapid-melting growth from Si (111) micro-seeds,” Solid-State Electronics, vol. 60 pp. 22-25, (2011)
[21] Ichiro Mizushima, Kaoru Toko, and Yasuharu Ohta, “Mesh-shape-and-size controlled rapid-melting growth for the formation of single-crystalline (100), (110) and (111) Ge networks on insulators,” APPLIED PHYSICS LETTERS, vol. 98, (2011)
[22] Kaoru Toko, Yasuharu Ohta, Takashi Sakane, and Taizoh Sadoh, “Single-crystalline (100) Ge networks on insulators by rapid-melting growth along hexagonal mesh-pattern,” APPLIED PHYSICS LETTERS, vol. 98, (2011)
[23] Takanori Tanaka, Kaoru Toko, Taizoh Sadoh, and Masanobu Miyao, “High Quality Single-Crystalline Ge-Rich SiGe on Insulator Structures by Si-Doping Controlled Rapid Melting Growth,” Applied Physics Express, vol. 3, (2010)
[24] Kaoru Toko, Masashi Kurosawa, and Hiroyuki Yokoyama, “(100)Orientation-Controlled Ge Giant-Stripes on Insulating Substrates by Rapid-Melting Growth Combined with Si Micro-Seed Technique,” Applied Physics Express, vol. 3, (2010)
[25] Kaoru Toko, Takanori Tanaka, and Yasuharu Ohta, “Defect-free Ge-on-insulator with (100), (110), and (111) orientations by growth-direction-selected rapid-melting growth,” APPLIED PHYSICS LETTERS, vol. 97, (2010)
[26] Masanobu Miyao, Takanori Tanaka, Kaoru Toko, and Masanori Tanaka, “Giant Ge-on-Insulator Formation by Si–Ge Mixing-Triggered Liquid-Phase Epitaxy,” Applied Physics Express, vol. 2, (2009)
[27] Tatsuya Hashimoto, Chiaki Yoshimoto1, Takuji Hosoi1, Takayoshi Shimura, and Heiji Watanabe, “Fabrication of Local Ge-on-Insulator Structures by Lateral Liquid-Phase Epitaxy:Effect of Controlling Interface Energy between Ge and Insulators on Lateral Epitaxial Growth,” Applied Physics Express, vol. 2, (2009)
[28] Masanobu Miyao, Kaoru Toko, Takanori Tanaka, and Taizoh Sadoh, “High-quality single-crystal Ge stripes on quartz substrate by rapid-melting-growth.” APPLIED PHYSICS LETTERS, vol. 95, (2009)
[29] Kaoru Toko,a_ Takashi Sakane, Takanori Tanaka, Taizoh Sadoh, and Masanobu Miyaob, “Defect-free single-crystal Ge island arrays on insulator by rapid-meltinggrowth combined with seed-positioning technique,” APPLIED PHYSICS LETTERS, vol. 95, (2009)
[30] Kaoru Toko_, Takanori Tanaka, Taizoh Sadoh, and Masanobu Miyao, “High-Hole-Mobility Single-Crystalline Ge Thin Films Formed on Insulating Substrates by SiGe Mixing-Triggered Directional Melting Growth,” Japanese Journal of Applied Physics, vol. 49, (2010)
[31] Kaoru Toko, Takanori Tanaka, Taizoh Sadoh, Masanobu Miyao, “Formation of single-crystalline Ge stripes on quartz substrates by SiGe mixing-triggered liquid-phase epitaxy,” Thin Solid Films, vol. 518, (2010)
[32] T. Tanaka a, M. Tanaka, M. Itakura, T. Sadoh, M. Miyao, “Giant growth of single crystalline Ge on insulator by seeding lateral liquid-phase epitaxy,” Thin Solid Films, vol. 518, (2010)
[33] Kaoru Toko, Takashi Sakane, Takanori Tanaka, Taizoh Sadoh, Masanobu Miyao, “Liquid-phase epitaxial growth of Ge island on insulator using Ni-imprint-induced Si crystal as seed,” Thin Solid Films, vol. 518, (2010)
[34] M. Bruel, B. Aspar, A. Japcques, A. Herve, “Smart-Cut: A new silicon on insulator material technology based on hydrogen implantation and wafer bonding,” Japanese Journal of Applied Physics, vol. 36, pp. 1636-1641, (2010)
[35] Gianni Taraschi *, Arthur J. Pitera, Eugene A. Fitzgerald, “Strained Si, SiGe, and Ge on-insulator: review of wafer bonding fabrication techniques,” Solid-State Electronics, vol. 48, (2004)
[36] Shu Nakaharai, Tsutomu Tezuka, Naoharu Sugiyama, “Characterization of 7-nm-thick strained Ge-on-insulator layer fabricated by Ge-condensation technique,” APPLIED PHYSICS LETTERS, vol. 83, (2003)
[37] S. M. Sze, Kwok K. Ng, “Physics of Semiconductor Devices.” Third Edition, WILEY-INTERSCIENCE, (2007)