近年許多研究指出，鍺的能帶結構可透過錫的加入而改變，使導帶的Γ帶及L帶以不同的幅度下降，亦即直接及間接能隙皆變小。這樣的特性使得鍺錫的吸收波段紅移，在錫含量夠高時，吸收波段將可涵蓋至>2微米，且可達到直接能隙的能帶結構，因此可廣泛應用在紅外光之發光與吸收元件，對導航及軍事的應用尤為重要。本論文的研究重點即分析分子束磊晶的鍺錫合金材料特性及光電元件的變溫物理機制，以此找到最優化的材料生長方法及元件操作條件。接著也首次實現了純四族的紅外光影像焦平面陣列系統，為四族光電子領域開啟了全新的可能性。
材料特性分析方面，我們以非破壞性的方式調變鍺錫晶格內應力釋放程度，分析其拉曼光譜。以往調變材料應力的實驗多為破壞性，材料品質易受損，且樣品無法做後續製程。而在本研究中，我們利用不同溫度的後退火處理，非破壞性地調變應力，過程中樣品並無損傷。分析其拉曼平移和平面應力的線性關係，得到關係常數b=-299.3 cm^(-1)。
接著我們分析鍺錫發光二極體極光偵測器的變溫物理機制。在鍺錫發光二極體的研究中，我們製作並量測了生長在矽基板上的鍺/鍺錫/鍺 p-i-n異質結構發光二極體在溫度25至150 K下，以低電流密度(13 A/cm2)注入載子時的電致發光特性。在發光光譜中，我們觀察到了無聲子協助及有聲子協助之發光訊號。我們也分析了材料之非直接能隙值與溫度的關係，能隙和溫度的Varshni經驗常數α與β分別為4.88×〖10〗^(-4) eV/K及130 K，以此經驗常數我們將可預測元件在不同溫度下的光譜特性。
在光偵測器研究中，我們將鍺/鍺錫/鍺p-i-n異質結構生長在鍺基板上，製作成光偵測器，變溫(300K至25K)分析其在背面照光下之光響應率變化。隨溫度變化，吸收波段和響應電流的大小都有變化。分析結果顯示，光電流隨溫度變化主要受吸收層內載子遷移率影響，因此在125K的溫度下可得到最佳的光響應，此操作溫度可利用液態氮輕易達到。此研究示範了鍺錫光偵測器可以背向入射方式操作，即可應用於本文後續研究之紅外光成像系統。
基於前述研究，我們將鍺基板上成長之鍺/鍺錫/鍺p-i-n異質結構製作成320×256的焦平面陣列，並在-15℃下成功拍攝鎢絲燈泡的影像，觀察到可見光相機看不到的“熱點”，以灰階的方式呈現在影像中。在此研究中，材料是生長在鍺塊材的基板上，因此部分光線無法穿透鍺基板進入主動層，未來若將基板改為Ge-on-Si或Ge-on-SiO2/Si基板，不僅可大幅改善偵測器靈敏度的問題，更可以與其他光連結元件同時整合在矽晶片上。

In recent years, researches indicate that the band structure of Ge can be engineered with the incorporation of Sn, which can eventually lead to a red-shift in its optical transition wavelength range. Moreover, with sufficient Sn composition, the GeSn alloy will become direct-bandgap material. These make GeSn an important material for infrared opto-electronic applications such as navigation and military. In this dissertation, the major work is to analyze GeSn material properties, and investigate physics mechanisms in opto-electronic devices based on GeSn, so that we have determined the optimized material growth parameters and device operation conditions. For the first time, we demonstrated a group-IV-based focal plane array imaging sensor, opening a new vision for group-IV photonics.
For material characterization, we modify the strain relaxation in GeSn lattice through non-destructive post-annealing method. Most of experiments that modify the strain are destructive, so material quality is degraded, and the samples cannot be used for further device fabrication; while in this work, we anneal samples with different temperature to modify the strain without destroying the samples. The Raman shift of Ge-Ge longitudinal optical phonon mode is in a linear relationship with the in-plane strain in the GeSn films with a coefficient b=-299.3 cm^(-1). Such a relationship enables characterization of GeSn epilayers using the readily accessible Raman spectroscopy.
Later, we analyze temperature-dependent optical transition properties in GeSn based light-emitting diode and photodetector. In the investigation of GeSn-based light emitting diode, we fabricated a Ge/GeSn/Ge p-i-n light emitting diode on Si substrate, and measured the electroluminescence under low injection current of 13 A/cm2 with different operating temperatures from 25 to 150K. In the emission spectra, we observed no-phonon assistant and phonon-assistant replicas. The indirect bandgap of GeSn active layer is increased with the decreasing temperature following Varshni’s empirical expression with α=4.88×〖10〗^(-4) eV/K and β=130 K.
For GeSn-based photodetector, we grew a Ge/GeSn/Ge p-i-n heterostructure on a Ge wafer, and fabricated it into a photodiode for photodetection. We measured the temperature dependent photo-responsivity of the device under back-illumination over a wide temperature range from 300K down to 25 K. Results show that photocurrent is mainly affected by the carrier mobility in the active layer. The maximum responsivity happens at 125 K, which can easily be achieved with liquid nitrogen. This investigation demonstrates the feasibility of a GeSn-based photodetector that can be operated with back-side illumination for applications in image sensing systems.
After establishing the temperature dependent characterization of GeSn single photodetector, we fabricated the Ge/GeSn/Ge heterostructure into a 320×256 image sensor focal plane array. Under -15℃, an image of a tungsten-filament light bulb was attained with observation of gray-scale “hot spot”infrared features not seen using a visible-light camera. This is the first demonstration of group-IV near-infrared imaging sensing focal plane array. For future works, if the substrate is replaced by Ge-on-Si or Ge-on-SiO2/Si wafers, not only detection sensitivity will be significantly improved, more complete on-chip integration of group-IV photonics can be achieved.

Signature page
Acknowledgement…………………………………………………………………...... i
Abstract (Chinese)……………………….………………………………………….... ii
Abstract (English)...……………………………………………………………….…. iv
Table of contents……………………………………………….……………..….…. vii
List of figures……………………………………………………….……………….. xi
List of tables………………………………………………………………..…….… xvi
Chapter 1 Introduction………………..…………………….……………………….... 1
1.1 Background of group-IV photonics………………....……………...….......... 2
1.2 Bandgap Engineering of Ge-based materials……………………………….. 3
1.2.1 Heavily n-type doped tensile strained Ge………………..................... 3
1.2.2 Sn incorporation into Ge host material…………………………......... 6
1.3 Potential applications of Sn-based materials on group-IV photonics…......... 9
1.3.1 Light-emitting diodes………………….…………………………….. 9
1.3.2 Photodetectors…………………………….………………………... 13
1.3.3 Image sensing focal plane arrays…………….…............................... 16
Chapter 2 Experimental Techniques…..…………………………….......…............... 18
2.1 Samples growth.............………………………………………..………….. 18
2.1.1 Sample preparation…………………………………………………. 18
2.1.2 Molecular beam epitaxy……………………….…………………… 19
2.2 Material properties characterization..…………………...…………………. 22
2.2.1 X-ray diffraction………………………......………………………... 22
2.2.2 Transmission electron microscopy…………..……………………... 27
2.2.3 Raman spectroscopy…………………………..……………………. 27
2.3 Devices fabrication…………………………………….......……................. 28
2.4 Optical measurements………………………….…………………...……... 29
2.4.1 Electroluminescence measurement………………………….……… 29
2.4.2 Photo-response measurement……………………………………..... 30
Chapter 3 The strain dependence of GeSn Raman shift……..……………………… 32
3.1 Introduction…………………………………............................................... 32
3.2 Experimental details………………………...…………………………....... 33
3.3 Results and discussion……………………………………...……………… 35
3.3.1 Determining Sn compostion and strain…………………………...... 35
3.3.2 Raman analysis…………………………………………................... 40
3.4 Summary of Chapter 3………………………………………...................... 44
Chapter 4 Temperature-dependent electroluminescence from GeSn heterojunction light-emitting diode on Si substrate………………………………..………………... 45
4.1 Introduction………………………………………………………………... 45
4.2 Experimental details……………………………………………………….. 46
4.3 Results and discussion……………………………………………………... 47
4.4 Summary of Chapter 4…………………………………………………….. 53
Chapter 5 Sn-based Ge/GeSn/Ge p-i-n photodetector operated with back-side illumination………………………………………………………………………….. 55
5.1 Introduction…………………………………………..……………………. 56
5.2 Experimental details………………………………………………….......... 56
5.3 Results and discussion……………………………………………………... 60
5.4 Summary of Chapter 5…………………………………………………...... 67
Chapter 6 Ge0.975Sn0.025 320×256 imager chip for 1.6-1.9 μm infrared vision.......... 69
6.1 Introduction…………………...……………………………….....………... 69
6.2 Experimental details..……………………………………….……………... 70
6.3 Results and discussion……………………………………………………... 72
6.4 Summary of Chapter 6……………………………………………….......... 77
Chapter 7 Summary and future works…………………………….....…………….... 79
7.1 Summary…………………………………………………………………... 79
7.2 Future works……………………………………………………….............. 81
References…………………………………………………………………………... 84
Publication list...…………………………………………………………………….. 94

[1] R. A. Soref, Proc. IEEE 81, 1687 (1993).
[2] M. Lipson, J. Lightwave Technol. 23, 4222 (2005).
[3] N. Izhaky, M. T. Morse, S. Koehl, O. Cohen, D. Rubin, A. Barkai, G. Sarid, R. Cohen, and M. J. Paniccia, IEEE J. Sel. Top. Quantum Electron. 12,1688 (2006).
[4] H. Lin, Ph.D. thesis, Stanford University, 2012.
[5] A. Liu, R. Jones, L. Liao, D. S-Rubio, D. Rubin, O. Cohen, R. Nicolaescu, and M. Paniccia, Nature 427, 615 (2004).
[6] R. A. Soref, Nat. Photonics 4, 495 (2010).
[7] Y. Ishikawa, K. Wada, D. D. Cannon, J. Liu, H. C. Luan, and L. C. Kimerling, Appl. Phys. Lett. 82, 2044 (2003).
[8] J. Liu, X. Sun, D. Pan, X. Wang, L. C. Kimerling, T. L. Koch, and J. Michel, Opt. Express 15, 11272 (2007).
[9] J. F. Liu, D. D. Cannon, K. Wada, Y. Ishikawa, S. Jongthammanurak, D. T. Danielson, J. Michel, and L. C. Kimerling, Appl. Phys. Lett. 87, 011110 (2005).
[10] C. G. Van de Walle, Phys. Rev. B 39, 1871-1883 (1989).
[11] J. Liu, J. Michel, W. Giziewicz, D. Pan, K. Wada, D. D. Cannon, S. Jongthammanurak, D. T. Danielson, L. C. Kimerling, J. Chen, F. O. Ilday, F. X. Kartner, and J. Yasaitis, Appl. Phys. Lett. 87, 103501 (2005).
[12] J. Michel, J. Liu, and L. C. Kimerling, Nat. Photonics 4, 527 (2010).
[13] X. Sun, J. Liu, L. C. Kimerling, and J. Michel, Appl. Phys. Lett. 95, 011911 (2009).
[14] X. Sun, J. Liu, L. C. Kimerling, and J. Michel, Opt. Lett. 34, 1198 (2009).
[15] J. Liu, X. Sun, L. C. Kimerling, and J. Michel, Opt. Lett. 34, 1738 (2009).
[16] R. E. Camacho-Aguilera, Y. Cai, N. Patel, J. T. Bessette, M. Romagnoli, L. C. Kimerling, and J. Michel, Opt. Express 20, 11316 (2012).
[17] J. R. Jain, A. Hryciw, T. M. Baer, D. A. B. Miller, M. L. Brongersma, and R. T. Howe, Nat. Photonics 6, 398 (2012).
[18] D. S. Sukhdeo, J. Petykiewicz, S. Gupta, D. Kim, S. Woo, Y. Kim, J. Vuckovic, K. C. Saraswat, and D. Nam, Opt. Express 23, 33249 (2015).
[19] J. Petykiewicz, D. Nam, D. S. Sukhdeo, S. Gupta, S. Buckley, A. Y. Piggott, J. Vuckovic, and K. C. Saraswat, Nano Lett. 16, 2168 (2016).
[20] R. F. C. Farrow, D. S. Robertson, G. M. Williams, A. G. Cullis, G. R. Jones, I. M. Young, and M. J. Dennis, J. Cryst. Growth 54, 507 (1981).
[21] V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menendez, Phys. Rev. B 73, 125207 (2006).
[22] W. J. Yin, X. G. Gong, and S. H. Wei, Phys. Rev. B 78, 161203 (2008).
[23] R. Roucka, J. Mathews, R. T. Beeler, J. Tolle, J. Kouvetakis, and J. Menendez, Appl. Phys. Lett. 98, 061109 (2011).
[24] M.-Y. Ryu, T. R. Harris, Y. K. Yeo, R. T. Beeler, and J. Kouvetakis, Appl. Phys. Lett. 102, 171908 (2013).
[25] H. H. Tseng, H. Li, V. Mashanov, Y. J. Yang, H. H. Cheng, G. E. Chang, R. A. Soref, and G. Sun, Appl. Phys. Lett. 103, 231907 (2013).
[26] H. H. Tseng, K. Y. Wu, H. Li, V. Mashanov, H. H. Cheng, G. Sun, and R. A. Soref, Appl. Phys. Lett. 102, 182106 (2013).
[27] F. Gencarelli et al., ECS Journal of Solid State Science and Technol. 2, 134 (2013).
[28] Z. Zhou, B. Yin, and J. Michel, Light: Science & Application 4, e385 (2015).
[29] J. Mathews, R. T. Beeler, J. Tolle, C. Xu, R. Roucka, J. Kouvetakis, and J. Menendez, Appl. Phys. Lett. 97, 221912 (2010).
[30] M. Oehme, E. Kasper, and J. Schulze, ECS J. Solid State Sci.Technol. 2, R76 (2013).
[31] J. D. Gallagher, C. L. Senaratne, C. Xu, P. Sims, T. Aoki, D. J. Smith, J. Menendez, and J. Kouvetakis, J. Appl. Phys. 117, 245704 (2015).
[32] C. Chang, H. Li, S. H. Huang, L. C. Lin, and H. H. Cheng, Jpn. J. Appl. Phys., Part 1 55, 04EH03 (2016).
[33] J. Mathews, R. Roucka, J. Xie, S. Q. Yu, J. Menendez, J. Kouvetakis, Appl. Phys. Lett. 95, 133506 (2009).
[34] S. Su, B. Cheng, C. Xue, W. Wang, Q. Cao, H. Xue, W. Hu, G. Zheng, Y. Zuo, and Q. Wang, Opt. Express 19, 6400 (2011).
[35] M. Oehme, M. Schmid, M. Kaschel, M. Gollhofer, D. Widmann, E. Kasper, and J. Schulze, Appl. Phys. Lett. 101, 141110 (2012).
[36] A. Gassenq, F. Gencarelli, J. Van Campenhout, Y. Shimura, R. Loo, G. Narcy, B. Vincent, and G. Roelkens, Opt. Express 20, 27297 (2012).
[37] M. Oehhme, D. Widmann, K. Kostecki, P. Zaumseil, B. Schwartz, M. Collhofer, R. Koerner, S. Bechler, M. Kittler, E. Kasper, and J. Schulze, Opt. Lett. 39, 4711 (2014).
[38] C. Chang, H. Li, S. H. Huang, H. H. Cheng, G. Sun, and R. A. Soref, Appl. Phys. Lett. 108, 151101 (2016).
[39] C. Chang, H. Li, C. T. Ku, S. G. Yang, H. H. Cheng, J. Hendrickson, R. A. Soref, and G. Sun, Appl. Opt. 55, 10170 (2016).
[40] V. R. D’Costa, Y. Fang, J. Mathews, R. Roucka, J. Tolle, J. Menendez, and J. Kouvestakis, Semicond. Sci. Technol. 24, 115006 (2009).
[41] R. Roucka, J. Mathews, C. Weng, R. Beeler, J. Tolle, J. Menendez, and J. Kouvestakis, IEEE J. Quantum Electron. 47, 213 (2011).
[42] D. Zhang, C. Xue, B. Cheng, S. Su, Z. Liu, X. Zhang, G. Zhang, C. Li, and Q. Wang, Appl. Phys. Lett. 102, 141111 (2013).
[43] M. Oehme, K. Kostecki, K. Ye, S. Bechler, K. Ulbricht, M. Schmid, M. Kaschel, M. Gollhofer, R. Korner, W. Zhang, E. Kasper, and J. Schulze, Opt. Express 22, 839 (2014).
[44] B. R. Conley, A. Mosleh, S. A. Ghetmiri, W. Du, R. A. Soref, G. Sun, J. Margetis, J. Tolle, H. A. Naseem, and S. Q. Yu, Opt. Express 22, 15639 (2014).
[45] GEMINI OBSERVATORY, “IR transmission spectra,” http://www.gemini.edu/sciops/telescopes-and-sites/observing-condition-constraints/ir-transmission-spectra
[46] D. A. Scribner, M. R. Kruer, and J. M. Killiany, Proceedings of the IEEE 79, 66 (1991).
[47] P. W. Kruse, Semiconductors and Semimetals 5, 15 (1970).
[48] A. Rogalski, Infrared Physics & Technology 43, 187 (2002).
[49] Y. Arslan, F. Oguz, and C. Besikci, IEEE J. Quan. Electron. 50, 957 (2014).
[50] A. Y. Cho, and J. R. Arthur, Prog. Solid State Chem. 10, 157 (1975).
[51] J. E. Ayers, J. Cryst. Growth 135, 71 (1994).
[52] S. Marklund, Phys. Status Solidi B 92, 83 (1979).
[53] S. F. Li, M. R. Bauer, J. Menendez, and J. Kouvestakis, Appl. Phys. Lett. 84, 867 (2004).
[54] V. R. D’Costa, J. Tolle, R. Roucka, C. D. Poweleit, J. Kouvetakis, and J. Menendez, Solid State Commun. 144, 240 (2007).
[55] S. J. Su, W. Wang, B. W. Cheng, W. X. Hu, G. Z. Zhang, C. L. Xue, Y. H. Zuo, and Q. M. Wang, Solid State Commun. 151, 647 (2011).
[56] M. Rojas-Lopez, H. Navarro-Contreras, P. Desjardins, O. Gurdal, N. Taylor, J. R. A. Carlsson, and J. E. Greene, J. Appl. Phys. 84, 2219 (1998).
[57] R. Cheng, W. Wang, X. Gong, L. F. Sun, P. F. Guo, H. L. Hu, Z. X. Shen, G. Q. Han, and Y. C. Yeo, ECS J. Solid State Sci. 2, 138 (2013).
[58] H. Lin, R. Chen, Y. J. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, Appl. Phys. Lett. 98, 261917 (2011).
[59] H. Li, Y. X. Cui, K. Y. Wu, W. K. Tseng, H. H. Cheng, and H. Chen, Appl.Phys. Lett. 102, 251907 (2013).
[60] R. Chen, H. Lin, Y. J. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, Appl. Phys. Lett. 99, 181125 (2011).
[61] W. Kern, J. Electrochem. Soc. 197, 1887 (1990).
[62] H. Chen, L. W. Guo, Q. Cui, Q. Huang, and J. M. Zhou, J. Appl. Phys. 79, 1167 (1996).
[63] H. J. Mcskimin, and P. Andreatch, J. Appl. Phys 34, 651 (1963).
[64] P. Moontragoon, Z. Ikonic, and P. Harrison, Semicond. Sci. Technol. 22, 742 (2007).
[65] P. Parayanthal, H. Fred, and Pollak, Phys. Rev. Lett. 52, 1822 (1984).
[66] F. Cerdeira, C. Buchenau, M. Cardona, and F. H. Pollak, Phys. Rev. B 5, 580 (1972).
[67] G. Sun, R. A. Soref, and H. H. Cheng, J. Appl. Phys. 108, 033107 (2010).
[68] G. Sun, R. A. Soref, and H. H. Cheng, Opt. Express 18, 19957 (2010).
[69] J. Weber and M. I. Alonso, Phys. Rev. B 40, 5683 (1989).
[70] R. R. Lieten, K. Bustillo, T. Smets, E. Simoen, J. W. Ager, III, E. E. Haller, and J. P. Locquet, Phys. Rev. B 86, 035204 (2012)
[71] Y. P. Varshni, Physica 34, 149 (1967).
[72] S. M. Sze, Physics of Semiconductor Devices (Wiley, New York, 1981) 2nd ed.
[73] L. Via, H. Hochst, and M. Cardona, Phys. Rev. B 31, 958 (1985).
[74] W. Du, Y. Y. Zhou, S. A. Ghetmiri, A. Mosleh, B. R.Conley, A. Nazzal, R. A. Soref, G. Sun, J. Tolle, J. Margetis, H. A. Naseem, and S. Q. Yu, Appl. Phys. Lett. 104, 241110 (2014).
[75] T. Martin, R. Brubaker, P. Dixon, M. A. Gagliardi, and T. Sudol, Proc. SPIE 5783, 121 (2005).
[76] Y. H. Peng, H. H. Cheng, V. I. Mashanov, and G. E. Chang, Appl. Phys. Lett. 105, 231109 (2014).
[77] H. A. Macleod, Thin-Film Optical Filters, 3ed ed. (Institute of Physics Publish, Bristol/Philadelphia, 2001).
[78] D. Aspnes and A. Studna, Phys. Rev. B 27, 985 (1983).
[79] E. D. Palik, Handbook of Optical Constants of Solids (Academic Press, New York, 1985).
[80] A. Korkin, P. S. Krstic, and J. C. Wells, Nanotechnology for Electronics, Photonics, and Renewable Energy (Springer Science + Business Media, 2010).
[81] P. Y. Yu, Fundamentals of Semiconductors: Physics and Materials Properties, 3rd ed. (Springer, Berlin/Heidelberg/New York, 2005).
[82] H. Li, C. Chang, H. H. Cheng, G. Sun, and R. A. Soref, Appl. Phys. Lett 108, 191111 (2016).
[83] D. A. Neamen, Semiconductor Physics and Devices, 3rd ed. (McGraw-Hill, 2003).
[84] F. J. Morin, Phys. Rev. B 93, 62 (1954).
[85] S. Su, W. Wang, B. Cheng, G. Zhang, W. Hu, C. Xue, Y. Zuo, and Q. Wang, J. Cryst. Growth 317, 43 (2011).
[86] E. Kasper, J. Werner, M. Oehme, S. Escoubas, N. Burle, and J. Schulze, Thin Solid Films 520, 3195 (2012).
[87] S. Zaima, O. Nakatsuka, N. Taoka, M. Kurosawa, W. Takeuchi, and M. Sakashita, Sci. Technol. Adv. Mater. 16, 043502 (2015).
[88] S. F. Tang, C. D. Chiang, P. K. Weng, Y. T. Cau, J. J. Luo, S. T. Yang, C. C. Shih, S. Y. Lin, and S. C. Lee, IEEE Photonics Technol. Lett. 18, 986 (2006).
[89] H. Li, H. H. Cheng, L. C. Lee, C. P. Lee, L. H. Su, and Y. W. Suen, Appl. Phys. Lett. 104, 241904 (2014).