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21）R. Yoshimine, K. Moto, T. Suemasu, and K. Toko, “Advanced solid-phase crystallization for high-hole mobility (450 cm2 V–1s–1) Ge thin film on insulator,” Appl. Phys. Express 11 (3), 031302 (2018).
22）T. Mizoguchi, T. Imajo, T. Suemasu, and K. Toko, “Four-step heating process for solid-phase crystallization of Ge leading to high carrier mobility,” Appl. Phys. Express 13 (10), 101005 (2020).
23）T. Imajo, T. Ishiyama, N. Saitoh, N. Yoshizawa, T. Suemasu, and K. Toko, “Record-High Hole Mobility Germanium on Flexible Plastic with Controlled Interfacial Reaction,” ACS Appl. Electron. Mater. 4, 269 (2022).
24）T. Ozawa, T. Imajo, T. Suemasu, and K. Toko, “High thermoelectric power factors in polycrystalline germanium thin films,” Appl. Phys. Lett. 119, 132101 (2021).
25）K. Nozawa, T. Nishida, T. Ishiyama, T. Suemasu, and K. Toko, “n-Type Polycrystalline Germanium Layers Formed by Impurity-Doped Solid-Phase Growth,” ACS Appl. Electron. Mater. 5, (2023).
26）K. Nozawa, T. Ishiyama, T. Nishida, N. Saitoh, N. Yoshizawa, T. Suemasu, and K. Toko, “High-electron mobility P-doped polycrystalline GeSn layers formed on insulators at low temperatures,” Appl. Phys. Lett. 122 (20), 201901 (2023).
27）K. Moto, S. Maeda, K. Igura, L. Huang, A. Morimoto, K. Yamamoto, and K. Toko, “High-Mobility p-Channel Thin-Film Transistors Based on Polycrystalline GeSn” Adv. Electron. Mater. 2400901 (2025).
28）T. Sadoh, Y. Kai, R. Matsumura, K. Moto, and M. Miyao, “High Carrier Mobility of Sn-Doped Polycrystalline-Ge Films on Insulators by Thickness-Dependent Low-Temperature Solid-Phase Crystallization,” Appl. Phys. Lett. 109, 232106 (2016).
29）C. Xu, X. Gong, M. Miyao, and T. Sadoh, “Enhanced Mobility of Sn-Doped Ge Thin-Films (≤50 nm) on Insulator for Fully Depleted Transistors by Nucleation-Controlled Solid-Phase Crystallization,” Appl. Phys. Lett. 115, 042101 (2019).
30）K. Moto, R. Yoshimine, T. Suemasu, and K. Toko, “Improving Carrier Mobility of Polycrystalline Ge by Sn Doping,” Sci. Rep. 8, 14832 (2018).
31）K. Moto, N. Saitoh, N. Yoshizawa, T. Suemasu, and K. Toko, “Solid-phase crystallization of densified amorphous GeSn leading to high hole mobility (540 cm2/Vs),” Appl. Phys. Lett. 114 (11), 112110 (2019).
32）S. Maeda, T. Ishiyama, N. Saitoh, N. Yoshizawa, T. Suemasu, and K. Toko, “Interfacial Nucleation Control in Amorphous GeSn Thin Films Using Bilayer Structure,” Cryst. Growth Des. 23 (8), 5535-5540 (2023).
33）T. Mizoguchi, T. Imajo, J. Chen, T. Sekiguchi, T. Suemasu, and K. Toko, “Composition dependent properties of p- and n-type polycrystalline group-IV alloy thin films,” J. Alloys Compd. 887, 161306 (2021).
34）M. Saito, T. Nishida, N. Saitoh, N. Yoshizawa, T. Suemasu, and K. Toko, “Solid-phase crystallization of gallium arsenide thin films on insulators,” Mater. Sci. Semicond. Process. 124, 105623 (2021).
35）K. Igura, K. Nozawa, T. Ishiyama, T. Suemasu, and K. Toko, “Strain-dependent grain boundary properties of n-type germanium layers,” Sci. Rep. 14 (1), 7812 (2024).
36）K. Nozawa, K. Igura, T. Mizoguchi, N. Saitoh, N. Yoshizawa, T. Suemasu, and K. Toko, “Hydrogen Passivation Effects on Polycrystalline Germanium Thin Films,” NPG Asia Materials (2025) in press.
■High-quality synthesis of germanium-based thin films for optical applications
■Kaoru Toko
■Professor, Institute of Applied Science, University of Tsukuba
