Controllable Synthesis of Narrow-Gap van der Waals Semiconductor Nb2GeTe4 with Asymmetric Architecture for Ultrafast Photonics

Yongping Dai; Qiang Yu; Xiaoxin Yang; Kun Guo; Yan Zhang; Yushuang Zhang; Junrong Zhang; Jie Li; Jie Chen; Haiqin Deng; Tianhao Xian; Xiao Wang; Jian Wu; Kai Zhang

doi:10.1021/acsnano.1c10241

Controllable Synthesis of Narrow-Gap van der Waals Semiconductor Nb₂GeTe₄ with Asymmetric Architecture for Ultrafast Photonics

ACS Nano. 2022 Mar 22;16(3):4239-4250. doi: 10.1021/acsnano.1c10241. Epub 2022 Feb 22.

Authors

Yongping Dai^{1

2}, Qiang Yu^{1

3}, Xiaoxin Yang^{2

4}, Kun Guo³, Yan Zhang¹, Yushuang Zhang⁵, Junrong Zhang¹, Jie Li¹, Jie Chen^{1

6}, Haiqin Deng³, Tianhao Xian⁷, Xiao Wang⁴, Jian Wu³, Kai Zhang¹

Affiliations

¹ CAS Key Laboratory of Nanophotonic Materials and Devices & Key Laboratory of Nanodevices and Applications, i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), Chinese Academy of Sciences, Suzhou 215123, China.
² Nano Science and Technology Institute, University of Science and Technology of China, Suzhou 215123, China.
³ College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China.
⁴ Shenzhen Key Laboratory of Nanobiomechanics, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China.
⁵ Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, College of Materials Science and Engineering, Hunan University, Changsha, Hunan 410082, China.
⁶ Shanghai IC R&D Center, Shanghai 201210, China.
⁷ State Key Laboratory of Advanced Optical Communication System and Networks, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China.

PMID: 35191693
DOI: 10.1021/acsnano.1c10241

Abstract

Ultrafast photonics has become an interdisciplinary topic of great consequence due to the spectacular progress of compact and efficient ultrafast pulse generation. Wide spectrum bandwidth is the key element for ultrafast pulse generation due to the Fourier transform limitation. Herein, monoclinic Nb₂GeTe₄, an emerging class of ternary narrow-gap semiconductors, was used as a real saturable absorber (SA), which manifests superior wide-range optical absorption. The crystallization form and growth mechanism of Nb₂GeTe₄ were revealed by a thermodynamic phase diagram. Furthermore, the Nb₂GeTe₄-SA showed reliable saturation intensity and larger modulation depth, ascribed to a built-in electric field driven by the asymmetric crystal architecture confirmed via X-ray diffraction, polarized Raman spectra, and scanning transmission electron microscopy. Based on the Nb₂GeTe₄-SA, femtosecond mode-locked operation with good overall performance was achieved by a properly designed ring cavity. These results suggest that Nb₂GeTe₄ shows great promise for ultrafast photonic applications and arouse interests in exploring the intriguing properties of the ternary van der Waals material family.

Keywords: Nb2GeTe4; asymmetric architecture; polarized Raman spectroscopy; thermodynamic phase diagram; ultrafast photonics.