Anisotropic Charge Carrier and Acoustic Phonon Dynamics of Tin Selenide Studied by Transient Reflectivity Spectroscopy

Wen-Yen Tzeng^1*, Chien-Chun Ko², Chia-Nung Kuo³, Jiunn-Yuan Lin², Chin Shan Lue³, Chih-Wei Luo^1,4,5

¹Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
²Institute of Physics, National Chiao Tung University, Hsinchu, Taiwan
³Department of Physics, National Cheng Kung University, Tainan, Taiwan
⁴Taiwan Consortium of Emergent Crystalline Materials, Ministry of Science and Technology, Taipei, Taiwan
⁵Center for Emergent Functional Matter Science, National Chiao Tung University, Hsinchu, Taiwan

* Presenter:Wen-Yen Tzeng, email:cccaa.ep00g@g2.nctu.edu.tw

Tin selenide (SnSe) has emerged as an appealing 2D material that attracting interest due to the application in thermoelectric energy conversion and optoelectronics devices. Herein, orientation- and temperature-dependent pump-probe experiments were conducted on SnSe single crystals to study the dynamics of photoexcited charge carriers and coherent acoustic phonons along the zigzag and armchair orientations. Since the puckered layered structure, the anisotropic transmission leads to a significant difference in the transient reflection spectra along the zigzag direction and the armchair direction of SnSe. The 1-THz acoustic phonon mode was observed in both zigzag and armchair directions with the relaxation timescale of ps. The 1-THz phonon mode along the zigzag direction has longer lifetime and survives at high temperatures. In contrast, the 45-GHz acoustic phonon mode was only observed along the armchair direction and exists over 600 K. This study offers a fundamental understanding of quasiparticles and optical responses in SnSe, and would be necessary for the applications of the thermoelectric and optoelectronic in 2D materials.

Keywords: Thermoelectric, Optoelectronic, Two-dimensional material