Anisotropic Terahertz Emission from Bi2Se3 Thin Films with Inclined Crystal Planes

Sun Young Hamh; Soon-Hee Park; Jeongwoo Han; Jeong Heum Jeon; Se-Jong Kahng; Sung Kim; Suk-Ho Choi; Namrata Bansal; Seongshik Oh; Joonbum Park; Jun Sung Kim; Jae Myung Kim; Do Young Noh; Jong Seok Lee

doi:10.1186/s11671-015-1190-y

Anisotropic Terahertz Emission from Bi2Se3 Thin Films with Inclined Crystal Planes

Nanoscale Res Lett. 2015 Dec;10(1):489. doi: 10.1186/s11671-015-1190-y. Epub 2015 Dec 15.

Authors

Sun Young Hamh¹, Soon-Hee Park², Jeongwoo Han³, Jeong Heum Jeon⁴, Se-Jong Kahng⁵, Sung Kim⁶, Suk-Ho Choi⁷, Namrata Bansal⁸, Seongshik Oh⁹, Joonbum Park¹⁰, Jun Sung Kim¹¹, Jae Myung Kim¹², Do Young Noh¹³, Jong Seok Lee¹⁴

Affiliations

¹ Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 500-712, South Korea. syhamh@gist.ac.kr.
² Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 500-712, South Korea. parksh@gist.ac.kr.
³ Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 500-712, South Korea. jwh@gist.ac.kr.
⁴ Department of Physics, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul, 136-701, South Korea. enaxn@korea.ac.kr.
⁵ Department of Physics, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul, 136-701, South Korea. sjkahng@korea.ac.kr.
⁶ Department of Applied Physics, College of Applied Science, Kyung Hee University, Yongin, 446-701, South Korea. sung@khu.ac.kr.
⁷ Department of Applied Physics, College of Applied Science, Kyung Hee University, Yongin, 446-701, South Korea. sukho@khu.ac.kr.
⁸ Department of Electrical and Computer Engineering, Rutgers, The State University of New Jersey, 94 Brett Road, Piscataway, NJ, 08854, USA. bnamz@rutgers.edu.
⁹ Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ, 08854, USA. ohsean@physics.rutgers.edu.
¹⁰ Department of Physics, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang, Gyeongbuk, 790-784, South Korea. june0521@postech.ac.kr.
¹¹ Department of Physics, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang, Gyeongbuk, 790-784, South Korea. js.kim@postech.ac.kr.
¹² Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. kjmsy@gist.ac.kr.
¹³ Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 500-712, South Korea. dynoh@gist.ac.kr.
¹⁴ Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 500-712, South Korea. jsl@gist.ac.kr.

Abstract

We investigate the surface states of topological insulator (TI) Bi2Se3 thin films grown on Si nanocrystals and Al2O3 substrates by using terahertz (THz) emission spectroscopy. Compared to bulk crystalline Bi2Te2Se, film TIs exhibit distinct behaviors in the phase and amplitude of emitted THz radiation. In particular, Bi2Se3 grown on Al2O3 shows an anisotropic response with a strong modulation of the THz signal in its phase. From x-ray diffraction, we find that the crystal plane of the Bi2Se3 films is inclined with respect to the plane of the Al2O3 substrate by about 0.27°. This structural anisotropy affects the dynamics of photocarriers and hence leads to the observed anisotropic response in the THz emission. Such relevance demonstrates that THz emission spectroscopy can be a sensitive tool to investigate the fine details of the surface crystallography and electrostatics of thin film TIs.

Keywords: Bi2Se3; Terahertz emission; Thin film; Topological insulator.