Abstract-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

http://www.pubfacts.com/detail/26694079/Anisotropic-Terahertz-Emission-from-Bi2Se3-Thin-Films-with-Inclined-Crystal-Planes

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.

Affiliation

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-Strong emission of terahertz radiation from nanostructured Ge surfaces

Chul Kang¹, Jung Woo Leem², Inhee Maeng¹, Tae Heon Kim³, Jong Seok Lee³,Jae Su Yu^2,a) and Chul-Sik Kee^1,b)
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a) E-mail: jsyu@khu.ac.kr
b) E-mail: cskee@gist.ac.kr
Appl. Phys. Lett. 106, 261106 (2015); http://dx.doi.org/10.1063/1.4923372

Indirect band gap semiconductors are not efficient emitters of terahertz radiation. Here, we report strong emission of terahertz radiation from germanium wafers with nanostructured surfaces. The amplitude of THz radiation from an array of nano-bullets (nano-cones) is more than five (three) times larger than that from a bare-Ge wafer. The power of the terahertz radiation from a Ge wafer with an array of nano-bullets is comparable to that from n-GaAs wafers, which have been widely used as a terahertz source. We find that the THz radiation from Ge wafers with the nano-bullets is even more powerful than that from n-GaAs for frequencies below 0.6 THz. Our results suggest that introducing properly designed nanostructures on indirect band gap semiconductor wafers is a simple and cheap method to improve the terahertz emission efficiency of the wafers significantly.