Abstract-Surface and interface states of Bi2Se3 thin films investigated by optical second-harmonic generation and terahertz emission

S. Y. Hamh1, S.-H. Park1, S.-K. Jerng2, J. H. Jeon2, S. H. Chun2, J. H. Jeon3, S. J. Kahng3, K. Yu4, E. J. Choi4, S. Kim5, S.-H. Choi5, N. Bansal6, S. Oh7, Joonbum Park8, Byung-Woo Kho8, Jun Sung Kim8 and J. S. Lee1,a)

1 Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
2 Department of Physics and Graphene Research Institute, Sejong University, Seoul 143-747, Korea
3 Department of Physics, Korea University, Seoul 136-701, Korea
4 Department of Physics, University or Seoul, Seoul 130-743, Korea
5 Department of Applied Physics, College of Applied Science, Kyung Hee University, Yongin 446-701, Korea
6 Department of Electrical and Computer Engineering, Rutgers, The state University of New Jersey, Piscataway, New Jersey 08854, USA
7 Department of Physics and Astronomy, Rutgers, The state University of New Jersey, Piscataway, New Jersey 08854, USA
8 Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
a) Electronic mail: jsl@gist.ac.kr
Appl. Phys. Lett. 108, 051609 (2016); http://dx.doi.org/10.1063/1.4941420

We investigate the surface and interface states of Bi2Se3 thin films by using the second-harmonic generation technique. Distinct from the surface of bulk crystals, the film surface and interface show the isotropic azimuth dependence of second-harmonic intensity, which is attributed to the formation of randomly oriented domains on the in-plane. Based on the nonlinear susceptibility deduced from the model fitting, we determine that the surface band bending induced in a space charge region occurs more strongly at the film interface facing the Al2O3 substrate or capping layer compared with the interface facing the air. We demonstrate that distinct behavior of the terahertz electric field emitted from the samples can provide further information about the surface electronic state of Bi2Se3.