Structural analysis of Bi2Se3 thin films on various substrates
C. K. Cheng1*, H. Y. Lin2, K. H. Chen2, X. Q. Zhang3, Y. H. Lee3, C. H. Hsu4, J. Kwo2, M. Hong1
1Grad. Inst. Appl. Phys. and Dept. Phys., National Taiwan University, Taipei, Taiwan
2Dept. Phys., National Tsing Hua University, Hsinchu, Taiwan
3Dept. of Mat. Sci. and Eng., National Tsing Hua University, Hsinchu, Taiwan
4National Synchrotron Radiation Research Center, Hsinchu, Taiwan
* presenting author:Chao Kai Cheng,
Bi2Se3, a three-dimensional topological insulator with spin momentum locking surface states, is a very promising material in spintronic devices. However, the Fermi level of Bi2Se3 tends to locate in the bulk conduction band due to the high defect density. To further reduce the numbers of defects, we extended our investigation to Bi2Se3 deposited on various substrates with different lattice mismatch including Al2O3 (0001), graphene/6H-SiC (0001), CaF2 (111) and MoS2/ Al2O3 using molecular beam epitaxy. High-resolution X-ray diffraction (HR-XRD) and atomic force microscope (AFM) were used to examine the structural quality and the morphology of the films. All Bi2Se3 films were (0001) along the surface normal with lattice constant closed to bulk value and the observed pendellosung fringes revealed very high crystallinity. The amount of twin domains were analyzed from off-normal phi scans and in-plane coherence length were calculated from Scherrer equation. We found that Bi2Se3 twin domains could be suppressed using CaF2 (111), which has the smallest lattice mismatch than others substrates. On the other hand, Bi2Se3 grown on MoS2/Al2O3 showed the longest coherence length along in-plane direction, which were consistent with the triangular shaped, larger domain size observed in AFM.

Keywords: Topological insulators, X-ray diffraction, Atomic force microscope