Epitaxial Growth and Determination of Band Alignment of Bi2Te3-WSe2Vertical van der Waals Heterojunctions

Artificial heterojunctions formed by vertical stacking of dissimilar two-dimensional (2D) transition metal dichalcogenide (TMD) monolayer materials in a chosen sequence hold tantalizing prospects for futuristic atomically thin circuits. The emergence of 2D topological insulators (TI), including Bi2Te3, Bi2Se3, and Sb2Te3, represents a new class of 2D building blocks and can complement the existing artificial heterojunctions as a result of their intriguing surface states protected by the time-reversal symmetry. However, the determination of band alignments of such 2D TI/TMD vertical heterojunctions, the key parameter for designing HJ-based electronic/photonic devices, which lies in the development of epitaxy growth, remains in its infancy. Here, we demonstrate the epitaxy growth of 2D TI/TMD vertical heterojunctions comprised of Bi2Te3/WSe2 with atomically clean interfaces that are spectroscopically accessible, and theoretically tractable. Cross-sectional scanning transmission electron microscopy (STEM) images and the presence of interlayer-coupled characteristics from Raman spectroscopy collectively confirm the neat stacking of Bi2Te3/WSe2 with the absence of unwanted containments. Microbeam X-ray photoelectron spectroscopy (μXPS) measurement coupled with the density functional theory (DFT) calculations and electrical characteristics of field effect transistors quantitatively reveals the type-II alignment of vertically stacked of quintuple layers (QL) Bi2Te3/WSe2. Meanwhile, the type-III band emerges when transitioning to multi-quintuple layer (MQL) Bi2Te3/WSe2. The finding here provides a well-defined example of the epitaxy growth paradigm, the interlayer coupling-electronic properties relationship, for these emerging 2D TI/TMDs vertical heterojunctions.

Citation

Yang, C.-W., Tang, H.-L., Sattar, S., Chiu, M.-H., Wan, Y., Chen, C.-H., … Tung, V. (2020). Epitaxial Growth and Determination of Band Alignment of Bi2Te3–WSe2 Vertical van der Waals Heterojunctions. ACS Materials Letters, 2(10), 1351–1359. doi:10.1021/acsmaterialslett.0c00254

Acknowledgements

V.T., and M.-H.C. are indebted to the support from the King Abdullah University of Science and Technology (KAUST), KAUST Catalysis and Solar Centres, and Office of Sponsored Research (OSR) under Award No: OSR-2018-CARF/CCF3079. S.S. thanks High Performance Computing Center North (HPC2N) National Supercomputer Center in Linkping (NSC) for allocation of time and resources, through the Swedish National Infrastructure for Computing (SNIC). H.-L.T. acknowledges the partial support from the Ministry of Science and Technology of Taiwan (MOST-108-2917-I-564-036). We thank Prof. D. A. Muller and Dr. Z. Chen for the helpful discussion on STEM and Prof. Q. Tong for the useful discussion on DFT simulations.