Epitaxial Growth and Determination of Band Alignment\nof Bi₂Te₃–WSe₂ Vertical van\nder Waals Heterojunctions

Abstract

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