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.

中文翻译：

---

Bi ₂ Te ₃ -WSe ₂垂直范德华异质结的外延生长和能带取向的确定

通过以选定的顺序垂直堆叠不同的二维（2D）过渡金属二卤化双金属（TMD）单层材料形成的人工异质结具有诱人的未来原子薄电路前景。包括Bi ₂ Te ₃，Bi ₂ Se ₃和Sb ₂ Te ₃在内的二维拓扑绝缘体（TI）的出现代表一类新的2D构建基块，并且由于其时空对称性保护了其有趣的表面状态，因此可以补充现有的人工异质结。然而，这种2D TI / TMD垂直异质结的能带对准的确定仍处于起步阶段，而2D TI / TMD垂直异质结是设计基于HJ的电子/光子器件的关键参数，它位于外延生长的发展过程中。在这里，我们演示了由Bi ₂ Te ₃ / WSe ₂组成的2D TI / TMD垂直异质结的外延生长具有原子上干净的界面，该界面在光谱上可访问，并且在理论上易于处理。横截面扫描透射电子显微镜（STEM）图像和拉曼光谱的层间耦合特征的存在共同证明了Bi ₂ Te ₃ / WSe ₂的整齐堆叠，并且没有多余的杂质。微束X射线光电子能谱（μXPS）测量结合密度泛函理论（DFT）计算和场效应晶体管的电气特性定量地揭示了垂直堆叠的五层（QL）Bi ₂ Te ₃ / WSe ₂的II型排列。同时，当过渡到多五重层（MQL）Bi ₂ Te ₃ / WSe ₂时，出现了III型带。此处的发现为这些新兴的2D TI / TMD垂直异质结提供了外延生长范例的良好定义示例，即层间耦合-电子特性关系。