Figure 1: Structural characterization of Bi₂Te₃ films.

(a) X-ray diffraction out-of-plane θ–2θ scan of the Bi₂Te₃/GaAs heterostructure. (b) The in-plane ϕ scan with (105) Bi₂Te₃ and (200) GaAs diffraction peaks. Two domains of Bi₂Te₃ are observed. (c) The surface morphology of a 200 nm-thick Bi₂Te₃ thin film measured by AFM. The flat terraces and steps of quintuple layers (QLs) are observed. The scale bar within the AFM image and the colour scale bar represent 1 μm and 10 nm, respectively. The root-mean-square surface roughness is 2.2 nm. (d) The schematic illustration of two Bi₂Te₃ domains with a 60° rotation on the GaAs (111) surface. Because of the three-fold symmetry of the [001] axis, each domain is described as a triangle with different colours (red and blue). (e) High-resolution cross-sectional high-angle annular dark field scanning tunnelling electron microscopy (HAADF-STEM) results. The high-magnification image clearly shows the sequence of Bi and Te atoms, which are labelled as Te (1)–Bi–Te (2)–Bi–Te (1) atoms (Te: orange, Bi: purple). The scale bar is 10 nm. (f) The line scan across the Bi₂Te₃ QLs in the white box area in (e) shows the different intensity of Bi and Te atoms, and the van der Waals gap.