Growth and characterization of molecular beam epitaxy-grown Bi₂Te_3-xSe_x topological insulator alloys

We report a systematic study on the structural and electronic properties of Bi₂Te_3-xSe_x topological insulator alloy grown by molecular beam epitaxy (MBE). A mixing ratio of Bi₂Se₃ to Bi₂Te₃ was controlled by varying the Bi:Te:Se flux ratio. X-ray diffraction and Raman spectroscopy measurements indicate the high crystalline quality for the as-grown Bi₂Te_3-xSe_x films. Substitution of Te by Se is also revealed from both analyses. The surfaces of the films exhibit terrace-like quintuple layers and their size of the characteristic triangular terraces decreases monotonically with increasing Se content. However, the triangular terrace structure gradually recovers as the Se content further increases. Most importantly, the angle-resolved photoemission spectroscopy results provide evidence of single-Dirac-cone like surface states in which Bi₂Te_3-xSe_x with Se/Te-substitution leads to tunable surface states. Our results demonstrate that by fine-tuned MBE growth conditions, Bi₂Te_3-xSe_x thin film alloys with tunable topological surface states can be obtained, providing an excellent platform for exploring the novel device applications based on this compound.