Weak antilocalization and gigahertz acoustic phonons in Bi₂Se₂Te and Bi₃Se₂Te-dominated thin films grown using pulsed laser deposition

We reported a comparative study on the material–magnetotransport properties of topological insulator Bi₂Se₂Te and a ternary Bi₃Se₂Te-dominated thin films. The Bi-Se-Te thin films were grown on c-plane sapphire using pulsed laser deposition at various substrate temperatures (T_S) of 180 – 300 °C. The highly c-axis-oriented films exhibited the Bi₂Se₂Te phase (at T_S = 180, 220 °C), and a mixed phase of dominant Bi₃Se₂Te and mimor Bi₂Se₂Te (at T_S = 260, 300 °C). In addition, XPS and EDS results confirmed the near stoichiometry compositions of Bi₂Se₂Te and Bi₃Se₂Te phases. In high magnetic fields, the magnetoresistance (MR) curves of Bi₂Se₂Te and Bi₃Se₂Te obeyed B² power law, and the carrier mobility was determined to be increased monotonically from 61.3 to 86.9 cm²/Vs when T_S increased from 180 to 300 °C. In low magnetic fields, MR curves of both Bi₂Se₂Te and Bi₃Se₂Te-dominated films presented two-dimensional weak antilocalization at low temperatures, possibly due to topological surface states in the thin films. Furthermore, we observed two acoustic phonon modes at 33.46 ± 0.69 GHz and 61.30 ± 1.75 GHz in both Bi₂Se₂Te and Bi₃Se₂Te-dominated thin films induced by ultrafast laser pulses.