Thickness-dependent magnetotransport and ultrafast dynamic properties of epitaxial Bi2Se3/InP(111) thin films grown using pulsed laser deposition

Bi₂Se₃ thin films with various thicknesses of 44, 94, 190 QL (1 QL = 0.955 nm) were epitaxially grown on InP (111) substrates using a Bi₂Se₈ target and pulsed laser deposition. All the Bi₂Se₃ thin films exhibited highly c-axis preferred orientation and well in-plane orientation with six-fold symmetric diffraction patterns of Bi₂Se₃{015} facets. The films had a clean and smooth surface with triangular step-and-terrace pyramid features and a small average roughness R_a ≤ 1.47 nm. The hardness and Young's modulus of a 190 QL-thick epitaxial Bi₂Se₃ film were found to be 2.1 ± 0.1 GPa and 58.6 ± 4.1 GPa, respectively. The Bi₂Se₃ thin films exhibited the typical two-dimensional weak antilocalization magnetoresistance (2D WAL MR) in a low magnetic field regime (B ± 0.5T). Meanwhile, they presented a parabola-like MR behavior for 190-QL-thick film, and linear MR for the thinner films at a high B field regime (B ≥ 3 T). The MR results suggest the presence of 2D topological surface states together with a dominant bulk state in the Bi₂Se₃ films. Furthermore, we observed two gigahertz acoustic phonon modes at 24.04 ± 2.05 GHz and 48.11 ± 2.02 GHz in the Bi₂Se₃ films induced by ultrafast laser pulses.