Thickness-dependent magnetotransport properties and terahertz response of topological insulator Bi₂Te₃thin films

We report the thickness (d) dependence of structural, morphological, magneto-transport properties as well as terahertz (THz) response in the 0.25–2.25 THz range of topological insulator Bi₂Te₃thin films grown by pulsed laser deposition (PLD). The Bi₂Te₃films exhibit a highly c-axis orientation (textured films) and two Raman-active modes of E² _gat 102.5 cm⁻¹and A² _1gat 134.8 cm⁻¹. The films obtain relatively low carrier concentration between 2.0 × 10¹⁹and 4.4 × 10¹⁹ cm⁻³. The films present two-dimensional weak (2D WAL) antilocalization magnetoresistance in a low magnetic field (B) and the 2D WAL shows thickness dependence, suggesting the presence of topological surface states (TSS). The THz transmittance increases owing to increased resistivity (associated with a decreased carrier concentration) when film thickness decreases from 152 to 16 QL. The complex conductance is well described by the Drude-Lorentz model with three components of the Drude surface, Drude bulk, and phonon. The Drude spectral weight (SW) of the surface is dominant and independent of the thickness. Besides, the Drude SW of the bulk and phonon SW linearly increase with increasing thickness.