Thickness-dependent structural evolution and quantum transport properties of Bi2Se3 thin films grown by thermal evaporation

Bismuth selenide (Bi 2 Se 3 ) is a prototypical topological insulator that exhibits robust surface states with spin-momentum locking and high carrier mobility, making it a key material for quantum and spintronic applications. We systematically investigated the thickness-dependent morphological evolution and quantum transport properties of Bi 2 Se 3 thin films grown by a two-step thermal evaporation method. Films with thicknesses of 3–80 quintuple layers (QL) were deposited under high vacuum and annealed at 200 °C. Ultrathin films (≤ 9 QL) exhibited island-like discontinuous morphology and high resistance, while thicker films (> 9 QL) formed continuous, c-axis-oriented crystalline layers with enhanced smoothness and conductivity. The highest Raman peak intensity was obtained for the 9-QL film due to enhanced electron-phonon coupling, suggesting that 9 QL is the critical thickness for coherent phonon and carrier behavior. Magnetotransport measurements revealed weak antilocalization at low fields and an increasing contribution from bulk transport channels at high fields in thicker films. These findings provide insights into the nucleation-to-coalescence transition of layered Bi 2 Se 3 films and establish 9–40 QL as the optimal thickness range for accessing topological surface transport in quantum devices.