Pulsed laser deposition of highly c-axis oriented thin films of BSTS topological insulator

Topological insulators (TIs) are quantum materials characterized by an insulating bulk and ro- bust metallic surface states protected by time-reversal symmetry. Although the growth of binary TIs such as Bi2Se3 by pulsed laser deposition (PLD) is well established, binary TIs generally fail to exhibit a truly bulk-insulating state because naturally occurring defects lead to unintentional doping resulting in substantial bulk conduction. In this work, we report the growth of highly c-axis–oriented thin films of the quaternary topological insulator BiSbTe1.5Se1.5 (BSTS), which provides a highly insulating bulk state that is crucial for exploiting nontrivial metallic surface transport. We demonstrate that the film composition can be readily tuned by varying the de- position conditions, which is more tedious with bulk single-crystal growth techniques. Growth parameters including substrate temperature, background argon pressure, and target-to-substrate distance strongly influence the structural, morphological, and lattice dynamical properties of the PLD-grown BSTS thin films. Films deposited under optimized conditions are granular, highly c-axis oriented, and exhibit all four Raman-active modes characteristic of the R3m space group. Temperature-dependent sheet resistance measurements confirm strongly bulk-insulating behav- ior with dominant surface metallic transport at low temperatures. Consistent with this surface- dominated transport, magnetoresistance measurements reveal enhanced weak antilocalization with two conduction channels arising from the surface states. This study establishes PLD as a simple and versatile route for fabricating high-quality, bulk-insulating TI thin films with tunable compositions.