Effect of Sn Doping on Surface States of Bi₂Se₃ Thin Films

Bi₂Se₃, widely studied as a topological insulator, has great potential for applications in low power electronics and quantum computing. Intrinsic doping, however, presents a persistent challenge, leading to predominantly bulk conduction. In this work, we use substitutional Sn dopants to control the Fermi level in MBE-grown Bi₂Se₃ films. Scanning Tunneling Microscopy (STM) shows a shift in the local density of states towards the Dirac point as more Sn is incorporated, with density functional theory calculations corroborating the STM results, showing that Sn adds metallic states near the Fermi level that are localized to the defect sites while leaving the Dirac cone undisturbed. Electronic transport measurements show increasing weak antilocalization with doping level, demonstrating that the Sn defects increase the separation between bulk and surface states, though bulk conduction remains a dominant component. However, the macroscopic behavior is still dominated by bulk conduction due to the localized Sn states within the bulk. Overall, we find that Sn doping is a promising method for enhancing the contribution of surface states in Bi₂Se₃.