Effect of Sn Doping on Surface States of Bi₂Se₃ Thin Films

Abstract

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 Bi2Se3 films. Scanning tunneling microscopy (STM) shows a shift in the local density of states toward the Dirac point as more Sn is incorporated. Density functional theory calculations elucidate 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 demonstrate that the Sn defects increase the separation between bulk and surface states, though bulk conduction remains a dominant component.

Nonlinear Hybrid Surface-Defect States in Defective Bi2Se3

“…We will henceforth refer to vacancies in the surface (bulk) QL with a subscript "s"("b"). An Se vacancy in a 6 ×6×6 QLs slab corresponds to a defect concentration of ∼ 10 19 cm −3 (in-plane concentration = 2.6 × 10 13 cm −2 ), comparable to the values reported in experiments, 17,28 which range from 10 11 to 10 20 cm −3 . We note that previous theory works 8,9 simulated a single Se vacancy per 3×3 in-plane supercell, while we use 6×6 and 5×5 in-plane supercells.…”

“…Selenium vacancies (VSe) are known to be a common defect in Bi 2 Se 3 and are assumed to be responsible for the n-type doping of the as-grown crystals. , Due to the high volatility of selenium, the formation of additional vacancies on the surface of cleaved Bi 2 Se 3 slabs is expected. This is possibly responsible for the observed aging of the slabs as they show changes in electronic properties with time. , Though a vast literature exists on the formation energy of Se vacancies in Bi 2 Se 3 , ,,− very little is discussed about the nature of the defect states, their placement in the electronic band structure, and the effect of their positions on the properties of Bi 2 Se 3 surface states. Furthermore, most theoretical works have either considered very large densities of vacancies, such as a surface termination with all top selenium atoms removed, or symmetric defects on both surfaces that preserve the inversion symmetry of the slab .…”

Non-linear hybrid surface-defect states in defective Bi$_2$Se$_3$

“…We will henceforth refer to vacancies in the surface (bulk) QL with a subscript 's'('b'). An Se vacancy in a 6×6×6 QLs slab corresponds to a defect concentration of ≈ 10 19 cm −3 (in-plane concentration = 2.6 × 10 13 cm −2 ), comparable to the values reported in experiments, 15,22 which range from 10 11 to 10 20 cm −3 . Additional details of charge-states of the VSe defects and their stability under different conditions are given in the Supplement (S4).…”

Synthesis and Properties of Bismuth Selenide Based Nanolaminates for Application in Thermoelectrics

“…Such an increase of the Seebeck coefficient was accompanied by the decrease of the resistivity of the Bi 1.925 Sn 0.075 Se 3 ≈40% from 1.2·10 –5 Ω m down to 0.75·10 –5 Ω m in comparison with the undoped Bi 2 Se 3 film, presumably due to the increase of the charge carrier concentration from 2.35·10 19 cm –3 to 3·10 19 cm –3 (Table 1) as a result of the Sn doping, which was previously observed also for the Sn‐doped Bi 2 Se 3 thin films. [ 33 ] This resulted in a significant increase of the PF of the Bi 1.925 Sn 0.075 Se 3 ultrathin film in comparison with Bi 2 Se 3 ultrathin films (0.65 mW m –1 K –2 versus 0.2 mW m –1 K –2 , Table 1). The increase of the Seebeck coefficient and simultaneous decrease of the resistivity of the Bi 1.925 Sn 0.075 Se 3 ultrathin film may also indicate the formation of the RL in the Bi 2 Se 3 band gap, and thus, optimal Sn dopant concentration for the enhancement of the PF of Bi 2 Se 3 ultrathin films.…”