Defect Role in the Carrier Tunable Topological Insulator (Bi${}_{1-x}$Sb${}_x$)${}_2$Te${}_3$ Thin Films

Abstract

Alloys of Bi${}_2$Te${}_3$ and Sb${}_2$Te${}_3$ ((Bi${}_{1-x}$Sb${}_x$)${}_2$Te${}_3$) have played an essential role in the exploration of topological surface states, allowing us to study phenomena that would otherwise be obscured by bulk contributions to conductivity. Thin films of these alloys have been particularly important for tuning the energy of the Fermi level, a key step in observing spin-polarized surface currents and the quantum anomalous Hall effect. Previous studies reported the chemical tuning of the Fermi level to the Dirac point by controlling the Sb:Bi composition ratio, but the optimum ratio varies widely across various studies with no consensus. In this work, we use scanning tunneling microscopy and Landau level spectroscopy, in combination with X-ray photoemission spectroscopy to isolate the effects of growth factors such as temperature and composition, and to provide a microscopic picture of the role that disorder and composition play in determining the carrier density of epitaxially grown (Bi,Sb)${}_2$Te${}_3$ thin films. Using Landau level spectroscopy, we determine that the ideal Sb concentration to place the Fermi energy to within a few meV of the Dirac point is $x\sim 0.7$. However, we find that the post- growth annealing temperature can have a drastic impact on microscopic structure as well as carrier density. In particular, we find that when films are post-growth annealed at high temperature, better crystallinity and surface roughness are achieved; but this also produces a larger Te defect density, adding n-type carriers. This work provides key information necessary for optimizing thin film quality in this fundamentally and technologically important class of materials.

arXiv comment5 figures, 6 pages

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Cited by in corpus (6)

• Realizing gapped surface states in magnetic topological insulator MnBi${}_{2-x}$Sb${}_x$Te${}_4$
• Charge Carrier Mediation and Ferromagnetism induced in MnBi6Te10 Magnetic Topological Insulators by antimony doping
• Characterizing the chemical potential disorder in the topological insulator (Bi${}_{1-x}$Sb${}_x$)${}_2$Te${}_3$ thin films
• Spectroscopic signature of surface states and bunching of bulk subbands in topological insulator (Bi${}_{0.4}$Sb${}_{0.6}$)${}_2$Te${}_3$ thin films
• Phonon and defect mediated quantum anomalous Hall insulator to metal transition in magnetically doped topological insulators
• Evidence for nitrogen gas surface doping of the Bi${}_2$Se${}_3$ topological insulator