Bulk-induced 1/f noise at the surface of three-dimensional topological insulators

Abstract

Slow intrinsic fluctuations of resistance, also known as the flicker noise or 1/f-noise, in the surface transport of strong Topological Insulators (TIs) is a poorly understood phenomenon. Here, we have systematically explored the 1/f-noise in Field-Effect Transistors (FET) of mechanically exfoliated Bi_1.6Sb_0.4Te₂Se TI films when transport occurs predominantly via the surface states. We find that the slow kinetics of the charge disorder within the bulk of the TI induces mobility fluctuations at the surface, providing a new source of intrinsic 1/f-noise that is unique to bulk TI systems. At small channel thickness, the noise magnitude can be extremely small, corresponding to the phenomenological Hooge parameter γ_H as low as ≈10^–4, but it increases rapidly when channel thickness exceeds ∼1 μm. From the temperature (T)-dependence of noise, which displayed sharp peaks at characteristic values of T, we identified generation-recombination processes from interband transitions within the TI bulk as the dominant source of the mobility fluctuations in surface transport. Our experiment not only establishes an intrinsic microscopic origin of noise in TI surface channels, but also reveals a unique spectroscopic information on the impurity bands that can be useful in bulk TI systems in general.