Bulk-impurity induced noise in large-area epitaxial thin films of topological insulators

TL;DR

This study investigates low-frequency noise in large-area epitaxial topological insulator films, revealing that bulk defects dominate noise behavior even in ultra-thin films, with implications for electronic device stability.

Contribution

It provides a detailed analysis of noise mechanisms in topological insulator thin films, highlighting the role of bulk defects and defect states in surface transport noise.

Findings

Bulk defects are the main noise source in 10 nm films.

Noise exhibits generation-recombination signatures related to defect states.

Magnetic field dependence of noise resembles that of trivial semiconductors.

Abstract

We report a detailed study on low-frequency 1/f-noise in large-area molecular-beam epitaxy grown thin (10 nm) films of topological insulators as a function of temperature, gate voltage, and magnetic field. When the Fermi energy is within the bulk valence band, the temperature dependence reveals a clear signature of generation-recombination noise in the defect states in the bulk band gap. However, when the Fermi energy is tuned to the bulk band gap, the gate voltage dependence of noise shows that the resistance fluctuations in surface transport are caused by correlated mobility-number density fluctuations due to the activated defect states present in the bulk of the topological insulator crystal with a density of D$_{it}=3.2\times10^{17}$ cm$^2$eV$^{-1}$. In the presence of a magnetic field, noise in these materials follows a parabolic dependence, which is qualitatively similar to mobility and charge-density fluctuation noise in non-degenerately doped trivial semiconductors. Our studies reveal that even in thin films of (Bi,Sb)$_2$Te$_3$ with thickness as low as 10 nm, the intrinsic bulk defects are the dominant source of noise.