Transport properties of a 1000-nm HgTe film: the interplay of surface and bulk carriers

TL;DR

This study investigates the transport properties of a thick HgTe film, revealing the coexistence of surface and bulk states, tunable carrier types, high mobility, and complex quantum oscillation patterns, contributing to understanding topological and bulk electronic behaviors.

Contribution

It provides the first detailed analysis of transport in a fully relaxed, thick HgTe film, demonstrating the coexistence of surface and bulk states and their influence on quantum transport phenomena.

Findings

Tunable transition from electron to hole transport via gate voltage

High electron mobility exceeding 300,000 cm²/Vs

Observation of multiple SdH oscillation frequencies linked to different states

Abstract

We report on systematic study of transport properties of a 1000-nm HgTe film. Unlike to thinner and strained HgTe films, which are known as high-quality three-dimensional (3D) topological insulators, the film under study is much thicker than the limit of pseudomorphic growth of HgTe on a CdTe substrate. Therefore, it is expected to be fully relaxed and has the band structure of bulk HgTe, i.e., a zero gap semiconductor. Nevertheless, since the bands inversion the two-dimensional (2D) topological surface states are still expected to exist. To check this claim we studied classical and quantum transport response of the system. We demonstrate that by tuning the top-gate voltage one can change the electron-dominating transport to the hole one. The highest electron mobility is found to be more than $300 \times 10^3$ cm$^2$/Vs. The system exhibits Shubnikov-de Haas (SdH) oscillations with a complicated pattern and shows up to 5 independent frequencies in corresponding Fourier spectra. They are attributed to the topological surface states, Volkov-Pankratov states and spin-degenerate bulk states in the accumulation layer near the gate. The observed peculiarities of the quantum transport are the strong SdH oscillations of the Hall resistance, and the suppressed oscillatory response of the topological surface states.