Growth, characterization, and transport properties of ternary (Bi1-xSbx)2Te3 topological insulator layers

TL;DR

This study investigates the growth, composition, and electronic transport of (Bi1-xSbx)2Te3 topological insulator layers, demonstrating tunable Fermi levels and dual-channel conduction through molecular beam epitaxy and various spectroscopic and transport measurements.

Contribution

It provides a comprehensive analysis of how Sb content affects the structural and electronic properties of (Bi1-xSbx)2Te3 layers, including Fermi level tuning within the topological surface states.

Findings

Fermi level shifts from conduction to valence band with increasing Sb content

Transport occurs via two independent channels in the transition region

Fermi level can be tuned from n- to p-type using a gate electrode

Abstract

Ternary (Bi1-xSbx)2Te3 films with an Sb content between 0 and 100% were deposited on a Si(111) substrate by means of molecular beam epitaxy. X-ray diffraction measurements confirm single crystal growth in all cases. The Sb content is determined by X-ray photoelectron spectroscopy. Consistent values of the Sb content are obtained from Raman spectroscopy. Scanning Raman spectroscopy reveals that the (Bi1-xSbx)2Te3 layers with an intermediate Sb content show spatial composition inhomogeneities. The observed spectra broadening in angular-resolved photoemission spectroscopy (ARPES) is also attributed to this phenomena. Upon increasing the Sb content from x=0 to 1 the ARPES measurements show a shift of the Fermi level from the conduction band to the valence band. This shift is also confirmed by corresponding magnetotransport measurements where the conductance changes from n- to p-type. In this transition region, an increase of the resistivity is found, indicating a location of the Fermi level within the band gap region. More detailed measurements in the transition region reveals that the transport takes place in two independent channels. By means of a gate electrode the transport can be changed from n- to p-type, thus allowing a tuning of the Fermi level within the topologically protected surface states.