Metallic conduction through van der Waals interfaces in ultrathin hbox{Bi}_2hbox{Te}_3 films

Ko Obayashi,Shinichiro Hatta,Tetsuya Aruga,Hiroshi Okuyama

doi:10.1038/s41598-021-85078-9

Abstract

While the van der Waals (vdW) interface in layered materials hinders the transport of charge carriers in the vertical direction, it serves a good horizontal conduction path. We have investigated electrical conduction of few quintuple-layer (QL) hbox {Bi}_2hbox {Te}_3 films by in situ four-point probe conductivity measurement. The impact of the vdW (Te–Te) interface appeared as a large conductivity increase with increasing thickness from 1 to 2 QL. Angle-resolved photoelectron spectroscopy and first-principles calculations reveal the confinement of bulk-like conduction band (CB) state into the vdW interface. Our analysis based on the Boltzmann equation showed that the conduction of the CB has a long mean free path compared to the surface-state conduction. This is mainly attributed to the spatial separation of the CB electrons and the donor defects located at the Bi sites.

Highlights

Layered materials consisting of two-dimensional (2D) atomic frameworks have attracted much attention for their potential applications in future devices based on hetero- and nano-structures[1,2,3]
Each Bi2Te3 spot has an arc shape, but is sharp along the radial direction, which shows that large domains of the ultrathin films are epitaxially grown on Si(111) with distribution of domains rotated by ≤ 4.9◦ about the [111] axis
The behavior observed at 1–5 quintuple layer (QL) is consistent with previous reports[18,20], and demonstrates that the few-QL films have one or more metallic states

Summary

Introduction

Layered materials consisting of two-dimensional (2D) atomic frameworks have attracted much attention for their potential applications in future devices based on hetero- and nano-structures[1,2,3]. Electronic coupling at the vdW interface is weak, it can play a subtle but significant role in the band formation and physical properties of few-layer films. Previous studies showed that the 4-QL film was found to be thick enough to host bulk-like gapless TSS. This thickness, critical difference in band structure near the band gap was indicated between 1- and 2-QL films. We investigated electronic and transport properties of a few-QL Bi2Te3 films by combining angle-resolved photoelectron spectroscopy (ARPES), four-point-probe (4PP) conductivity measurement and first-principles band calculation. A large increase in sheet conductivity was observed from 1 to 2 QL due to the formation of a bulk-like conduction band (CB), whose electron density is highly concentrated at the vdW interface. The localization of the CB state prevents conducting electrons from being scattered by the Bi antisite defect

Methods

Results

Conclusion