Europium Doping Impact on the Properties of MBE Grown Bi2Te3 Thin Film.

Katarzyna Balin,Pascal Ruello,Maciej Zubko,Mateusz Weis,Ruizhe Gu,Jacek Szade,Bartosz Wilk,Marcin Wojtyniak

doi:10.3390/ma13143111

Abstract

The impact of europium doping on the electronic and structural properties of the topological insulator Bi2Te3 is studied in this paper. The crystallographic structure studied by electron diffraction and transmission microscopy confirms that grown by Molecular Beam Epitaxy (MBE) system film with the Eu content of about 3% has a trigonal structure with relatively large monocrystalline grains. The X-ray photoemission spectroscopy indicates that europium in Bi2Te3 matrix remains divalent and substitutes bismuth in a Bi2Te3 matrix. An exceptional ratio of the photoemission 4d multiplet components in Eu doped film was observed. However, some spatial inhomogeneity at the nanometer scale is revealed. Firstly, local conductivity measurements indicate that the surface conductivity is inhomogeneous and is correlated with a topographic image revealing possible coexistence of conducting surface states with insulating regions. Secondly, Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) depth-profiling also shows partial chemical segregation. Such in-depth inhomogeneity has an impact on the lattice dynamics (phonon lifetime) evaluated by femtosecond spectroscopy. This unprecedented set of experimental investigations provides important insights for optimizing the process of growth of high-quality Eu-doped thin films of a Bi2Te3 topological insulator. Understanding such complex behaviors at the nanoscale level is a necessary step before considering topological insulator thin films as a component of innovative devices.

Highlights

The efficiency, stability, and lifetime of any device is strongly dependent on the stability of compounds and alloys that a given device is made of
In our previous paper [34], we have studied the multilayered structures of Bi2 Te3 and europium and shown that the interface between the layers is not stable and the reaction that took place at room temperature led to the decomposition of the originally layered structure and formation of new phases
The molecular beam epitaxy system was used for the growth of two thin films of Bi2 Te3

Summary

Introduction

The efficiency, stability, and lifetime of any device is strongly dependent on the stability of compounds and alloys that a given device is made of. The attempts to understand the particular state of matter are crucial points of understanding its implications for application in advanced electronic devices. This gain in importance when exotic states of matter are considered. Namely the insulating character of the bulk and metallic character of the surface, was observed in a large group of materials, which were later classified as topological insulators [1,2]. Among classified topological insulators the Bi2 Te3 compound, considered as good material for thermoelectric [3,4] and optoelectronic [5,6] applications, was selected as the subject of this study. Topological insulators (TIs) are a novel type of quantum materials of which the bulk part is a band insulator whereas the Materials 2020, 13, 3111; doi:10.3390/ma13143111 www.mdpi.com/journal/materials

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