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

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.

Effect of Sr Doping on Structural and Transport Properties of Bi2Te3

“…Under adopted growth conditions in this paper, stoichiometric Bi 2 Te 3 epi-layers are obtained with no signs of Bi-BLs, as evidenced by angular position of narrow diffraction peaks and supported by a rather high carrier mobility for sample with x = 0. As compared with Eu-doped Bi 2 Te 3 [43] or Sr-doped Bi 2 Se 3 films [31], our Sr x Bi 2 Te 3 layers do not suffer from progressing structural disorder with doping level. On the contrary, as evidenced from (0 0 6) reflection thickness fringes (Figure 2b), moderate broadening of diffraction peaks (see Figure 2a along with column ∆ω (0015) of Table 1) and free carrier mobility (Figure 5b) in Sr x Bi 2−x Te 3 layers high crystallinity is preserved for x up to 0.2.…”

Hydrogen‐Assisted Synthesis of Large‐Size 2D Bismuth Telluride Flakes for Broadband Photodetection up to 2 µm

“…[ 8b,9c,10 ] However, further development of Bi 2 Te 3 ‐based photodetectors is limited by the fact that Bi 2 Te 3 single flakes are currently only available with a lateral size of up to few tens of micrometers. Up to now, there are various methods for synthesizing Bi 2 Te 3 , including mechanical exfoliation, [ 9a ] molecular beam epitaxy (MBE), [ 11 ] liquid phase synthesis, [ 9c,10b,12 ] and chemical vapor deposition (CVD). [ 8b,13 ] Mechanical exfoliation is only suitable for proof‐of‐concept because of its low yield and tiny size.…”

“…[ 9a ] Although high‐quality and large‐scale Bi 2 Te 3 single crystals can be obtained by MBE, the technique still suffers from high cost, long time consuming (growth rate is only 1 µm h −1 ), and strict lattice matching with substrates. [ 11 ] Liquid phase synthesis has a high yield, but the lateral size of Bi 2 Te 3 is only a few nanometers to a few micrometers, and the residual solvent on the sample surface will reduce its performance. [ 9c,10b,12 ]…”

“…Broadband photodetection including optical communication wavelength band (1260-1675 nm) [1] is extremely important due to its wide applications in information communications, space only 1 µm h −1 ), and strict lattice matching with substrates. [11] Liquid phase synthesis has a high yield, but the lateral size of Bi 2 Te 3 is only a few nanometers to a few micrometers, and the residual solvent on the sample surface will reduce its per formance. [9c,10b,12] In contrast, CVD is considered to be a more promising approach for synthesizing large-size 2D materials with electronic-grade quality and reasonable cost.…”