Strain in epitaxial Bi2Se3 grown on GaN and graphene substrates: A reflection high-energy electron diffraction study

Abstract

Topological insulator (TI) has been one of the focus research themes in condensed matter physics in recent years. Due to the relatively large energy bandgap, Bi2Se3 has been identified as one of the most promising three-dimensional TIs with application potentials. Epitaxial Bi2Se3 by molecular-beam epitaxy has been reported by many groups using different substrates. A common feature is that Bi2Se3 grows readily along the c-axis direction irrespective of the type and condition of the substrate. Because of the weak van deer Waals interaction between Bi2Se3 quintuple layers, the grown films are reported to be strain-free, taking the lattice constant of the bulk crystal. At the very initial stage of Bi2Se3 deposition, however, strain may still exist depending on the substrate. Strain may bring some drastic effects to the properties of the TIs and so achieving strained TIs can be of great fundamental interests as well as practical relevance. In this work, we employ reflection high-energy electron diffraction to follow the lattice constant evolution of Bi2Se3 during initial stage depositions on GaN and graphene, two very different substrates. We reveal that epitaxial Bi2Se3 is tensile strained on GaN but strain-free on graphene. Strain relaxation on GaN is gradual.

Strain in epitaxial high-index Bi2Se3(221) films grown by molecular-beam epitaxy

“…3). 22 In particularly, strain relaxation in Bi2Se3(111) is much quicker than the theoretical prediction for growth of covalent crystal (compared (ii) and (iii) in Fig. 3), signifying the inability of strain-bearing at the vdW hetero-interfaces.…”

“…22 It is unfortunate that growth of Bi2Se3 preferably proceeds along c-direction irrespective of the substrates used. 23,24 Therefore, strain-free Bi2Se3 epifilms almost always result even for very thin layers.…”

A study on the epitaxial Bi2Se3 thin film grown by vapor phase epitaxy

“…All the diffraction peaks in the figure are from the (0003) The reason of such quality differences depends remarkably on the selection of substrates, and the method used, even though Bi 2 Se 3 film is deposited layer by layer through van der Waals epitaxy. 21 Substrates with less lattice mismatch, such as InP, 19 GaN, 22 and MgO, 23 tend to have less non-uniform strain during the growth. From the comparison we conclude that although the samples prepared by using our simple CVD system does not, on a statistical average, have the same crystalline quality as the samples grown by using sophisticated MBE system, the data does show comparable results with some MBE-grown samples, 20 and better structural quality than films grown using a similar method.…”

Effect of an external electric field on the electronic properties of SnS2/PbI2 van der Waals heterostructures

“…Aer the total energy optimization, the lattice constants of monolayer SnS 2 and PbI 2 are respectively collected as 3.61Å and 4.67Å as exhibited in Table 1, that the agreements with previous studies are preeminent. 8,22,32 The properties of monolayer SnS 2 and PbI 2 are intensely sensitive to in-plane strains 43,44 so that the impact of strain on electronic structure should be reduced. To minimize the lattice mismatch between the stacking blocks, the supercell of this heterostructure is built by…”

“…Ever since the successful manufacture of isolated graphene was reported, 1 two dimensional (2D) materials have become the subject of extensive research because of their superior optical and electronic properties. Hence, a broad family of 2D materials like graphene, such as BN, 2 transition metal dichalcogenides [3][4][5] and topological insulators [6][7][8] etc., has been widely explored to solve that pristine graphene has a zero bandgap. Among them, recently, the SnS 2 2D lms 9,10 have been poured unordinary attentions due to environmentally friendly and earth-abundant.…”