Mode of Growth of Ultrathin Topological Insulator Bi₂Te₃ Films on Si (111) Substrates

Abstract

Layered materials such as graphene, bi-, and multilayer graphene as well as various compounds of topological insulators are currently in the focus of interest due to their extraordinary physical properties related to Dirac surface states. The ability to grow thin films of these complex layered materials is the key to explore their fundamental phenomena giving insights into modern solid-state physics. However, complex materials composed of layers only weakly bonded via van der Waals forces offer unmatched challenges for the deposition of thin epitaxial films. Here, we report on the growth of Bi 2 Te 3 ultrathin films on Si (111) substrates using molecular beam epitaxy. Special emphasis is put on the nucleation phenomena and growth dynamics studied in detail by in situ scanning tunnelling microscopy and high-resolution scanning transmission electron microscopy. The morphology of the Bi 2 Te 3 surface and the structure of the Si(111)/Bi 2 Te 3 interface as well as the formation of threading dislocations and crystal domains are studied at the atomic level. Our data indicate that the film is formed via the nucleation of islands, which float on the substrate; thus, the islands are only weakly bonded to the substrate and rather mobile. Apparently, these floating islands are able to arrange themselves by moving in the x−y direction to perfectly coalesce and form a continuous film. The results present a crucial step toward understanding growth and defect formation in this class of materials and thus pave the avenue to a higher control over both their structural and electronic properties, in order to study the electronic properties of the Dirac surface states.

Review of 3D topological insulator thin‐film growth by molecular beam epitaxy and potential applications

“…Similar work has been demonstrated during the growth of Bi 2 Te 3 on Si(111) substrates [54]. A Te atomic layer has been used to terminate a Si(111) surface and very high quality Bi 2 Te 3 thin films with sharp interface and few structural defects were obtained.…”

Topological Insulator Film Growth by Molecular Beam Epitaxy: A Review

“…As discussed in Section 2.1.4, silicon substrates have dangling bonds which must be satisfied before growth can occur. As shown by Borisova et al [41], these bonds can be terminated using a monolayer of Te upon which Bi 2 Te 3 can nucleate in one of six possible orientations. The van der Waals bonding between the Te monolayer used to passivate the silicon substrate and the Bi 2 Te 3 overlayer leads to a fully relaxed film within the first or second monolayer.…”

“…In addition to surface oxides, a large fraction of the available substrates have surface dangling bonds which must be satisfied. Again, there has been some success in passivating these surfaces by supplying a chalcogenide overpressure [39][40][41] or by depositing a monolayer of bismuth [42]. These growth challenges as well as the relatively high cost of many lattice-matched substrates is why most growth continues on sapphire.…”

“…When these two domains meet, an antiphase domain will form in which the unit cell of the TI is shifted vertically by the height of one atomic step in the underlying substrate. This type of defect has a negative influence on the electrical properties of the film [34,41] and is difficult to remove without growing on isostructural substrates, though ideas for reducing antiphase domains are discussed below.…”

Photon drag effect in(Bi1−xSbx)2Te3three-dimensional topological insulators

“…The samples were grown by molecular beam epitaxy (MBE) on Si(111) substrates in the so-called van der Waals (vdW) growth mode [49]; that is, there are only weak bonds between the substrate and the TI epilayers, so that the large lattice mismatch does not hinder the growth of single-crystal TI films with a high structural quality [50][51][52]. Before insertion into the MBE chamber, the Si(111) surface was chemically cleaned to remove the native SiO 2 and to passivate the surface with hydrogen.…”