Epitaxial growth of topological insulator Bi2Se3 film on Si(111) with atomically sharp interface

Abstract

Atomically sharp epitaxial growth of Bi 2 Se 3 films is achieved on Si (111) substrate with MBE (Molecular Beam Epitaxy). Two-step growth process is found to be a key to achieve interfacial-layer-free epitaxial Bi 2 Se 3 films on Si substrates. With a single-step high temperature growth, second phase clusters are formed at an early stage. On the other hand, with low temperature growth, the film tends to be disordered even in the absence of a second phase. With a low temperature initial growth followed by a high temperature growth, secondphase-free atomically sharp interface is obtained between Bi 2 Se 3 and Si substrate, as verified 2 by RHEED (Reflection High Energy Electron Diffraction), TEM (Transmission Electron Microscopy) and XRD (X-Ray Diffraction). The lattice constant of Bi 2 Se 3 is observed to relax to its bulk value during the first quintuple layer according to RHEED analysis, implying the absence of strain from the substrate. TEM shows a fully epitaxial structure of Bi 2 Se 3 film down to the first quintuple layer without any second phase or an amorphous layer.

Topological Insulator Materials

“…However, in the case of tetradymite TI materials, thanks to the existence of the van der Waals gap between the QLs, the lattice matching with the substrate is not crucial and the epitaxial growth proceeds in the so-called van der Waals epitaxy mode, 195) in which the substrate and the films are only weakly bonded with the van der Waals force and hence the lattice matching condition is greatly relaxed. In particular, epitaxial growths of Bi 2 Se 3 have been reported for various substrates including Si(111), [181][182][183][184] grapheneterminated 6H-SiC(0001), 174,185) SrTiO 3 (111), 186) GaAs (111), 187) sapphire (0001), 173,188,189) CdS(0001), 190) and InP (111). 191) It turned out that the control of the substrate temperature is the most crucial ingredient for obtaining high-quality films of Bi 2 Se 3 with a large area of atomically flat terraces.…”

“…189) In particular, a two-step method in which the depositions of the first layer and subsequent layers are done at different temperatures, to promote initial adhesion and crystallization separately, has been reported to yield best quality films. 173,182,183,188,189) For the TCI material SnTe, a technique called hot-wall epitaxy has been used in the past, 196) yielding good quality samples with a reasonably high mobility ($2700 cm 2 V À1 s À1 ). For SnTe which is a cubic material with rock-salt structure, good lattice matching is crucial for epitaxial growth.…”

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

“…This is called Van der Waals epitaxy [40,41], which relaxes the lattice-matching condition required for most common epitaxial growth of covalent semiconductors and their heterostructures. Because of this, a variety of substrates have been chosen for the growth of TIs, despite the large lattice mismatch between the films and the substrates, and relatively good epitaxial films have been achieved from various reports [11,[22][23][24][25][26][27][28][42][43][44][45][46][47][48][49]. Their lattice constants and their mismatches to different TIs are shown in Fig.…”

“…Similar to hydrogen termination, Se atoms have also been used to terminate Si(111) surface. By carefully treating Si(111) substrate with a monolayer of Se at ~100 °C before the growth of Bi 2 Se 3 layer, sharp Bi 2 Se 3 /Si interfaces have been obtained [45]. The substrate temperature was shown to be very critical.…”

“…Long-lasting RHEED oscillations, with the oscillation period (growth rate) solely depending on the Bi flux, have been observed. [24][25][26]45]. More recently, the growth has been done with the use of cracker cell [49,57].…”