Growth of Ultrathin Bi${}_2$Se${}_3$ Films by Molecular Beam Epitaxy

Abstract

Bi${}_2$Se${}_3$ is a widely studied 3D topological insulator having potential applications in optics, electronics, and spintronics. When the thickness of these films decrease to less than approximately 6 nm, the top and bottom surface states couple, resulting in the opening of a small gap at the Dirac point. In the 2D limit, Bi${}_2$Se${}_3$ may exhibit quantum spin Hall states. However, growing coalesced ultra-thin Bi${}_2$Se${}_3$ films with a controllable thickness and typical triangular domain morphology in the few nanometer range is challenging. Here, we explore the growth of Bi${}_2$Se${}_3$ films having thickness down to 4 nm on sapphire substrates using molecular beam epitaxy that were then characterized with Hall measurements, atomic force microscopy, and Raman imaging. We find that substrate pre-treatment -- growing and decomposing a few layers of \BiSe before the actual deposition -- is critical to obtaining a completely coalesced film. In addition, higher growth rates and lower substrate temperatures led to improvement in surface roughness, in contrast to what is observed for conventional epitaxy. Overall, coalesced ultra-thin Bi${}_2$Se${}_3$ films with lower surface roughness enables thickness-dependent studies across the transition from a 3D-topological insulator to one with gapped surface states in the 2D regime.

References in corpus (5)

• Discovery (theoretical prediction and experimental observation) of a large-gap topological-insulator class with spin-polarized single-Dirac-cone on the surface
• Epitaxial growth of topological insulator Bi2Se3 film on Si(111) with atomically sharp interface
• Molecular beam epitaxy of high structural quality Bi2Se3 on lattice matched InP(111) substrates
• Optimization of the growth of the van der Waals materials Bi2Se3 and (Bi0.5In0.5)2Se3 by molecular beam epitaxy
• Self-assembled nano-columns in Bi2Se3 grown by molecular beam epitaxy

Cited by in corpus (3)

• Design of spin-orbital-textures in ferromagnetic/topological insulator interfaces
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• Strained topological insulator spin-orbit torque random access memory (STI-SOTRAM) bit cell for energy-efficient Processing in Memory