Stability of low-carrier-density topological-insulator Bi₂Se₃ thin films and effect of capping layers

Abstract

Although over the past number of years there have been many advances in the materials aspects of topological insulators (TI), one of the ongoing challenges with these materials is the protection of them against aging. In particular, the recent development of low-carrier-density bulk-insulating Bi2Se3 thin films and their sensitivity to air demands reliable capping layers to stabilize their electronic properties. Here, we study the stability of the low-carrier-density Bi2Se3 thin films in air with and without various capping layers using DC and THz probes. Without any capping layers, the carrier density increases by ~150% over a week and by ~280% over 9 months. In situ-deposited Se and ex situ-deposited Poly(methyl methacrylate) (PMMA) suppresses the aging effect to ~27% and ~88% respectively over 9 months. The combination of effective capping layers and low-carrierdensity TI films will open up new opportunities in topological insulators.

Quantized Faraday and Kerr rotation and axion electrodynamics of a 3D topological insulator

“…Films grow a quintuple layer (1 unit cell) at a time (1 QL ∼1 nm). 50 nm MoO 3 was deposited in-situ and was followed by 100 nm amorphous Se to reduce aging effects (42). Details on the growth can be found elsewhere (18).…”

Solution to the Hole-Doping Problem and Tunable Quantum Hall Effect in Bi2Se3 Thin Films

“…In order to check the effect of the air exposure, we subsequently grew another set of samples with Se capping layer, which was previously shown to be effective in protecting the surface of Bi2Se3 films from air exposure 28 . As depicted in Figure 1b, the Se capping does make a difference and 50 QL Bi2Se3 film on Al2O3 is now converted to p-type.…”

Edge modes and Fabry-Perot plasmonic resonances in anomalous-Hall thin films

“…Such systems include the 2D surface of a general 3D topological insulator. [25][26][27][28][29][30][31][32][33][34] In such cases, the low-energy electronic states possess linear dispersions and behave as massless Dirac fermions. When time reversal symmetry is broken by, e.g., a local magnetisation 28,35 or a magnetic field [35][36][37][38] then gaps open in the surface band structure.…”