Electronic Conduction Channels Engineered in Topological Insulator Sputtered Thin Films

Abstract

Sb 2 Te 3 is a topological insulator (TI) material that can be used in a wide range of applications from energy harvesting to Spin-Orbitronics. In this paper, the structural, electrical, and thermal transport properties of nanocrystalline ion beam sputtered Sb 2 Te 3 thin films were studied. Films with thicknesses between 35 and 300 nm, with nanocrystallites of sizes 10−20 nm, have a high resistivity between 0.072 and 2.03 Ω cm at 300 K, increasing with cooling. The Seebeck coefficient demonstrates the coexistence of n-type and p-type conduction, the latter being more prominent at high temperatures and in thicker films. The morphological and transport properties reveal that the films are constituted by two layers having different majority charge carriers, with the electronic bulk conduction being described by two semiconductor layers conducting in parallel, one p-type at the surface and another n-type, each described by an activation energy-dependent conductivity. Besides these bulk contributions, weak antilocalization (WAL) cusps are observed in the magnetoconductance below 10 K and at low magnetic fields. Analysis of the WAL hints that there is one twodimensional conduction channel open at low temperatures for the thinner films, whereas for the thicker film, this 2D conduction appears to be masked by the bulk channels. However, a magnetic localization length L Φ between 62 and 90 nm at 2 K is observed for all thin films. This behavior suggests that as the bulk activation energy conductions freeze out at low temperatures, the electrical conduction is carried by the supposed 2D state, which appears to have some of the features of a TI surface state. Through these measurements, we demonstrate that the type of dominant conduction can be controlled by the Sb 2 Te 3 film thickness in these large area sputtered films, while the conduction at low temperatures appears to be dominated by a robust TI state.

Unveiling the emergence of topological quantum phase transitions in the bidirectional transport of carriers through helical edge states in bismuth selenide

“…The use of topological materials to design efficient carrier transport channels has been demonstrated recently to benefit from 2D conducting surface states [7]. Applications that feature an integration of such low-dimensional conducting channels into device architectures and circuits can offer low-resistance interconnects to maximize the microelectronic reliability and performance of electronic circuits especially when is it desirable to realise high carrier conductivities.…”