Nanoscale physics

Quantum size effects and transport properties of Bi2(Te1-xSex)3 
3D-topological insulators thin films

Rogachova O.I., Doroshenko G.M., Sipatov O.Yu., Nashchekina O.M.

National Technical University “Kharkiv Polytechnic Institute”, 2, Kyrpychova St., Kharkiv 61002, Ukraine
E-mail: rogachova.olena@gmail.com

The V2VI3 compounds and their solid solutions are among the best low-temperature thermoelectric (TE) materials. Today they are increasingly being used in thin-film TE converters. Recently it has been discovered that V2VI3 compounds belong to a new type of objects of nanophysics - 3D topological insulators (TI) with spin-polarized surface states, protected by time reversal symmetry, and unique properties, which can be more clearly observed in thin films. All this stimulates studying these materials in the thin film state. 
Electron confinement in low-dimensional structures leads to quantum size effects, which are manifested in thin films through an oscillatory behavior of the thickness dependences of kinetic coefficients. We observed such size-dependent oscillations in Bi2Te3 and Bi2Se3 thin films in [1,2]. The goal of the present work is to find out how the anion substitution in Bi2 (Te1-x Sex) alloys and the presence of a topological layer affect the manifestation of quantum size oscillations. 
Thin films with thicknesses d=15-85 nm were prepared by thermal evaporation in vacuum of the Bi2 (Te0.9 Se0.1) crystal and subsequent deposition onto glass substrates. It was established that the dependences of electrical conductivity, the Seebeck coefficient and the Hall coefficient on d exhibit an oscillatory behavior with a certain period. The experimental results were interpreted within the framework of notions about size quantization of the electron spectrum and taking into account the presence of the topological metallic surface layer in the films.

1.	Rogacheva E.I., Budnik A.V., Sipatov A.Yu, Nashchekina O.N., Dresselhaus M.S., Thickness dependent quantum oscillations of transport properties in topological insulator Bi2Te3 thin films // Appl. Phys. Lett.- 2015.- 106,- 053103 (1-5).
2.	Rogacheva E.I., Menshikova S.L., Sipatov A.Yu., Nashchekina O.N., Thickness-Dependent Quantum Oscillations of the Transport Properties in Bismuth Selenide Thin Films // Thin Solid Films. - 2019.- 684, P.31-35.