Topological Insulator Thin Films Starting from the Amorphous Phase - Bi$_2$Se$_3$ as Example

TL;DR

This paper introduces a simple method to produce large-area amorphous Bi$_2$Se$_3$ thin films that transform into topological insulator crystalline structures upon annealing, with detailed electrical and magnetic property analysis.

Contribution

It demonstrates a novel, accessible approach to synthesize topological insulator thin films starting from amorphous phases, verified by multiple characterization techniques.

Findings

Amorphous Bi$_2$Se$_3$ films exhibit Mott variable range hopping conduction.

Annealed films transform into crystalline topological insulators confirmed by X-ray and Raman.

Magnetoresistance shows weak anti-localization at low temperatures.

Abstract

We present a new method to obtain topological insulator Bi$_2$Se$_3$ thin films with a centimeter large lateral length. To produce amorphous Bi$_2$Se$_3$ thin films we have used a sequential flash-evaporation method at room temperature. Transmission electron microscopy has been used to verify that the prepared samples are in a pure amorphous state. During annealing the samples transform into the rhombohedral Bi$_2$Se$_3$ crystalline strcuture which was confirmed using X-ray diffraction and Raman spectroscopy. Resistance measurements of the amorphous films show the expected Mott variable range hopping conduction process with a high specific resistance compared to the one obtained in the crystalline phase (metallic behavior). We have measured the magnetoresistance (MR) and the Hall effect (HE) at different temperatures between 2 K and 275 K. At temperatures $T \lesssim 50$ K and fields $B \lesssim 1$ T we observe weak anti-localization in the MR; the Hall measurements confirm the n-type character of the samples. All experimental results of our films are in quantitative agreement with results from samples prepared using more sophisticated methods.