**1. Introduction**

In the recent years because of unique feature of topologically protected surface states which have strong spin-orbit coupling the three-dimensional (3D) topological insulators (TIs) like Bi2 Se3, Bi<sup>2</sup> Te3 and their counterpart alloys have attracted tremendous and intense research

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

attention [1–4]. The surface states which has been observed, are believed to be protected against time-reversal-symmetry, owing to the fact that, electrons in the surface state behave as dirac electrons as in case of 3D TI [5], which can be applied to spintronics devices [6], quantum computing [7] and it is necessary to investigate TI from the transport point of view in order to address the electronic properties of Dirac electrons. In terms of weak antilocalization (WAL) effect in thin films [8, 9], nanoribbons [10] and 3D TI crystals [11, 12], several research groups have already analyzed this transport behavior, by making small scale devices using conventional lithography techniques, but no paper has yet reported to observe this magnetotransport behavior in Bi<sup>2</sup> Te3 thin film Hall Bar device without using lithography techniques. Also in terms of potential applications in magnetic sensors and magnetic random access memory [13], materials exhibiting linear magnetoresistance (LMR) are found to be promising candidates. The linear MR behavior in Bi<sup>2</sup> Se3 [14, 15] and Bi<sup>2</sup> Te3 [16, 17] has been revealed in recent literatures and these TIs provide an ideal platform to study the origin of LMR because of the unique surface states that are naturally zero band gaps with linear dispersion.

It is necessary to grow a high quality TI thin film, in order to observe this magnetotransport behavior in topological insulator Bi<sup>2</sup> Te3 . Molecular beam epitaxy (MBE) in this respect has demonstrated and found to be suitable in producing samples with carrier mobilities higher than the bulk crystals with precise control on the growth rate, out of modern thin film growth techniques. In order to realize layer by layer growth and obtaining the right stoichiometry [18] this technology is very important. Here, with respect to weak antilocalization (WAL) and magnetoresistance (MR), we report on the magnetotransport measurement. After fabrication, the thin film Hall Bar device is subjected to Physical Property Measurement System (PPMS), where the magnetic field is applied perpendicular to the plane of Hall Bar device. At programmed temperatures, by sweeping the magnetic field between −9 T and + 9 T, the Longitudinal Resistance is measured.

> thin film sample synthesized from the MBE, with the help of RIE the thin film hall Bar was made, using the etching mask placed over the sample on the sample holder. With the aid of

> gas for 30 s, the etching was done for getting the required Hall Bar structure. Finally, on the same sample holder, Au (40 nm)/Cr (40 nm) metal ohmic contacts were made with the help of thermal evaporation, using the metal mask over the thin film Hall Bar sample. With dimension of 2 mm long and 1.5 mm wide we obtained our fabricated Topological Insulator

Te3

thin film Hall Bar device. The **Figure 1a** shows the Schematic diagram of the device

Using AFM in a tapping mode, the topography of thin films was evaluated and by scanning a scratch deliberately made on as-grown thin films, the thickness was reliably determined. With the help of Siemens D-500 X-ray Diffractometer (XRD) further structural analyses were also carried out. In **Figure 2b** and **c** representative topographic AFM images of Bi2Te3 thin films are shown respectively, suggesting a layer-by-layer growth mode, revealing the ultra-smooth

topological insulator thin film hall bar device and the 7 ×

thin film hall bar device.

Observation of the Weak Antilocalization and Linear Magnetoresistance in Topological…

http://dx.doi.org/10.5772/intechopen.76900

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CF<sup>4</sup>

Bi2 Te3

fabrication with image of Bi<sup>2</sup>

**3. Characterizations**

Te3

**Figure 1.** Methodology of fabrication of topological insulator Bi<sup>2</sup>

7 mm dimension of the thin film hall bar device in **Figure 1b** and **c**, respectively.
