Terahertz study on the optical properties of bismuth telluride (Bi2Te3)

• Main Author: Lim, Wen Xiang
• Other Authors: Chia Ee Min, Elbert
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Science::Physics
• Online Access: http://hdl.handle.net/10356/59934
• Institution: Nanyang Technological University

In this report, we will investigate the optical properties and carrier dynamics of topological insulators. Terahertz Time-Domain Spectroscopy (THz-TDS) were conducted in the range of 0.4 - 2.8 THz at temperatures as low as 15 - 300 K, on samples such as single-layer graphene and bismuth telluride (Bi2Te3). The study of single-layer graphene provides the groundwork for understanding the Drude model which could be used to model the 2D surface carrier dynamics of Bi2Te3. Topological insulators are materials with conducting surface states and insulating bulk states. Therefore, the use of Drude-Lorentz model is necessary to study the optical properties and carrier dynamics of Bi2Te3. Within our frequency range, the refractive index of a single-layer graphene, ranges from 20 - 120 with a carrier density of approximately ~10^15 m^-2. The density fluctuations were attributed to the random impurities located between the interface of single-layer graphene and p-doped silicon. For the topological insulator Bi2Te3, the refractive index ranges from 8 - 42. We have observed two optical phonon modes E1g and A11g present at 1.1 THz and 1.6 THz, respectively. However, we did not manage to model any Drude contributions to the conductivity of Bi2Te3. This could be due to the dominance of the phonon modes which results in the suppression of the Drude term.