Experimental studies on the growth,characterization and topological properties Bi2Te3 thin film

• Main Authors: Yu-Sung Chen, 陳宥菘
• Other Authors: Yuan-Huei Chang
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/32221214421422708526

碩士 === 國立臺灣大學 === 應用物理所 === 103 === Topological insulator (TI) has attracted a lot of attention because of their unique properties. The topological insulator has an insulating bulk state and a gapless metallic surface state. The metallic surface state is topologically protected from scattering by magnetic impurities and defects and has an electric conduction property which is dramatically different from the traditional 3D materials. Bismuth telluride (Bi2Te3) belong to this class of innovative new material and in this thesis we report the successful growth of large area, high quality Bi2Te3 thin film. In this work, physical vapor deposition (PVD) method was used to grow Bi2Te3 thin film on the sapphire (Al2O3) substrate or nanoplate on silicon dioxide substrate. During the growth, the Bi2Te3 powder and the sapphire was placed 15 cm apart in a quartz tube and the temperatures of the source powder and of the substrates were kept at 480 °C or 500 °C and 280 °C, respectively. The structural characteristics of the samples were carefully examined by using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS), the measurement results indicate that the samples have the right chemical composition and are of high crystalline quality. Phi scan measurement shows our film has two domain. The thickness and roughness of the films were analyzed by using atomic force microscopy (AFM). For electric measurements Bi2Te3 Hall bar device was made by using photo-lithography, the physical property measurement system (PPMS) was the employed to measure resistivity, carrier concentration, mobility, and magneto-resistivity of the sample. Electrical measurement showed that Bi2Te3 thin film has insulator behavior when the temperature is above 165 K, metal-insulator transition occurs at 165 K and when the temperature is below at 165 K, the sample becomes metallic. Carrier concentration in this sample is 4.8×1018 (cm-3) at 3 K, the sample’s mobility is 46.7 (cm2/Vs) at 300 K and increases to 192.43 (cm2/Vs) at 3 K. Magneto-resistivity measurement showed that at low temperature a sharp resistance dip appears around B = 0 appeared, a manifestation of the weak anti-localization. WAL was found at low magnetic field in the magneto-resistivity measurement, and showed that the sample has the property expected for a topological insulator. Hikami-Larkin-Nagaoka equation was used to fit the magneto-resistivity curve, and the fitting parameters are α=-0.74, and l_ϕ=136 nm, respectively. Linear non-saturating magneto-resistivity (LMR) at high magnetic field also indicates that the sample has the properties expected for a topological insulator. Key words: Bi2Te3 ; Thin film growth ; PVD