Fermi level tuning and electronic properties of epitaxial topological insulators (Sb1-xBix)2Te3

Abstract

In this experiment we grow the (Bi1-xSbx)2Te3 ternary alloy thin film on Sapphire substrate by fixing Te and Sb flux ratio before grown by Molecular beam epitaxy We only change the rate of Bi vapor deposition to adjust the content ratio of Bi in the film Since the deposition rate can be controlled by beam flux monitor which reading gas partial pressure in order to adjust the flux ratio Bi:Sb:Te = 0~1:1:17 By different doping ratios we can tune Fermi level position to investigate transport property of n-type to p-type transition range and decrease the bulk state carrier contributions of Sb2Te3 and Bi2Te3 to enhance surface state The Sb gas partial pressure is fixed at 3×108 (torr) Due to the lower flux ratio would improve surface roughness Then we confirm preliminary results by in-situ RHEED measured that the crystal structure is single crystal and the surface is flat The crystal orientation quality and film thickness were confirmed by XRD and TEM In optical measurement E_g^1 、E_g^2 、A_1g^1 、A_1g^2 were observed by Raman spectroscopy and four optical vibration modes were compared with the EDS analysis of TEM to estimate the proportion of Sb under different Bi flux ratio In terms of surface characteristics there are AFM and STM The former can observe the layer by layer structure of the film surface and confirm the surface roughness while the latter can observe the atomic arrangement of the surface of the film and the local electronic energy state analysis of the STS measurement Finally the relationship between the band structure and the carrier transmission characteristics is compared by ARPES and transport measurement

Date of Award	2019
Original language	English
Supervisor	Jung-Chun Huang (Supervisor)