High Quality Bi2Te3 Thin Films for Potential Optoelectronic Application Yanwen Liu, Weiyi Wang, Cheng Zhang, Ping Ai, Faxian Xiu Department of Physics and State Key Laboratory of Surface Physics Fudan University, Shanghai, 200433, China Structural Analysis Quantum Oscillation Introduction (b) Optical Absorption of Surface States in TI (a) FSdH=(ћ/(2πe)) X πkF2 n2D=kF2/4π Onsager relation 4QL @ 2K (c) ħω3>ΔE μ μ ħω1 ħω2 n1=1.35×1012cm-1 n2=2.45×1012cm-1 (e) (d) Reduce the thickness τ=4.18×10-13s Idealized Band Structure of topological insulator (TI) mcyc=0.148 me 3D TI Quasi-2D TI XRD pattern of the sample (45QL) in θ-θ geometry, indicating the thin film has a c-axis alignment; Raman spectrum confirm the thin film are well stacked along <111>. l=1.79×10-7m EF=154 meV Gapless bandgap in analogy to graphene Tunable surface bandgap (ultra-thin) µ =0.58 m2 V-1s-1 VF=4.28×105m/s RT and Hall data ---- High absorbance ---- Wide spectrum range ---- Enhanced absorbance ---- Better performance photodetector Lifshitz-Kosevich (LK) theory Dingle plot I II Δσxx(T)/Δσxx=λ(T)/sinh(λ(T)); λ(T)=2π2kBTmcyc/(ћeB) Ln[ΔRxxBsinh(λ(T))]~[2π2EF/(τeVF2)] l=VFXτ; µ=(eτ)/mcyc Why TI on mica by MBE? Shubnikov-de Hass oscillations of a 4QL Bi2Te3 thin film. (a) and (b) Hall resistance Ryx and its first derivative; (c) the fast Fourier transform of (b);(c) and (d)Temperature dependence of the amplitudes of normalized conductivity and the dingle plot. Muscovite mica Molecular Beam Epitaxy (MBE) Properties: Atomically smooth Chemically inert Thermally stable, Highly transparent, Flexible Perfectly insulating K O Optical Properties Al MBE system in MRC Si Advantages: Low density of defects Larger size thin films Accurate doping control van de Waals Epitaxy Motivation: Metallic behavior and temperature-independent features were observed at two regimes of R-T data. Nonlinearity in Ryx suggests more than one conductive channels. Improve materials quality of TI by combining equilibrium growth and van de Waals Epitaxy on transparent substrate toward optoelectronic application. Temperature dependent MR data Experimental Transmission spectra of Bi2Te3 thin films on Mica substrates, showing the thickness-dependent behavior. Superior NIR transparency in ultra-thin films can be used as transparent conductive substrates in optoelectronics. Vxy Vxx I B (-9~+9 T) mica Bi2Te3 3.9 nm 2.5 5.0 7.5 10.0 µm General route for TI growth Cr-doped Bi2Te3 thin film 4QL 5QL 6QL mica Schematics of measurement Thickness determination Longitudinal resistance (Rxx) Transverse resistance (Rxy) 1 µm 8QL 10QL 15QL Temperature dependent MR data reveal sharp cusps in thinner thin films at lower field regime and the linear magnetoresistance (LMR) at higher field regime. Quantum Oscillation was observed in 4QL thin film at lower temperature. Results Weak Antilocalization Effect 500nm 500nm 1 µm Bi2Se3 thin film Sb-Bi2Se3 thin film Topographic and Growth mode (b) (a) (b) Conclusion (a) 4QL 10QL (b) High quality Bi2Te3 thin films exhibited atomically smooth terraces over an ultra-large area have been fabricated on Muscovite mica substrates by MBE. The availability of such high quality TI thin films on the transparent mica substrates will facilitate the investigation of the quantum interface effect and the manipulation of the surface states, providing the possibility of exploring the potential application of TI in optoelectronics. 1 μm 1 μm Roughness =0.211nm Roughness =0.335nm (c) Hikami-Larkin-Nagaoka (HLN) Theory (c) (d) Mica substrate 1st QL 2nd QL 3rd QL where is the phase coherence length (a) Normalized MR data of Bi2Te3 thin films; (b) HLN mode fitting to extract the prefactor α and Lᵩ;(c) Temperature dependence of the coherence length L extracted. We gratefully acknowledge the financial support from the department. *To whom correspondence should be addressed: faxian@fudan.edu.cn Layer-by-layer model (a)Representative AFM topographic images of Bi2Te3 thin films with a thickness of (a) 4QL and (b) 10 QL on mica substrates, (c) Profile along the yellow line in (b) implies the layer-by-layer mode as sketched in (d).