1. 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, , 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 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:
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).