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Quantum Confinement of Crystalline Silicon Nanotubes
Binghai
1
Yan ,
Gang
1
Zhou ,
Xiao Cheng
2
Zeng ,
Bing-Lin
1
Gu ,
and Wenhui
1
Duan*
1Department
of Physics,Tsinghua University, Beijing 100084,China;
2Departments of Chemistry and Physics, University of Nebraska, Lincoln, NE 68588,USA
Crystalline silicon nanotubes(c-SiNTs), synthesized in experiments recently, are nanotubes of Si crystalline
structure with tube-wall-thickness of several nanometers, which are expect to have more advantages to exhibit
quantum confinement effect and potential applications than silicon nanowires(SiNWs).
Our work studied the electronic, optical and quantum confinement properties of c-SiNTs with
both uniform thickness and non-uniform thickness from first-principles.
Method
Thickness(σ)
Diameter
• Density-functional theory.
• The local density approximation.
• Norm-conserving pseudopotentials.
• Numerical atomic orbitals.
• SIESTA package.
TEM image of c-SiNT in experiments (left) and structural model of c-SiNT along
[111]: lateral view (middle) and cross section (right).
Results
CBM
VBM
Uniform thickness c-SiNTs. The band structure of
nanotubes with D=1.80 nm and diffrenet thickness. The
band gap increases significantly as the thickness
becomes smaller due to quantum confinement.
Non-uniform thickness c-SiNTs. The wave-functions of the VBM and
CBM are due mainly to atoms located in the thicker side of the tube wall,
referred as effective confinement region (ECR). The band gap also
depends mainly on ECR.
Conduction
Channel
SEPARATE
FET
For Si nanowires, the dopants will scatter the
carriers a lot because the conduction channel and
the dopants are in the same position.
However, providing the impurity scattering and
increasing the conductance is very important to
improve the performance of devices, such as FET,
Dopant
Impurity
For c-SiNTs with non-uniform thickness, the non-uniformity of
the VBM and CBM shows a way to spatially separate the doping
impurities from the conducting channel in doped SiNTs.
Practically, the performance of the SiNT-based transistors may
be substantially improved by selective p/n doping in the thinner
side of the tube wall, in the spirit of modulation doping.
Summary
Our study clearly reveals the unique electronic properties of c-SiNTs, especially the effect of non-uniformity
in wall thickness, suggesting a new modulation doping method aiming to high-performance nanodevices.
Acknowledgement
We thank Prof. Jisoon Ihm and Dr. Chaoxing Liu for their helpful discussions.

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