Confined Ultrathin Silicon Nanowires P.D. Tran, T.J. Macdonald, B. - - PowerPoint PPT Presentation

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SiNWs

5 µm 5 µm 500 nm

Photo-responsive Properties on Locally Confined Ultrathin Silicon Nanowires

http://bionanoengineering.com

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P.D. Tran, T.J. Macdonald, B. Wolfrum, R. Stockmann, A. Offenhausser, T. Nann and B. Thierry

Ian Wark Research Institute, University of South Australia, Australia Peter Grünberg Institute, Forschungszentrum Juelich GmbH, Juelich, Germany

Why Ultrathin Silicon Nanowire ?

 Silicon nanowires (SiNWs) are promising functional building blocks for novel

• ptoelectronic devices1,2

 Down-scaling to ultrathin SiNWs open up opportunities to explore new fundamental properties of one-dimensional materials  high performance nanoscaled devices  The performance of planar SiNWs optoelectronic devices is currently limited by the inherent low fill factor and light reflection  CdTe quantum dots (QDs) are high-efficiency fluorescence materials with tuneable emission wavelength  “light harvesting antenna” for ultrathin SiNWs devices

• 1. Zhang, A.; Kim, H.; Cheng, J.; Lo, Y

.-H. Nano Letters 2010, 10, (6), 2117-2120.

• 2. Garnett, E.; Yang, P. Nano Letters 2010, 10, (3), 1082-1087.

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Aim: To fabricate and improve the performance of novel, locally confined ultrathin SiNWs photo-resistors

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The Fabrication

• 1. SiNWs Patterning
• 2. Localized Etching
• 3. Packaging

SiNWs patterning by e-beam lithography and TMAH etching  Wafer-scaled homogeneity of the Si device layer thickness (~ 40nm)  Highly-ordered SiNWs (WxL: 200 nm x10 µm) with smooth trapezoidal shape

a b c d

nm

500 nm 5 µm

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The Fabrication

0.5 1 1.5 2 2.5 3 3.5 4 65 55 45 35

Etch rate (nm/s) Temperature (oC)

Optimization of the TMAH wet etching using isopropanol additive for localized etching

• 1. SiNWs Patterning
• 2. Localized Etching
• 3. Packaging

0.95 nm 0.12 nm

a b

1.2 nm 0.0 nm 1.1 nm

• 0.1 nm

c

1.3 nm

• 0.1 nm

e

1.4 nm 0.0 nm

d f

0.0 nm 3 nm

Pristine Si 35oC 45oC 55oC 65oC Oxidation + HF

 A very slow (~0.5 nm/s) and well-controlled TMAH etching rate on Silicon (100) was obtained  Atomic smooth Si surface is maintained after etching (rms roughness ~0.15 nm)

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The Fabrication

• 1. SiNWs Patterning
• 2. Localized Etching
• 3. Packaging

Ultrathin SiNWs were fabricated with thickness down to ~20 nm by localized wet-etching with optimized TMAH  Compatible with device integration techniques  Thickness scalable to sub-20 nm  Straight forward and easy to implement

20 nm

e f

500 nm 5 µm

40 nm 20 nm

40 nm

100 nm 200 nm Si SiO2

Si SiO2

Ultrathin SiNW

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The Fabrication

• 1. SiNWs Patterning
• 2. Localized Etching
• 3. Packaging

A novel wafer-scaled top-down process for the fabrication of locally thinned-down silicon nanowires based device has been developed

g h i j

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Ultrathin SiNWs Characterizations

Ids (µA) a Vds (V) Time (s) b

• 100

100 200 300 400 500 600 700 3.4 3.6 3.8 4.0 4.2

Ids (µA) Dark 1.28 1.2 0.85 0.75 0.5

 High photosensitive, LOD: 0.75 mW.cm-2  High photoresponsivity, R ~ 104 A/W >> 0.7A/W ( commercial silicon PIN photodiode)  Good time response: t = 0.003s  High mobility photocarriers are generated in high quality ultrathin SiNWs

c

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Ultrathin SiNWs Characterization

• 3
• 2
• 1

1 2 3

• 8
• 4

4 8 12 16 20 24

Dark 254 nm 365 nm 680 nm

Ids (µA) Vds (V)

5 10 15 20

• 1

1 2 3 4 Bias at 2.0 V Bias at -2.0 V

Ids (µA) Time (minute) OFF ON ON

• 3
• 2
• 1

1 2 3

• 10
• 5

5 10 15 20 25 273 K 298 K 313 K 343 K

Ids (µA) Vds (V)

 Broad light detection spectrum: 254 nm  680 nm  Thermal stability: 0oC  70oC  Long-term stable measurement: 20 mins  Highly photo-responsive and stable

ultrathin SiNWs

a b c

• 0.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 10 20 30 40

Dark 365 nm/Bare Si 365nm/Si-QD 680nm/Bare Si 680nm/Si-QD

Ids (µA) Vds (V)

0.0 0.2 0.4 0.6 0.8 1.0 2 4 6 8 10

Dark Bare Si Si/QD

Ids (µA) Vds (V)

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Quantum dot – SiNWs hybrids

b a

 10 nm CdTe quantum dots nanoparticle were successfully synthesised  ~ 59 ± 10% improvement in photocurrent response of QD-SiNWs measure under 365 nm UV light due the QDs emitting in the visible region.  Initial measurement on solar full spectrum (300  1400 nm; 100 mW/cm2) show ~20 % increasing in photocurrent response  Fast, stable and highly photoresponsive new nanostructures based on

quantum dots - SiNWs hydrids have been developed

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Conclusion and Outlook

 A novel and straight-forward top-down fabrication of functional ultrathin SiNWs has been developed  The fabricated ultrathin SiNWs have demonstrated ultrahigh photo-responsivity, high photosensitivity, stability, durability and fast response  QD modified SiNWs have shown an improvement of the photocurrent measured under UV light while preserving their performance in visible light Potential to apply this novel process to fabricate sub-10 nm thin SiNWs Exciting applications for opto-electronics and photovoltaics hydrid systems

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Acknowledgements

• Dr. Dirk Mayer, Dr. Venesa Maybeck, Dr. Stefan Trellenkamp - Forschungszentrum

Jülich, Germany

• Dr. Xuan Thang Vu - University of Applied Sciences Kaiserslautern, Germany
• Dr. Tong Duy Hien - Nanosens Research Co., Netherland
• Asso/Prof. Steve Madden - Australian National University, Australia
• This work was performed in part at the SA and ACT nodes of the Australian

National Fabrication Facility, a company established under the National Collaborative Research Infrastructure Strategy to provide nano and micro- fabrication facilities for Australia’s researchers. Thank for the financial support from: + Australian Technology network – German Academic Exchange Service (DAAD) award + NH&MRC 631939 research project