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Fabrication and Characterization of Well- Aligned Zinc Oxide Nanowire Arrays and their realizations in Schottky-Device Applications. Kin Mun Wong 1 , Liaoyong Wen 1 , Yaoguo Fang 2 , Fabian Grote 1 , Hui Sun 1 , and Yong Lei 2. DPG conference in Dresden 2011.

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Dpg conference in dresden 2011

Fabrication and Characterization of Well-

Aligned Zinc Oxide Nanowire Arrays and their

realizations in Schottky-Device Applications

Kin Mun Wong1, Liaoyong Wen1, Yaoguo Fang2, Fabian Grote1, Hui Sun1, and Yong Lei2

DPG conference in Dresden 2011

1Institute of Materials Physics and Center for Nanotechnology, University of Muenster, Wilhelm-Klemm-Str. 10, 48149 Muenster, Germany

2Institute of Nanochemistry and Nanobiology, Shanghai University, Shanghai 201800, China


Outline
Outline

  • FabricationofwellalignedZnO NWs arraysusing UTAM as a substrate

  • Device applicationoftheZnO NWs arrays

    asSchottkyDiodes


Fabrication of well aligned vertical ZnO

NWs on ultrathin alumina membranes

(a)

Au nanodots

ZnO NWs on the UTAM are grown

by CVD at 550 oC under 400 mbar

at a constant nitrogen flow of

150 cm3/min

UTAM

0.5 μm

(b)

Well vertical alignment of the

ZnO NWs due to the well ordered

underlying UTAM pore structure

1μm

(c)

1 μm


(a)

(b)

(c)

(d)

Growth process of the vertical well ordered ZnO nanowires arrays

  • Thermal Evaporation of Au on the UTAM surface

  • (b) ZnO + C → Zn + CO (by graphite), negative charges (e.g. C2O42-) attract Zn atoms to the UTAM for the nucleation process to begin

  • (c) Mergence of the Zn atoms into (0001)-oriented quasihexagonal ZnO nuclei upon precipitation and oxidation

  • (d) Due to the intense (0001)-oriented growth direction, vertical ZnO NWs

  • are formed after prolonged growth from the nuclei


Process of fabricating horizontal arrays

of ZnO NWs Schottky diodes

The ZnO NWs as constructed by our method are densely packed (with approximately 4x105 NWs in an area of 1 cm-2) and are demonstrated to be functional as Schottky diodes.

The overall process of fabricating horizontal arrays of ZnO NWs Schottky diodes


(a)

(b)

(c)

(d)

Length of the ZnO NWs reach

181 m in 40 minutes

Rapid growth of the NWs due to the plentiful supply of zinc vapor and oxygen near the substrate

Temperature : 950 oC

Growth of the ZnO NWs by the CVD process


(a)

(b)

(c)

(d)

Dry contact printing process for the realization

of the well aligned arrays of ZnO Schottky diodes

Directional sliding of the donor

substrate with respect to the

receiver substrate

NWs were effectively sheared from the donor substrate

90% of the NWs are highly

Aligned in the direction of the

Sliding motion

NWs are aligned along the

[0001] direction (or c-axis), retain

their orginal alignment on the

donor substrate

Ag electrodes on the ZnO NWs

formed by thermal evaporation

Separation between the electrodes

 20 m


I-V Characterization of the Zinc Oxide Nanowire Arrays

(a)

(b)

Movement of the positive and

negative probes along the

neighbouring pairs of electrodes

for the I-V measurements

Rectifying behavior in the negative voltage region with some differences in the forward biased current for all the 9 electrode pairs


(a)

(b)

I-V characteristics of horizontally aligned ZnO NWs arrays of Schottky diodes

Zinc and oxygen alternating layers along the c-axis results in a spontaneous polarization, P which leads to a potential gradient along the length of the individual NW

Decrease of the foward biased current when the number of sequential electrodes increases due to the increased number of Schottky barriers

P, which is oriented along the NW direction (towards the source electrode) leads to a build in potential decreasing along the NW c-axis direction

Increase in the turn on voltage


(a)

(b)

25 μm

SEM image of a single ZnO NW device on the Si substrate

Length of the ZnO NW ~ 100 m

I-V characteristics of nine different single ZnO NW Schottky diode


The ideality factor and the barrier height of the

single ZnO NW Schottky diode is obtained from

the respective I-V characteristics

Weak linear dependency of the barrier height on the ideality factor indicates lateral inhomogeneity of the ZnO NW Schottky contacts due to the difference in the inhomogeneity in the Schottky contact corresponding to the different diode-to-diode interface

The high ideality factor is due to the interface states of the thin interfacial layer between the Ag electrode and the ZnO NW as an interfacial layer with surface states forms easily on the surface of the ZnO NW


Conclusion

  • Fabrication of well-aligned arrays of vertical ZnO nanowires using an UTAM as a substrate

  • Fabrication of a large area of repeatable, densely packed and horizontally well-aligned arrays of ZnO NWs Schottky diodes along their c-axis using a simple and viable two-step method

  • Our technique for the realization of Schottky device applications opens a possibility for the mass scale production of the ZnO NW based devices for flexible electronics.


Acknowledgements

Funding

Surface Nano-Structuring Group

Group Leader: Prof. Dr. Yong Lei

Group Members:

Stefan Bartels

Fabian Grote

Christian Heckel

Peter Heß

Stefan Ostendorp

Dr. Hui Sun

Nina Winkler

Dr. Kin Mun Wong

Feng Xu

Dr. Shikuan Yang

Dr. Huaping Zhao



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