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
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
• Fabrication of well aligned ZnO NWs arrays using UTAM as a substrate
• Device application of the ZnO NWs arrays
as Schottky Diodes
Fabrication of well aligned vertical ZnO NWs on ultrathin alumina membranes
Well vertical alignment of theZnO NWs due to the well orderedunderlying UTAM pore structure
ZnO NWs on the UTAM are grownby CVD at 550 oC under 400 mbarat a constant nitrogen flow of 150 cm3/min
0.5 μm
UTAM
Au nanodots
(a)
1 μ m
(b)
1 μm
(c)
(a) (b)
(c)(d)
(a) 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
Growth process of the vertical well ordered ZnO nanowires arrays
Process of fabricating horizontal arraysof 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 reach181 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
NWs were effectively sheared from the donor substrate
NWs are aligned along the [0001] direction (or c-axis), retaintheir orginal alignment on thedonor substrate
Ag electrodes on the ZnO NWsformed by thermal evaporationSeparation between the electrodes
20 m
Directional sliding of the donorsubstrate with respect to thereceiver substrate
90% of the NWs are highlyAligned in the direction of theSliding motion
(a)
I-V Characterization of the Zinc Oxide Nanowire Arrays
Movement of the positive andnegative probes along the neighbouring pairs of electrodesfor the I-V measurements
(b)
Rectifying behavior in the negative voltage region with some differences in the forward biased current for all the 9 electrode pairs
(b)
Decrease of the foward biased current when the number of sequential electrodes increases due to the increased number of Schottky barriers
Increase in the turn on voltage
I-V characteristics of horizontally aligned ZnO NWs arrays of Schottky diodes
(a)
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
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
I-V characteristics of nine different single ZnO NW Schottky diode
SEM image of a single ZnO NW device on the Si substrate
Length of the ZnO NW ~ 100 m
25 μm
(a)
-3 -2 -1 0 1 2 3
0
4
8
12
16
20
1# electrode
2# electrode
3# electrode
4# electrode
5# electrode
6# electrode
7# electrode
8# electrode
9# electrode
I (nA
)
Vds (voltage)
(b)
8 10 12 14 16 18 200,4
0,5
0,6
0,7
0,8
0,9
1,0
Single ZnO NW Schottky diodes
Ideality Factor
Bar
rier
Hei
gh
t, d
(eV
)
The ideality factor and the barrier height of the single ZnO NW Schottky diode is obtained fromthe respective I-V characteristics
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
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
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.
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
Acknowledgements
Funding
Thank you for your attention
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