Supporting Information
A ZnO nanowire resistive switch
K.R.G.Karthik1,3, Rajiv Ramanujam Prabhakar2,L.Hai1, Sudip.K.Batabyal2, Y.Z.Huang2*and
S.G.Mhaisalkar1,2,3
1
School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore
639798
2
Energy Research Institute @NTU (ERI@N), Nanyang Technological University, Research Techno Plaza, 5th Storey,
50 Nanyang Drive, Singapore 637553
3
TUM CREATE Centre for Electromobility, 62 Nanyang Drive, Block N1.2, Singapore 637459
* yzhuang@ntu.edu.sg
Synthesis:
ZnO nanowires were synthesized by carbo-thermal reduction method. ZnO powder and
graphite powder were first mixed together at 1:1 molar ratio followed by grinding and placing
in a horizontal tube furnace system with n-type silicon substrates coated with 2 nm thin layer of
Au catalyst as growth substrates. The system was then pumped down to 1.5 × 10-2 mbar and a
constant flow of Ar (200 sccm) and O2 (10 sccm) was maintained in the furnace. The
temperature was ramped up to 900 °C and then maintained at this condition for 45 mins. The
nanowires were physically characterized by X-ray diffraction13 and SEM as single crystalline
wurtzite ZnO nanowires.
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SCLC discussion:
Fig S1. I vs V2 plot implying a SCLC mode of conduction observed after switching.
The conductivity (σ) of such a device can be explained in terms of µSCLC and n0 as
σ= (1/ρ)= n0eµSCLC
(1)
2
where ρ= RA/d is the resistivity, R the resistance of the device, A= πr 2, and r the radius of the
nanowire (50 nm). For a device exhibiting two resistive states (LRS and HRS) for the same
voltage we have
d/RLRSA = nLRSeµSCLC
(2)
d/RHRSA = nHRSeµSCLC
(3)
Hence, the number of charge carriers in HRS state is given by
nHRS = (RLRS nLRS)/RHRS
(4)
The symmetry of the I-V curve is due to two considerations


The work function of the contact electrodes is same on either sides of the nanowire. The
schottky barrier is the only reason for asymmetry here, which has been reduced by
annealing. Hence we expect symmetry in I-V characteristics.
The second point to be considered is the method of testing the device. While both ends
of the nanowire are contacted to Pt electrodes, the bias is applied on one end of the
nanowire as shown in the Fig S1. Negative or positive bias will only change the direction
of motion of the charge carriers (electrons).
ZnO nanowire
Applied bias V through
Pt contact
To ground through Pt
contact
O2- surface
Zn+2 surface
Fig S2. A ZnO nanowire device model with the testing configuration.
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Hence, the electrons will be eventually trapped due to the polar charges immaterial of the direction of
flow through the nanowire as shown in the Fig S2. It must be noted that, trapping phenomena need not
depend on the polarity of the applied bias.
Pt electrode
Electrons
Positive bias
Polar charge
traps
Flow of electrons
Pt electrode
Negative bias
Flow of electrons
Fig S3. A schematic of the flow of electrons through the nanowire.
The fabricated-annealed device (Fig 5 from manuscript)was tested at room temperature with
the set voltage 0.5V as the ON state and the reset voltage 0V as the OFF state. The reading
voltage considered in this case to be 0.3V exhibits the HRS with a low current reading (0.04 nA)
and LRS with a higher current reading (0.06 nA). Depending on the direction of the applied
reading voltage, the device shows two distinct currents.
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