metal oxide nanowires: synthesis, characterization and...
TRANSCRIPT
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Jia Grace Lu
Dept. of Chemical Engineering and Materials Science &
Dept. of Electrical Engineering and Computer Science
University of California, Irvine
Metal Oxide Metal Oxide NanowiresNanowires: Synthesis, : Synthesis, Characterization and Device Applications Characterization and Device Applications
-
(courtesy ZL Wang)
Challenges and ProspectChallenges and Prospect
# of Tr
ansisto
rs/Chip
4Kb64Kb
1Mb
16Mb
256Mb
10
100
1000
10000
1970 1980 1990 2000 2010 2020Year
1.E+04
1.E+06
1.E+08
1.E+10
1.E+12Minimum Dimension (nm)
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““ThereThere’’s Plenty of Room at the Bottoms Plenty of Room at the Bottom””-- Richard Feynman, 1959Richard Feynman, 1959
Vision: Vision: To synthesize To synthesize nanoscalenanoscale building blocks with building blocks with precisely controlled size and composition, and precisely controlled size and composition, and assemble them into larger structures with unique assemble them into larger structures with unique properties and functions.properties and functions.
““ThereThere’’s Plenty of Room at the Bottoms Plenty of Room at the Bottom””
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Characterization Characterization (Electron (Electron Microscopy, SPM, Microscopy, SPM, LowLow--T, HighT, High--B)B)
Nano Materials Nano Materials ((nanotubenanotube, , nanowiresnanowires, , ultra thin filmsultra thin films) & & Device Fabrication Device Fabrication
Nano Device Nano Device Application (FET,Application (FET,Sensor, Sensor, SET SET ……))
Source DranNanowire
SiO2
Ni/Au Ni/Au
Gate
Science and Engineering in the Science and Engineering in the nanonano--WorldWorld
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Semiconductor NanomaterialsQuasiQuasi--oneone--dimensional semiconductor nanostructures: dimensional semiconductor nanostructures:
Q1D physical properties Q1D physical properties High aspect ratioHigh aspect ratioConductivity control (Conductivity control (pp--type/ type/ nn--type)type)BandgapBandgap engineeringengineering
Electronic and photonic device applicationsElectronic and photonic device applicationsField effect transistors Schottky-barrier rectifiersLED & LasersSensorsSensorsSingle electron transistors Memory cells Logic gates
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NanoNano MaterialsMaterials
15o
Ga2O3 Fe2O3B
Ag-TCNQ ZnOGaN
-
MotivationMotivation
Device applications:Device applications:Transparent electronicsTransparent electronicsUV light emitter and UV light emitter and detectordetectorChemical sensorsChemical sensorsElectroElectro--mechanical mechanical devicesdevices
Lower power consumptionLower power consumptionHigher sensitivityHigher sensitivityBetter gate modulationBetter gate modulationFaster response timeFaster response timeTunable band gapTunable band gap
NanowiresZnO
conducting channel
λD
-
Synthesis and Characterization Synthesis and Characterization of of NanowiresNanowires
CVD synthesisCVD synthesisElectrical transportElectrical transportScanning surface potential microscopyScanning surface potential microscopyChemicalChemical sensing propertysensing propertyOptical propertyOptical property
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Single Crystal Single Crystal NanowiresNanowires : Vapor: Vapor--LiquidLiquid--Solid MechanismSolid Mechanism
O2Catalyst
Zn O2
Catalyst: Au Alloy Supersaturation Crystal growth
-
Single Crystal Single Crystal NanowiresNanowires
• VLS growth mechanism
• SEM image of nanowires, with diameter ranging from ~20 to 100 nm
• High resolution TEM shows ZnO nanowires are single crystal. The distance between neighboring lattice planes is 0.52 nm, andgrowth direction is along [001] -- c axis
Chang et al., Chem of Materials (2004)
Ar+O2
Zincpowder
Quartzvial
Open endof vial Nano-
Crystals collecting substrate
20 30 40 50 60 70 80 90
0
1000
2000
3000
(200
)(2
01)
(203
)
(202
)
(112
)
(103
)(110
)
(102
)
(100
)(0
02)
ZnO Nanostructures JCPDS 89-0510
2θ
Inte
nsity
(a.u
.)
(101
)
C axis
HRTEM done in Japan
-
Out
b1
b2
b3
b4
b5
Control of Nanostructure MorphologyControl of Nanostructure Morphology
Furnace
QuartzTube
B A ZnC
O2 Gas Flow
Quartz Vial
-
Si wafer
- Si wafer
- Resist: PMMA
- E-beam lithography
- Catalyst deposition
Control of PositionControl of Position
-
- Si wafer
- Resist: PMMA
- Catalyst deposition
- Ebeam lithography
Si wafer- Liftoff:
remove PMMA
- CVD growth
Control of PositionControl of Position
-
Home-made anodic alumina membrane (AAM), 5 micron thick.
Al2O3 substrate
Al2O3 substrate
Al2O3 substrate
AAOtemplate
BottomelectrodeAdhesion
layer
Short Snnanorod
ZnOnanowires
• Vertical aligned ZnO nanowires array has promising potentials for nanoelectronics/optoelectronics.
• Anodic alumina membrane is an ideal template to integrate vertical aligned nanowires.
Schematic of nanowire synthesis process
400 nm
Control of Alignment Control of Alignment
-
Vg
Source Drain
Back Gate
SiO2
P++Si
Vds
NW
Furnace
QuartzTube
B A ZnC
O2 Gas Flow
Quartz Vial
Control of Electric PropertiesControl of Electric Properties
-2 -1 0 1 2-3
-2
-1
0
1
2
3
I ds (µ
A)
Vds (V)
Chip B Chip C
Higher Conductivity
-20 -10 0 10 20
0
50
100
150
200
Vg,t(C)I ds
(nA
)
Vg (V)
Chip B Chip C
-20 -10 0 10 20
0
50
100
150
200
I ds (
nA)
Vg (V)
Chip B Chip C
g,tV (B)
-
SiO2/p++ Si
Define alignment marks using ebeam lithography and metal deposition
Disperse NWs on substrateand locate the coordinates
1st resist layer: MMA/MAA2nd resist layer: PMMA
e-e-
Ebeam writing
Developing
Metal depositionLiftoff
Electrode Contact using Ebeam-lithography
-
Electrode Contact using Photolithography
SiO2/p++ Si
Disperse NWs
Spin coat resist
Cover the resist with a mask
UV
UV Exposure
DevelopingMetal depositionLiftoff
-
Band Diagram of Electrode ContactBand Diagram of Electrode Contact
Ohmic contactSchottky junction
EF-ZnOEF - Ni
Before contact
Ec
Ev
Ni ZnO
After contact
Work function (Φ) of materials:
ΦTi = 4.3 eV
ΦNi = 5.2 eV
ΦZnO = 4.3 eV
EZnO = 3.4 eV
ΦNi > > ΦZnO > ΦTi
Ti ZnO
φBEF - Ni
-
Source DrainNanowire
SiO2
p++ Si
Vg
Vds
Gate
NanowireNanowire Field Effect Transistor Field Effect Transistor
e
V
LCn gt⋅−=
)/2ln(/2/ 0 rhLC πεε≈
))/2ln(/2/()/( 0 rhLVdVdI dsg πεεµ =
r: NW radius; L: NW channel length; h: gate oxide thickness;
Vgt: gate threshold voltage; dI/dVg: transconductance.
Capacitance per unit length:
Carrier concentration per unit length:
Mobility:
-
I-V curves under different gate voltages
(b)
-10 -5 0 5 10 15
0
8
16
24
32
I (nA
)
Vg (V)
Vds=100mV Vds=75mV Vds=50mV Vds=25mV
Vgt=-8.37V
Transconductance at different source-drain biases
Electrical Transport PropertiesElectrical Transport Properties
• Three-terminal electrical measurements show n-type behavior.
• Carrier concentration ne ~ 107 cm-1; and mobility µe~ 80 cm2/V•s
-4 -2 0 2 4
-1600
-1200
-800
-400
0
400
Vds (V)
I (nA
)
Vg=6 V Vg=4 V Vg=2 V Vg=0 V Vg=-2 V Vg=-4 V Vg=-6 V
Z. Fan et al., APL (2004)
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High Performance High Performance ZnOZnO NW FETNW FET
-10 -5 0 5 10
-200
-100
0
100
200
Ids
(nA
)
Vds (mV)
Vg=-20V Vg=-16V Vg=-12V Vg= -8V Vg= -4V Vg= 0V
-30 -20 -10 0 10 20 30
0
100
200
300
Ids
(nA
)
Vg (V)
2mV 4mV 6mV 8mV10mV
ZnO nanowires show significant enhancement in mobility after surface passivation.
Q1D concentration ~ 9 x 107 cm-1 ; 3D concentration ~1.16 x 1018 cm3
Q1D carrier mobility ~ 1200 cm2/Vs
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ThermionicThermionic EmissionEmission
-1.0 -0.5 0.0 0.5 1.0-800
-600
-400
-200
0
200
400
600
I (nA
)
Vds (V)
290 K 333 K 373 K 428 K 473 K
Con
duct
ance
(nS
)
1000/T2.0 2.4 2.8 3.2 3.6
103
210
110
010
(c)
• Electric current was observed to increase monotonically with temperature.
• An effective energy barrier height of 0.3 eV is estimated from the thermionic emission model: I ~ exp(-φb/kT).
-
Top view of ZnO nanowire array embedded in AAM.
•Chemical vapor deposition is used to grow ZnO nanowires array.
•Electrical transport through individual nanowires is characterized with conductive AFM probes.
Vertical Nanowire Array
I-V characteristic of an individual vertical ZnO nanowire in AAM.
-
Scanning Surface Potential MicroscopyScanning Surface Potential Microscopy
Source Drain
Back gate
Vac
VdsSiO2
~
Vtip
sampletipdc VVV −=
acdc VVdzdC
F ⋅=
• The uniformity of nanowire and the property of electrode contact was studied using scanning surface potential microscopy by probing local electric potential distribution.
• Conductive AFM tip is biased with a DC signal and an AC signal. AC signal is used to drive tip resonant vibration and DC signal can be controlled by feedback loop to trace the surface potential on sample.
-
Surface Potential and Tip GatingSurface Potential and Tip Gating
Topography and surface potential image of a ZnO nanowire FET.
Cross section analysis of surface potential image gives the potential drop on device: VAB = 0.26 V; VBC = 0.30 V; VCD = 0.89 V
Source
Drain
Scanning direction
Vds
Vg
-1.0 -0.5 0.0 0.5 1.00
1
2
3
4
5
Ids
(nA
)
Time (s)
-
Back gating Back gating vsvs tip gatingtip gating
Source DrainNanowire
Back gateVg
Vds
SiO2
Source Drain
Back gate
Vg
Vds
SiO2
-10 -5 0 5 10-1200
-1000
-800
-600
-400
-200
0
200
Vds (V)
I (nA
)
Vbg=-20 VVbg=-10 VVbg=0 VVbg=10 VVbg=20 V
-10 -5 0 5 10-500
-400
-300
-200
-100
0
I (nA
)
Vds (V)
Vtg=-20VVtg=-10VVtg=0VVtg=10VVtg=20V
• Electrical transport results are obtained for both AFM tip gating and Si back gating.
• It is observed that negative tip gating has significant local depletion effect on FET and increases the height of effective barrier for electron conduction. However, positive tip gating does not strongly enhance the conductance of NW.
-
Back gating Back gating vsvs tip gatingtip gating
• Gate potential affect conductance of NW by band bending.
• Si Back gate potential affects the entire FET, but AFM tip gate potential only affects the local region and creates an energy barrier at negative Vg.
Back gating Tip gating
EFDrai n SourceNW
(d)
φbs EF
φbd
Von
Drai n SourceNWEF
Von
Drai n Source
φbt
NW
φ bs
Ecnegat i ve Vg
posi t i ve VgEF
-
Chemical SensingChemical Sensing
Adsorbed molecules(H2,O2,NO2,NH3,CO, C2H5OH,…)
Nanowire
Current transport
Electrons
0 50 100 150 200 250 3000.0
0.2
0.4
0.6
∆G/G
0
NW radius (nm)
O2
Source Drain
Gate
Nanowi r e channel
Depletion region
increases with reduced nanowire radius.
S = ∆G/GoSensitivity:
-6 -4 -2 0 2 4 6-6
-4
-2
0
2
4
Vds (V)
I (µ
A)
0ppm 10ppm 20ppm
-10 -5 0 5 10 150.00.51.01.52.02.53.0
I (µA
)
Vg (V)
0 ppm 10 ppm 20 ppm
Vds= 5 V
NO2
-
NONO22 OxidingOxiding SensingSensing
• Response time is defined as time when conductance drops 1/e from maximum.
• Response time decreases with increasing concentration.
0 100 200 300 400
0
200
400
600
800
1000 Start of NO2
1 ppm
20 ppm10 ppm
5 ppmCur
rent
(nA
)
Time (s)
2 ppm
0 5 10 15 200
10
20
30
40
Res
pons
e tim
e (s
)
NO2 concentration (ppm)
T=A×N -0.6
-
Gate Tunable SensitivityGate Tunable Sensitivity
-8 -4 0 4 80.0
0.2
0.4
0.6
0.8
1.0
Vg (V)δG
/G0
Sensitivity to5 ppm NO 2
bVa
Sg +
∝
-6 -4 -2 0 2 4 6
-0.4
-0.2
0.0
0.2
0 ppm0.2 ppm0.4 ppm0.6 ppm
Vg = -5 V
I (µA
)
Vds (V)
Chemical Sensing properties of nanowire FET largely depend on gate potential.
Gate adjusts the position of the Fermi level of the channel, affect the surface processes.
à Gate voltage tunes the detection range.
Z. Fan and J. G. Lu, APL ( 2005).Z. Fan, et al, APL (2004).
-6 -4 -2 0 2 4 6
-8
-4
0
4
8
Vds (V)I (
µA)
0 ppm10 ppm20 ppm30 ppmVg = 30 V
-6 -4 -2 0 2 4 6
-1.2
-0.8
-0.4
0.0
0.4
Vg= 0 V
0ppm1ppm2 ppm5 ppm10 ppm20 ppm
I (µA
)
Vds (V)
NO2
-
Electrically Refreshable SensingElectrically Refreshable Sensing
0 200 400 600 800 1000 1200
200
400
600
800
1000
1200
1400
T = 300 K
I (n
A)
Time (s)
10 ppmNO2
T = 453 K
Vg= 0 V
Vg= -60 V
-200 0 200 400 600 800 1000 1200 1400 1600-150
0
150
300
450
600 10 ppmNO2
I (nA
)
Time (s)
T = 300 K
At room temperature, chemisorbed molecules are quite difficult to be desorbed.
Thermal desorption and ultra-violet illumination are conventional ways to refresh nanowire.
For oxidizing gas, a strong negative gate field greatly facilitates desorption and is capable to quickly refresh nanowire sensor.
Z. Fan and J. G. Lu, APL (2005).
-
DistinguishabilityDistinguishability
0 20 40 60 80 1000
20
40
60
80
100
2.5 ppm NO2,k=0.12
I (nA
)
Time (s)
5 ppm NO2,k=0.10
10 ppm NO2,k=0.16
10 ppmNO2
recoveryregion
Vg =-20 V Vg =0 V
800 850 900 950 1000 1050
-40
0
40
80
120
160
I (nA
)
Time (s)
0 20 40 60 800
20
40
60
80
2% NH3,k=0.23
1% NH3, k=0.25
0.5% NH3 , k=0.27
I (nA
)
Time (s)
Temporal response of NO2 and NH3 to a negative gate voltage pulse demonstrates a potential distinguishable sensing.
-
Gate Refresh Voltage
• Different activation energy for NO2 and NH3adsorption.
• Distinguishable gate refresh voltage.
VgSiO2
p ++ Si
S D
Vds
-
Reducing Sensing PropertiesReducing Sensing Properties
0 1000 2000 3000 4000 5000-20
0
20
40
60
80
100
0.5%CO on
0.5%CO on
0.5%CO on
0.5%CO off
I (nA
)
Time (s)
T= 500K
20% O2 in
0.5%CO on
0.5%CO off
0.5%CO off
0 400 800 1200 160035
40
45
50
55
1% NH3off1% NH3off0.5% NH3off
1% NH3 on1% NH3on
I (nA
)
Time (s)
0.5% NH3 on
T=500K
Exposure nanowire to CO at 500K in O2 ambient increase nanowire conductance by reaction:
−− +→+ eCOOCO 2
Exposure nanowire to NH3 at 500K in Ar ambient increase nanowire conductance also, but by electron direct transferring from NH3 to nanowire.
Ef
EcEf
500 K300 KEv
Ec
Ev
µNH3 µNH3
-
Optical Property of Optical Property of ZnOZnO
Photoluminescence and photoconductivity spectrum of single ZnO nanowire
Z. Fan, et al., APL (2004).
200 400 600 800 1000
0
40
80
120
160
Cur
rent
(nA
)
Input optical wavelength (nm)
Vds= 0.2 V
200 400 600 800
100
200
300
400
500
600
700
Wavelength (nm)
PL
inte
nsity
(a. u
.)
0 50 100 150 200
4
8
12
16
20
24
28
0 20 40 60 80
0
20
40
60
80
Turn on laser
Cur
rent
(nA
)
(min)
Turn off laser
Cur
rent
(nA
)
Time (s)
Vacuum
Air
Due to the adsorption of oxygen:Due to the adsorption of oxygen:OO22 + + ee ?? OO22--
Td ~ 8 s in airTd > 1 hr in vacuum(Td is defined as the time for current drop from Imaxto Imax/e)
-
PhotoconductivityPhotoconductivity
-2 -1 0 1 2 3-20
0
20
40
60
80
100
120
140
160
-4 0 4 8 12
0
10
20
30
Cur
rent
(nA
)
Gate Voltage (V)
Cur
rent
(nA
)
Drain voltage (V)
Without 633nm illumination
With 633 nmillumination
Without 633nm illumination
With 633nm illumination
• Light illumination results in an increase in nanowire carrier concentration and conductance, and a slight decrease in mobility.
• Power law dependence of photocurrent to the input optical power is due to the finite number of impurity states.
(b)75
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
0
15
30
45
60
Cur
rent
(nA
)
Laser power (mW)
Vds= 2 V
I=A×P0.43
-
PhotoluminescencePhotoluminescence
Blue-shift as diameter decreases
Diameter dependence
340 360 380 400 420-2000
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
22000
24000
26000
392nm
383nm
Inte
nsity
/ a.
u.
Wavelength/ nm
Dia(100-200nm) Dia(20-100nm) Dia(6-20nm)
381nm
Temperature dependence
LT PL spectroscopy indicate the nanowiresare of high crystal quality.
(data taken at Göttingen University)
2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
300 K
200 K
100 K
12 K
Inte
nsity
/ a.
u.energy / eV
-
Polarization Dependent Polarization Dependent PhotodetectionPhotodetectionLight
NW
E||
E?
• Nanowire conductance is minimized when the incident field is polarized perpendicular to the long axis.
• Such anisotropy has potential application for polarization dependent photodetector and optical gated switch.
Z. Fan et al., APL (2004)
30 60 90 120 150 180 210
600
800
1000
1200
1400
1600
365 nm UV
Vds
= 2 V
Vds
= 5 V
Polarization Angle (degree)
Cur
rent
(n
A)
E
E
broadband light
Nanowire diameter
-
Summary on Summary on ZnOZnO NanowireNanowire
Single crystal ZnO nanowires are synthesized and configured as field effect transistors. Electrical transport studies show ZnO nanowires are n-type semiconductor.
Scanning surface potential microscopy demonstrates that electrical property of the nanowire is uniform.
Chemical sensing results indicate the future application of ZnO FET as a self-contained, gate tuned, and gate refreshable chemical sensor.
Optical studies show its potential applications in nanoscale optoelectronics.
-
Gallium OxideGallium Oxide
nn Ceramic metal oxide Ceramic metal oxide nn n n --type semiconducting at high type semiconducting at high
temperature temperature nn wide bandgap ~ 4.9eVwide bandgap ~ 4.9eVnn Carrier concentration ~ 10Carrier concentration ~ 101313 cmcm--33 at at
10001000°°CC(M. Fleischer and (M. Fleischer and H.MeixnerH.Meixner, , J. J. ApplAppl. Phys.,. Phys., 74, 300, 1993)74, 300, 1993)
nn BaseBase--centered monoclinic structurecentered monoclinic structurenn a =12.23 a =12.23 ÅÅ, b =3.04 , b =3.04 ÅÅ, c =5.8 , c =5.8 ÅÅ
nn Potential Applications:Potential Applications:nn High temperature gas sensorHigh temperature gas sensornn Optoelectronics deviceOptoelectronics device
-
Electron MicroscopyElectron Microscopy
nn Dimension:Dimension: length~10length~10--3030µµm, m, diameter~20diameter~20--200nm200nm
nn VLS (VaporVLS (Vapor--LiquidLiquid--Solid) catalytic growth Solid) catalytic growth mechanismmechanism
nn BaseBase--Centered Monoclinic crystalline structureCentered Monoclinic crystalline structurenn Several growth direction can be observed:Several growth direction can be observed:
A.A. [111] spacing ~0.25nm[111] spacing ~0.25nmB.B. [001] spacing ~0.55nm[001] spacing ~0.55nmOthers [200], [Others [200], [--130] 130] ……
Au
A
15o
B
P. Chang et al., APL (2006)
-
XRD & PL CharacterizationsXRD & PL Characterizations
30 40 50 60 70 80
0
1000
(510
)(-11
1)
(403
,512
,-71
2)
(600
,-31
2,11
2)
(-31
1,-4
02,2
02)(0
02,-
202)
(111
)
(-40
1,40
0)
Ga2O3 nanowires
JCPDS 43-1012
Inte
nsi
ty (a
.u.)
2θ (degree)
• CuKα (λ=1.54 Å) source• As grown nanowire sample matches the β-Ga2O3diffraction pattern• Single phase• The strongest peak is (111)
300 350 400 450 500 550
0
30000
60000
Inte
nsi
ty (a
.u.)
Wavelength (nm)
100K 150K 200K 250K 300K
414nm
• Blue-Green broad emission is contributed by Gallium-oxygen vacancy pair (acceptor-donor) formed trapped excitons
(T. Harwing, et al., J. Solid State Chem., 24, 255, 1978)(Vasil’tasiv et al., Ukr. Fiz. Zh., 33, 1320, 1988)
νh++′→+ •oGaox
ox
Gao V )V ,V (V )V ,V (
-
nn Intrinsic:Intrinsic:It shows very low conductance (insulating, high It shows very low conductance (insulating, high resistance~10resistance~101616ΩΩ) at room temperature ) at room temperature
nn nn--type doping:type doping: SbSb5+5+, W, W6+6+, , etcetcnn pp--type doping:type doping:
Zn atoms can be acceptorsZn atoms can be acceptorsnn Ionic crystal radii size:Ionic crystal radii size:
ZnZn2+ 2+ : 0.074nm, Ga: 0.074nm, Ga3+ 3+ : 0.062nm : 0.062nm (R. D. Shannon, (R. D. Shannon, ActaActa CrystallographicaCrystallographica, A32, 751, (1976), A32, 751, (1976)
ooGa O2V 'Zn22ZnO ++=••
nn Setup (diffusion doping):Setup (diffusion doping):Pure Zn powder in Pure Zn powder in ArAr inert ambient, inert ambient, 450? for 15 minutes
Extrinsic DopingExtrinsic Doping
-
Transport Properties (ITransport Properties (I--V)V)
-20 -10 0 10 20
-10
0
10
20
30
Cu
rren
t (p
A)
Bias Voltage Vds (Volt)
Vg= 30V Vg= 0V Vg=-30V
• Improved transport properties - up to 3 order increase in magnitude
• p-type semiconducting behavior - from gate voltage dependence
Vds
VgSiO 2
p ++ Si
)/2ln(2(th)V 0g
rhep
πεε×=
ds0V2)/2ln(
VI
πεεµ
rhLdd
gh ×=
Carrier concentration
Carrier mobility
(R.Martel et al., Appl. Phys. Lett. , 73, 2447, 1998)
-
Transport Properties (ITransport Properties (I--Vg)Vg)
-80 -60 -40 -20 0
0
2
4
6
8
Cu
rren
t (n
A)
Gate Voltage Vg (Volt)
dI/dVg= -0.988x10-9 A/V
Vg(th)= -74.7 V
ex. h = 200nm, r = 60nm, L = 2.12µm, ε = 3.9 (permittivity of SiO2)
p = 5.3×108 cm-1 (4.6×1018 cm-3) µh = 3.5×10-2 cm2/Vs
Vg
Source Drain
Back Gate
Vds
NW
Transconductance dI/dVg = -0.988×10-9 A/V
Threshold VoltageVg(th) = -74.7 V
-
-40 -20 0 20 40
100
200
300
400
Vds = 2.0 V
I (pA
)
Vg (V)
•(b)
As-grown Fe2O3 nanobelts are configured as field-effect transistors showing n-type behavior.
For the p-type Zn doping, the nonlinear I-V arises from the Schottky contact formation due to nanobelt Fermi level shifts as a result of doping.
-6 -4 -2 0 2 4 6
-900
-600
-300
0
300
600
900
I (pA
)
Vds
Vg = 10 VVg = 0 VVg = -10 V
EFEc
Ni Fe2O3
φφ
NiFe2O3
Vacuum
p-type Zn doping
EF EVNiFe2O3
φNi
VacuumφFe2O3
Ec
-6 -4 -2 0 2 4 6 8
-80
-40
0
40
80
-120 -80 -40 0 4045505560657075
I (nA
)
Vg (V)
Vds=5VI (nA
)
Vds (V)
Vg=-100 VVg=-50 VVg=0 VVg=100 V
Z. Fan et al., APL (2005)
Extrinsic Doping Extrinsic Doping -- FeFe22OO33 NanobeltsNanobelts
-
““Small wonders, endless frontiersSmall wonders, endless frontiers””“…nanotechnology will be central to the next epoch of the information age, and will be as revolutionary as science and technology at the micron scale have been since theearly ’70s.” –– John Armstrong, 1991John Armstrong, 1991
Vo
Vi1 VcVi2
Vcc
AAO template
Bottomelectrodes
Top electrodes
Nanowires
SiO2p ++ Si
S D
Vg Vds