林永昌. outline band structure of graphene chemical doping electrical transport theoretical...
TRANSCRIPT
林永昌
Outline
• Band structure of graphene• Chemical doping• Electrical transport• Theoretical explanation• Conclusion
Band structure of graphene
(near k point, linear relation)
M. I. Katsnelson, Mater. today 10, 20 (2007)J. B. Oostinga et al., Nature mater. 7, 151 (2008)
The unit cell consisting of two atoms.
Chemical doping
M. S. Strano, Science 301, 1519 (2003)
Diazonium: p-type doping
Electrical transport (p-type)
pristine
doped
annealing
Suppression of electron conduction.hole
electron
Electrical transport (n-type)
Suppression of hole conduction.
electronhole
Density of state in graphene
Theoretical explanation nonequilibrium Green’s function formalism (NEGF)
Dopant-induced potential barrier in the grpahene channel:
Fluctuating potential (Short-range scattering)
Homogeneous barrier
Coulombic potential barrier(long-range scattering)
N-type doping hole electron
Multiple reflections
Effect of electrode properties
E=0 E=UB Gds (min)
hole electron
NH3 plasma experiment
1200 1400 1600 2600 2700
Intensity (a. u.)
Raman shift (cm-1)Vg (V)
G (μ
S)1583
1587
1588
-10 0 10 20 30 40
160
200
240
280
-20 -10 0 10 20
60
80
100
120
-40 -20 0 20 400
20
40
60
(a)
(b)
(c)
(d)Pristine (p-type doping)
NH3 plasma 120sec(n-type doping)
prinstine
60sec
120sec
Some transport data
-2 -1 0 1 2
-4
-2
0
2
4
Ids
(nA
)
Vds (mV)
-90 -60 -30 0 30 60 90
4
8
12
16
20
Ids
(nA
)
Vg (V)
T=2.5KVds = 5mV
T=2.5KR=400Kohm
-20
0
20
40
60
80
100
120
140
160
180
200
220
240
260
280
300
320
340
360
380
400
420
Inte
nsity
(a.
u.)
1 200 1 400 1 600 1 800 2 000 2 200 2 400 2 600 2 800 3 000Raman shift (cm-1)
264
2.8
158
7.6
E valuation Copy
1587.6 / W=10.38
2642.8 / W= 27.9
DE A7 (D17-S19)
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
-40
-20
0
20
40
Ids
(nA
)
Vds (mV)
-90 -60 -30 0 30 60 90
0
10
20
30
40
50
60
Ids
(nA
)
Vg (V)
T=2.5KVds = 0.5mV
T=2.5KR=14Kohm
0
50
100
150
200
250
300
350
400
450
Inte
nsity
(a.
u.)
1 200 1 400 1 600 1 800 2 000 2 200 2 400 2 600 2 800 3 000Raman shift (cm-1)
264
3.8
159
0.1
E valuation Copy
1590.07 / W= 13.4 2643.8 / W= 29.83
DE A7 (D17-S16)
Conclusion• The doping–induced conductance asymmetry is
caused by a combination of the neutrality point misalignment at the electrode/cannel interface and the nonconstant DOS of the graphene electrodes.
• Homogeneous potential cause conductance suppression of only one carrier type, while inhomogeneous potential cause both type.
• If metal-induced doping of graphene electrodes occurs, the conductance exhibits asymmetry even the channel is intrinsic.
Thank you