Post on 02-Feb-2016
description
Silvano De Franceschi
Laboratorio Nazionale TASC INFM-CNR, Trieste, Italy
http://www.tasc.infm.it/~defranceschis/SilvanoHP.htm
Nanowire growth and properties Integration with Si technology Manipulation and NEMS Single electron transport Gate-controlled proximity supercurrent
Outline
goldparticle
liquidAu-InPeutect
vapor
nano
wire
time
Catalytic (VLS) crystal growth
Semiconductor nanowires
Key features:
• nanoscale diameter (few to 100 nm)
• High aspect ratio (1-100 micron long)
• Versatility in composition
heterojunctions
p-n junctions
hollow
Possible nanowire structures
coaxial
10 nm
InP wire on SiO2
[111]
• Zinc Blende • [111] direction
Before growth
Bakkers et al., JACS 2003, 125, 3440
Hollow core wall
5 nm
wall
Zinc Blende crystal structure
200 nm
InP Tubes
50 nmCoaxial wires
Group III modulationPosition (nm)
Cou
nts
20100
600
400
200
0
Ga
P
In
InP
GaP
Heterojunctions
Group V modulation0 10 20 30 40 50 60 70
0
50
100
150
200
250
300
350
Sec
tion
leng
th (
nm)
Growth time (sec)
GaAs
GaP
GaP GaPGaP GaP
GaAs GaAs GaAsAu
100 nm
GaP: 1.8 nm/sec
GaAs: 5.0 nm/sec
Björk et al., NanoLetters 2, 87 (2002)
InAs
InP
InAs
• Almost atomically sharp interfaces • No strain-induced dislocations (stress can relax at the surface)
(001
)Heterostructures nanowires
(Samuelson’s group – Lund)
(Chemical beam epitaxy, MOVPE)
Epitaxial InP wires on Ge
5 m
InP
Ge
-10 -5 0 5 10-4
-2
0
2
4
I subs
trat
e (A
)
Vtip
(mV)
I
The InP/Ge heterointerface provides a low-resistance Ohmic contact between wire and substrate
HR TEM
Conducting AFM
More recently: epitaxial InP on Si!
Integration of III-V devices with Si technology
[See also Mårtensson et al.,
Nano Letters 4, 1987 (2004)]
Vsd (mV)
I (m
V)
Silicon
Gate
Source
Drain
III-V
Vertical transistor
Silicon
Source
Drain
p
n
Nano LED
III-V devices on silicon
NANOWIRE LED:Gudiksen et al., Nature (2002)NANOWIRE LASERS:Johnson et al., Nature Materials (2002)Duan et al., Nature (2003)
Enhanced speed Enhanced transconductanceSmall footprint
More on Nanowire devices…
Law et al., Science 305, 1269 (2004).
Nanowire optical waveguides
Dick et al., Nature Materials 3, 380 (2004).
Nanowire trees
Cui et al., Science 293, 1289 (2001).
Nanowire biosensors
AFM manipulation
Electrically-driven nanowire cantilever
Nanowire “string”
After wet etching…
following subsequent AFM manipulation….
Vs-d
Vgate
SiO2
Si p+
Device fabrication:- wires deposited on p-type
Si wafer with a 250-nm-thick surface oxide
- Ti/Al contacts defined by e-beam lithography
Low-temperature transport in semiconductor NWs
InP & InAs n-type nanowires
Diameter: 25 – 140 nm
Length: 2 – 20 m
Single-electron tunneling in InP nanowires
VS
D [m
V]
Vgate [mV]
+4
-4
0
0 -100 -200 -300 -400
L~600 nmT~350 mKEc~1 meV
• Differential conductance (black: low, white: high);• Many diamonds visible. Not so regular, but very stable and reproducible.• Single & Multiple(probably two)-island behavior
Typical island size:~100 nm
L
-100 -90 -80 -70 -60 -50 -40 -30
0.00
0.01
0.02
0.03
Co
nd
ucta
nce
(e
2 /h)
Gate voltage (mV)
B = 31 mT B = 0.5 T
V (V
)
Vg (mV) Vg (mV)
gBBg = 1.5 ± 0.2
InP-nanowire quantum dot: Zeeman spin splitting
E
N N+1
Tunable Quantum Dots
top gates
source
drain
Side gates
Few-electron quantum dots in InAs/InP nanowires
Björk et al., Nano Lett. 4, 1621 (2004)InAs QD
InP barriers
S SN (1-D or 0-D)
Kasumov et al, Science 284 (’99)Morpurgo et al., Science 286 (’99)Buitelaar et al., PRL 89 (’02); PRL 91 (‘03)Jarillo-Herrero et al. (unpublished)
Superconductor Nanowire Superconductor
For T < 1.2 K
Only a few experiments done on similar hybrid systems based on carbon nanotubes:
Superconducting contacts => Proximity effect
Low contact resistance => no Coulomb blockade
InAs nanowire devices
500 nm500 nm
Ti(10 nm)/Al(120 nm)
Lsd = 60 – 500 nm
I+
I-
V+V-
I+
I-
V+V-
Vgate
SiO2
Si (p+)
4-point contacts:InAs [100]
Lsd
W
sour
ce
drai
n
Device resistances: 0.4 – 4 K
-150 -100 -50 0 50 100 150
-40
-20
0
20
40
IR
IC
V
(V
)
I (nA)
Supercurrent in InAs nanowires
T = 40 mK
IC = 136 nARN = 417 ICRN = 60 V ~ 0/e
Hysteretic behavior due to strong capacitive coupling between source and drain
0 4100
101
102
I C(n
A)
RN(k)
(90 % device yield!)
Enhanced conductance for 20<V<20
High contact transparency (T~75%)
0.0 0.4
0
1
100 mT
0 mT
I (A
)V (mV)
B=0
20/e
Multiple Andreev reflection
0.0 0.5
1.0
1.5
RNdI
/dV
V2
V3
V1
V (mV)
0.0 0.40
1
100 mT
0 mT
I (A
)V (mV)
-2 -1 0 1 2
1.0
1.5
RNdI
/dV
V/20
From 3 different devices:
Peaks at Vn=20/ne:V1=20/eV2= 20/2eV3= 20/3e
Normal Super
N S
T < Tc
And
reev
ref
lect
ion
in a
S-N
junc
tion
Field-effect control of the supercurrent
Supercurrent fluctuations correlate with normal-state universal conductance fluctations
-2 -1 0 1 2
-10
0
10
-71 V -61 V -50 V -40 V -30 V -20 V -10 V 0 V
V
(V
)
I (nA)
Vgate
-70 -60 -50 -40 -30 -20 -10 0 10 20 30
-2
-1
0
1
2
Vg (V)
I (n
A)
0 5 10 15 20
dV/dI (kOhm)
#S1_B (Iv_8_14 (1026; 1027)
246810
GN (e
2/h)
-70 -60 -50 -40 -30 -20 -10 0 10 20 30
-2
-1
0
1
2
Vg (V)
I (n
A)
0 5 10 15 20
dV/dI (kOhm)
#S1_B (Iv_8_14 (1026; 1027)
246810
GN (e
2/h)
-70 0-2
0
2I (
nA)
Vg (V)0 30 k
2
4
GN (2
e2/h
)
Electron transport through the nanowire is diffusive and phase coherent
=> mesoscopic Josephson junctions
First Josephson Field Effect Transistors:
Takayanagi et al., PRL (1985). Kleinsasser et al., Appl. Phys. Lett. (1989). Nguyen et al., Appl. Phys. Lett. (1990).
-40 0 40 80 120-60
-30
0
30
60
-4
4
N = 0
-3
-2
3
2
1
V
(V
)
I (nA)
w/o rf rf = 4.836 GHz
No.6B
-1
V=10 V
V= (/2e)rf
= 2.068 V for 1 GHz
“Quantized voltage steps depending on RF frequency” 0 5 10
0
10
20 No.6B 2.068 uV/GHz
V (V
)
rf (GHz)
AC Josephson effect: Rf irradiation => Shapiro steps
Shapiro steps: rf-power dependence
200 400
-60
-40
-20
0
20
40
60300 600 900
-80
-60
-40
-20
0
20
40
60
80
I (n
A)
Irf (arb.)
0 001 1 1
-1 -1 -1
23
45
67
8
-2-3
-4-5
-6-7-8
0
1
2
3
4
5
-1
-2
-3
-4
-5
rf = 2 GHz rf = 4 GHz rf = 5 GHz
IN ~ N-th order Bessel function with IC,fit = 34 nA > IC,exp = 26 nA
IC
IN=1
IN=2
IN=3
IN=4
(a) (b) (c)
0 2 4 6 80
5
10
15
20
25
In
=4 (
nA
)
Iac
(arb.) Bessel
0
5
10
15
20
25
In
=3 (
nA
)
0
5
10
15
20
25
In
=2 (
nA
)
n2
0
5
10
15
20
25
In
=1 (
nA
)
0
5
10
15
20
25
Ic (n
A)
Sam. #6B, rf = 5 GHz
Ic,fit
= 34 nA
Gate-controlled SQUID
Jorden van DamFloris ZwanenburgL. GurevichYong-Joo DohLeo Kouwenhoven
Erik BakkersAarnoud RoestLou-Fe Feiner
Philips Eindhoven:
Epitaxial III-V nanowires on Ge [Nature Materials 3, 769 (2004)]Nanowire SET [Appl. Phys. Lett. 83, 344 (2003)] Nanowire JOFET [Science 309, 272 (2005)] Nanowire SQUID [unpublished]
References
Collaborators