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