Semiconductor Nanowires - Scuola Normale Superiore di Pisahomepage.sns.it/heun/Talk-ZJU.pdf · • Semiconductor Nanowires • Quantum Hall physics, solid-state interferometry •

Stefan Heun

NEST, Istituto Nanoscienze-CNR and

Scuola Normale Superiore, Pisa, Italy

Semiconductor Nanowires

Leaning Tower in Pisa

Pisa and Hangzhou: Twin towns since 2008

Institute of Nanoscience-

National Research Council

• NEST (Pisa)

• NNL (Lecce)

• S3 (Modena)

• Adm. Genova

Research Activities at NEST

• SAW-driven electronic dynamics, lab-on-chip

• THz quantum cascade lasers

• Semiconductor Nanowires

• Quantum Hall physics, solid-state interferometry

• Hybrid and superconducting structures

• Quantum dots

• Graphene and artificial graphene

• Nanobiotechnology







• Quantum dots



Scanning gate Microscopy

AFM at 300 mK at 9 Tesla







• Quantum dots



Compositional Mapping of QDs

XPEEM with synchrotron

radiation







• Quantum dots



Hydrogen on Graphene

UHV variable temperature STM







• Quantum dots



Outline

• III-V Nanowires at NEST: Growth and

Research

• Pd-assisted Growth of InAs NWs

Outline


Research


People

• CBE Growth: D. Ercolani, Ang Li, and L. Lugani (NEST-SNS),

Lucia Sorba (NANO-CNR)

• NWs Devices: S. Roddaro, A. Pescaglini, A. Pitanti, F.

Beltram (NEST-SNS) and A. Tredicucci (NANO-CNR)

• Hybrid Devices: P. Spathis, S. Biswas and F. Giazotto (NANO-

CNR)

• TEM: F. Rossi, L. Nasi, G. Salviati (IMEM-CNR), V. Grillo

(NANO-CNR), M. Gemmi (IIT@NEST)

• Pd:InAs: S. Heun (NANO-CNR), B. Radha and G. Kulkarni

(JNCASR, Bangalore)

CBE Facility

Riber Compact-21

CBE system

Group III :

TMIn, TEGa, TMAl

Group V :

TBAs, TBP, TDMASb,

TMSb

n-doping: TBSe

Hybrid nanodevices

InAs NW

Josephson Junctions

S. Roddaro et al.,

Nano Res. 4 (2011) 259.

F. Giazotto et al.,

Nature Physics, in press,

arXiv:1102.4207.

InAs NW - Vanadium

SQUID

Probing surface potential

using RTN

Electron

occupation of

defects on the

surface of NWs

is a sensitive

measure of the

local surface

potential.

J. Salfi et al., ACS Nano 5 (2011) 2191.

In collaboration with Harry Ruda’s group from U Toronto, Canada

Single

trap

Two traps

InAs/InP axial

heterostructured NWs

High-T single-electron devices

Tuning of dot energy spectrum

with electric dipole moment

InAs/InP NW QD

CB up to 50K

S. Roddaro et al.,

Nanoletters 11 (2011) 1695.

AlAs nanowiresTEM Analysis

Very fast oxydationAng Li et al., Crystal Growth & Design, submitted.

AlAs-GaAs CS NWs

Ang Li et al., Crystal Growth & Design, submitted.

InSb/InAs NWs

InSb: <110> zone axis, InAs: <2-1-10> zone axis

HR TEM Analysis

D. Ercolani el al. Nanotechnology 20, 505605 (2009)

A. Pitanti et al., Phys. Rev. X, submitted.

InAs-InSb NWs

as RT n-n diodes

Broken band gap alignment (type III)

leads to rectifying behaviour.

InAs-InP-InSb NWs

Insertion of an InP layer strongly enhances the

rectification.

Room T

HRTEM

A. Pitanti et al., Phys. Rev. X, submitted.

Outline


Research


Motivation

• NWs have a high potential for electronic, optoelectronic

and sensor applications

• Au is the commonly used catalyst: inert and stable

• Pd is an attractive candidate: good ohmic contacts to

semiconductors

• Pd has a high molecular connectivity useful for bio-

sensing application

• Pd shows a high hydrogen response

• Pd nanoparticles: direct-write electron beam resist

Experimental details

• Pd catalysts: few nm-thick spin coated Pd(SC8H17)2 and

Pd(SC16H33)2 films and thermolysis at 300oC for 30 min

-> 5-15 nm sized Pd particles

• Deoxidation at 520oC with TBA -> Pd particles davg=35nm

• InAs NWs are grown by CBE with TMIn (0.1-0.45 Torr) and

TBAs (1-3Torr) MO precursors

• Tgrowth: 300-360oC

• Growth time: 2 and 4 hrs

InAs substrate orientation(100)

(111)A

(111)B

NWs density is 14±2 mm2

<011> directions under 55.5±2.3°=> <111>

S. Heun et al., Crystal Growth & Design 10 (2010) 4198.

RHEED patterns

Calculated diffraction

patterns

Zincblende NWs

Wurzite NWs

Exerimental observed

patterns


NWs: smooth and

zigzagged sidewalls

Triangular base with {112}A

side facets

Most of the triangles are

oriented along [-211]

Few oriented [2-1-1] : insertion

of rotation stacking fault

2D growth but not close to the

NWs (MO capture )

Tapered wires => small diffusion

constant

HRSEM


HAADF TEM

Triangular section with {211}-type side facets


EDX: catalyst particle study

Both catalyst particles are crystalline : BCC B2 structure

Composition Pd:In 1:1

InPd

No Pd in the NWs

S. Heun et al., Small 6 (2010) 1935.

Growth on patterned

substrates

Pd(SC16H33) 2 is

negative-tone direct-

write e-beam resist


HRTEM of zigzagged NWs

[2-1-1] direction

[1-10] direction

Extended defects: stacking faults

FFT

S. Heun et al., Small 6 (2010) 1935.

Geometrical Phase AnalysisZigzagged NWs Smooth NWs

r

o

Rotation maps

Radial axial strain maps

X= [01-1] Y=[111]


NWs: smooth and

zigzagged sidewalls

Triangular base with {112}A

side facets

Most of the triangles are

oriented along [-211]

Few oriented [2-1-1] : insertion

of rotation stacking fault

2D growth but not close to the

NWs (MO capture )

Tapered wires => small diffusion

constant

HRSEM


NW distributionGrowth rates:

3.23nm/min 3.82nm/min24nm

40nm

32nm

57nm

30nm

w

w

w Lrdt

dL

for 12

S. Heun et al., Small 6 (2010) 1935.

Bimodal distribution

330C


3.23nm/min 3.82nm/min24nm

40nm

32nm

57nm

30nm

48nm

w

w

w Lrdt

dL

for 12

S. Heun et al., Small 6 (2010) 1935.


330C

340C


3.82 nm/min 3.23 nm/min24nm

40nm

32nm

57nm

30nm

48nm

w

w

w Lrdt

dL

for 12

S. Heun et al., Small 6 (2010) 1935.


330C

340C


3.82 nm/min 3.23 nm/min

w= 17 ± 3 nm; = 1.2 nm min-1

Model by J. Johansson et al. J. Phys. Chem 109, 13567 (2005)

24nm

40nm

32nm

57nm

30nm

48nm

S. Heun et al., Small 6 (2010) 1935.


330C

340C

HRTEM: catalyst particle study

Particle is smooth

and 0.6 aspect ratio

Particle is more faceted

and 0.5 aspect ratio

In

S. Heun et al., Small 6 (2010) 1935.

Zigzagged NWs

• Periodic sawtooth faceting already observed for Si and

GaAs NWs.

• For III-V: faceting of sidewalls in alternating {111} and

{002} planes observed (Zou et al, Small 3 (2007) 389).

For not stable facets parallel to the growth

direction => Sawtooth faceting

(Ross et el. PRL 95, (2005) 146104)

Thermodynamic arguments suggest that

inward (outward) force induced by the liquid

catalyst particles favour the introduction of

the other facet = > zigzagged NWs

Zigzagged vs. smooth NWs

• Model of Ross suggests VLS growth mode for

zigzagged NWs.

• Period and amplitude of sawtooth should scale

with NW diameter

• Here: critical diameter

• Faceting of catalyst particles is generally

associated with the VSS growth mode.

• Smooth NWs grow in VSS mode.


• Zigzagged NWs from liquid catalyst particles

• Solid catalyst particles => smooth sidewalls

• Two different growth mechanisms: VLS

(zigzagged) versus VSS (smooth)

• Size dependence of the melting T: small

particles are liquid while large are solid


• This model naturally

explains the observed

bimodality of the tip-

diameter distribution

• Variation temperature

of 10K => 20nm of

the critical diameter

24nm

40nm

32nm

57nm

30nm

48nm

Summary

• Pd-assisted growth of InAs NWs.

• Two distinct classes of NWs: smooth and

zigzagged.

• Bimodal NWs distribution: above (below) a critical

diameter NWs are smooth (zigzagged)

• Zigzagged NWs grow from liquid (VLS) particles

while smooth NWs grow from solid (VSS) particles.

• InAs NWs on patterned substrates by employing

Pd(SC16H33)2 as a direct-write e-beam resist.

Documents

Semiconductor Nanowires - Scuola Normale Superiore di Pisahomepage.sns.it/heun/Talk-ZJU.pdf · • Semiconductor Nanowires • Quantum Hall physics, solid-state interferometry •