Fabrication and applications of semiconductor nanostructures

Lucia Sorba

Istituto Nanoscienze-CNR

NEST (Pisa) L. Sorba

NNL (Lecce) G. Gigli

S3 (Modena) E. Molinari

Adm. Genova (with Nano, SPIN, IOM)

project admin, recruitment

Established on February 2010

www.nano.cnr.it

Institute of Nanoscience

Mission

The primary objective of the Institute is the fundamental study and the manipulation of systems at the nanometric scale. Its wide and multidisciplinary research activities include:

• Synthesis and fabrication of nanostructures and devices.

• Experimental and theoretical-computational studies of their properties and functionality.

• Knowledge and expertise are used to develop applications in several fields, from energy and environment to nanomechanics, nano(bio)technologies, and nanomedicine.

• Special attention to projects and advanced technologies of industrial interest.

Institute of Nanoscience

• Strong interaction with Universities

• 252 people (103 Young)

• Budget : 4.4 Milion Euro (projects)

3.5 Milion Euro (FFO-pers. incl)

• Equipment intensive >50Milion Euro

Outline

• Part I Semiconductor nanowires (Pisa)

• Part II Semiconductor nanostructures (Lecce)

Motivation

Semiconductor nanowires:

• strain issues: heterostructures

Motivation

Semiconductor nanowires:

• high control of density and

dimension

200nm

600 650 700 750 800 8500

20

40

60

NW

s C

ou

nt

(a.u

.)

Total Length (nm)2μm

85 90 95 100 105 1100

20

40

60

N

Ws

Co

un

t (a

.u.)

InSb Diameter (nm)200nm

(a)

(b)

(c)

(d)

Gold assisted growth

Bottom-up growth approach

InAs NWs

Diameter 20-100nm

Length up to 2-5 mm

Hexagonal cross section

Wurzite crystal structure

Doping n=1016 -1019 cm-3

Hybrid nanodevices

S-InAs NW-S High critical current

Ic=350nA

S. Roddaro et al., Nano Res., 3(9) (2010), 676–684 P. Spathis et al., Nanotechnology ,22, (2011), 105201 F. Giazotto et al., Nature Physics, 7, (2011), 857.

Vj

InAs NW embedded in a

SQUID

InAs/InP axial heterostructured NWs

High-T single-electron devices

Tuning of energy spectrum with electric dipole moment due to absence of surface depletion for InAs

S. Roddaro et al., Nano Lett 11, 1695-1699 (2011)

InAs/InP heterostructured NWs

High-T single-electron devices

S. Roddaro et al., Nano Lett 11, 1695-1699 (2011)

CB up to 50K

Enhancement of the level spacing

High-T single-electron devices

Electrostatic Spin Control in InAs/InP Nanowire Quantum Dots

L. Romeo et al , Nano Lett. 12, 4490–4494 (2012)

Single-triplet transition

InSb

Optoelectronics:

Direct band gap: Eg=0.17 eV l=7.3 mm

me* =0.014 me

me =7.7·104 cm2/V·s (300 K)

Quantum electronics:

Landé g-factor>60

Spintronics:

ZT=S2sT/k=0.6 at 673 K

Thermoelectricity: Large spin-orbit :

Majorana fermion detection

InAs-InSb NWs

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

HR TEM Analysis

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

InAs-InSb NWs

Strain maps as obtained by geometrical

phase

analysis.

InAs-InSb n-n heterojunction diodes

Low capacitance diodes (AttoFarad ) => improved cut off frequency for high speed operation detectors

A. Pitanti et al., Phys. Rev X 1, 011006 (2011)

InAs and InSb semiconductors are both n-type (fast) but has a broken-gap alignment of the electronic bands at the heterojunction.

Strong asymmetry in the I-V characteristic is expected

Schroedinger-Poisson 1D (bulk)

A. Pitanti et al., Phys. Rev X 1, 011006 (2011)

InAs-InSb n-n heterojunction diodes

Two-terminals device

-3 -2 -1 0 1 2 3

0

2

4

6

8

10

-2 -1 0 1 2

-0.4

-0.2

0.0

0.2

0.4

Cu

rre

nt (n

A)

VSD

(V)

VSD

(V)

Room-T

- Good rectification

- Roughly estimated cutoff

frequency (1/2pRC) ~ 300 THz

A. Pitanti et al., Phys. Rev X 1, 011006 (2011)

InAs-InSb

n-n heterojunction diodes

InAs-InP-InSb n-n heterojunction diodes

Room -T

InAs-InP-InSb

n-n heterojunction diodes

InP insertion reduces the direct conductivity and suppresses the thermionic contribution in reverse bias

Why NWs can be used for THz detectors?

• Very low capacitance devices

(~ attoFarad, almost not measurable)

• Planar technology for contacts, gates, antennas, etc.

• Can make arrays in a relatively easy way

• Quantum design is possible

InAs NW FET - THz detectors

10-11

10-10

10-9

10-8

10-7

-10 -5 0 5 10

0

0.5

1.0

1.5

2.0

-10 -5 0 5 10

Res

pon

siv

ity

(V

/W)

VG (V)

NE

P (

W/√

Hz)

(1)

(2)

(a)

(b)

Antenna orientation ┴ GHz source polarization Antenna orientation // GHz source polarization

M.S. Vitiello et al. Nano Letters, 12, 96 2012

NWFETsTHzdetectors

S

D

G

200 nm Broad band bow tie equiangular

antenna Log-periodic circular-toothed

antenna

M.S.Vi elloetal.NanoLe ers,12,96(2012)

Photoresponse*

Collaboration: D. Coquillant, W. Knap University of Montpellier II

Strong resonant photoresponse is

predicted in materials having plasma

damping rates < freq. incoming rad. and <

1/τ → High mobility required

Noise Equivalent Power

Improvements • 1-order of magnitude reduction of the NW resistance through pretreatments •log-periodic antenna properly resonant with the QCL frequency • Lapping of the substrate at sub-wavelength values (< 100 um) NEP : 6 × 10-11 W/Hz1/2

M.S Vitiello et al. APL 100, 241101, 2012

NoiseEquivalentPower

10-11

10-10

10-9

-3 -2 -1 0 1 2 3

Gate Voltage (V)

NE

P (

W/√

Hz)

Improvements

• 1-order of magnitude reduction of the

NW resistance through pretreatments • Design of log-periodic antenna properly resonant with the QCL frequency

• Lapping of the substrate at sub-wavelength values (< 100 um)

Ø NEP : 6 × 10 -11 W/ Hz1/ 2

Ø 1 order of magnitude increase

Responsivity

M.S Vitiello et al. APL 100, 241101, 2012

Highly sensitive, RT detection of THz QCL emission

M.S Vitiello et al. APL 100, 241101, 2012

Gate Voltage (V)

Res

ponsi

vit

y (

V/W

)

θ

(a)

(b)

D

G S

S

G

D

100 nm

G. Scalari et al. Laser & Photon. Rev. 3, No. 1–2, 45(2009)

Highly sensitive, RT detection of THz QCL emission

0

5

10

15

-3 -2 -1 0 1 2 30

0.5x10-5

Gate Voltage (V)

Resp

onsi

vit

y (

V/W

)

I sd (

A)

90°

60°

45°

0°

(c)

θ

(a)

(b)

D

GS

S

G

D

100 nm

G. Scalari et al. Laser & Photon. Rev. 3, No. 1–2, 45(2009)

M.S Vitiello et al. APL 100, 241101, 2012

AlAs – GaAs system: Lattice matched Widely used for bandgap engineering Theoretical results predicted direct band gap in AlAs Wurtzite structures ( A. De et al. Phys. Rev. B, 2010, 81,155210)

Potential optoelectronic applications

Motivation

AlAs-GaAs NWs

AlAs-GaAs NWs

Exp: a= 3.9±0.1Å and c=6.5±0.1Å

Th : a= 4.003Å and c= 6.537Å A. LI et al. 2011, Crystal Growth & Design, 11,

4053

Resonant Raman spectroscopy on single core-shell NW

Direct bandgap

𝛤7 symmetry to be resonantly enhanced @ 3.3 eV

𝛤8 symmetry is predicted for the lowest conduction band @ 1.971 eV

Stefan Funk, et al. ACS NANO 7, 1400

(2013)

A. De et al. Phys. Rev. B, 2010,

81,155210,.

PART I Conclusions

• Nanowire technology represents a powerful research and development platform for fundamental physics investigations (InAs, InAs/InP High-T single-electron devices, hybrid devices) .

• InSb/InP/InAs heterostructured NWs show potential interest due their outstanding electronic properties and InAs NW FET can be employed as THz detectors.

• AlAs Wurtzite NWs have direct band gap and then they have a potential interest in optoelectronic devices.

People • CBE Growth: D. Ercolani, U. Gomes, Ang Li and E. Husanu (NEST, Pisa).

• NWs Devices: S Roddaro, A. Pescaglini, A. Pitanti, L. Romeo, F. Beltram , M. Vitiello and A. Tredicucci (NEST. Pisa)

.

• Hybrid Devices: P. Spathis, S. Biswas and F. Giazotto (NEST, Pisa)

.

• TEM: F. Rossi, L. Nasi, G. Salviati (IMEM-CNR), and M. Gemmi (IIT@NEST).

• Raman Spectroscopy: S.Funk, I.Zardo (WSI, Munchen, D ).

Outline

• Semiconductor nanostructured devices (Lecce)

-2 -1 0 1 2-10

0

10

20

30

40

Co

nd

ucta

nce(m

S)

i_diodo1_buio

i_diodo1_luce

G_diodo1_buio

Voltage (V)

Cu

rren

t (m

A)

-2 -1 0 1 2-10

0

10

20

30

40

50

Ballistic Diodes on GaAs

p-HEMT structure

2DEG m ≈8000 cm2/V·s

n= 6.75·1011 cm-2

Threshold ≤ 50mV

asymmetry factor (Id/Ir)

better than 2x104

Reverse current ≤ 10-8 A

I–V characteristic

Cooperation with ST

Applications: low power

electronics, EM energy

harvesting, THz sensors

Formation process of self-rolling stuctures

The finale shape depends

from the total strain and

the geometry.

By removing the sacrificial layer the two layers with opposite strain release the elastic energy bending the structure

Strain driven 3D nanostructures self-rolling induced

by strain release

Z

Y

X

Patent “Integrated

Triaxial magnetic

sensor”

Sensitivity: 0.03 V/T

Hall voltages versus the

mechanical angle

R=85 mm

microscale dimensions compatible

with CMOS technology

Power density

30.2 mW/mm3

Resonant

frequency

64 Hz

AlN Piezoelectric rings

for energy harvesting

D=350 nm

Multiwalled tube as

building-block for

metamaterials

9 turns

Piezoelectric structures for energy harvesting (RMEMS)

R=85 mm

Power density 30.2 mW/mm3

Sacrificial layer SiO2

Mo layer2

AlN

Mo layer1 AlN

Mo

Rolled up layers (ring structure)

100nm

0.5mm 100 nm

Mo

Resonance frequency 64 Hz

Excellent elastic properties and additional

torsional degree of freedom result to high power

density and efficiency at low frequency

AlN/Mo

A. Massaro et al., Appl. Phys. Lett 98, 052502 (2011)

3D magnetic sensor

bilayer

p-HEMT structur

Z

Y

X

Patent “Integrated Triaxial magnetic sensor” No: P03246 EP

2DEG m ≈8000 cm2/V·s n= 6.75·1011 cm-2

Sensitivity: 0.03 V/T

L. Sileo et al , J. Microelectronic Eng. 87, 1217 (2010)

1D Photonic structures on GaN

Patent OPTICAL LOGIC GATE, Pub. No.: WO/2010/058432 [F. A. Bovino et al, OPTICS EXPRESS, 17, 18337(2009)]

E-beam writing combined with deep dry-etching (ICP plasma etching with SiCl4/N2/Ar) allows to obtain high aspect ratio and vertical wall

T. Stomeo et al., SPIE 2010 V. Tasco et al., SPIE 2010

1-D Photonic crystal on

GaN/AlGaN µ-cavity

Collaboration with SELEX S.I. e Università “La sapienza”

Strong enhancement in

SHG emission

Development of a reliable

process to fabricate

GaN/AlGaN 1D-PhC

microcavities with nonlinear

optical properties

The integration of 1D-PhC

grating amplifies the

signal by exploiting the

double effect of cavity

resonance and non linear

GaN enhancement.

MOCVD

FWHM=57 arcsec

5 10 15 20 25 30

100

101

102

103

260 A/W

He_Cd laser l=325nm - 0,20 mW

optical area 0,5mm x 0,5mm

MSM GaN PD

W Schottky contactsR

esp

on

siv

ity [

A/W

]

Voltage [V]

Cr/Au Schottky contacts

i=4mm

i=5mm

i=4mm

i=5mm

372 A/W

8,72 A/W

6,81 A/W

High temperature and high responsivity

AlGaN deep UV photodetectors

Device working up to 400 °C and 260 nm

High quality semiconductor materials. Patent: An optical system …, WO 2005064315 A1 [M. Mello et al, SENSOR, (2008)]

Electronic devices on GaN

nb ≤ 1x1013 cm-3

X-ray FWHM ≈60 arcsec

Innovative growh technique and new technological process

2DEG carrier density ≥ 1x1013 cm-2

Mobility > 2000 cm2/Vs on HEMT structures

In cooperation with SELEX

S.I. and University of

Modena and Reggio Emilia

The “single step” technology allows to

automatically achieve foot’s gate alignment

and independent head/foot ratio for power

management

[V. Tasco et al., Jour. of App. Phys. vol. 105, 063510, (2009)]

[B. Poti et al, Jour. of Optics A: Pure and Applied Optics, v 8, S524, (2006)]

[M.N. Mello et al., Jour. of Optics A: Pure and Applied Optics, v 8, S545, (2006)]

10 GHz power sweep Ft ≈ 80 GHz

Columnar growth and

mosaicity nearly suppressed

Part II Conclusions

• Ballistic diodes have potential interest on low power electronics, EM energy harvesting and THz sensors.

• Free standing 3D nanostructures are employed for 3D magnetic sensors or RMEMS for elastic energy harvesting

• GaN/AlGaN nanostructures are used for 1DPc, electronic devices and photodetectors

People

NNL Nano-CNR: V. Tasco, M.T. Todaro, M. De Giorgi, A. Passaseo Uni Salento: M. De Vittorio, R. Cingolani Collaborations: SELEX, ELSAG, AVIO, AGILENT, ST, Universita’ La Sapienza

Thank your for your attention