This document provides an overview of the Institute of Nanoscience and its research activities related to semiconductor nanostructures and their applications. The institute has over 250 researchers studying the fundamental properties and manipulation of nanoscale systems through synthesis, fabrication, experimental and theoretical studies of nanostructures and devices. Key areas of research include semiconductor nanowires for applications in electronics, optoelectronics and spintronics. Heterostructured nanowires of InAs, InSb and InP are investigated for high mobility transistors and terahertz detectors. Strain-driven self-assembly is used to create 3D nanostructures for applications in sensing, energy harvesting and photonics.

1. Fabrication and applications of
semiconductor nanostructures
Lucia Sorba
Istituto Nanoscienze-CNR

2. 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

3. 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.

4. 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

5. Outline
• Part I Semiconductor nanowires (Pisa)
• Part II Semiconductor nanostructures (Lecce)

6. Motivation
Semiconductor nanowires:
• strain issues: heterostructures

7. Motivation
Semiconductor nanowires:
• high control of density and
dimension
200nm
6
0
20
40
60
NWsCount(a.u.)
2μm
8
0
20
40
60
NWsCount(a.u.)
200nm
(a)
(b)
(c)
(d)

8. Gold assisted growth

9. Bottom-up growth approach

10. InAs NWs
Diameter 20-100nm
Length up to 2-5 mm
Hexagonal cross section
Wurzite crystal structure
Doping n=1016 -1019 cm-3

11. 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

12. InAs/InP axial heterostructured NWs

13. 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

14. High-T single-electron devices
S. Roddaro et al., Nano Lett 11, 1695-1699 (2011)
CB up to 50K
Enhancement of the level spacing

15. 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

16. 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

17. InAs-InSb NWs
InSb: <110> zone axis, InAs: <2-1-10> zone axis
HR TEM Analysis
D. Ercolani el al. Nanotechnology 20, 505605 (2009)

18. InAs-InSb NWs
Strain maps as obtained by geometrical
phase
analysis.

19. 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)

20. 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

21. 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
Current(nA)
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

22. InAs-InP-InSb
n-n heterojunction diodes

23. Room -T
InAs-InP-InSb
n-n heterojunction diodes
InP insertion reduces the direct
conductivity and suppresses the
thermionic contribution in reverse
bias

24. 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

25. 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
Responsivity(V/W)
VG (V)
NEP(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
NW FETs THz detectors
S
D
G
200 nm
ad band bow tie equiangular
antenna
Log-periodic circular-toothed
antenna
M.S. Vi ello et al. Nano Le ers, 12, 96 (2012)
Strong resonant photoresponse is
predicted in materials having plasma
damping rates < freq. incoming rad. and <
1/τ → High mobility required

26. 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
Noise Equivalent Power
10
-11
10
-10
10
-9
-3 -2 -1 0 1 2 3
Gate Voltage (V)
NEP(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)
ØNEP : 6 × 10-11 W/ Hz1/ 2
Ø1 order of magnitude increase
Responsivity
M.S Vitiello et al. APL 100, 241101, 2012

27. Highly sensitive, RT detection of THz QCL
emission
M.S Vitiello et al. APL 100, 241101, 2012
Gate Voltage (V)
Responsivity(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 3
0
0.5x10
-5
Gate Voltage (V)
Responsivity(V/W)
Isd(A)
90°
60°
45°
0°
(c)
θ
(a)
(b)
D
G
S
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

28. 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

29. AlAs-GaAs NWs
Exp: a= 3.9±0.1Å and c=6.5±0.1Å
Th : a= 4.003Å and c= 6.537ÅA. LI et al. 2011, Crystal Growth & Design, 11,
4053

30. 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,.

31. 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.

32. 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 ).

33. Outline
• Semiconductor nanostructured devices
(Lecce)

34. -2 -1 0 1 2
-10
0
10
20
30
40
Conductance(mS)
i_diodo1_buio
i_diodo1_luce
G_diodo1_buio
Voltage (V)
Current(mA)
-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

35. 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

36. 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

37. 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)

38. 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)

39. 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

40. FWHM=57 arcsec
5 10 15 20 25 30
10
0
10
1
10
2
10
3
260 A/W
He_Cd laser l=325nm - 0,20 mW
optical area 0,5mm x 0,5mm
MSM GaN PD
W Schottky contacts
Responsivity[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)]

41. 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

42. 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

43. 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

44. Thank your for your attention