Transport Phenomena in Materials Processing Poirier-Geiger.PDF
POLAR MATERIALS: FROM PHYSICAL PHENOMENA TO APPLICATIONS · POLAR MATERIALS: FROM PHYSICAL...
Transcript of POLAR MATERIALS: FROM PHYSICAL PHENOMENA TO APPLICATIONS · POLAR MATERIALS: FROM PHYSICAL...
POLAR MATERIALS: FROM
PHYSICAL PHENOMENA TO
APPLICATIONS
Lucian Pintilie
National Institute of Materials Physics, Atomistilor 405A, Magurele, Romania E-mail address: [email protected]
Conferinţa Diaspora în Cercetarea Ştiinţifică şi Invăţământul Superior din România
Eveniment aflat sub Înaltul Patronaj al
Preşedintelui României.
1 Timisoara, 25-28 Aprilie 2016
2 Timisoara, 25-28 Aprilie 2016
Outlines
Introduction
Interfaces in ferroelectrics
Self-doping in epitaxial ferroelectrics
Polar heterostructures
Light and polar materials
Next steps
Timisoara, 25-28 Aprilie 2016 3
Introduction
NTT Technical Review 8 (2010)
Polar materials (inorganic)
Lack of center of symmetry-polar axis-polarization-
pyroelectricity, ferroelectricity, piezoelectricity, non-linear
optical effects
Polar semiconductors
(e.g. GaN, AlN, ZnO) Ferroelectrics, especially those with
perovskite structure (e.g. BaTiO3,
Pb(Zr,Ti)O3, or multiferroics (BiFeO3)
Timisoara, 25-28 Aprilie 2016 4
The Nobel Prize in Physics 2014 - awarded jointly to Isamu Akasaki,
Hiroshi Amano and Shuji Nakamura "for the invention of efficient blue light-
emitting diodes which has enabled bright and energy-saving white light
sources“.
AlN – for high voltage, high power electronic
devices
Timisoara, 25-28 Aprilie 2016 5
Applications of ferroelectrics Non-volatile memories (exploiting the reversible polarization); ultrasound generation and reception, micro-motors, actuators, MEMS (exploiting the piezoelectriv effect); thermal imaging (exploiting the pyroelectric effect); optical switches; energy harvesting (solar reactor, photovoltaic).
Timisoara, 25-28 Aprilie 2016 6
Interfaces in ferroelectrics In many cases the sample is a capacitor-electrode interfaces
How interact polarization with the interface?
Multi-layers and super-lattices-internal interfaces
How do the interfaces affect the macroscopic properties?
Samples prepared by pulsed laser deposition-epitaxy (minimizing extrinsic effects)
PZT, BaTiO3, BiFeO3; single crystal substrate-SrTiO3; bottom SrRuO3 electrode
Timisoara, 25-28 Aprilie 2016 7
Timisoara, 25-28 Aprilie 2016 8
The electrode-ferroelectric interface
Polarization controlled properties of electrode interface
C-V characteristics obtained for different metals as top electrodes on: a) PZT grown on STO (001);
b) BTO grown on STO (001); c) PZT grown on STO (111); d) BTO grown on STO (111).
Timisoara, 25-28 Aprilie 2016 9
-6 -4 -2 0 2 4 6
-100
-80
-60
-40
-20
0
20
40
60
80
100
Po
lari
za
tio
n (C
/cm
2)
Voltage (V)
SRO
Pt
Cu
Au
-0,8
-0,6
-0,4
-0,2
0,0
0,2
0,4
0,6
0,8
Cu
rre
nt (m
A)
300 K
a)
-8 -6 -4 -2 0 2 4 6 8-100
-80
-60
-40
-20
0
20
40
60
80
100
Po
lari
za
tio
n (C
/cm
2)
Voltage (V)
SRO
Cu
b)
-80
-60
-40
-20
0
20
40
60
80
Cu
rre
nt (
A)
150 K
-6 -4 -2 0 2 4 6-100
-80
-60
-40
-20
0
20
40
60
80
100
Pola
rizatio
n (C
/cm
2)
Voltage (V)
SRO
Pt
Cu
Au
c)
300 K-0,4
-0,2
0,0
0,2
0,4
Cu
rren
t (m
A)
-6 -4 -2 0 2 4 6-50
-40
-30
-20
-10
0
10
20
30
40
50
SRO
Po
lari
za
tio
n (C
/cm
2)
Voltage (V)
150 Kd)
-80
-60
-40
-20
0
20
40
60
80
Cu
rre
nt (
A)
Hysteresis loops recorded for the PZT layer deposited on (001)STO (a), for the BTO layer
deposited on (001)STO (b), for PZT film deposited on (111)STO (c), and for BTO film deposited on
(111)STO.
Timisoara, 25-28 Aprilie 2016 10
CS
CF
RF
Rc
Schottky contacts
Timisoara, 25-28 Aprilie 2016 11
Potential barrier not correlated with work function
Large density of free carriers
Timisoara, 25-28 Aprilie 2016 12
PRB 75, 104103 2007
Polarization term 0.7-0.9 eV
P=1 C/m2
εop=6
εst=60 or 40
0 200 40020
40
60
80
100
120
140
160
Die
lectr
ic c
on
sta
nt
Thickness (nm)
Potential barrier around 1 eV
XPS results – 1.4-1.7 eV the potential barriers at electrode interfaces ACS Appl. Mater. Interfaces 6, 2929−2939 (2014)
J. Phys. D: Appl. Phys. 44, 255301 (2011)
The barrier is not the simple difference between metal
work function Φm
and the electron affinity of the
ferroelectric material χf – interface states?
Timisoara, 25-28 Aprilie 2016 13
S factor
2
0
0
11.01
1
S
eDS
JAP 36, 3212 (1965)
APL 74, 1168 (1999)
PRL 58, 1260 (1986)
S~0.3 for PZT
Dδ~1.6x1014 cm-2eV-1 (ε=40)
P~90 μC/cm
2 (E
g~3.5 eV)!
It can be that polarization acts as “interface states”, pinning the
Ferrmi level and controlling the height of the potential barriers
Timisoara, 25-28 Aprilie 2016 14
XPS investigation
Metal deposition-2 monolayers;
4 monolayers…10 nm
XPS spectra recorded after
each deposition
The shift of the binding energy
was monitored as function of
metal thickness
Band bending occurs at the
interface
0.2-0.5 eV for both PZT and
BTO
Timisoara, 25-28 Aprilie 2016 15
Tranzitie de faza indusa de grosime in super-
retele PZT-PZO (feroelectric-antiferoelectric).
Cu scaderea grosimii straturilor componente faza
antiferoelectrica devine feroelectrica.
Applied Physics Letters 91, 122915 (2007)
Timisoara, 25-28 Aprilie 2016 16
Interfacial polarization
Timisoara, 25-28 Aprilie 2016 17
Self-doping in epitaxial ferroelectrics
AFM/PFM studies revealing that upward polarization is dominant
in epitaxial PZT films
Timisoara, 25-28 Aprilie 2016 18
The density of the free
carriers increases with
decreasing the thickness of
the PZT films
The deduced empirical law is:
)(
102)(
273
nmdmn
x
Polarization induced self-
doping
Scientific Reports 5, 14974
(2015)
0 50 100 150 200 250 300
94
95
96
97
98
Po
lari
za
tio
n (
C/c
m2)
Thickness (nm)
Timisoara, 25-28 Aprilie 2016 19
There is a variation of stoichiometry with thickness, suggesting different
densities of cation and oxygen vacancies as the thickness increases
Timisoara, 25-28 Aprilie 2016 20
Suggested model-oxygen vacancies
pmv O
Free charge from
oxygen vacancies
Free charge from
the bottom SRO
electrode
Bound polarization
charges
0F
B
OF
0FO )(2
exp21)(21
deEgne
P
d
f
Tk
EEdeEgn
e
P
dn mm
v
v
d
PBAnVc
vOECO
)(3
)(
102)(
273
nmdmn
x
e
PdeEgnVfPB
A
mEC
2)()(
3
0F
Tk
EEf v
B
OFexp21
A= 3.09 ± 0.05
f~10
10 % of oxygen
vacancies are
ionized
Tk
EE
nn
v
v
v
B
OF
O
O
exp21
Timisoara, 25-28 Aprilie 2016 21
Polar heterostructures
150K
350K
450K
Pt-PZT-ZnO (MFS) structures
epitaxial columnar
policristalin
J. Appl. Phys. 112, 104103 (2012);
Appl. Phys. Lett. 96, 012903 (2010)
Orientation of the C-V hysteresis dependent on
structural quality and temperature
Timisoara, 25-28 Aprilie 2016 22
Artificial multiferroic structures-combination of
ferroelectric and ferrimagnetic materials.
Timisoara, 25-28 Aprilie 2016 23
Light and polar materials
Light – photovoltaic
pyroelectric
J. Mater. Chem. A, 2014, 2, 6027–6041 | 6029
dTdPp S /
)/( dtdTApip
A current is generated when there is a
temperature variation of the sample
Intrinsic internal electric field
to separate the charge
carriers
Timisoara, 25-28 Aprilie 2016 24
J. Appl. Phys. 110, 044105 (2011)
Short-circuit
photocurrent dependes
on the electrode
materials
Photovoltaic
Timisoara, 25-28 Aprilie 2016 25
Necache et al., Nature Photonics DOI: 10.1038/NPHOTON.2014.255
Efficiency 8.1 % by band-gap engineering in a multilayer!
Timisoara, 25-28 Aprilie 2016 26
Solar cells with (MA)PbI3
SEM image of the stack
Standard structure
FTO TiO2
perovskit
HTM-spiro-OMeTAD
Au electrodes, maximum area of 5x5 mm2
12 %-best performance ever obtained in Romania for any type of solar cells studied up to now-possibility to improve by optimizing
the process and component materials.
(MA)PbI3 molecules (blue-yellow) have electric dipole moments- tend to be
correlated resulting in a net polarization of the cell
Timisoara, 25-28 Aprilie 2016 27
Pyroelectric
Epitaxial PZT films grown by PLD on SRO/STO substrates and with top SRO contacts
Polycrystalline films grown by spin coating on Pt/Si substrates and with top Pt contacts
18 20 22 24 26
101
103
105
-50 0 50 100 150 200 250 300 35010
0
101
102
103
104
105
Inte
ns
ity
(a
rb.
un
it.)
Phi (0)
STO
SRO
PZT
PZ
T
Inte
nsity (
cps)
2 Theta (degrees)
SR
O
ST
O PZT
Structural characterization of the PZT films: XRD (left); PFM (middle); TEM (right)
AlN and ZnO thin films grown by RF-sputtering on Si substrates and with top Cu
electrodes
ZnO AlN
Timisoara, 25-28 Aprilie 2016 28
a) the frequency dependence of the
pyroelectric signal obtained from the
Pt/PZT/SRO/STO active element);
b) the dependence of the pyroelectric signal
on 1/ω, evidencing the frequency ω0
where the heating conditions for the
sample are changing from relatively
uniform to non-uniform;
c) the PFM image of the free surface of the
PZT layer, evidencing the presence of
the 90 domains.
Applied Physics Letters 103, 232902 (2013)
Phys. Rev. Lett. 109, 257602 (2012).
p~19x10-4 C/m2K
Timisoara, 25-28 Aprilie 2016 29
Optical amplification of the pyroelectric signal through the photogeneration of
free carriers by the continuous UV illumination
Timisoara, 25-28 Aprilie 2016 30
10 100
10
100
Pyro
ele
ctr
ic s
ignal (
V)
Frequency (Hz)
AlN ZnO
p=12.4 μCm-2K-1 for AlN
p~3 μCm-2K-1 for ZnO
Inferior to ferroelectrics but may work at
elevated temperatures, where ferroelectrics
are no longer pyroelectrically active
Timisoara, 25-28 Aprilie 2016 31
Next steps
strain engineering-induction of ferroelectric
phase in nominally non-ferroelectric materials
rectifying and ohmic contacts on ferroelectric-
ferrotronics?
doping-manipulating the concentration of free
carriers in close relation with polarization
band-gap tuning-adjusting band-gap for
optimal light absorption in ferroelectric solar
cells
pyro-photo combination-novel concepts for
light sensors (optical amplification and filtering)
Timisoara, 25-28 Aprilie 2016 32
Collaborators Samples
Dr. Chirila
Cristina
Dr. Luminita
Hrib
Dr. Stancu
Viorica
Structure
Dr. Pasuk
Iuliana
Drd. Raluca
Negrea
Dr. Corneliu
Ghica
XPS, PFM
Dr. Cristian Mihail
Teodorescu
Dr. Apostol
Nicoleta
Drd. Laura
Abramiuc
Dr. Trupina
Lucian
Electric, magnetic charac.
Drd. Andra Georgia
Boni
Drd.Mihaela Botea
Dr. Iuga Alin
Drd. Simona
Greculeasa
Dr. Pintilie Ioana
Dr. Kuncser Victor
Dr. George
Stan
Photovoltaic
Dr. Cristina
Besleaga
Timisoara, 25-28 Aprilie 2016 33
Funding
Funding Program/Project:
IFA-CEA
INTERFACING OXIDES (IFOX)
Project 8 SEE/2014 (EEA-JRP-RO-NO-2013-1)
Complex Idea Project “Effect of interfaces on charge
transport in ferroic/multiferroic heterostructures”
Project NOPYDET
Timisoara, 25-28 Aprilie 2016 34
THANK YOU FOR
YOUR ATTENTION!