G. Kioseoglou
SEMICONDUCTOR SPINTRONICS
George KioseoglouMaterials Science and Technology, University of Crete
Spin as new degree of freedom in quantum device structures
G. KioseoglouResearch Activities
Research activities are focused on electrical spin injection and detection of spin polarized electrons into semiconductors.
magnetic contacts• ZnMnSe• Fe• FeGa• MnGa
tunnel barriers• Shottky• Al2O3
• MgO
semiconductors• GaAs QWs• Si• InGaAs• Quantum Dots
Essential Requirements for Spintronics Devices
• Efficient electrical injection • Efficient spin transport• Control of spin carriers• Effective detection
G. Kioseoglou
• MBE growth (NRL)• Comprehensive characterization
• magnetic (SQUID, FMR)• transport (Hall, etc)• structural (TEM, x-ray diff)• composition (XRF)• magneto-optical
• Theory and modeling
MBEMBE
Growth and characterization
G. KioseoglouDMS as a spin contact :ZnMnSe
n-ZnMnSe/AlGaAs/GaAs/AlGaAs
• spin-polarized electron injection• giant Zeeman splitting ∆E=gBH
ge ~ 30; spin splittings >> kT
• 100% spin polarized
optical polarization
GaAs
ZnMnSe
Pcirc =I(+) - I(-)
I(+) + I(-) Pspin=n n-
+n n
Pspin = Pcirc (QWs)
Pspin = 2 Pcirc (bulk)0 2 4 6 8
0
20
40
60
80
I=300A , V=2.7VOp
tic
al P
ola
riza
tio
n (
%)
Magnetic Field (T)
T=4.5K
PRB62, 8180 (2000) APL79, 3098 (2001)
G. KioseoglouFe based GaAs Spin-LEDs
Fe AlGaAs
metal semicond
-40
-30
-20
-10
0
10
20
30
40
-4 -2 0 2 4O
pti
cal P
ola
riza
tio
n (
%)
Magnetic Field (T)
Fe out of plane
T=5 K
APL82, 4092 (2003)
APL80, 1240 (2002)
APL84, 4334 (2004)
B B0
ˆ z
n-AlGaAs
i-GaAs
p-AlGaAs
Fe
+
-
+ -
G. Kioseoglou
-50
-40
-30
-20
-10
0
10
20
30
40
50
-3 -2 -1 0 1 2 3
EL data
SQUID at T=20K
I=4.2mAV=2.3 V
Magnetic Field (T)
Ele
ctr
on
sp
in p
ola
riza
tio
n (
%)
T=20K
APL91, 122515 (2007)
Spin injection from FeGa and MnGa into GaAs
-4 -3 -2 -1 0 1 2 3 4-30
-20
-10
0
10
20
30
Cir
cu
lar
Po
lari
zati
on
(%
)
Magnetic Field (T)
MnAs:out of plane magnetization
EL data
PL data
APL97, 041103 (2010)
FeGa/Al2O3/GaAs MnGa/Al2O3/GaAs
G. Kioseoglou Silicon Spintronics
Si / Si-Ge$ 120 Billion
- extensive technology- extensive infrastructure
Si is an ideal host for SpinSLow spin-orbit scattering is basic material property - low atomic mass - crystal inversion symmetry - low nuclear hyperfine interaction
Long
spi
n lif
etim
es fo
r
both
don
or-b
ound
and
free
elec
trons
in S
i
G. KioseoglouElectrical Spin Injection from Fe/Al2O3 & Fe/SiO2 into Si
zBB ˆ0
p-Si(001) substrate
150 nm p-Si
70 nm i-Si
70 nm n-Si
Al2O3
10 nm Fe
+ -
-4
-3
-2
-1
0
1
2
3
4
-6 -4 -2 0 2 4 6
Cir
cula
r P
ola
riza
tio
n (
%)
T=5KI=10mA, V=2.1V
Magnetic Field (T)
TO
TA
Fe magnetization
non-magneticB.T. Jonker and G. KioseoglouNat. Phys. 3, 542 (2007)
G. Kioseoglou et al, APL94, 122106 (2009)
C.H. Li et al, APL95, 172101 (2009)
0.95 1 1.05 1.1
2mA, 2.6V
Photon Energy (eV)
EL
Inte
nsi
ty (
arb
. un
its)
T=5K
0T
3T 2TO
TA
TO
P(TA) = 1.7 P(TO)
G. KioseoglouQuantifying electron spin polarization from EL
direct gapOptical
polarization Electron spin polarization
^T1 ^L^T2
6 -
8 -
5
125'
so7+
8+
15
2'
indirect gap - the spin pol depends strongly on the phonon branch that mediates the opt transition
Huge theoretical effort to understand spin orientation in Si
p-type THEORY : P(TA) = 1.6 P(TO)
Pengke Li and Hanan Dery, PRL105, 037204 (2010)
13%Experiment:P_TAsub=3.5%
Spin injection efficiency 27%
G. Kioseoglou
Fe
AlGaAs(n)
AlGaAs(p)
GaAsQW(i)
QD
GaAs(p)
e
h
Fe
AlGaAs(n)
AlGaAs(p)
GaAsQW(i)
QD
GaAs(p)
e
hhGaAs
GaAs
InAs
1 nm
-6
-4
-2
0
2
4
6
-8 -6 -4 -2 0 2 4 6 8
200 K300 K
120 K
Op
tica
l P
ola
riza
tio
n (
%)
Magnetic Field (T)
Fe out of planemagnetization
• electrical spin injection up to RT• DP mechanism is suppressed
Fe based InAs QD Spin-LEDs
G. Kioseoglou
1120 1160 1200 1240 1280 1320
EL
Inte
nsi
ty (
arb
. un
its
)
Energy (meV)
T=5KB=0T
58 meV
3mA, 2.6V
1150 1200 1250 1300 1350
EL
Inte
nsi
ty (
arb
. un
its
)
Energy (meV)
32 meV
T=5KB=0T
0.3mA, 1.6V
reduced growth rate reduced density increased uniformity in size
G. Kioseoglou
1.70 1.72 1.74 1.76 1.78 1.80 1.82 1.84 1.86
1200
1250
1300
1350
1400
1450 T=5KB=0T
d
WL
Low bias
En
erg
y (m
eV)
Bias (V)
p
s
1.8 2.0 2.2 2.4 2.6 2.8 3.0
1200
1250
1300
1350
1400
1450
WL
f
d
p
Inte
nsi
ty
s
En
erg
y (m
eV)
T=5KB=0T
High bias
Bias (V)
0259.3518.6777.9103712961556181520742334259328523111337136303889414944084667492651865445570459646223648267417001726075197779803882978556881690759334959498531.011E41.037E41.063E41.089E41.115E41.141E41.167E41.193E41.219E41.245E41.270E41.296E41.322E41.348E41.374E41.400E41.426E41.452E41.478E41.504E41.530E41.556E41.582E41.608E41.633E41.659E41.685E41.711E41.737E41.763E41.789E41.815E41.841E41.867E41.893E41.919E41.945E41.971E41.996E42.022E42.048E42.074E42.100E42.126E42.152E42.178E42.204E42.230E42.256E42.282E42.308E42.334E42.359E42.385E42.411E42.437E42.463E42.489E42.515E42.541E42.567E42.593E42.619E42.645E42.671E42.697E42.722E42.748E42.774E42.800E42.826E42.852E42.878E42.904E42.930E42.956E42.982E43.008E43.034E43.060E43.085E43.111E43.137E43.163E43.189E43.215E43.241E43.267E43.293E43.319E43.345E43.371E43.397E43.423E43.448E43.474E43.500E43.526E43.552E43.578E43.604E43.630E4
Filling of the electronic shell-states
Continuous evolution of shell intensity with bias
G. Kioseoglou et al, PRL 101, 227203 (2008)
G. KioseoglouAnother approach: P vs E
1200 1240 1280 1320 1360-6
-4
-2
0
2
4
6
8
d-shell
p-shell
EDC
B
A
Po
larization
(%)
Energy (meV)
30mA, 3.0 V
EL
Inte
nsi
ty (
arb
. u.)
s-shell
0 1 2 3 4 5 6-2
0
2
4
6
8E
B
Cir
cu
lar
Po
lari
zati
on
(%
)
T= 5K30mA,3V
D
C
Magnetic Field (T)
Polarization exhibits maxima shifted with respect to intensity shell-peaks
due to intershell exchange energy
Vxsp=7±2 meV Vx
sp=13.5±1 meV
• first measurement of the s-p and p-d intershell exchange energies• a significant step towards understanding spin-polarized carriers in QDs
G. Kioseoglou et al, PRL 101, 227203 (2008)
G. Kioseoglou
2000 2002 2004 2006 20080
50
100
150
200
250
300
350
400
450
500
CIT
AT
ION
S IMPACT
ZnMnSe/GaAsPRB62, 8180 (2000)
Fe/GaAsAPL80, 1240 (2002)APL82, 4092 (2003)
Fe/SiNat Physics3,
542 (2007)
G. Kioseoglou
Dr. Jonker (NRL)
Dr. Goswami (NRL)-microscopy
Prof. Petrou (SUNY Buffalo)
Dr. Pawel HawrylakQuantum Theory Group,
Institute for Microstructural Sciences, Ottawa
Collaborations
Prof. Hanan DeryUniversity of Rochester, NY
THEORY
G. Kioseoglou
G. KioseoglouTheory: 2 e-h pairs/QD – Sz=-1
Initial state
Final state
speespsin VEEE
spf EE
s-p exchange between spin polarized electrons
s-shell hole + p-shell elec
s-shell exciton
σ +The outgoing photon carries the initial-state exchange energy of the spin-polarized electrons
G. Kioseoglou
B B0
ˆ z
n-AlGaAs
i-GaAs
p-AlGaAs
Fe
+-
+ -
100 mm