Transcript Document

G. Kioseoglou
SEMICONDUCTOR SPINTRONICS
Spin as new degree of freedom
in quantum device structures
George Kioseoglou
Materials Science and Technology, University of Crete
Research Activities
Essential Requirements for
Spintronics Devices
•
•
•
•
G. Kioseoglou
Efficient electrical injection
Efficient spin transport
Control of spin carriers
Effective detection
Research activities are focused on electrical spin injection and
detection of spin polarized electrons into semiconductors.
magnetic contacts
• ZnMnSe
• Fe
• FeGa
• MnGa
semiconductors
tunnel barriers
• GaAs QWs
• Shottky
• Si
• Al2O3
• InGaAs
• MgO
• Quantum Dots
Growth and characterization
• MBE growth (NRL)
• Comprehensive characterization
• magnetic (SQUID, FMR)
• transport (Hall, etc)
• structural (TEM, x-ray diff)
• composition (XRF)
• magneto-optical
• Theory and modeling
MBE
MBE
G. Kioseoglou
DMS as a spin contact :ZnMnSe
G. Kioseoglou
n-ZnMnSe/AlGaAs/GaAs/AlGaAs
• spin-polarized electron injection
• giant Zeeman splitting ∆E=gBH
80
Optical Polarization (%)
ge ~ 30; spin splittings >> kT
• 100% spin polarized
 
optical polarization

ZnMnSe
GaAs


Pspin = Pcirc (QWs)
Pspin = 2 Pcirc (bulk)
Pcirc =
I(+) - I(-)
I(+) + I(-)
Pspin=
60
T=4.5K
40
20
I=300A , V=2.7V
0
0
2
4
6
Magnetic Field (T)
8
n - n
n + n
PRB62, 8180 (2000) APL79, 3098 (2001)
Fe based GaAs Spin-LEDs
B  B0zˆ
40
T=5 K
n-AlGaAs
i-GaAs
p-AlGaAs
30
20
10
0
-10
-20
Fe out of plane
-30
-40
-4
-2
0
2
4
Magnetic Field (T)
metal
Fe AlGaAs

+
Fe
semicond


-
Optical Polarization (%)
+ 
G. Kioseoglou
APL80, 1240 (2002)
APL82, 4092 (2003)
APL84, 4334 (2004)
Spin injection from FeGa and MnGa into GaAs
FeGa/Al2O3/GaAs
MnGa/Al2O3/GaAs
50
30
Circular Polarization (%)
Electron spin polarization (%)
30
EL data
SQUID at T=20K
40
20
10
T=20K
0
-10
-20
I=4.2mA
V=2.3 V
-30
20
10
0
-10
EL data
PL data
MnAs:out of plane
magnetization
-20
-40
-50
-30
-3
-2
-1
0
G. Kioseoglou
1
2
3
-4
-3
-2
-1
0
1
2
Magnetic Field (T)
Magnetic Field (T)
APL91, 122515 (2007)
APL97, 041103 (2010)
3
4
Silicon Spintronics
Si / Si-Ge
$ 120 Billion
- extensive technology
- extensive infrastructure
Si is an ideal host for SpinS
Low spin-orbit scattering is basic material property
- low atomic mass
- crystal inversion symmetry
- low nuclear hyperfine interaction
G. Kioseoglou
Electrical Spin Injection from Fe/Al2O3 & Fe/SiO2 into Si
Al2O3
10 nm Fe
T=5K
2mA, 2.6V
EL Intensity (arb. units)
+

- B  B0 zˆ
3T
0.95
C.H. Li et al, APL95, 172101 (2009)
2TO
1
1.05
1.1
Photon Energy (eV)
4 T=5K
Circular Polarization (%)
150 nm p-Si
G. Kioseoglou et al, APL94, 122106 (2009)
TA
0T
70 nm i-Si
B.T. Jonker and G. Kioseoglou
Nat. Phys. 3, 542 (2007)
TO


70 nm n-Si
p-Si(001) substrate
G. Kioseoglou
TA
3 I=10mA, V=2.1V
TO
2
1
0
P(TA) = 1.7 P(TO)
-1
non-magnetic
-2
-3
Fe magnetization
-4
-6
-4
-2
0
2
Magnetic Field (T)
4
6
Quantifying electron spin polarization from EL
G2'
G8G6-
G15
^
T
G25'
^1
T
G+8
D
G7+ so
^
L
D1
2
D5
indirect gap - the spin pol depends
direct gap
Optical polarization
G. Kioseoglou
Electron spin polarization
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)
13%
Experiment:P_TAsub=3.5%
Spin injection efficiency 27%
Pengke Li and Hanan Dery, PRL105, 037204 (2010)
Fe based InAs QD Spin-LEDs
e
AlGaAs
GaAs
(n)
QW(i)
G. Kioseoglou
AlGaAs
(p)
Fe
GaAs
(p)
QD
Optical Polarization (%)
6
h
120 K
200 K
300 K
4
GaAs
Fe out of plane
magnetization
2
InAs
0
GaAs
-2
-4
1 nm
• electrical spin injection up to RT
• DP mechanism is suppressed
-6
-8
-6
-4
-2
0
2
4
Magnetic Field (T)
6
8
G. Kioseoglou
reduced density increased uniformity in size
3mA, 2.6V
T=5K
B=0T
EL Intensity (arb. units)
EL Intensity (arb. units)
reduced growth rate
58 meV
0.3mA, 1.6V
T=5K
B=0T
32 meV
1150
1200
1250
Energy (meV)
1120
1160
1200
1240
1280
Energy (meV)
1320
1300
1350
Filling of the electronic shell-states
G. Kioseoglou
Continuous evolution of shell intensity with bias
Low bias
1450
WL
Energy (meV)
1400
1350
d
1300
p
1250
T=5K
B=0T
WL
1400
f
1350
d
1300
p
1250
s
1200
s
1200
1.70 1.72 1.74 1.76 1.78 1.80 1.82 1.84 1.86
Bias (V)
1.8
2.0
2.2
2.4
2.6
2.8
Bias (V)
G. Kioseoglou et al, PRL 101, 227203 (2008)
3.0
Intensity
T=5K
B=0T
Energy (meV)
1450
High bias
3.630E4
3.604E4
3.578E4
3.552E4
3.526E4
3.500E4
3.474E4
3.448E4
3.423E4
3.397E4
3.371E4
3.345E4
3.319E4
3.293E4
3.267E4
3.241E4
3.215E4
3.189E4
3.163E4
3.137E4
3.111E4
3.085E4
3.060E4
3.034E4
3.008E4
2.982E4
2.956E4
2.930E4
2.904E4
2.878E4
2.852E4
2.826E4
2.800E4
2.774E4
2.748E4
2.722E4
2.697E4
2.671E4
2.645E4
2.619E4
2.593E4
2.567E4
2.541E4
2.515E4
2.489E4
2.463E4
2.437E4
2.411E4
2.385E4
2.359E4
2.334E4
2.308E4
2.282E4
2.256E4
2.230E4
2.204E4
2.178E4
2.152E4
2.126E4
2.100E4
2.074E4
2.048E4
2.022E4
1.996E4
1.971E4
1.945E4
1.919E4
1.893E4
1.867E4
1.841E4
1.815E4
1.789E4
1.763E4
1.737E4
1.711E4
1.685E4
1.659E4
1.633E4
1.608E4
1.582E4
1.556E4
1.530E4
1.504E4
1.478E4
1.452E4
1.426E4
1.400E4
1.374E4
1.348E4
1.322E4
1.296E4
1.270E4
1.245E4
1.219E4
1.193E4
1.167E4
1.141E4
1.115E4
1.089E4
1.063E4
1.037E4
1.011E4
9853
9594
9334
9075
8816
8556
8297
8038
7779
7519
7260
7001
6741
6482
6223
5964
5704
5445
5186
4926
4667
4408
4149
3889
3630
3371
3111
2852
2593
2334
2074
1815
1556
1296
1037
777.9
518.6
259.3
0
Another approach: P vs E
C
E 8
4
B
A
2
0
-2
p-shell
s-shell
d-shell
1200 1240 1280 1320 1360
Polarization (%)
EL Intensity (arb. u.)
6
Circular Polarization (%)
D
30mA, 3.0 V
T= 5K
30mA,3V
8
E
6
D
4
C
G. Kioseoglou
Polarization exhibits maxima
shifted with respect to
intensity shell-peaks
due to
intershell exchange energy
2
B
0
-4
-6
-2
0
1
2
3
4
5
6
Magnetic Field (T)
Energy (meV)
• first measurement of the s-p and p-d
intershell exchange energies
• a significant step towards
understanding spin-polarized carriers in QDs
Vxsp=7±2 meV
Vxsp=13.5±1 meV
G. Kioseoglou et al, PRL 101, 227203 (2008)
IMPACT
G. Kioseoglou
500
450
400
ZnMnSe/GaAs
PRB62, 8180 (2000)
Fe/GaAs
APL80, 1240 (2002)
APL82, 4092 (2003)
CITATIONS
350
300
250
200
Fe/Si
Nat Physics3,
542 (2007)
150
100
50
0
2000
2002
2004
2006
2008
Collaborations
Dr. Jonker (NRL)
Dr. Goswami (NRL)-microscopy
Prof. Petrou (SUNY Buffalo)
THEORY
Prof. Hanan Dery
University of Rochester, NY
Dr. Pawel Hawrylak
Quantum Theory Group,
Institute for Microstructural Sciences, Ottawa
G. Kioseoglou
G. Kioseoglou
Theory: 2 e-h pairs/QD – Sz=-1 G. Kioseoglou
Initial state
Ein  Es  Esp  V
sp
ee
s-shell
exciton
Final state
s-shell hole
+ p-shell elec
s-p exchange between
spin polarized electrons
E f  E sp
σ+
The outgoing photon carries the initial-state
exchange energy of the spin-polarized electrons
G. Kioseoglou
B  B0zˆ
+ -
+

Fe
n-AlGaAs
i-GaAs
p-AlGaAs
100 mm