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