Detection of current induced Spin polarization with a co-planar spin LED

J. Wunderlich (1), B. Kästner (1,2), J. Sinova (3), T. Jungwirth (4,5)

(1) Hitachi Cambridge Laboratory, UK

(2) National Physical Laboratory, UK

(3) Texas A&M University, USA

(4) Institute of Physics ASCR, Czech Republic

(5) University of Nottingham, UK

Thanks to A.H. MacDonald, University of Texas

- Current induced spin-polarization:

Levitov, Mal’shukov, Spin-Hall

- Experimental results

- Conclusion / Outlook

OUTLINEOUTLINE

- by asymmetrical optical recombination in a pn-junction

- by applying an electric field Ex

x

y

z x

y

z x

y

z

Ex = 0

kx

ky Ex > 0

Sy

Ex = 0

kx

ky Ex > 0

Ex = 0

kx

ky Ex > 0

Sy

x

y

z x

y

z x

y

z x

y

z x

y

z x

y

z

Ex = 0

kx

ky Ex > 0

Sy

Ex = 0

kx

ky Ex > 0

Ex = 0

kx

ky Ex > 0

Sy

[Mal’shukov et al., PRB 65 241308(R) (2002)][Levitov et al , Zh. Eksp. Teor. Fiz. 88, 229 (1985)]

InplaneInplane polarization for a [001] grown GaAs quantum well

““Levitov effect” “Mal’shukov effect”Levitov effect” “Mal’shukov effect”

0

20

E [

meV

]

a

HH+

HH-LH

- +

-20

0

20

0

20

E [

meV

]

a

HH+

HH-LH

- +

-20

0

20

-0.2 0.0 0,2

ky [nm-1]

Spin Hall effectSpin Hall effect

Spin-orbit coupling “force” deflects like-spinlike-spin particles

I

_ FSO

FSO

_ __

V=0

non-magnetic

Spin-current generation in non-magnetic systems Spin-current generation in non-magnetic systems without applying external magnetic fieldswithout applying external magnetic fields

Spin accumulation without charge accumulationexcludes simple electrical detection

p -AlG a As

i-G a As

n- -d o p e d AlG a As

e tc he d

QW

I

Top Emission

Side Emission

Electrode

Spin polarization detected through circular polarization of emitted lightSpin polarization detected through circular polarization of emitted light

Conventional vertical spin-LED

Novel co-planar spin-LED

Y. Ohno et al.: Nature 402, 790 (1999)

R. Fiederling et al.: Nature 402, 787 (1999)

B. T. Jonker et al.: PRB 62, 8180 (2000)

X. Jiang et al.: PRL 90, 256603 (2003)

R. Wang et al.: APL 86, 052901 (2005)

…

● Light emission near edge of the 2DHG

● 2DHG with strong and tunable SO

● Spin detection directly in the 2DHG

● No hetero-interface along the LED current

2DHG2DHG

2DEG2DEG

p -AlG a As

i-G a As

n- -d o p e d AlG a As

e tc he d

QW

I

Top Emission

Side Emission

Electrode

Spin polarization detected through circular polarization of emitted lightSpin polarization detected through circular polarization of emitted light

Conventional vertical spin-LED

Novel co-planar spin-LED

Y. Ohno et al.: Nature 402, 790 (1999)

R. Fiederling et al.: Nature 402, 787 (1999)

B. T. Jonker et al.: PRB 62, 8180 (2000)

X. Jiang et al.: PRL 90, 256603 (2003)

R. Wang et al.: APL 86, 052901 (2005)

…

● No hetero-interface along the LED current

● Spin detection directly in the 2DHG

● Light emission near edge of the 2DHG

● 2DHG with strong and tunable SO

2DHG2DHG

2DEG2DEG

p-AlGaAs

i-GaAs

n--doped AlGaAs n- -doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs

etched

n--doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs n- -doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs

etched

n--doped AlGaAs

-200

-100

0

-2 -1 0 1 2

p EF

p, n [1018

/cm3]

VB CB

Energy [eV]

z [n

m]

0 1 2

p-AlGaAs

i-GaAs

n--doped AlGaAs n- -doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs

etched

n--doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs n- -doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs

etched

n--doped AlGaAs

-2 -1 0 1 2-200

-100

0

p, n [1018

/cm3]

VB CB

z [n

m]

Energy [eV]

0 1 2

EF

n

Wafer design based on Schrödinger-Poisson simulations

CO-PLANAR CO-PLANAR pn pn - JUNCTION- JUNCTION

n - region p - region

Carrier density: n = 0.8 1012 cm-2 p = 2.0 1012 cm-2

Mobility: µHn 2900 cm2/Vs µHp 3400 cm2/Vs

pn - junction● Rectifying ● Light emission for e VBias EG

● Light emission near junction in p-region

np10 µm

6 8 10 12

-100

-50

0

50

100

150

B [T]

0.0

0.5

1.0

1.5

2.0

R2P

-qu

adra

tic

fit

[]

RH

all [

k]

0 2 4 6 8 104

6

8

10

12

B [T]

0

2

4

6

8

10R

2P [

k]

RH

all [

k]

-12 -10 -8 -6 -4 -2 0 2

0.0

0.2

0.4

0.6

0.8

Bia

s C

urre

nt in

A

Bias Voltage in V

Reverse breakdown:VR = -11.5V (T = 4.2K)

0.0 0.5 1.0 1.5 2.0

1E-11

1E-9

1E-7

1E-5

1E-3

300K 4.2K

Cur

rent

[A]

Voltage [V]

Light emission

● 2D transport characteristics

-150

-100

-50

0

-2 -1 0 1 2

p-AlGaAs

i-GaAs

n--doped AlGaAs n- -doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs

etched

n--doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs n- -doped AlGaAs

p-AlGaAs

i-GaAs

n--doped AlGaAs

etched

n--doped AlGaAs

p -AlGaAs

GaAs

1m

z [n

m]

Energy [eV]

E

z

Electron – 2D holes recombination

possible

-150

-100

-50

0

-2 -1 0 1 2

-+

Band-flattening if forward biased

0 -50 -100 -150-2

-1

0

1

2

E [

eV]

p-AlGaAs

n-AlGaAs

GaAs/AlGaAs superlatticeGaAs substrate

etched

2DEG2DHG

i-GaAs

y

z GaAsp-AlGaAs

n-AlGaAs

GaAs/AlGaAs superlatticeGaAs substrate

etched

2DEG2DHG

i-GaAs

y

z GaAs

z [nm]

0

2

4

6

8

10

Wafer 1

Wafer 2

Int

[a.u.]

E [eV]1.48 1.49 1.50 1.51 1.52

0

2

4

6

8

10

I

X

I

X

PL

p-AlGaAs

GaAs

0 -50 -100 -150-2

-1

0

1

2

E [

eV]

p-AlGaAs

n-AlGaAs

GaAs/AlGaAs superlatticeGaAs substrate

etched

2DEG2DHG

i-GaAs

y

z GaAsp-AlGaAs

n-AlGaAs

GaAs/AlGaAs superlatticeGaAs substrate

etched

2DEG2DHG

i-GaAs

y

z GaAs

z [nm]

0

2

4

6

8

10

Wafer 1

Wafer 2

Int

[a.u.]

E [eV]1.48 1.49 1.50 1.51 1.52

0

2

4

6

8

10

I

X

I

X

PL

0

2

4

6

8

10

Wafer 1

Wafer 2

Int

[a.u.]

E [eV]1.48 1.49 1.50 1.51 1.52

0

2

4

6

8

10

I

X

I

X

PL

p-AlGaAs

GaAs

Sub GaAs gap spectra analysis: PL vs EL

X : bulk GaAs excitons

I : recombinationwith impurity states

Sub GaAs gap spectra analysis: PL vs EL

Wafer 1

0 -50 -100 -150-2

-1

0

1

2

Wafer 2

Int

[a.u.]

E [eV]

E [

eV]

0

2

4

6

8

10

1.48 1.49 1.50 1.51 1.520

2

4

6

8

10

p-AlGaAs

n-AlGaAs

GaAs/AlGaAs superlatticeGaAs substrate

etched

2DEG2DHG

i-GaAs

y

z GaAsp-AlGaAs

n-AlGaAs

GaAs/AlGaAs superlatticeGaAs substrate

etched

2DEG2DHG

i-GaAs

y

z GaAs

z [nm]

I

X

I

X

A

A

B

B

C

PLEL

p-AlGaAs

GaAs

X : bulk GaAs excitons

I : recombinationwith impurity states

BB ( (A,CA,C): ): 3D electron – 3D electron – 2D hole 2D hole recombinationrecombination

+-

Wafer 1

0 -50 -100 -150-2

-1

0

1

2

Wafer 2

Int

[a.u.]

E [eV]

E [

eV]

0

2

4

6

8

10

1.48 1.49 1.50 1.51 1.520

2

4

6

8

10

p-AlGaAs

n-AlGaAs

GaAs/AlGaAs superlatticeGaAs substrate

etched

2DEG2DHG

i-GaAs

y

z GaAsp-AlGaAs

n-AlGaAs

GaAs/AlGaAs superlatticeGaAs substrate

etched

2DEG2DHG

i-GaAs

y

z GaAs

z [nm]

I

X

I

X

A

A

A

A

B

B

B

B

C

C

PLEL

p-AlGaAs

GaAs

Sub GaAs gap spectra analysis: PL vs EL

X : bulk GaAs excitons

I : recombinationwith impurity states

BB ( (A,CA,C): ): 3D electron – 3D electron – 2D hole 2D hole recombinationrecombination

Bias dependent emission wavelength for 3D electron – 2D hole Bias dependent emission wavelength for 3D electron – 2D hole recombination recombination [A. Y. Silov et al., APL 85, 5929 (2004)][A. Y. Silov et al., APL 85, 5929 (2004)]

++--

EXPERIMENT

2DHG 2DEG

Occupation-asymmetry mostly due to

“Mal’shukov effect”

Light polarization due to recombination with SOLight polarization due to recombination with SO--split split holehole--subbandsubband in a in a pp--nn LED under forward biasLED under forward bias

spin operators of holes: j=3s

-0.2 0.0 0.2-0.50

-0.25

0.00

0.25

0.50

<sx>HH+

<sx>HH-

<sz>HH--

<<sszz>>HHHH++

<S

>

ky [nm-1]

spin-polarization of HH+ and HH- subbands

-0.2 0.0 0.2-0.50

-0.25

0.00

0.25

0.50

-0.2 0.0 0.2-0.50

-0.25

0.00

0.25

0.50

<sx>HH+

<sx>HH-

<sz>HH--

<<sszz>>HHHH++

<S

>

ky [nm-1]

spin-polarization of HH+ and HH- subbands

inin--planeplane polarization

0

20

E [

meV

]

a

HH+

HH-LH

- +

-20

0

20

ky [nm-1]

3D electron-2D hole Recombination

-0.2 0.0 0,2

0

20

E [

meV

]

a

HH+

HH-LH

- +

-20

0

20

ky [nm-1]

3D electron-2D hole Recombination

0

20

E [

meV

]

a

HH+

HH-LH

- +

-20

0

20

ky [nm-1]

0

20

E [

meV

]

a

HH+

HH-LH

- +

-20

0

20

0

20

E [

meV

]

a

HH+

HH-LH

- +

-20

0

20

0

20

E [

meV

]

a

HH+

HH-LH

- +

-20

0

20

ky [nm-1]

3D electron-2D hole Recombination

-0.2 0.0 0,2

s=1/2 electrons to j=3/2 holes plus selection rules

circular polarization of emitted light

Microscopic band-structure calculations of the 2DHG:

12.00 12.05 12.10 12.15 12.20 12.25 12.30

0

1

2

3

4

5

6

7

1.488 1.494 1.500 1.506 1.513 1.519 1.525

[eV]

EL

inte

nsi

ty [

a.u

.]

energy [103 cm

-1]

-5.0

-2.5

0.0

2.5

5.0

Deg

ree of C

ircular p

olarizatio

n [%

]

Circular Polarization of EL detected at perpendicular to 2DHG plane

z

j

z

j

z

j

-10

-5

0

5

10

Deg

ree of C

ircular p

olarizatio

n [%

]

12.00 12.05 12.10 12.15 12.20 12.25 12.30

0

1

2

3

4

5

6

1.488 1.494 1.500 1.506 1.513 1.519 1.525

[eV]

EL

inte

nsi

ty [

a.u

.]

energy [103 cm

-1]

Inplane Circular Polarization (= 85º) detected at B = + 3T.

-10

-5

0

5

10

Deg

ree of C

ircular p

olarizatio

n [%

]

12.00 12.05 12.10 12.15 12.20 12.25 12.30

0

1

2

3

4

5

6

1.488 1.494 1.500 1.506 1.513 1.519 1.525

[eV]

EL

inte

nsi

ty [

a.u

.]

energy [103 cm

-1]

Inplane Circular Polarization (= 85º) detected at B = 3T.

Wafer 1

Int

[a.u.]

E [eV]

0

2

4

6

8

10

0

2

4

6

8

10I

XA B

PLEL

1.48 1.50 1.52

1.500 1.505-20

-10

0

10

20

Bz = +3T

Bz = -3T-10

-5

0

5

10

Bx = +3T

Bx = -3T

E [eV]-3 -2 -1 0 1 2 3

xy

z , B

xy

z , B

B [T]

x, By

z

x, By

z

x, By

α

x, By

z

x, By

z

x, By

x, By

z

x, By

z

x, By

z

x, By

α

CP

[%]

1.500 1.505-20

-10

0

10

20

Bz = +3T

Bz = -3T-10

-5

0

5

10

Bx = +3T

Bx = -3T

E [eV]-3 -2 -1 0 1 2 3

xy

z , B

xy

z , B

B [T]

x, By

z

x, By

z

x, By

α

x, By

z

x, By

z

x, By

x, By

z

x, By

z

x, By

z

x, By

α

CP

[%]

In-plane

detection angle

Circular Polarization

1.500 1.505-20

-10

0

10

20

Bz = +3T

Bz = -3T-10

-5

0

5

10

Bx = +3T

Bx = -3T

E [eV]-3 -2 -1 0 1 2 3

xy

z , B

xy

z , B

B [T]

x, By

z

x, By

z

x, By

α

x, By

z

x, By

z

x, By

x, By

z

x, By

z

x, By

z

x, By

α

CP

[%]

1.500 1.505-20

-10

0

10

20

Bz = +3T

Bz = -3T-10

-5

0

5

10

Bx = +3T

Bx = -3T

E [eV]-3 -2 -1 0 1 2 3

xy

z , B

xy

z , B

B [T]

x, By

z

x, By

z

x, By

α

x, By

z

x, By

z

x, By

x, By

z

x, By

z

x, By

z

x, By

α

CP

[%]

NO perp.-to-plane component of polarization at B=0NO perp.-to-plane component of polarization at B=0

BB≠0 behavior consistent with SO-split HH subband≠0 behavior consistent with SO-split HH subband

In-plane

detection angle

Perp.-to plane

detection angle

Circular Polarization

j

SHE

Spin Hall Effect Spin Hall Effect

Perpendicular-to-plane spin-polarization

EXPERIMENT

Spin Hall Effect

2DHG

2DEG VT

VD

Spin Hall Effect Device

1 .5 mc h a n n e l

n

n

py

xz

L E D 1

L E D 2

I P

xy

zIp

-Ip

ILED 1

Experiment “A”

xy

zIpILED 1

ILED 2

Experiment “B”

Experiment “B”

1.505 1.510 1.515 1.520

-1

0

1

xy

zIpILED 1

ILED 2

CP

[%]

1.505 1.510 1.515 1.520

-1

0

1

xy

zIpILED 1

ILED 2

xy

zIpILED 1

ILED 2

CP

[%]

Experiment “A”

-1

0

1

xy

zIp

-Ip

ILED 1

CP

[%]

-1

0

1

xy

zIp

-Ip

ILED 1

-1

0

1

xy

zIp

-Ip

ILED 1

xy

zIp

-Ip

ILED 1

CP

[%]

Opposite perpendicular polarization for opposite Opposite perpendicular polarization for opposite IIpp currents currents

or opposite edges or opposite edges SPIN HALL EFFECT SPIN HALL EFFECT

Comparing extrinsic and intrinsic SHE contribution for our system by taking HH mass and mobility in account:

-within the intrinsic SHE regime- larger contribution from intrinsic SHE

Changing confinement, charge carrier density, via gating, wafer design, temperature dependence,etc.

Outlook

2DHG

2DEG

2DEG GATEGATE jpn

GATEGATE j

SHE in with differently confined 2DHG

2DHG

2DHG

2DEG

SHE in 2DHG and 2DEG

n

p2 0 m

MMM

ex tB

M

Before

and

after an in-planemagnetic field was applied

Stray-field into the inversion layer

Expect field strength at2DEG of approx. 0.1 –0.2 T

12.15 12.20 12.25 12.30

1.506 1.513 1.519 1.525

[eV]

energy [103 cm-1]

0.0

1.0

Circu

lar po

larization

[%]

[T]B

[nm]z[nm]x

z

M

x

d

z

M

x

z

M

x

dd = 50 nm

[T]B

[nm]z[nm]x

z

M

x

d

z

M

x

z

M

x

dd = 50 nm

z

M

x

d

z

M

x

z

M

x

dd = 50 nm

[T]B

[nm]z[nm]x

z

M

x

d

z

M

x

z

M

x

dd = 50 nm

[T]B

[nm]z[nm]x

z

M

x

d

z

M

x

z

M

x

dd = 50 nm

z

M

x

d

z

M

x

z

M

x

dd = 50 nm

[T]B [T]B [T]B

[nm]z [nm]z [nm]z[nm]x [nm]x [nm]x

z

M

x

d

z

M

x

z

M

x

dd = 50 nm

z

M

x

d

z

M

x

z

M

x

d

z

M

x

z

M

M

x

d

z

M

x

z

M

x

d

z

M

M

x

z

M

M

x

dd = 50 nm

[T]B [T]B [T]B

[nm]z [nm]z [nm]z[nm]x [nm]x [nm]x

z

M

x

d

z

M

x

z

M

x

d

z

M

x

z

M

M

x

d

z

M

x

z

M

x

d

z

M

M

x

z

M

M

x

dd = 50 nm

z

M

x

d

z

M

x

z

M

x

d

z

M

x

z

M

M

x

d

z

M

x

z

M

x

d

z

M

M

x

z

M

M

x

dd = 50 nm

magnetic particle on top of 2DEG channel

MFM micrograph

Locally induced Electron spin polarizationLocally induced Electron spin polarization

Conclusion

• Spin polarization due to occupation-asymmetryDetection of in-plane net-spin-polarization

• spin-Hall effect in hole systemDetection of perpendicular-to-plane polarization