Detection of current induced Spin polarization with a co-planar spin LED J. Wunderlich (1), B....
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Transcript of Detection of current induced Spin polarization with a co-planar spin LED J. Wunderlich (1), B....
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