Semiconductor spintronics in ferromagnetic and non-magnetic

woundcallousSemiconductor

Nov 1, 2013 (3 years and 5 months ago)

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Semiconductor spintronics in ferromagnetic and non
-
magnetic
p
-
n junctions

Tom
áš

Jungwirth





Universit
y of Nottingham



Bryan Gallagher, Tom Foxon,


Richard Campion, Kevin Edmonds,


Andrew Rushforth,

et al.



Hitachi & Univ. Cambridge




Andrew Irvine,

David Williams,

Elisa de Ranieri, Byonguk Park,

Sam Owen,
et

a
l.

Institute of Physics ASCR



Vít Novák
,

Kamil Olejník, Miroslav Cukr,

Jorg Wunderlich
,

Alexander Shick
,

Karel Výborný,
Jan Zemen, Jan Ma
š
ek,

Josef Kudrnovsk
ý
, Franti
š
ek M
á
ca,

Jairo Sinova, Zden
ě
k V
ý
born
ý
,

Vlastimil Jurka, Karel Hru
š
ka, et al.


University of Texas



Allan MacDonald et al.

Outline

1. Ferromagnetic semiconductor


spintronics (GaMnAs)



-

ferromagnet like Fe,Ni,…


singular
d

/dT

at
T
c




-

semiconductor like GaAs:C


p
-
n junction transistor

2. Non
-
magnetic semiconductor


spintronics



-

spin detection via spin
-
injection
Hall effect


-

spin
-
photovoltaic


p
-
n junction cell

Ni

GaMnAs

Ferromagnetic semiconductor (Ga,Mn)As

E
F

DOS

Energy

spin


spin


<< 1% Mn

~1% Mn

>2% Mn

onset of ferromagnetism near MIT

Very dilute and random moments



compare with dense&ordered Fe, Ni,..

Very heavily doped semiconductor



compare with GaAs:C MIT at 0.01%C

Critical behavior of resistivity near T
c

Ordered magnetic semiconductors

Disordered DMSs

Sharp critical behavior of resistivity at T
c

Broad

peak near T
c

and

disappeares

in annealed optimized materials

Eu


chalcogenides

Fisher&Langer, PRL‘68

singular

Nickel

Scattering off correlated spin
-
fluctuations

singular

Eu
0.95
Gd
0.05
S

Fisher&Langer, PRL‘68

singular

Nickel

Scattering off correlated spin
-
fluctuations

singular

Eu
0.95
Gd
0.05
S

Fisher&Langer, PRL‘68

singular

Nickel

Scattering off correlated spin
-
fluctuations

singular

GaMnAs

Eu
0.95
Gd
0.05
S

Novak et al., PRL‘08

Optimized materials with

upto ~8% Mn
Ga

and T
c

upto
~190 K

Optimized (Ga,Mn)As materials


well behaved itinerant ferromagnets
resembling Fe, Ni, ….

Annealing sequence of

a 8% Mn
Ga

material

Optimized materials with

upto ~8% Mn
Ga

and T
c

upto
~190 K

Low
-
voltage gating of the highly doped GaAs:Mn

Conventional MOS FET: ~10
-
100 Volts
Ohno et al. Nature ’00, APL ‘06

All
-
semiconductor p
-
n junction FET

Owen, et al. New J. Phys.‘09


d
p

d
p

E
gap

V
G

p

n

p

n

Significant depletion in 5
-
10 nm (Ga,Mn)As at
V
G
~ E
gap
~1 Volts

Low
-
voltage gating of the highly doped GaAs:Mn

Conventional MOS FET: ~10
-
100 Volts
Ohno et al. Nature ’00, APL ‘06

Significant depletion in 5
-
10 nm (Ga,Mn)As at
V
G
~ E
gap
~1 Volts

2x 10
19

cm
-
3

All
-
semiconductor p
-
n junction FET

Owen, et al. New J. Phys.‘09

Numerical simulations

Low
-
V tunable coercivity

Switching by short low
-
V pulses

Low
-
V accummulation/depletion

(Ga,Mn)As p
-
n junction spintronic transistor

Zener kinetic
-
exchange (Ga,Mn)As SC with ~8%Mn
Ga


T
c



190 K

compare with Stoner MnAs metal with 100%Mn
Ga



T
c



300 K



T
c
in (Ga,Mn)As in fact remarkable large
T
c
‘s

8%Mn
Ga

0%Mn
Ga

Edmonds et al. APL‘08



Other semiconductor hosts, e.g. Li(Zn,Mn)As

Mn
Zn

isovalent


no doping limit & independent control
of carrier and moment concentrations



Proximity effects in FS/FM hybrids

Magnetic behavior of a (Ga,Mn)As interfacial layer at room
-
T

Masek et al., PRL‘07

Maccherozzi et al., PRL‘08

1
st

part summary remarks



Low
-
V gating of GaMnAs by ferroelectric gate

A superhybrid
ferromagnetic/ferroelectric/semiconductin FET

Stolichnov et al., Nature Materials ‘08

Maruyama et al., Nature Nanotechnology ‘08



Electrical gate control of ultra
-
thin Fe on Au

40% change of magnetic anisotropy by modest
electric fields at room
-
T

2. Non
-
magnetic semiconductor


spintronics



-

spin detection via spin
-
injection
Hall effect


-

spin
-
photovoltaic


p
-
n junction cell

Ni

GaMnAs

1. FM SC spintronics (GaMnAs)


Summary






singular
d

/dT

at
T
c




very well behaved itinerant FM






p
-
n junction transistor


controlled by ~1V fields




high
-
speed SC (opto
-
) spintronics

Spin
-
detection in semiconductors

Ohno et al. Nature’99, others



Magneto
-
optical imaging


non
-
destructive



lacks nano
-
scale resolution


and only an optical lab tool




MR Ferromagnet




electrical



destructive and requires


semiconductor/magnet hybrid


design & B
-
field to orient the FM




spin
-
LED



all
-
semiconductor



destructive and requires


further conversion of emitted


light to electrical signal


Datta
-
Das transistor

Spin
-
detection in semiconductors

Ohno et al. Nature’99, others

Crooker et al. JAP’07, others



Magneto
-
optical imaging


non
-
destructive



lacks nano
-
scale resolution


and only an optical lab tool




MR Ferromagnet




electrical



destructive and requires


semiconductor/magnet hybrid


design & B
-
field to orient the FM




spin
-
LED



all
-
semiconductor



destructive and requires


further conversion of emitted


light to electrical signal




Spin
-
injection Hall effect





non
-
destructive



electrical



100
-
10nm resolution with current lithography



in situ
directly along the SC channel


(all
-
SC requiring no magnetic elements in the structure or B
-
field)


Wunderlich et al. arXives:0811.3486


Family of spintronic Hall effects

(induced by spin
-
orbit coupling)









+ + + +

+ + + +










j
q
s

nonmagnetic

Spin
-
polarizer

(e.g. ferromagnet,


light)

Spin injection Hall effect (SIHE)

SIHE: spatially dependent unlike AHE in uniformly polarized systems


Family of spintronic Hall effects

(induced by spin
-
orbit coupling)
























+ + + + + + + + + +

j
q
s

nonmagnetic

Spin
-
polarizer

(e.g. ferromagnet ,


light)

Spin injection Hall effect (SIHE)

SIHE: spin
-
polarized charge current unlike (i)SHE


Family of spintronic Hall effects

(induced by spin
-
orbit coupling)

22

i

p

n

2DHG

Optical injection of spin
-
polarized charge currents into Hall bars




GaAs/AlGaAs planar 2DEG
-
2DHG photovoltaic cell

-

2DHG

i

p

n

23

Optical injection of spin
-
polarized charge currents into Hall bars




GaAs/AlGaAs planar 2DEG
-
2DHG photovoltaic cell

i

p

n

2DHG

2DEG

24

Optical injection of spin
-
polarized charge currents into Hall bars




GaAs/AlGaAs planar 2DEG
-
2DHG photovoltaic cell

2DHG

2DEG

e

h

e

e

e

e

e

h

h

h

h

h

V
H

25

Optical injection of spin
-
polarized charge currents into Hall bars




GaAs/AlGaAs planar 2DEG
-
2DHG photovoltaic cell

Optical spin
-
generation area near the p
-
n junction

Simulated band
-
profile

p
-
n junction bulit
-
in potential (depletion length ) ~ 100 nm



self
-
focusing of the generation area of counter
-
propagating e
-

and h
+

Hall probes further than 1

m from the p
-
n junction



safely outside the spin
-
generation area

see also Bernevig

et al., PRL‘06

Spin
-
diffusion along the channel

of injected spin
-


electrons

Spin
-
charge dynamics in disordered 2DEG with

in
-
plane Rashba (

)
/ Dresselhaus (

) spin
-
orbit fields


SO
-
length (~1

m)

see also Bernevig

et al., PRL‘06

Spin
-
diffusion along the channel

of injected spin
-


electrons

Local spin
-
dependent transverse deflection
due to skew scattering

Spin
-
charge dynamics in disordered 2DEG with

in
-
plane Rashba (

)
/ Dresselhaus (

) spin
-
orbit fields


SO
-
length (~1

m) >> mean
-
free
-
path (~10 nm)

0

1

2

3


SIHE device realization

n3,n2,n1: local SIHE

n0: averaged
-
SIHE / AHE

Spin
-
generation

area


-

V
sd
= 0V

0

1

2

3


SIHE detection at n2

R
Hall

[

]


+

n1

n2

Linear in the degree of circular polarization of light


spin
-
polarization of injected el.

SIHE survives to high temperatures


-


+

SIHE angle ~ 10
-
3

& +/
-

alternating on a

m scale, all as expected from theory


-


+

n0

n1

n2

n3


H

[10
-
3
]

2
nd

part . summary remarks



Spin
-
photovoltaic cell: polarimeter on a SC chip requiring no magnetic elements,


external magnetic field, or bias; form IR to visible light depending on the SC




Spin
-
detection tool for other device concepts (e.g. Datta
-
Das transistor)





Basic studies of quantum
-
relativistic spin
-
charge dynamics also in the intriguing


and more controversial strong SO regime in archetypal 2DEG systems