Semiconductor spintronics in ferromagnetic and non-magnetic p-n junctions
Tomas Jungwirth
University of Nottingham
Bryan Gallagher, Tom Foxon, Richard Campion, Kevin Edmonds,
Andrew Rushforth, et al.
Hitachi Cambridge, Univ. Cambridge
Jorg Wunderlich, Andrew Irvine, David Williams, Elisa de Ranieri, Byonguk Park, Sam Owen, et al.
Institute of Physics ASCR
Vít Novák, Alexander Shick, Karel Výborný, Jan Masek, Josef Kudrnovsky, et al.
Texas A&M, University of Texas
Jairo Sinova, Allan MaDonald et al.
Outline
1. Ferromagnetic semiconductor spintronics (GaMnAs)
- ferromagnet like Fe,Ni,… singular d/dT at Tc
- 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
Ni
GaMnAs
Ferromagnetic semiconductor (Ga,Mn)As
EF
DO
S
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 Tc
Ordered magnetic semiconductors Disordered DMSs
Sharp critical behavior of resistivity at Tc Broad peak near Tc and disappeares in annealed optimized materials
Euchalcogenides
00~)( SSSST ii
Fisher&Langer, PRL‘68 ~)( dFsingular
Nickel
Scattering off correlated spin-fluctuations
UdF ~)~(
vcdTdUdTd /~/singular
Eu0.95Gd0.05S
00~)( SSSST ii
Fisher&Langer, PRL‘68 ~)( dFsingular
Nickel
Scattering off correlated spin-fluctuations
UdF ~)~(
vcdTdUdTd /~/singular
Eu0.95Gd0.05S
00~)( SSSST ii
Fisher&Langer, PRL‘68 ~)( dFsingular
Nickel
Scattering off correlated spin-fluctuations
UdF ~)~(
vcdTdUdTd /~/singular
GaMnAsEu0.95Gd0.05S
Novak et al., PRL ‚08
Optimized materials withupto ~8% MnGa and Tc upto ~190 K
Optimized (Ga,Mn)As materials well behaved itinerant ferromagnets
resembling Fe, Ni, ….
Annealing sequence ofa 8% MnGa material
Optimized materials withupto ~8% MnGa and Tc upto ~190 K
8%MnGa0%MnGa
Zener kinetic-exchange (Ga,Mn)As SC with ~8%MnGa Tc 190 K
compare with Stoner MnAs metal with 100%MnGa Tc 300 K
Below room-temperature Tc in (Ga,Mn)As but in fact remarkable large Tc ‘s
Edmonds et al., APL‘08
MIT in p-type GaAs:
- C (30meV) ~ 1018 cm-3
- Mn (110meV) ~1020 cm-3
Mobilities in GaAs:Mn:
- 3-10x larger in GaAs:C- similar in GaAs:Mg
Short-range p-d kinetic-exchange (hybridization) alone cannot bind the hole
same type of MIT (screening of long-range Coulomb) as with C, … but shifted to significantly higher dopings
GaAs:Mn – a doped p-type semiconductor
Mn-d localmoments
As-p holes
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. arXiv:0807.0906
dp
dp
Egap VG
p n p n
Significant depletion in 5-10 nm (Ga,Mn)As at VG ~ Egap ~1 Volts
snm' ~])(
)(2[ 2/1
pnp
VEnd Ggap
p
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 VG ~ Egap ~1 Volts
2x 1019 cm-3
All-semiconductor p-n junction FET Owen, et al. arXiv:0807.0906
Numerical simulations
Low-V tunable coercivity
Switching by short low-V pulses
Low-V accummulation/depletion
(Ga,Mn)As p-n junction spintronic transistor
Low-V controlled Kc and Ku magnetic anisotropies
-1V +3 V
Experiment Theory
Ni
GaMnAs
1. FM SC spintronics (GaMnAs) Summary
singular d/dT at Tc very well behaved itinerant FM p-n junction transistor controlled by ~1V fields high-speed SC (opto-) spintronics
2. Non-magnetic semiconductor spintronics
- spin detection via spin-injection Hall effect
- spin-photovoltaic p-n junction
Ni
GaMnAs
1. FM SC spintronics (GaMnAs) Summary singular d/dT at Tc 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
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
jqs
––– – –– – –– – –
+ + + + + + + + + +AHE
Ferromagnetic(polarized charge current)
nonmagnetic (pure spin current)
js––– – –– – –– – –
+ + + + + + + + + +iSHE
(induced by spin-orbit coupling)
jqs
––– – –– – –– – –
+ + + + + + + + + +AHE
Ferromagnetic(polarized charge current)
– – – – – – – – – – –
+ + + + + + + + + +
jqs
nonmagneticSpin-polarizer(e.g. ferromagnet , light)
Spin injection Hall effect (SIHE)Spin injection Hall effect (SIHE)
nonmagnetic (pure spin current)
js––– – –– – –– – –
+ + + + + + + + + +iSHE
SIHE: spin-polarized charge current unlike (i)SHE
Family of spintronic Hall effects (induced by spin-orbit coupling)
jqs
––– – –– – –– – –
+ + + + + + + + + +AHE
Ferromagnetic(polarized charge current)
– – – – + + + +
+ + + + – – – –
jqs
nonmagneticSpin-polarizer(e.g. ferromagnet, light)
Spin injection Hall effect (SIHE)Spin injection Hall effect (SIHE)
nonmagnetic (pure spin current)
js––– – –– – –– – –
+ + + + + + + + + +iSHE
SIHE: spatially dependent unlike AHE in uniformly polarized systems
Family of spintronic Hall effects (induced by spin-orbit coupling)
23
i pn2DHG
Optical injection of spin-polarized charge currents into Hall bars
GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell
-
2DHGi pn
24
Optical injection of spin-polarized charge currents into Hall bars
GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell
i
p
n2DHG
2DEG
25
Optical injection of spin-polarized charge currents into Hall bars
GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell
2DHG
2DEG
e
h
ee
ee
e
hh
h
h h
VH
26
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 1m from the p-n junction safely outside the spin-generation area
see also Bernevig et al., PRL‘06
Spin-diffusion along the channelof injected spin- electrons
Spin-charge dynamics in disordered 2DEG within-plane Rashba () / Dresselhaus () spin-orbit fields
SO-length (~1m)
see also Bernevig et al., PRL‘06
Spin-diffusion along the channelof injected spin- electrons
Local spin-dependent transverse deflection due to skew scattering ~10nm
Spin-charge dynamics in disordered 2DEG within-plane Rashba () / Dresselhaus () spin-orbit fields
SO-length (~1m) >> mean-free-path (~10 nm)
Our 2DEG in the weak spin-orbit, strong scattering regime non-controversial
Typical spin-orbit length in GaAs 2DEG ~ m
injected spins will rotate at m scale
Hall effect in the diffusive regime dominated by skew-scattering
Hall angles ~10-3 (comparable to AHE in FMs)
In-plane SO field
Diffusion of out-of-plane injected spins
Skew-scattering off SO-imputity potential
Corresponding Hall angle for a givenout-of-plane polarization
0123
SIHE device realization
n3,n2,n1: local SIHE n0: averaged-SIHE / AHE
Spin-generation area
0 25 50 750
10
20
RL [
k]
tm [s]
-50
-25
0
25
50
-
Vsd= 0V
0123
SIHE detection at n2
RH
all [
]
+
-1.0 -0.5 0.0 0.5 1.0
-10
-5
0
5
10
H [
10-3 ]
( ) / (
)
-1.0 -0.5 0.0 0.5 1.0-2
-1
0
1
2
H [
10-3 ]
( ) / (
)
n1 n2
Linear in the degree of circular polarization of light spin-polarization of injected el.
0 30 60 90 120 150 180-5
0
5 100K 160K (x2) 220K (x3)
H [1
0-3]
tm [s]
SIHE survives to high temperatures
-
+
SIHE angle ~ 10-3 & +/- alternating on a m scale, all as expected from theory
0 10 20 30 40 50-10
-5
0
5
10
n0 (x3) n2
tm [s]
H [1
0-3]
n1 (x3) n3 (x3)
-
+
n0n1n2n3
H [10-3]
x [m]
2. Non-magnetic SC spintronics Summary
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
Ga
As
Mn-
h+
h+
Mn-
Ga
AsMn