Semiconductor spintronics in ferromagnetic and non-magnetic p-n junctions Tomas Jungwirth University of Nottingham Bryan Gallagher, Tom Foxon, Richard

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


Nickel


UdF ~)~(


Eu0.95Gd0.05S

00~)( SSSST ii


Nickel


UdF ~)~(


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


– – – – – – – – – – –

+ + + + + + + + + +

jqs

nonmagneticSpin-polarizer(e.g. ferromagnet , light)

Spin injection Hall effect (SIHE)Spin injection Hall effect (SIHE)


js––– – –– – –– – –

+ + + + + + + + + +iSHE

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

Family of spintronic Hall effects (induced by spin-orbit coupling)

jqs

––– – –– – –– – –

+ + + + + + + + + +AHE


– – – – + + + +

+ + + + – – – –

jqs

nonmagneticSpin-polarizer(e.g. ferromagnet, light)

Spin injection Hall effect (SIHE)Spin injection Hall effect (SIHE)


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



i

p

n2DHG

2DEG

25



2DHG

2DEG

e

h

ee

ee

e

hh

h

h h

VH

26



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

Documents

Semiconductor spintronics in ferromagnetic and non-magnetic p-n junctions Tomas Jungwirth University of Nottingham Bryan Gallagher, Tom Foxon, Richard