Diluted Magnetic Semiconductors

David FerrandEquipe mixte CNRS-CEA-UJF “Nanophysique et semiconducteurs”

Laboratoire de Spectrométrie Physique, BP 87 38402 Saint Martin d’Hères

Injection and manipulation of spins in semiconductors

M. Kohda et al, Jpn. J. Appl. Phys., Part 2 40, L1274 (2001)

Electrical spin injection, spin transport, tunnel structure

R. Mattana et al, Phys Rev Lett, 90 166601 (2003)

Kroutvar et al., Nature 432,81 (2004)

Spin manipulation

II : High band gap diluted magnetic semiconductors GaMnN/ZnCoO ZnCrTe

Outline

I : Spins localized in II-VI heterostructures

2. CdTe quantum dots doped with a single Mn atom

1. GaMnN, ZnCoO2. ZnCrTe

1. Modulation doped heterostructures : II-VI Ferromagnetic quantum wells

I II Valence mixte I, II, III… III IV V VI VII VIII

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Rb Sr Y Zr Nb Mo Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

II

II-VI semimagnetic heterostructures

Cd0.7Mg0.3Te

Cd0.7Mg0.3TeCdTe

Cd0.88Zn0.12Tesubstrate

L

ZnTe

ZnTe

ZnTesubstrate

CdTeCdTe

CdTe/CdMgTe quantum wells

CdTe/ZnTe quantum dots

Magnetic alloys : Cd1-xMnxTe, Zn1-xMnxTe

Mn : 4s2 3d5

With a large Mn solubility up to 75%

S=5/2 localized spinsIsoelectronic element

Almost perfect semiconducting properties

Magnetic properties : Short range antiferromagnetic interactionsa

J. Furdyna et al, JAP 64 R29 (1988)

kT << J1

AF

eff

TT

xC

0

cwTT

xC

0

J2, J3~0.5K

N.N pairs J1~20K

0,0 0,1 0,2 0,3 0,4 0,50,00

0,01

0,02

0,03

0,04

0,050,0 0,1 0,2 0,3 0,4 0,5

0,00

0,01

0,02

0,03

0,04

0,05

Mn content x

xeff

Small concentration of free spins

Studies at low temperatureswith diluted alloys

p type modulation doped CdMnTe QWs

Mn Compositions 0-4%Hole densities 1-3 1011 cm-2

Magnetic quantum well Cd(1-x)MnxTe 80 Å

Barrierspacer

2D hole gas

SubstrateCdMgTe

80 Å

E1

HH1

Nitrogen

0 100 200 300 400 500 600

1010

1011

Hol

e G

as C

once

ntra

tion

(cm

-2)

Cap layer Thickness (Å)

Surface doped CdMnTe QW

15 nm < z < 60 nm

After surface oxydation

Mn Compositions 0-11%Hole densities 1-2 1011 cm-2

W. Maslana, 2003

Magneto-optical spectroscopy : Giant Zeeman effect

Photon

E1

HH HH Excitons

+1

-1

1670 1680 1690 1700 1710 1720 1730 1740 1750 1760T=1.9K

Xhh B=+4 T+

-

HH -1

HH +1

Excitons

G.S

V

NS Mn

z )(

zeff SxN )(0

N0~0.2 eVN0~-1 eV

N0~few 1022 cm-3

±1/2

±3/2

)(.)(. MnhhMnee RrSRrSH

~-100 meV nm3 < 0

~25 meV nm3 > 0

Holes :

Electrons :

zSz

1650 1660 1670

-

+

400G

300G

200G

100G

0G

Photoluminescence 2.1K

2.4% Mn, p=1.6 1011cm-2

Energie (meV)

PL

(u.a

.)

PL at 2.1K, 2.4% Mn, 1.61011 cm-2

Haury et al, 1997

0 5001661

1662

1663

1664

1665

1.65K

PL Energy

(meV)

Magnetic field (Oe)

-2 -1 0 1 2 3 4 50.00

0.05

p-doped

undoped

Inverse susceptibility

(T/meV)

Temperature (K)

0 400

4.2K

Susceptibility

0 5001661

1662

1663

1664

1665

1.65K

PL Energy

(meV)

Magnetic field (Oe)

-2 -1 0 1 2 3 4 50.00

0.05

p-doped

undoped

Inverse susceptibility

(T/meV)

Temperature (K)

0 400

4.2K

Interactions ferromagnétiques induite par le gaz 2D

Tcw ~ 2 à 3 K > 0Tcw~-TAF=-2K < 0

Susceptibility measurements : Curie Weiss temperature

Coll. P. Kossacki, Warsaw

1700 1710

1.49 K

1.65

1.87

2.05

2.19

2.80

3.03

4.2 K

0V

PL In

tens

ity (a

.u.)

Energy (meV)

a

1700 1710

1.49 K1.65

1.88

2.05

2.19

2.82

2.97

b4.2 K

-1V

V

QW

barriers

p doped

n doped

undoped

Electrical control through an electrostatic gate

Hole gas depleted

H. Boukari et al, Phys. Rev. Lett. 88, 207204 (2002)

Tc

AFP2

eff0 TxCTC Comparison with mean field model predictions

Kossacki 2001

X 2.3

4% Mn

LA D

Fh2

2D D.O.S

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

Tem

pera

ture

(K

)

Mn content x (%)

Effective Mn content : xeff

TC > TCW ?

T. Dietl, Warsaw

TEM C. Bougerol.TEM C. Bougerol.

"Stranski-Krastanow"

h > hcSK

3D-coherent islands

Magnetic CdMnTe/ZnTe QDs

Strained induced CdTe/ZnTe QDs:

QDs density: 1010 cm-2

Size: d=25nm, h=3nm (Lz<<Lx,Ly)

UHV-AFM image ofUHV-AFM image of CdTe QDs on ZnTe.CdTe QDs on ZnTe.

Introduction of Mn atoms (3d5 4s2 ) carrying S=5/2 localized spin

Thèse L Maingault, H. Mariette

CdTe/ZnTe QDs doped with a single Mn atom

1950 2000 2050 2100

d 0,25 m

d 0,5 m

d 20 m

6,5 MLs

PL

Int

ensi

ty (

arb.

uni

ts)

Energy (meV)

meV50

eV50

Single dot spectroscopy :

Mn density = QDs density

Strained induced Cd(Mn)Te/ZnTe QDs:

Mn segregationMn segregationduring the growth ofduring the growth ofa spacer layer a spacer layer

Thèse L Maingault, H. Mariette

Thèse Y. Léger

100 m

Reference CdTe/ZnTe QDsReference CdTe/ZnTe QDs

Reference CdTe/ZnTe QD : :

Electron : s=1/2Anisotropic hole Jz=3/2

z

Jz=±3/2 // Oz

s=1/2

Growth axis

L. Besombes et al., Phys. Rev. Lett. 93, 207403 (2004)

B=0

+1

-1

G.S.

B=0

±1

-1

+1

S=5/2

CdTe QDs with an individual Mn spin

Mn-doped CdTe/ZnTe QDs:Mn-doped CdTe/ZnTe QDs:

6 twofold degenerateexcitonics levels

Total splitting 1.3 meV

Individual Mn-doped CdTe/ZnTe QDsIndividual Mn-doped CdTe/ZnTe QDs

Thèse Y. Léger

Exciton-Mn Exchange Coupling

2)(

3 MnhMnh RrI

zzMnheMne SjISIHH ..0

2)( MneMne RrI

S=5/2

Complexe X - Mn : s=1/2 + Jz=3/2 + S=5/2

zZBMn BSg

Mn2+

eh

eh

eh

eh

1zJ

X-5/2Jz = -1 Jz = +1

-3/2

-1/2

+1/2+3/2

+5/2Jz = -1

+5/2

+3/2

+1/2

-1/2-3/2

-5/2Jz = +1

Overall splitting : )3(2

5MnhMne II

Ie-Mn=-70 eV and Ih-Mn =350 eV.Detection and manipulation of a single Mn spin

Diamagnetic shift.

Changes in the PL intensity distribution.

Large anticrossing for five of the exciton lines around 6T.

Splitting of the six exciton lines.

Mn-Doped Individual QDs Under Magnetic Field

Additional tiny anticrossings.

NMn=0 NMn=1

1. GaMnN, ZnCoO2. ZnCrTe

II : High band gap diluted magnetic semiconductors GaMnN/ZnCoO

I II Valence mixte I, II, III… III IV V VI VII VIII

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Rb Sr Y Zr Nb Mo Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

II-VI : Cr2+ : 4s2 3d4

Co2+ : 4s2 3d7

III-V Mn 4s2 3d5 Acceptor : GaMnAs 3d5

Isoelectronic : 3d4

S. Sonoda et al. J.A.P. 156, 555 (2002)

MBE 3-6% Mn 2002

Tc>300K

(Ga,Mn)N2001

(Zn,Co)O : PLD 15-25% Co

K. Ueda et al, APL 79 988 (2001)

(Zn,Cr)Te

Towards room temperature diluted magnetic semiconductors ?

MBE 0< x < 50%

2003

H. Saito et al, 2003

- Paramagnetism + Ferromagnetism observed by SQUID

- No phase diagram with the magnetic ion compositionor correlation with other parameters

- Transport properties weakly sensitive to magnetic ions

-No sharp optical features close to band edges- No photoluminescence

Diluted high band gap alloys : GaMnN, ZnCoO

Tunnel junctions with (Zn,Co)O

ZnCrTe

High temperature ferromagnetism still controversial :

e t2BV BC

E

D.O.S

e t2

Partially filled d bands located within the gap ?

Cr2+ in II-VI

Mn3+ in III-V 3d4

E

BV BCe t2

Co2+ in ZnO 3d7

Ferromagnetism mediated by electrons ?

Al2O3 substrate

Buffer

WURTZITE epilayer c - axisZn1-xCoxO or Ga1-xMnxNGrown by Molecular Beam Epitaxy:•in CREHA Valbonne (Zn1-xCoxO)C. Deparis, C. Mohrhain•in Grenoble (Ga1-xMnxN)

e t2< 3d5BV BC

E

D.O.S

e t2

(Ga,Mn)N : 0.03% Mn

Magneto-optical spectroscopy of intraionic d-d transitions

Spin allowed transition at 1413 meV

4A2

Mn3+ 3d4

Tetrahedralcrystal field

Co2+ 3d7 5T2

5E2E

S=3/2

4F5D

S=2 Isoelectronic spins

(Zn,Co)O 2% Co

Spin forbidden transition at 1876 meV

W. Pacuski et al, Phys. Rev. B 73 035214 (2006)S. Marcet et al, cond-mat/0604025 2006

Ground state : Fine structure Hamiltonian parameters

g//=1.91gperp =1.98 Axial anisotropy : D=0.27 meV g//=2.28 Axial anisotropy : D=0.35 meV

)3/)1((.)( 2// SSSDSBgSBggH cccB

Axial anisotropy :

S. Marcet et al, cond-mat/0604025 2006

Evolution with of the magnetic ion concentration

Ga1-xMnxN

0,0 0,2 0,4 0,6 0,8 1,00,0

0,5

1,0

1,5

2,0

2,5

3,0

In

tegr

ated

Are

a [x

10 5

cm-2

]

Mn content [%]

Mn3+ incoporation up to about 1%

Zn1-xCoxO

0 1 2 3 4 5 6Co Concentration [%]

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1860 1880 1900

2E 2A

4A2

2E E

4A2

Photon Energy [meV]

Abs

orpt

ion

Coe

ffic

ient

[1/m

]

Co2+ incorporation up to 6%

W. Pacuski et al, Phys. Rev. B 73 035214 (2006)

1.7% Mn

Comparison with the magnetic propertiesGa1-xMnxN

0

0.5

1.0

1.5

2.0

2.5

0 5 10 15

0.5

1.0

1.50.4%Co

20K

7K

1.7K

Magnetic Field [T]Zee

man

Spl

itting

of ex

cito

n A

[m

eV]

Mea

n Spi

n of

Cob

alt

0

5

10

15

20

25

0 5 10 150

0.5

1.0

1.5

40K30K20K

10K

6K1.7K

2%Co

Magnetic Field [T]

-MC

D [de

g/m

]

Mea

n Spi

n of

Cob

alt

0

2

4

6

8

0 5 10 150

0.5

1.0

1.54.5%Co

30K

20K

7K

1.7K

Magnetic Field [T]

-MC

D [de

g/m

]

Mea

n Spi

n of

Cob

alt

Zn1-xCoxO

No ferromagnetism observed up to 10%Ferromagnetism observed for PLD samples

S. Marcet, Thèse Grenoble, 11/2005

6%

Ferromagnetism observed for 6% Mn : Tc~5K

R. Galera, Lab. L. Néel, Grenoble

0.20

0.25

0.30

0.35

0.40

0.45

0.50

3360 3380 3400 3420 3440 3460Energy [meV]

Ref

lect

ivity

x = 0.1%AB

C

∆Eshift = 6meV xMn = 0.004

<Sz> = 2 N0(α-β) =-1.2 eV

Exchange interactions with carriers

N0|α-β|=0.8 eVxMn = 0.004

∆Eshift = 1 meV

C

Energy

CB

A

B

+-VB

Conclusion

- II-VI Heterostructures :

- Carrier induced in CdMnTe quantum wells : Modulation doping or surface doping

- CdTe quantum dots doped with a single Mn ions : Manipulation and detection of a single spins

- High gap DMS :

- High temperature ferromagnetism still controversial

- GaMnN : Incorporation of isoelectronic Mn3+ ions : 3d4

Ferromagnetic exchange with holes Ferromagnetism observed at low temperature

-ZnCoO : Incorporation of Co2+ isoelectronic ions Paramagnetic behavior observed up to 10% Co spin carrier exchange smaller than in GaMnN

- Equipe mixte CEA-CNRS-UJF Grenoble, France L. Besombes, E. Bellet, Y. Biquard, J. Cibert, D. Halley, D. Ferrand, R. Giraud, S. Kuruda, E. Sarigianidou, H. Mariette Y. Leger, S. Marcet, L. Maingault, W. Pacuski, A. Titov

C. Deparis, C. Mohrain, CRHEA ValbonneK. Rode, M. Anane UMP CNRS-Thales, OrsayA. Dinia, E. Beaurepaire, M. Gallart, P. Gilliot IPCMS, Strasbourg, France

- Lab. L. Néel, France, Grenoble R. Galera, M. Amara, B. Barbara, J. Cibert

- Université de Varsovie, Pologne W. Maslana, W. Pacuski, P. Kossacki, J Gaj

E. Gheraeert, LEPES, Grenoble

- Institute of Materials Science, University of Tsukuba, Japan S. Marcet,. N. Nishizawa, T. Kumekawa, N. Ozaki, S. Kuroda and K. Takita

- Polish academy of science, IFPAN, Warsaw, Poland M. Sawicki, J. Jaroszynsky, S. Kolesnik, T. Dietl