1. Diluted Magnetic Semiconductors
David Ferrand
Equipe mixte CNRS-CEA-UJF “Nanophysique et semiconducteurs”
Laboratoire de Spectrométrie Physique, BP Saint Martin d’Hères

2. Injection and manipulation of spins in semiconductors
Electrical spin injection, spin transport, tunnel structure
M. Kohda et al, Jpn. J. Appl. Phys., Part 2 40, L1274 (2001)
R. Mattana et al, Phys Rev Lett, (2003)
Kroutvar et al., Nature 432,81 (2004)
Spin manipulation

3. Outline I : Spins localized in II-VI heterostructures
1. Modulation doped heterostructures : II-VI Ferromagnetic quantum wells
2. CdTe quantum dots doped with a single Mn atom
II : High band gap diluted magnetic semiconductors GaMnN/ZnCoO
ZnCrTe
1. GaMnN, ZnCoO
2. ZnCrTe

4. Isoelectronic element
II-VI semimagnetic heterostructures 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 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 Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn II
Cd0.7Mg0.3Te
Magnetic alloys : Cd1-xMnxTe, Zn1-xMnxTe
Mn : 4s2 3d5
With a large Mn solubility up to 75%
S=5/2 localized spins
Isoelectronic element
Almost perfect semiconducting properties L
CdTe
Cd0.7Mg0.3Te
Cd0.88Zn0.12Te
substrate
CdTe/CdMgTe quantum wells
ZnTe
CdTe
CdTe
ZnTe
ZnTe
substrate
CdTe/ZnTe quantum dots

5. Magnetic properties : Short range antiferromagnetic interactions
J2, J3~0.5K
N.N pairs
J1~20K
J. Furdyna et al, JAP 64 R29 (1988)
kT << J1
0,0
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 temperatures
with diluted alloys

6. p type modulation doped CdMnTe QWs
Surface doped CdMnTe QW
15 nm < z < 60 nm
After surface oxydation
Mn Compositions 0-11%
Hole densities cm-2
W. Maslana, 2003
Magnetic quantum well Cd(1-x)MnxTe 80 Å
spacer
Barrier
Substrate
CdMgTe
2D hole gas
Nitrogen E1
HH1
80 Å
Mn Compositions 0-4%
Hole densities cm-2

7. + - s+ s- b~-100 meV nm3 < 0 a~25 meV nm3 > 0 N0~few 1022 cm-3
Magneto-optical spectroscopy : Giant Zeeman effect
b~-100 meV nm3 < 0
a~25 meV nm3 > 0
Holes :
Electrons : E1
±1/2 +1 z
Photon -1 HH
HH Excitons
±3/2
HH -1
HH +1
Excitons
G.S s+ s-
N0a~0.2 eV
N0b~-1 eV
N0~few 1022 cm-3
T=1.9K
Xhh
B=+4 T + -

8. Susceptibility measurements : Curie Weiss temperature
PL at 2.1K, 2.4% Mn, 1.61011 cm-2
Haury et al, 1997
Interactions ferromagnétiques induite par le gaz 2D
Tcw ~ 2 à 3 K > 0
Tcw~-TAF=-2K < 0
Coll. P. Kossacki, Warsaw

9. Electrical control through an electrostatic gateV QW
barriers
p doped
n doped
undoped
H. Boukari et al, Phys. Rev. Lett. 88, (2002) Tc
Hole gas
depleted

10. Comparison with mean field model predictions
2D D.O.S
Kossacki 2001
X 2.3
4% Mn
Effective Mn content : xeff
TC > TCW ?
T. Dietl, Warsaw

11. Magnetic CdMnTe/ZnTe QDs Strained induced CdTe/ZnTe QDs:
UHV-AFM image of
CdTe QDs on ZnTe.
"Stranski-Krastanow"
h > hcSK
3D-coherent islands
QDs density: 1010 cm-2
Size: d=25nm, h=3nm
(Lz<<Lx,Ly)
TEM C. Bougerol.
Introduction of
Mn atoms (3d5 4s2 ) carrying S=5/2 localized spin
Thèse L Maingault,
H. Mariette

12. CdTe/ZnTe QDs doped with a single Mn atom
Single dot spectroscopy :
Mn density = QDs density
Strained induced Cd(Mn)Te/ZnTe QDs:
Mn segregation
during the growth of
a spacer layer
Thèse L Maingault,
H. Mariette
100 mm
Strained induced QDs
To study in detail the magnetic interaction between a single ion and indivual carriers in a zero dimensional system we realized QDs with a low density of Mn magnetic ions.
Take advantage of the intermixing of Mn during the growth….
Introduce individual spins in QDs: seggregation of Mn during the growth of a ZnTe spacer layer on a ZnMnTe layer
Sparce distribution of Mn at the surface when you start the growth of the CdTe QD layer
Target the same density of Mn and QDs
Introduce Mn in QDs, but random distribution of spins and QDs.
To access the optical properties of individual QDs …
Thèse Y. Léger

13. Reference CdTe/ZnTe QDs
B=0
B=0 -1
Electron : s=1/2
Anisotropic hole Jz=3/2 z
Jz=±3/2 // Oz
s=1/2
Growth axis +1 +1 ±1 -1
G.S.
L. Besombes et al., Phys. Rev. Lett. 93, (2004)

14. Individual Mn-doped CdTe/ZnTe QDs
6 twofold degenerate
excitonics levels
Total splitting 1.3 meV
S=5/2
CdTe QDs with
an individual Mn spin
Thèse Y. Léger

15. Exciton-Mn Exchange Coupling
S=5/2
Complexe X - Mn : s=1/2 + Jz=3/2 + S=5/2
Mn2+ e h e h
Jz = -1
-5/2
Jz = +1
+5/2 X
-3/2
+3/2
-1/2
+1/2
+1/2
-1/2
+3/2
-3/2 e h
Jz = -1
+5/2 e h
-5/2
Jz = +1 ) 3 ( 2 5 Mn h e I -
Overall splitting :
Ie-Mn=-70 meV and Ih-Mn =350 meV.
Detection and manipulation of a single Mn spin

16. Mn-Doped Individual QDs Under Magnetic Field
Splitting of the six exciton lines.
Diamagnetic shift.
Changes in the PL intensity
distribution.
Large anticrossing for five of the
exciton lines around 6T.
Additional tiny anticrossings.
NMn=0
NMn=1

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

18. Tc>300K Towards room temperature diluted magnetic semiconductors ?
2001
2002
(Ga,Mn)N
MBE 3-6% Mn
(Zn,Co)O : PLD 15-25% Co
Tc>300K
S. Sonoda et al. J.A.P. 156, 555 (2002)
K. Ueda et al, APL (2001)
(Zn,Cr)Te
MBE 0< x < 50%
H. Saito et al, 2003
2003

19. 3d4 3d7 e t2 E E e t2 D.O.S Cr2+ in II-VI Co2+ in ZnO Mn3+ in III-V
High temperature ferromagnetism still controversial :
Paramagnetism + Ferromagnetism observed by SQUID
ZnCrTe
No phase diagram with the magnetic ion composition
or correlation with other parameters
- Transport properties weakly sensitive to magnetic ions
Tunnel junctions with (Zn,Co)O
No sharp optical features close to band edges
No photoluminescence
Diluted high band gap alloys : GaMnN, ZnCoO e t2 BV BC E
D.O.S
Partially filled d bands located within the gap ?
Cr2+ in II-VI
Mn3+ in III-V
3d4 E BV BC e t2
Co2+ in ZnO
3d7
Ferromagnetism mediated by electrons ?

20. Zn1-xCoxO or Ga1-xMnxN e t2 E D.O.S < 3d5 c - axis
WURTZITE epilayer
c - axis
Buffer
Grown by Molecular Beam Epitaxy:
in CREHA Valbonne (Zn1-xCoxO)
C. Deparis, C. Mohrhain
in Grenoble (Ga1-xMnxN)
Al2O3
substrate e t2
< 3d5 BV BC E
D.O.S

21. Co2+ Mn3+ Magneto-optical spectroscopy of intraionic d-d transitions
(Ga,Mn)N : 0.03% Mn
(Zn,Co)O 2% Co
Spin forbidden transition at 1876 meV
W. Pacuski et al, Phys. Rev. B (2006)
Mn3+
3d4
Tetrahedral
crystal field
Co2+
3d7
5T2 5E 2E
S=3/2 4F 5D
S=2
Isoelectronic spins
Spin allowed transition at 1413 meV
S. Marcet et al, cond-mat/
4A2

22. Ground state : Fine structure Hamiltonian parameters
S. Marcet et al, cond-mat/
g//=1.91
gperp =1.98
Axial anisotropy : D=0.27 meV
g//=2.28
Axial anisotropy : D=0.35 meV
Axial anisotropy :

23. Evolution with of the magnetic ion concentration
Ga1-xMnxN
Zn1-xCoxO
Co2+ incorporation up to 6%
W. Pacuski et al, Phys. Rev. B (2006)
Mn3+ incoporation up to about 1%

24. Comparison with the magnetic properties
Ga1-xMnxN
S. Marcet, Thèse Grenoble, 11/2005
Zn1-xCoxO
No ferromagnetism observed up to 10%
Ferromagnetism observed for PLD samples
1.7% Mn
Ferromagnetism observed for 6% Mn : Tc~5K
R. Galera, Lab. L. Néel, Grenoble 6%

25. Exchange interactions with carriers
Energy CB A B s+ s- VB
x = 0.1% A B C
∆Eshift = 6meV
xMn = 0.004
<Sz> = 2
N0(α-β) =-1.2 eV
N0|α-β|=0.8 eV
xMn = 0.004
∆Eshift = 1 meV

26. 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

27. - 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
- Lab. L. Néel, France, Grenoble
R. Galera, M. Amara, B. Barbara, J. Cibert
Polish academy of science, IFPAN, Warsaw, Poland
M. Sawicki, J. Jaroszynsky, S. Kolesnik, T. Dietl
- Université de Varsovie, Pologne
W. Maslana, W. Pacuski, P. Kossacki, J Gaj
E. Gheraeert, LEPES, Grenoble
C. Deparis, C. Mohrain, CRHEA Valbonne
K. Rode, M. Anane UMP CNRS-Thales, Orsay
A. Dinia, E. Beaurepaire, M. Gallart, P. Gilliot IPCMS, Strasbourg, France
- Institute of Materials Science, University of Tsukuba, Japan
S. Marcet,. N. Nishizawa, T. Kumekawa, N. Ozaki,
S. Kuroda and K. Takita