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Diluted Magnetic Semiconductors
David Ferrand
Equipe 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
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, 90 166601 (2003)
Spin manipulation
Kroutvar et al., Nature 432,81 (2004)
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
II-VI semimagnetic heterostructures
I
Valence mixte I, II, III…
II
II
III
IV
V
VI
VII
H
VIII
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Sc
Ti
V
Cr
Rb
Sr
Y
Zr
Nb
Mo
Cs
Ba
La
Hf
Ta
W
Mn
Re
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
Mn : 4s2 3d5
Cd0.7Mg0.3Te
CdTe
Cd0.7Mg0.3Te
Isoelectronic element
S=5/2 localized spins
Cd0.88Zn0.12Te
substrate
CdTe/CdMgTe quantum wells
Magnetic alloys : Cd1-xMnxTe, Zn1-xMnxTe
With a large Mn solubility up to 75%
Almost perfect semiconducting properties
ZnTe
CdTe
CdTe
ZnTe
ZnTe
substrate
CdTe/ZnTe quantum dots
L
Magnetic properties : Short range antiferromagnetic interactions
a
J2, J3~0.5K
N.N pairs
J1~20K
J. Furdyna et al, JAP 64 R29 (1988)
kT << J1
xeff
0,0
0,05
0,1
0,2
0,3
0,4
0,5
0,05
0,04
0,04
0,03
0,03
0,02
0,02
0,01
0,01
0,00
0,0
0,1
0,2
0,3
Mn content x
0,4
0,00
0,5
Small concentration of free spins
Studies at low temperatures
with diluted alloys

C0 xeff
T  TAF

C0 x
T  Tcw
p type modulation doped CdMnTe QWs
Surface doped CdMnTe QW
Magnetic quantum well Cd(1-x)MnxTe 80 Å
spacer
Barrier
CdMgTe
Substrate
15 nm < z < 60 nm
After surface oxydation
2D hole gas
-2
Hole Gas Concentration (cm )
Nitrogen
W. Maslana, 2003
E1
HH1
10
11
10
10
0
100
200
300
400
500
600
Cap layer Thickness (Å)
80 Å
Mn Compositions 0-4%
Hole densities 1-3 1011 cm-2
Mn Compositions 0-11%
Hole densities 1-2 1011 cm-2
Magneto-optical spectroscopy : Giant Zeeman effect
   
   
H   e .S (re - RMn )   h .S (rh - RMn )
±1/2
E1
Sz
+1
z
Photon
-1
HH
±3/2
HH Excitons
Holes :
~-100 meV nm3 < 0
~25 meV nm3 > 0
Electrons :
HH -1
Excitons
( -  ) S z 
Xhh
N Mn
V
+
B=+4 T
HH +1

G.S
-
 N0 ( -  ) xeff Sz
N0~few 1022 cm-3
N0~0.2 eV
N0~-1 eV
1670
1680
T=1.9K
1690
1700
1710
1720
1730
1740
1750
1760
Susceptibility measurements PL
: Curie
EnergyWeiss temperature
(meV)
PL Energy
Photoluminescence 2.1K
11cm-2
Mn, p=1.6
10-2
11 cm
PL at 2.1K, 2.4% 2.4%
Mn, 1.610
(meV)
1665
1665
1664
Susceptibility
4.2K
+
0G
-
PL (u.a.)
100G
1.65K
1663
1664
1662
1663
4.2K
1.65K
1661
200G
1662
300G
1661
0
500
0
400
Magnetic field (Oe)
0
500
1660
Energie (meV)
400
Magnetic field (Oe)
400G
1650
0
1670
Inverse susceptibility
(T/meV)
Haury et al, 1997
Inverse susceptibility
(T/meV)
Interactions ferromagnétiques induite par le gaz 2D
Tcw~-TAF=-2K < 0
0.05
undoped
p-doped
Tcw ~ 2 à 3 K > 0
0.05
undoped
0.00
Coll. P. Kossacki, Warsaw
-2
-1
0 1
p-doped
2
3
4
Temperature (K)
5
Electrical control through an electrostatic gate
V
p doped
QW
barriers
undoped
n doped
H. Boukari et al, Phys. Rev. Lett. 88, 207204 (2002)
PL Intensity (a.u.)
a
0V
b
-1V
4.2 K
4.2 K
3.03
2.80
2.97
2.82
2.19
2.19
2.05
2.05
1.87
1.88
1.65
1.49 K
1.65
1.49 K
1700
1710
Tc
1700
1710
Energy (meV)
Hole gas
depleted
Comparison with mean field model predictions
TC  C0 xeff  P - TAF
2
2D D.O.S
 2D
 h  AF
Effective Mn content : xeff
L
6
4
3
2
1
0
0
1
2
3
4
5
6
Mn content x (%)
7
8
9
10
Critical temperature (K)
5
Temperature (K)
4
TC > TCW ?
Kossacki 2001
2
X 2.3
0
4% Mn
0
T. Dietl, Warsaw
1
2
11
-2
Carrier density (10 cm )
Magnetic CdMnTe/ZnTe QDs
Strained induced CdTe/ZnTe QDs:
3D-coherent islands
UHV-AFM image of
CdTe QDs on ZnTe.
QDs density: 1010 cm-2
h > hcSK
Size: d=25nm, h=3nm
(Lz<<Lx,Ly)
"Stranski-Krastanow"
TEM C. Bougerol.
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
Single dot spectroscopy :
Strained induced Cd(Mn)Te/ZnTe QDs:
6,5 MLs
 50meV
100 m
Mn segregation
during the growth of
a spacer layer
PL Intensity (arb. units)
d  20 m
d  0,5 m
 50eV
Mn density = QDs density
Thèse L Maingault,
H. Mariette
d  0,25 m
1950
2000
Energy (meV)
Thèse Y. Léger
2050
2100
Reference CdTe/ZnTe QDs
Reference CdTe/ZnTe QD :
B=0
Growth axis
z
s=1/2
B=0
-1
+1
±1
+1
-1
Jz=±3/2 // Oz
Electron : s=1/2
Anisotropic hole Jz=3/2
G.S.
L. Besombes et al., Phys. Rev. Lett. 93, 207403 (2004)
Individual Mn-doped CdTe/ZnTe QDs
 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
Exciton-Mn Exchange Coupling
S=5/2
 
H  H 0  I e-Mn e .S  I h-Mn jz .S z
  2
  e ( r - RMn )
I e- Mn
 g Mn  B S Z Bz
I h - Mn 

3
  2
 h (r - RMn )
Complexe X - Mn : s=1/2 + Jz=3/2 + S=5/2
Mn2+
X
Jz = -1
e
h
Jz  1
Jz = -1
e
h
-5/2
Jz = +1 e
h
-3/2
+3/2
-1/2
+1/2
+1/2
+3/2
-1/2
-3/2
+5/2
Jz = +1 e
-5/2
h
Overall splitting :
Detection and manipulation of a single Mn spin
+5/2
5
( I e - Mn - 3I h - Mn )
2
 Ie-Mn=-70 eV and Ih-Mn =350 eV.
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
II : High band gap diluted magnetic semiconductors GaMnN/ZnCoO
1. GaMnN, ZnCoO
2. ZnCrTe
I
Valence mixte I, II, III…
II
III
IV
V
VI
VII
H
VIII
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Sc
Ti
V
Cr
Rb
Sr
Y
Zr
Nb
Mo
Cs
Ba
La
Hf
Ta
W
II-VI : Cr2+ : 4s2 3d4
Co2+ : 4s2 3d7
Mn
Re
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
III-V Mn 4s2 3d5
Acceptor : GaMnAs 3d5
Isoelectronic : 3d4
Towards room temperature diluted magnetic semiconductors ?
2001
2002
(Zn,Co)O :
(Ga,Mn)N
MBE 3-6% Mn
PLD 15-25% Co
Tc>300K
S. Sonoda et al. J.A.P. 156, 555 (2002)
K. Ueda et al, APL 79 988 (2001)
(Zn,Cr)Te
2003
MBE 0< x < 50%
H. Saito et al, 2003
High temperature ferromagnetism still controversial :
ZnCrTe
- Paramagnetism + Ferromagnetism observed by SQUID
- No phase diagram with the magnetic ion composition
or correlation with other parameters
- Transport properties weakly sensitive to magnetic ions
-No sharp optical features close to band edges
- No photoluminescence
Tunnel junctions with (Zn,Co)O
Diluted high band gap alloys : GaMnN, ZnCoO
Partially filled d bands located within the gap ?
Ferromagnetism mediated by electrons ?
D.O.S
BV
e
t2
BC
BV
e
t2
E
Cr2+ in II-VI
Mn3+ in III-V
3d4
e
BC
E
t2
Co2+ in ZnO
3d7
Zn1-xCoxO or Ga1-xMnxN
Buffer
4x10
4
3x10
4
-1
4
Al2O3
substrate
1,7K 2,2% M n
2
Band edge
Band-level transitions
3
1
2x10
1x10
4
Absorption coefficient (cm )
-1
Absorption coefficient (cm )
Grown by Molecular Beam Epitaxy:
•in CREHA Valbonne (Zn1-xCoxO)
C. Deparis, C. Mohrhain
•in Grenoble (Ga1-xMnxN)
5x10
d-d intra-ionic
transitions
4
0
1,0
1,5
2,0
2,5
3,0
3,5
Energy (eV)
e
5x10
4
300K 6,6% Co
4x10
4
3x10
4
2x10
4
1x10
4
2
5
t2 < 3d
BC
E
e
t2
Band edge
Disorder ?
1
3
d-d intra-ionic
transitions
0
1,0
1,5
2,0
2,5
Energy (eV)
D.O.S
BV
c - axis
WURTZITE epilayer
3,0
3,5
Magneto-optical spectroscopy of intraionic d-d transitions
(Ga,Mn)N : 0.03% Mn
+ 11T
-1
2 K
11 T
-3
6
5
4
L3
3
2
Tetrahedral
crystal field
1
0,06
0,04
B =0
0,02
L2
-11T
-
0T
0
1408
1412
1416 1418
1870
Spin allowed transition at 1413 meV
S. Marcet et al, cond-mat/0604025 2006
3d4
S=2
5D
5E
1875
1880
Energy [m eV ]
Energy [m eV]
Mn3+
L3
L1
0,08
0,00
L1

-3
-1
Absorption coefficient [10 cm ]
0,10
B||c
L2
7
(Zn,Co)O 2% Co
Absorption Intensity [10 cm ]
8
Spin forbidden transition at 1876 meV
W. Pacuski et al, Phys. Rev. B 73 035214 (2006)
Co2+
5T
3d7
S=3/2
2
Isoelectronic spins
4F
2E
4A
2
Ground state : Fine structure Hamiltonian parameters
1879
L1
1878
Energy (m eV)
Energy (m ev)
1413,0
1412,5
L2
1412,0
L3
1411,5
L3+
1877
1875
L1+
1874
L2+
1873
L3-
1872
0
2
4
6
8
10
12
14
1871
Magnetic Field (T)
0
2
5
L3
L1
3
L2
2
+1
1
0
0
5
D : G .S
0
2
4
Energy (m eV)
+2
Energy (meV)
6
8
10
12
E
1412
-1
4
Magnetic Field (T)
1416
1414
L2-
L1-
1876
2
1876
1875
1874
E+
2
8
10
-2
M a g n e tic F ie ld (T )
+3/2
L1
L3
1
L2
+1/2
0
-1
4
-1
6
-1/2
A2
-2
-3/2
0
2
g//=1.91
gperp =1.98
4
6
8
10
12
Magnetic Field (T)
S. Marcet et al, cond-mat/0604025 2006
Axial anisotropy :
E-
E(E)

H  ( g// - g )B Bc Sc  g B.S  D(Sc2 - S (S 1) / 3)
Axial anisotropy : D=0.27 meV
g//=2.28
Axial anisotropy : D=0.35 meV
Evolution with of the magnetic ion concentration
Ga1-xMnxN
Zn1-xCoxO
0.8
3,0
Absorption Coefficient [1/m]
In te g ra te d A re a [x 1 0
5
cm
-2
]
0.9
2,5
2,0
1,5
1,0
0,5
0,0
0,0
0,2
0,4
0,6
Mn content [%]
0,8
4A 
2
2E 2A
0.7
0.6
0.5
4A 
2
2E E
0.4
0.3
0.2
1,0
0.1
0
1860
1880
1900
Photon Energy [meV]
0
1 2 3 4 5
Co Concentration [%]
Co2+ incorporation up to 6%
Mn3+ incoporation up to about 1%
W. Pacuski et al, Phys. Rev. B 73 035214 (2006)
6
1.5
T=1,7 K
3
25
0.4%Co
2
1.7KB||c 1.5
7K
1
1.7% Mn
0
0
1
2
3
4
1.0
5
Magnetic Field [T]
1.0
Zn1-xCoxO
B c
20K
S. Marcet, Thèse Grenoble, 11/2005
0.5
0.5
Mplan
Mplan'
Mc
Mc
A
###
20
-MCD [deg/m]
2.0
4
Mean Spin of Cobalt
2.5
Magnetization [ B / Mn]
Comparison with the magnetic
properties
Ga1-xMnxN
15
10
5
2%Co
1.7K 1.5
6K
10K
1.0
20K
30K
0.5
40K
6%
0
0
5
10
15
Magnetic Field [T]
R. Galera, Lab. L. Néel, Grenoble
Ferromagnetism observed for 6% Mn : Tc~5K
0
0
0
5
10
15
Magnetic Field [T]
No ferromagnetism observed up to 10%
Ferromagnetism observed for PLD samples
Exchange interactions with carriers
Energy
0.50
CB
-
Reflectivity
VB
+
A
B
0.40
0.35
C
0.30
B
0.25
C
0.20
3360
0,7
x = 0.1%
A
0.45
3380
3400
3420
Energy [meV]
3440
3460
0,6
2K
0,6
0,5
11T -
Reflectivity (a.u)
Reflectivity (e.u)
2K
0,5
0T
11T +
0,4
0,3
3490
3500
3510
3520
3530
3540
Photon Energy (meV)
0T
0,3
11T +
0,2
(Zn,Co)O : 0,4% Co
0,0
3360
3370
3380
3390
3400
3410
Photon Energy (meV)
xMn = 0.004
xMn = 0.004
N0(α-β) =-1.2 eV
∆Eshift = 1 meV
∆Eshift = 6meV
<Sz> = 2
0,4
0,1
(Ga,Mn)N : 0,4% Mn
11T -
N0|α-β|=0.8 eV
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
- 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