Transcript APS Meeting 2005 - University of Cincinnati

Magneto-optical properties of excitons
confined to single magnetic and
non-magnetic quantum dots
Thang B. Hoang, Sebastian Mackowski, Lyubov Titova,
Howard E. Jackson, Leigh M. Smith
University of Cincinnati
Piotr Wojnar, Grzegorz Karczewski, Jacek Kossut
Institute of Physics PAS, Warsaw, Poland
Supported by NSF and Centre of Excellence CELDIS (Poland)
3/22/05
APS Meeting 2005 - Los Angeles
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Motivation
 Study of single magnetic (CdMnTe/Cd0.4Zn0.6Te) and non-magnetic
(CdTe/ZnTe) quantum dots by using magneto-optical characterization
DMS
+1/2
Non-DMS
CB
-1/2
+1/2
σ-
σ+
Eg
σ
σ
+
-1/2
-
-3/2
+3/2
-3/2
VB
+3/2
B>0
Emission of
B=0
B>0
  and   give information about g*-factor,
and size of a quantum dot.
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APS Meeting 2005 - Los Angeles
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Samples
Molecular Beam Epitaxy:
New technique: (Mariette et al., App. Phy. Lett. 82, 4340 (2003))
CdTe/ZnTe
CdMnTe/Cd0.4Zn0.6Te
[001]
Te
ZnTe
CdTe
ZnTe
GaAs
2D
CdTe
CdTe
QDs
Cd0.4Zn0.6Te
25oC
oC
oC
280
220
UHV
n~100-1000 dots/µm2
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CdMnTe
QDs
GaAs
Can’t obtain without
new technique!!
APS Meeting 2005 - Los Angeles
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Solid Immersion Lens (SIL)
 To look at a small area on sample surface
laser
luminescence
(S.Mansfield and G.
Kino et al.,App. Phy.
Lett. 57, 2615 (1990))
Hemispherical SIL
(LAFN9 glass
n=1.83)
sample
Resolution~400nm
- SIL with index of refraction n will reduce laser spot size by
factor of n
- Increase collection efficiency (due to increase of numerical
aperture and reduce of total internal reflection)
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APS Meeting 2005 - Los Angeles
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Imaging method
sample
y-position
Spatial position(m)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
1.78
1.80
1.81
1.82
x-position
Single dot:
- spatial position
- emission energy
3D image
y-position
Defocused
laser
1.79
Emission Energy (eV)
x-position
5
Non-magnetic CdTe dots: Image
600
2.5
500
Intensity (arb)
3.0
1
2.0
y-position(m)
1.5
3
1.0
1
400
3
300
200
100
2
0.5
2
2.04
2.05
2.06
Energy (eV)
3.0
1.4
2.5
1
1.2
Intensity (Norm)
2.0
1.5
1.0
0.5
x-position
y-position
Dot 1
1.0
0.8
0.6
~400nm
0.4
0.2
0.0
0.0
0
1
2
x-position (m)
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-0.4
-0.2
0.0
0.2
0.4
Spatial positions (m)
APS Meeting 2005 - Los Angeles
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Non-magnetic CdTe dots: Dot size
1.2
2.5
Normalized Intensity
y-position(m)
3.0
2.0
1.5
1.0
0.5
2
0.9
E
Dot 2
0.6
0.3
0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
2.052
2.053
E
 3.12
B B
2.054
1
eV
E   B   B g * B    13.56 2
2
T
2
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2.056
(E=0.6meV)
2

2.055
Energy (eV)
x-position (m)
g* 
+
3T- 
0T
3T- 
e
r 2  r ~ 7nm
8. meff
(B=3T)
(aB ~ 10nm)
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Non-magnetic CdTe dots: g*-factor
3T
E1
QD1
Intensity (arb)
CdTe QDs
3MLs
T=6K
3
QD1
2.0x10
3
E1
9x10
+
1.6x10
-

-
3
3
3
1.4x10
1.960
4.0
1.961
1.962
3.0
2.5
2.0
1.5
2.0
2.1
2.2
2.3
Energy (eV)
?
Normalized Intensity
|g*|-factor
3
6x10
3
-
E2
+
QD2




g2=-3.65
2.207
2.208
2.209
2.210
Energy (eV)
B=3T
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7x10
1.963
3.5
Large dots
8x10
3
E2
Energy (eV)
B=3T
1.9
3T

g*1=-2.04
1.8x10
3
+
Intensity (arb)
2.2x10
QD2
E2
-
E1
+
E1 E2
-
1.0
+
g*1=-2.04
g*2=-3.65
0.5
0.0
-600
-300
Small dots
APS Meeting 2005 - Los Angeles
0
300
600
Energy (eV)
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Magnetic CdMnTe dots: Splitting
3500
3000
2.5
+
3T
2500
2
Intensity (arb)
Spatial position (m)
3.0

2.0
1
2T
2000
1T
1500
0T
3500

3000
-
1.5
1T
2500
2000
2T
1.0
1.78
1.79
1.80
1.81
1.82
1500
3x
Energy (eV)
1000
5K
1.80
1.81
1800
1.804
1.802
5meV
1500
0.2meV
CdTe
1.780
CdMnTe
T=5K
Dot 2
CdMnTe
1200
1.800

+
1.798

-
1.796
1.794
1.785
1.790
Energy (eV)
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1.79
3T
Energy (eV)
Energy (eV)
Intensity (arb)
2100
0T
1.795
1.800
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Magnetic field (T)
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Magnetic dot vs. non-magnetic dot
2400
kBT = 0.43 meV
Intensity (arb)
B=3T
T=5K

+
7meV
2000
Magnetic dot

CdMnTe
(g = 41)
-
sp-d
exchange
interaction
DMS
Non-DMS
x3
-1/2
+1/2
1600
0.6 meV
σ
+1/2
CB
σ-
σ
+
-
-1/2
-3/2
Eg σ +
+3/2
1200
-20
CdTe
Non- magnetic dot
-10
0
(g = -3.65)
10
-3/2
20
VB
B>0
B=0
+3/2
B>0
Energy (meV)
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APS Meeting 2005 - Los Angeles
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Conclusions
 Studied single magnetic and non-magnetic QDs grown by new
technique
 Non-magnetic dots: show dependence of exciton g*-factor on
emission energy (g* changes from -4 to -1.9)
 Magnetic quantum dots exhibit much larger energy splitting
(g*=41) (due to sp-d exchange interaction)
 Magnetic dots: large line-width due to the fluctuation of Mn+ ions
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APS Meeting 2005 - Los Angeles
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