3/22/05APS Meeting 2005 - Los Angeles1 Magneto-optical properties of excitons confined to single magnetic and non-magnetic quantum dots Supported by NSF.

3/22/05 APS Meeting 2005 - Los Angeles 1

Magneto-optical properties of excitons confined to single magnetic and

non-magnetic quantum dots

Supported by NSF and Centre of Excellence CELDIS (Poland)

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

3/22/05 APS Meeting 2005 - Los Angeles 2

Motivation

Study of single magnetic (CdMnTe/Cd0.4Zn0.6Te) and non-magnetic (CdTe/ZnTe) quantum dots by using magneto-optical characterization

+1/2-1/2

-3/2

+1/2

+3/2

σ -σ +

-1/2

+3/2

-3/2

Eg

VB

CBNon-DMS

DMS

B>0 B=0 B>0

σ -σ +

Emission of and give information about g*-factor,

and size of a quantum dot.

3/22/05 APS Meeting 2005 - Los Angeles 3

Samples

GaAs

ZnTe

[001]

Molecular Beam Epitaxy:

CdTe

280oC

2D

CdTe/ZnTe CdMnTe/Cd0.4Zn0.6Te

GaAs

Cd0.4Zn0.6Te

CdMnTeQDs

Te

25oC UHV

CdTeCdTeQDs

220oC

n~100-1000 dots/µm2

CdTeQDs

ZnTe

New technique: (Mariette et al., App. Phy. Lett. 82, 4340 (2003))

Can’t obtain without new technique!!

3/22/05 APS Meeting 2005 - Los Angeles 4

Solid Immersion Lens (SIL)

To look at a small area on sample surface

- 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)

Hemispherical SIL

(LAFN9 glass

n=1.83)

laser luminescence

Resolution~400nm

(S.Mansfield and G. Kino et al.,App. Phy. Lett. 57, 2615 (1990))

sample

5

Imaging method

1.78 1.79 1.80 1.81 1.820.0

0.5

1.0

1.5

2.0

2.5

3.0

Emission Energy (eV)

Sp

ati

al

po

sit

ion

(

m)

x-position

y-po

sitio

n

Defocused laser

sample

x-position

y-po

sitio

n

Emiss

ion e

nerg

y

3D imageSingle dot:

- spatial position

- emission energy

3/22/05 APS Meeting 2005 - Los Angeles 6

Non-magnetic CdTe dots: Image

0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 30.0

0.5

1.0

1.5

2.0

2.5

3.0

x-position (m)

y-p

os

itio

n (

m)

2.04 2.05 2.06

100

200

300

400

500

600

Inte

nsit

y (a

rb)

Energy (eV)

3

1

2

2

1

3

-0.4 -0.2 0.0 0.2 0.4

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Inte

ns

ity

(N

orm

)

Spatial positions (m)

x-position y-positionDot 1

~400nm

1

3/22/05 APS Meeting 2005 - Los Angeles 7

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0.5

1.0

1.5

2.0

2.5

3.0

y-p

os

itio

n (

m)

x-position (m)

Non-magnetic CdTe dots: Dot size

22 56.13*2

1

T

eVBgBE B

12.3*

B

Eg

B(B=3T)

nmrrm

e

eff

7~.8

22

22.052 2.053 2.054 2.055 2.056

0.0

0.3

0.6

0.9

1.2

Dot 2

No

rmal

ized

Inte

nsi

ty

Energy (eV)

3T- +

0T

3T- -

E

(E=0.6meV)

(aB ~ 10nm)

3/22/05 APS Meeting 2005 - Los Angeles 8

Non-magnetic CdTe dots: g*-factor

2.207 2.208 2.209 2.210

6x103

7x103

8x103

9x103

3T E2

+

Inte

ns

ity

(a

rb)

Energy (eV)

E2

-

g2=-3.65

QD2

1.960 1.961 1.962 1.9631.4x103

1.6x103

1.8x103

2.0x103

2.2x103

3T

Inte

ns

ity

(a

rb)

Energy (eV)

+

-

E1

-

E1

+

g*1=-2.04

QD1

-600 -300 0 300 6000.0

0.5

1.0

E2

+

E1

+E

1

-E2

-B=3Tg*

1=-2.04

g*2=-3.65

No

rma

lize

d In

ten

sit

y

Energy (eV)

1.9 2.0 2.1 2.2 2.3

1.5

2.0

2.5

3.0

3.5

4.0

CdTe QDs3MLs T=6K

QD1

QD2

|g*|

-fa

cto

r

Energy (eV)

B=3T

Small dotsLarge dots ?

3/22/05 APS Meeting 2005 - Los Angeles 9

Magnetic CdMnTe dots: Splitting

1.78 1.79 1.80 1.81 1.821.0

1.5

2.0

2.5

3.0

Energy (eV)

Sp

ati

al p

osit

ion

(

m)

0.0 0.5 1.0 1.5 2.0 2.5 3.0

1.794

1.796

1.798

1.800

1.802

1.804

+

-

En

erg

y (e

V)

Magnetic field (T)

CdMnTeT=5K

Dot 2

1500

2000

2500

3000

3500

3T

2T

1T

0T

0T

1T

2T

+

3T

1.79 1.80 1.811000

1500

2000

2500

3000

3500

-

Inte

nsit

y (

arb

)

Energy (eV)

3x

2

1

1.780 1.785 1.790 1.795 1.800

1200

1500

1800

2100

Inte

nsi

ty (

arb

)

Energy (eV)

5K

CdTe

CdMnTe

0.2meV

5meV

3/22/05 APS Meeting 2005 - Los Angeles 10

Magnetic dot vs. non-magnetic dot

-20 -10 0 10 20

1200

1600

2000

2400

Inte

ns

ity

(a

rb)

Energy (meV)

-

CdTe

CdMnTe

kBT = 0.43 meVB=3T

T=5K +

7meV

0.6 meV

x3

(g = -3.65)

(g = 41)Magnetic dot

Non- magnetic dot

sp-d exchange interaction

-1/2

-3/2

+1/2

+3/2

σ -

σ +

+1/2-1/2

+3/2

-3/2

Eg

VB

CBNon-DMS DMS

B>0 B=0 B>0

σ -σ +

3/22/05 APS Meeting 2005 - Los Angeles 11

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