Transcript PLMCN10-orals-15-Thursday-Th-33

POLARITON LIGHT EMITTING DEVICES: RELAXATION DYNAMICS
Dept of Materials Sci. & Tech
Microelectronics Group
University of Crete / IESL
Simos Tsintzos
Polariton
emitter
Top Mirror
Active region
Bottom
Mirror
Current
Polariton Physics at Crete
Spectroscopy & Fabrication
Prof. PG Savvidis
Prof. NT Pelekanos
Simos Tsintzos
Tingge Gao
Panos Tsotsis
MBE Growth
Prof. Z. Hatzopoulos
University of Crete
Collaborations
University of Cambridge
Prof. J. J. Baumberg
G. Christmann
FORTH-IESL
Dr. G. Kostantinidis
Dr. G. Deligeorgis
Funding: Greek Research Council, ΕΠΕΑΕΚ, EU FP7
III-V
Outline
• Demonstration of a polariton LED device
operating up to room temperature
• New schemes of electrical injection assisted
by LO phonon enhanced relaxation
• Electro/Photo-luminescence imaging of polariton
dispersions to track relaxation dynamics
• Conclusions
FORTH
Microelectronics Research Group
Univ. of Crete
First demonstration of strong coupling in MC
1992
Polariton Physics
Time
Parametric
amplification
Stimulated scattering
of polaritons
• Small progress
Polariton lasing
Polariton Devices
Polariton
Superfluidity
Polariton LEDs
Polariton
condensation
• Spectacular physics related to bosonic
character of polaritons
• Mature understanding
Polariton Laser
Diodes ?
J.R. Tischler et al, PRL 95, 036401 (2005) (organic)
A. Khalifa et al., Appl. Phys. Lett. 92, 061107 (2008) T = 10 K
D. Bajoni et al., Phys. Rev. B 77, 113303 (2008) T = 100 K
S. I. Tsintzos et al., Nature 453, 372 (2008), APL (2009) T = 315 K
Ultrahigh speed
Switches ?
Polariton LED
Electrical Injection in Microcavity
• Approach
Electrical injection of polaritons in strongly
coupled GaAs semiconductor microcavity
Polariton
LED
Fabricate p-i-n diode microcavities
for electrical injection
Measure polariton electroluminescence
and dispersion relations
• Technical challenges/issues
High resistivity of the DBR mirrors
high temperature
Doping related losses in DBR mirrors
and polariton robustness
doping profile
Injection issues: e.g. inhomogeneous pumping of QWs
FORTH
Microelectronics Research Group
Univ. of Crete
Microcavity Design
• Designed
to operate at high temperatures
• Multiple QWs to enhance Rabi splitting
FORTH
Microelectronics Research Group
Univ. of Crete
Polariton Electroluminescence
Emission collected normal to the device
• Clear anticrossing observed
• Direct emission from exciton polariton states
1.355
Energy
(eV)
(eV)
Energy
1.350
1.345
1.340
Upper Polariton
Lower Polariton
exciton
cavity
1.335
1.330
190
200
210
220
230
240
Temperature (K)
Temperature
(K)
Temperature tuning
Exciton ~ -0.38meV / K
Cavity ~ -0.102meV /K
•Rabi splitting of 4.4meV at 219 K
S. Tsintzos et al., Nature 453, 372 (2008)
FORTH
Microelectronics Research Group
Univ. of Crete
250
260
Room temperature Polariton LED
•Polariton LED with 8 QWs
to increase Rabi splitting
I=0.8mA
•Lateral injection scheme
to improve injection
ΔΤ=5K
S. Tsintzos et al, APL 94,071109 (2009)
Rabi splitting of ~4meV at T=288K
FORTH
Microelectronics Research Group
Univ. of Crete
Large Rabi splitting in GaAs QW MCs at (T=300K)
zero detuning
DBR
AlAs
Al0.15Ga0.85As
Θ
GaAs
QWs
DBR
AlAs
Al0.15Ga0.85As
• Clear anticrossing
• Rabi splitting of 6.5mev observed
FORTH
Microelectronics Research Group
Univ. of Crete
Fitting of Rabi Splitting versus T and N
GaAs
# QWs
N=8
(for zero detuning)
InGaAs
  4V 2  ( X   C ) 2
X,
C
Exciton, cavity mode
linewidths
X
with temperature

V(8), the only adjustable parameter
FORTH
Microelectronics Research Group
V ( 6)
V (8)

6
8
Univ. of Crete
Collapse of Strong Coupling Regime at High Densities
Relaxation
bottleneck
I2
~
need new injection schemes
that bypass bottleneck
T=235K
• Injection density at 22mA ~ 1010 pol/cm2
FORTH
Microelectronics Research Group
Univ. of Crete
Microcavity structure exploiting LO phonon
enhanced relaxation
LO-phonon
DBR
Electrons
DBR
polariton
holes
Using GaAs/AlGaAs QWs
FORTH
Microelectronics Research Group
Univ. of Crete
I=100uA
T=120K
EL Intensity
Θ
1.48
1.49
1.50
1.51
1.52
1.53
1.525
1.520
I=100uA
T=120K
1.515
1.510
1.505
1.500
Energy (eV)
5
8.7
13.1
21
25.4
29.7
36
45
52
60.5
73
83.7
91.4
100
120
140
160
180
200
231
250
280
303
351
401
501
610
658
709
760
827
920
1033
6
10
5
EL Intensity
1.54
Energy Dispersion (eV)
Electroluminescence of LO phonon-designed MCs
10
4
10
3
10
2
10
-5
0
5
10
15
20
25
30
35
1.50
1.51
•Red shift in EL caused by heating
• Due to series resistance of the DBRs
1.52
Energy (eV)
FORTH
45
Angle (Degrees)
1
10
1.49
40
Microelectronics Research Group
Univ. of Crete
Single shot imaging of the polariton dispersions
pin-hole
λ
CCD
θ
θ
EL
confocal
objective
E
θ
sample
4K
λ
θ
• Look at polariton population along the lower branch.
•Applicable to both PL and EL measurements on small mesas
FORTH
Microelectronics Research Group
Univ. of Crete
Integrated PL Intensity (a.u)
Power dependence Images
8
10
Strong Coupling
T=140K
Weak Coupling
7
10
6
10
5
10
4
10
3
10
2
10
1
10
0
10
0.1
1
10
Optical Power (mW)
Nonlinearity at very low power
Nonlinearity possibly due to
screening of diode built-in field
Enhanced Polariton Relaxation @ High Injection
3mW
T=70K
Integrated Intensity (a.u)
2mW
0.9mW
0.4mW
0.1mW
0
5
10
15
20
Angle (degrees)
FORTH
Microelectronics Research Group
Univ. of Crete
25
30
Enhanced Polariton Relaxation @ High Temperature
140K
P=0.4mW
T=140K
P=0.4mW
P=0.4mW
Integrated Intensity (a.u)
120K
T=60K
100K
80K
70K
0
5
10
15
20
Angle (degrees)
FORTH
Microelectronics Research Group
Univ. of Crete
25
30
Summary
• GaAs polariton LED device operating up to RT
• New approach to electrical injection exploiting
LO phonon enhanced relaxation
• Imaging shows enhanced relaxation at higher Temperatures
and Powers and collapse of bottleneck region.
Thank you
FORTH
Microelectronics Research Group
Univ. of Crete