View
217
Download
0
Category
Preview:
Citation preview
Current
POLARITON LIGHT EMITTING DEVICES: RELAXATION DYNAMICS
Simos TsintzosDept of Materials Sci. & TechMicroelectronics GroupUniversity of Crete / IESL
Polariton emitter
Active region
Bottom Mirror
Top Mirror
Polariton Physics at Crete
Spectroscopy & FabricationProf. PG Savvidis
Prof. NT Pelekanos
Simos Tsintzos
Tingge Gao
Panos Tsotsis
Funding: Greek Research Council, ΕΠΕΑΕΚ, EU FP7
Prof. J. J. Baumberg G. Christmann
MBE Growth
Prof. Z. Hatzopoulos III-V
University of Cambridge
Collaborations
FORTH-IESL
University of Crete
Dr. G. KostantinidisDr. G. Deligeorgis
• 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
Outline
FORTH Microelectronics Research Group Univ. of Crete
First demonstration of strong coupling in MC
Stimulated scattering of polaritons Parametric
amplification
Polariton lasingPolariton
condensationPolariton
SuperfluidityPolariton LEDs
J.R. Tischler et al, PRL 95, 036401 (2005) (organic)A. Khalifa et al., Appl. Phys. Lett. 92, 061107 (2008) T = 10 KD. Bajoni et al., Phys. Rev. B 77, 113303 (2008) T = 100 KS. I. Tsintzos et al., Nature 453, 372 (2008), APL (2009) T = 315 K
Polariton Physics
Polariton Devices
Polariton LaserDiodes ?
Ultrahigh speedSwitches ?
Time
• Spectacular physics related to bosoniccharacter of polaritons
• Mature understanding
Polariton LED
• Small progress
1992
• ApproachElectrical injection of polaritons in strongly
coupled GaAs semiconductor microcavity
Fabricate p-i-n diode microcavitiesfor electrical injection
Measure polariton electroluminescenceand dispersion relations
• Technical challenges/issues
High resistivity of the DBR mirrors
Doping related losses in DBR mirrorsand polariton robustness
Injection issues: e.g. inhomogeneous pumping of QWs
Electrical Injection in Microcavity
FORTH Microelectronics Research Group Univ. of Crete
high temperature
doping profile
Polariton LED
Microcavity Design
FORTH Microelectronics Research Group Univ. of Crete
• Designed to operate at high temperatures• Multiple QWs to enhance Rabi splitting
Polariton Electroluminescence
S. Tsintzos et al., Nature 453, 372 (2008)
Emission collected normal to the device
FORTH Microelectronics Research Group Univ. of Crete
260250240230220210200190Temperature (K)
1.355
1.350
1.345
1.340
1.335
1.330E
nerg
y (e
V)
Upper Polariton Lower Polariton exciton cavity
Temperature (K)
En
erg
y (e
V)
• Clear anticrossing observed
• Direct emission from exciton polariton states
Exciton ~ -0.38meV / KCavity ~ -0.102meV /K
Temperature tuning•Rabi splitting of 4.4meV at 219 K
Room temperature Polariton LED
•Polariton LED with 8 QWsto increase Rabi splitting
•Lateral injection scheme to improve injection
ΔΤ=5K
I=0.8mA
Rabi splitting of ~4meV at T=288K
FORTH Microelectronics Research Group Univ. of Crete
S. Tsintzos et al, APL 94,071109 (2009)
Large Rabi splitting in GaAs QW MCs at (T=300K)
FORTH Microelectronics Research Group Univ. of Crete
Θ
GaAs QWs
DBRAlAs
Al0.15Ga0.85As
DBRAlAs
Al0.15Ga0.85As
• Clear anticrossing
• Rabi splitting of 6.5mev observed
zero detuning
8
6
)8(
)6(
V
VV(8), the only adjustable parameter
Fitting of Rabi Splitting versus T and N
22 )(4 CXV
FORTH Microelectronics Research Group Univ. of Crete
(for zero detuning)
CX ,
Exciton, cavity modelinewidths
X with temperature
N=8GaAs
InGaAs
# QWs
Collapse of Strong Coupling Regime at High Densities
T=235K
2I~
Relaxation bottleneck
FORTH Microelectronics Research Group Univ. of Crete
• Injection density at 22mA ~ 1010 pol/cm2
need new injection schemes that bypass bottleneck
Microcavity structure exploiting LO phonon enhanced relaxation
FORTH Microelectronics Research Group Univ. of Crete
holes
DBR
polariton
LO-phononElectrons DBR
Using GaAs/AlGaAs QWs
Electroluminescence of LO phonon-designed MCs
FORTH Microelectronics Research Group Univ. of Crete
•Red shift in EL caused by heating• Due to series resistance of the DBRs
1.49 1.50 1.51 1.52101
102
103
104
105
106
EL
Inte
nsi
ty
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
Single shot imaging of the polariton dispersions
θ
FORTH Microelectronics Research Group Univ. of Crete
• Look at polariton population along the lower branch.
•Applicable to both PL and EL measurements on small mesas
objective
sample 4K
pin-hole
θ
θ
CCDθ
λ
λ
confocal
E
EL
Power dependence Images
Nonlinearity at very low power
Weak CouplingStrong Coupling
Nonlinearity possibly due to screening of diode built-in field
FORTH Microelectronics Research Group Univ. of Crete
Enhanced Polariton Relaxation @ High InjectionEnhanced Polariton Relaxation @ High Injection
0 5 10 15 20 25 30
Angle (degrees)
0.1mW
0.4mW
Inte
grat
ed In
tens
ity (
a.u)
0.9mW
2mW
3mWT=70K
FORTH Microelectronics Research Group Univ. of Crete
Enhanced Polariton Relaxation @ High TemperatureEnhanced Polariton Relaxation @ High Temperature
T=140K
P=0.4mW
T=60K
P=0.4mW
• 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
Summary
FORTH Microelectronics Research Group Univ. of Crete
Recommended