Current POLARITON LIGHT EMITTING DEVICES: RELAXATION DYNAMICS Simos Tsintzos Dept of Materials Sci. & Tech Microelectronics Group University of Crete / IESL Polariton emitter Active region Bottom Mirror Top Mirror

Polariton Physics at Crete Spectroscopy & Fabrication Prof. 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. Kostantinidis Dr. 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 lasing Polariton condensation Polariton Superfluidity Polariton LEDs J.R. Tischler et al, PRL 95, (2005) (organic) A. Khalifa et al., Appl. Phys. Lett. 92, (2008) T = 10 K D. Bajoni et al., Phys. Rev. B 77, (2008) T = 100 K S. I. Tsintzos et al., Nature 453, 372 (2008), APL (2009) T = 315 K Polariton Physics Polariton Devices Polariton Laser Diodes ? Ultrahigh speed Switches ? Time Spectacular physics related to bosonic character of polaritons Mature understanding Polariton LED Small progress 1992

Approach Electrical injection of polaritons in strongly coupled GaAs semiconductor microcavity Fabricate p-i-n diode microcavities for electrical injection Measure polariton electroluminescence and dispersion relations Technical challenges/issues High resistivity of the DBR mirrors Doping related losses in DBR mirrors and 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 Temperature (K) Energy (eV) Clear anticrossing observed Direct emission from exciton polariton states Exciton ~ -0.38meV / K Cavity ~ meV /K Temperature tuning Rabi splitting of 4.4meV at 219 K

Room temperature Polariton LED Polariton LED with 8 QWs to 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, (2009)

Large Rabi splitting in GaAs QW MCs at (T=300K) FORTH Microelectronics Research Group Univ. of Crete Θ GaAs QWs DBR AlAs Al 0.15 Ga 0.85 As DBR AlAs Al 0.15 Ga 0.85 As Clear anticrossing Rabi splitting of 6.5mev observed zero detuning

V(8), the only adjustable parameter Fitting of Rabi Splitting versus T and N FORTH Microelectronics Research Group Univ. of Crete (for zero detuning) Exciton, cavity mode linewidths with temperature N=8 GaAs InGaAs # QWs

Collapse of Strong Coupling Regime at High Densities T=235K ~ Relaxation bottleneck FORTH Microelectronics Research Group Univ. of Crete Injection density at 22mA ~ pol/cm 2 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-phonon Electrons 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

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 CCD θ λ λ confocal E EL

Power dependence Images Nonlinearity at very low power Weak Coupling Strong Coupling Nonlinearity possibly due to screening of diode built-in field

FORTH Microelectronics Research Group Univ. of Crete Enhanced Polariton High Injection

FORTH Microelectronics Research Group Univ. of Crete Enhanced Polariton 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