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Cornelius Grossmann. ULTRAFAST CONTROL OF POLARITON STIMULATED SCATTERING IN SEMICONDUCTOR MICROCAVITIES. G. Christmann , C. Coulson and J.J. Baumberg Nanophotonics Centre, Cavendish Laboratory, University of Cambridge. - PowerPoint PPT Presentation
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Cornelius Grossmann 1
ULTRAFAST CONTROL OF POLARITON STIMULATED SCATTERING IN SEMICONDUCTOR MICROCAVITIES
Cornelius Grossmann
G. Christmann, C. Coulson and J.J. BaumbergNanophotonics Centre, Cavendish Laboratory, University of Cambridge
N. T. Pelekanos, Z. Hatzopoulos, S. I. Tsinzos and P. G. SavvidisDepartment of Materials Science and Technology, University of Crete
PLMCN10, Cuernavaca, Mexico15th april 2010
Cornelius Grossmann 2
Strong coupling regime
Mirror MirrorActiveregion
C. Weisbuch et al., PRL 69 3314 (1992)
|excited,0> |ground,1>
h
Lower polariton
Upper polariton
Strong-coupling regime:reabsorption time < cavity lifetime
semiconductor microcavity
Exciton
Cavity
UPB
LPB
Energy
Momentum
coupling between a electronic transition and a Fabry-Perot mode
Cornelius Grossmann 3
Parametric scattering processparametric conversion:• probe stimulation at ks= 0• energy and momentum conservation!
Savvidis et. al., PRL 84 1547 (2000)
• coherent χ(3) process in semiconductor microcavities• χ(3)-nonlinearity: exciton-exciton interaction• probe gain highly dependent on pump-LPB resonance
2kp= ks+ki
2E(kp)= E(ks)+E(ki)
PumpEP, kP
EI, kI
ES, kS
Signal
Idler
χ(3)
Cornelius Grossmann 4
Under external bias
Polariton light emitting diode
D. Tsintzos et al., Nature 453 372 (2008)
Quantum confined Stark effect
conductionband
valence band
GaAs InGaAs GaAsGrowth axis
F
Applied bias
consequences
change of energy of excitonic transition separation of electron and hole wavefunctions
Cornelius Grossmann 5
Electrically pumped polariton devices
Optical bistability in GaAs-based Polariton LED
Bajoni et. al., PRL 101 266402 (2008)
Electroluminescence up to RT
Tsintzos et. al., APL 94 071109 (2009)Khalifa et. al., APL 92 061107 (2008)Bajoni et. al., PRB 77 113303 (2008)
Cornelius Grossmann 6
Motivation for the bias
The parametric scattering process is due to exciton-exciton interaction through χ(3)
-+
-+
- +
- +
The excitons are alignedTailoring of the exciton-exciton interaction
Consequences on the parametric amplification in microcavities?
Growth axis
F
Cornelius Grossmann 7
Experimental setup
fs mode-locked Ti:Sa laser system• pump spectrally filtered and broadband probe pulse• pump at the magic-angle• probe at k||= 0 • recording of
pump reflected spectrum incident probe reflected probe
• in parallel: electrical measurements
Cornelius Grossmann 8
Voltage scan: Stark effect
Ref
lect
ivity
(arb
. uni
ts)
1.4161.4121.4081.404Energy (eV)
2.5V
-2.4V
T=7.5 K LP
X
UP
C
1
1.416
1.414
1.412
1.410
1.408
1.406
1.404
1.402
1.400
Ener
gy (e
V)
210-1
Bias (V)
Stark tuning of the excitonsRabi splitting of 6 meV
Refle
ction
spec
tra
Cornelius Grossmann 9
Voltage scan: pump-probe
50
40
30
20
10
0
Gain
1.4161.4121.4081.404
Energy (eV)
Ipum
p
2.5V
-1.5V
c)
a)b)
LP(kp)
LP
UP
10
8
6
4
2
0
Peak
gain
210-1
Bias (V)
1.416
1.414
1.412
1.410
1.408
1.406
1.404
Energy
(eV)
210-1
Bias (V)
2 effects: • gain-loss at negative bias, dispersion-less
50
40
30
20
10
0
Gai
n
1.4161.4121.4081.404
Energy (eV)Ipum
p
2.5V
-1.5V
c)
a)b)
LP(kp)
LP
UP
10
8
6
4
2
0
Peak
gai
n
210-1
Bias (V)
1.416
1.414
1.412
1.410
1.408
1.406
1.404
Ener
gy (e
V)
210-1
Bias (V)
50
40
30
20
10
0
Gai
n
1.4161.4121.4081.404
Energy (eV)
Ipump
2.5V
-1.5V
c)
a)b)
LP(kp)
LP
UP
10
8
6
4
2
0
Peak
gai
n
210-1
Bias (V)
1.416
1.414
1.412
1.410
1.408
1.406
1.404
Ener
gy (e
V)
210-1
Bias (V)
500
0
Cur
rent
(A
)-2 0 2
Bias (V)
Cur
rent
(μA)
Bias (V)
pump onpump off
gain-loss at negative bias:detuning of pump and LPB
• gain dip at positive bias
Cornelius Grossmann 10
Negative bias: gain loss
• unbiased
• biased
Stark-tuning of excitons:pump out of resonance with LPB inefficient carrier injection
resonance of pump and LPB:efficient parametric amplification efficient carrier injection
Growth axis
No screening of external electric field!
Cornelius Grossmann 11
sharp gain dip
-20
-15
-10
-5
0
Current (
A)
1.00.80.60.4Bias (V)
x6
c)
a) b)
1.1 V
0.4 V
80
60
40
20
0
Gain
1.4121.4111.4101.4091.4081.407
Energy (eV)
40
30
20
10
0
Peak
gain
1.00.80.60.4Bias (V)
-20
-15
-10
-5
0
Current (
A)
1.00.80.60.4Bias (V)
x6
c)
a) b)
1.1 V
0.4 V
80
60
40
20
0
Gain
1.4121.4111.4101.4091.4081.407
Energy (eV)
40
30
20
10
0
Peak gain
1.00.80.60.4Bias (V)
100 mV
> 90%
sharp dip
additionalphotocurrentat this bias
50
40
30
20
10
0
Gai
n
1.4161.4121.4081.404
Energy (eV)
Ipump
2.5V
-1.5V
c)
a)b)
LP(kp)
LP
UP
10
8
6
4
2
0
Peak
gai
n
210-1
Bias (V)
1.416
1.414
1.412
1.410
1.408
1.406
1.404
Ener
gy (e
V)
210-1
Bias (V)
Cornelius Grossmann 12
Tunneling
-1.20
-1.16
-1.12
-1.08Ener
gy (e
V)
40200Position (nm)
0.40
0.36
0.32
0.28LP
LQW RQW
τc
τe
τtτLO
τΩ
τo
700fs8ps
20ps
2 competing processes• Rabi-oscillations: redistribution of e-/h-pairs over QWs • carrier tunneling: separation of e-/h-pairs
• LO-phonon induced tunneling 100 fs• carrier escape 180 ns, 230 fs• extra e- population creates extra scattering• OPO gain sensitive to broadening
C. Ciuti et al. PRB 62 R4825 (2000)
0.6
0.51.00.5
Bias (V)
LQW RQW
ωLO
Ee (eV)
Cornelius Grossmann 13
Summary & outlook
electrical control of the parametric gain sharp and dramatic gain modulation
Stark tuning with “small” electrical fields: ultrafast response expected Potential realization of Thz modulators?
Cornelius Grossmann 14
Support and funding
• Pavlos G. Savvidis et. al.: Polariton LED sample• Gabriel Christmann, Chris Coulson and Jeremy Baumberg: spectroscopy & simulation
Funding: • UK EPSRC EP/C511786/1, EP/F011393 • EU Clermont 4
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