Hot Hot electrons electrons and Hot and Hot phonons phonons in in Quantum Quantum Cascade Cascade Lasers Lasers Vincenzo Spagnolo, Miriam S. Vitiello, Gaetano Scamarcio CNR CNR - - INFM INFM – – University and Politecnico of Bari, Italy University and Politecnico of Bari, Italy • Motivation: all important device characteristics are strongly dependent from the electron energy relaxation processes and the mean energy of electron, phonon and lattice subsystems • Technique: • Photoluminescence and Raman Stokes-AntiStokes spectra with high spatial resolution (~ 1 µm) – PL: local lattice temperature; electronic temperature – Raman: optical phonon population; Results Results : : • • Hot Hot electrons electrons in in Sb Sb - - based based QCLs QCLs • • Non Non - - equilibrium equilibrium phonon phonon generation via generation via electrical electrical method method ( ( mid mid - - ir ir QCLs QCLs ) ) • • Superlinear Superlinear increase increase of hot of hot phonon phonon population population vs vs electrical electrical power ( power ( THz THz QCLs QCLs ) )
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Hot Hot electronselectrons and Hot and Hot phononsphonons in in Quantum Quantum CascadeCascade LasersLasers
Vincenzo Spagnolo, Miriam S. Vitiello, Gaetano ScamarcioCNRCNR--INFM INFM –– University and Politecnico of Bari, ItalyUniversity and Politecnico of Bari, Italy
• Motivation: all important device characteristics are strongly dependent from the electron energy relaxation processes and the mean energy of electron, phonon and lattice subsystems
• Technique:• Photoluminescence and Raman Stokes-AntiStokes spectra with high spatial
ResultsResults: : •• Hot Hot electronselectrons in in SbSb--basedbased QCLsQCLs•• NonNon--equilibriumequilibrium phononphonon generation via generation via electricalelectrical methodmethod ((midmid--irir QCLsQCLs))•• SuperlinearSuperlinear increaseincrease of hot of hot phononphonon populationpopulation vsvs electricalelectrical power (power (THzTHz QCLsQCLs))
What kind of phonons can be investigated What kind of phonons can be investigated in a (001) GaAsin a (001) GaAs--AlGaAsAlGaAs QCL structure ?QCL structure ?
Raman Raman SelectionSelection RulesRulesin in backscatteringbackscattering fromfrom devicedevice facetfacet
LO
TO
GaAs
AlGaAs
LO GaAs-like
LO AlAs-like
TO GaAs-like
TO AlAs-like
IF
LOGaAsIF
TOGaAsIF
LOAlAsIF
TOAlAsIF
Z(001)
X’
Y’
Y’(ZX’)Y’
DeformationDeformationPotentialPotential
The symmetry selection rules are broken close the resonances The symmetry selection rules are broken close the resonances
µµ-- Raman investigation of GaAsRaman investigation of GaAs-- AlGaAsAlGaAs RP THz RP THz QCLsQCLs
2nd Order
Inte
nsity
(a.u
) GaAs-IFTO
Stokes shift (cm-1)
0
10
20
250 300 350
*
VerifyVerify the ABSENCEthe ABSENCEof of ResonanceResonance ConditionsConditions
%71
2 <st
nd
II
Anti-Stokes/Stokes Intensity ratio vs Lattice temperature (device off)Anti-Stokes/Stokes Intensity ratio vs Lattice temperature (device off)