Polariton mediated resonant Raman scattering in II–VI microcavities:  Exciton lifetime effects

Semiconductor microcavities enable the study of polariton mediated inelastic light scattering with control of the exciton-photon coupling, and of the exciton and photon strength of the polariton wavefunction. We present a detailed study of the Raman efficiency due to optical phonons resonant with the upper polariton branches in II-VI cavities with embedded CdTe quantum wells. Cavities both in the strong coupling and very strong coupling regimes $(\Omega <E_b$ and $\Omega \sim E_b,$ respectively) are investigated. In the former, where the mode splitting $\Omega$ is smaller than the exciton binding energy $E_b,$ multibranch anticrossings with high order exciton states are observed. The Raman efficiency displays maxima close to the mode anticrossings (zero detuning) decreasing towards the pure excitonic and photonic regimes. This behavior basically reflects the optimization of the polariton coupling to the optical phonons and to exterior continuum photons. A marked steeper Raman efficiency reduction is observed for positive detunings, evidencing the important role of exciton dephasing in the Raman scattering process. Exciton lifetime effects are also apparent in the shape of the multibranch resonance Raman scan, and in the temperature dependence of the Raman efficiency.