Exciton-photon coupling

Our research concentrates on the many-bodied interactions within wide-gap II-VI semiconductors. Although not a commonly used materials system, the wide-gap II-VIs (usually comprising combinations of Zn, Cd, Se, S, Mg) allows semiconductor-generic interactions to be more readily observed than in the standard II-V materials system. Interactions include those involving "single-particles" such as electrons, holes, phonons as well as "complexes" such as excitons and biexctions. Most of our experiments are carried out at low temperature (4K - 70K) using ultrashort laser pulses. Principal techniques include four-wave mixing and time-resolved polarisation-dependent continuum-pump-probing.

In the past we have published our findings on such phenomena as quantum-beating, polarisation-beating, the influence of confinement for acoustic-phonon scattering, spin-relaxation within biexcitons and the cooling dynamics of the optically-created electron-hole plasma.

Currently we are focusing on the manipulation and interaction of photonic and electronic wave functions in II-VI quantum microcavities. The Fabry-Perot modes set up by the injection of light interact with the quantum well excitons when the two are brought into resonance. When this interaction exceeds the damping of the two composite oscillators a new pair of quasiparticles are formed, the exciton-polariton the dispersion of which is shown (calculated).

Hetrostructure used to study polariton dynamics along with the calculated dispersion of cavity-polaritons in III-V materials

The observation and study of polaritons in III-V materials (GaAlAs) has had much attention since the 1st observation by Weisbuch et al (1992). However the development of a practical polariton device is hindered by the low ionization temperature of III-V excitons (~100K). A II-VI-based device would offer an ideal solution to this since ZnSe excitons, for example, are stable up to room temperature.