Dynamical properties of excitonic quasi-particles in II-VI semiconductors

Abstract

This work focuses on the dynamics of exciton polaritons and exciton magnetic polarons in II-VI semiconductors. The propagation dynamics of exciton polaritons, formed between photons and the fundamental exciton resonance, are investigated in (Cd,Zn)Te crystal. Due to the polariton dispersion a sub-mm thick crystal can delay the propagation of light on a sub-ns scale, with the delay increasing as the photon energy approaches the energy of the exciton resonance. The Zeeman splitting induced by the application of an external magnetic field gives rise to polarization effects resulting in oscillations of the polarization of transmitted light in the time domain. The polarization effects including linear and circular birefringence are characterized and explained by a detailed model. Exciton polaron formation is studied in a semimagnetic CdMnSe quantum well surround by CdMgSe barriers. Here, unusual slow exciton magnetic polaron formation is observed and successfully attributed to autolocalization, a positive feedback mechanism between polaron formatation and the confinement of the hole of the exciton. This is enabled by the presence of Mn inside the quantum well and its absence in the barrier. This leads to a stronger confinement of the hole to the quantumn well if an external magnetic field is applied or an exciton magnetic polaron is formed. This additional confinement is confirmed using time resolved magneto spectrosopy by a reduction of exciton lifetime with the application of a Faraday magnetic field and a magnetic field induced anisotropy of the exciton g-factor.