DYNAMICAL PROPERTIES OF OPTICAL-EXCITATIONS IN II-VI STRUCTURES

Ultrafast dynamical properties and lasing in two-dimensional II-VI het erostructures reveal a manifold of physical mechanisms which are partl y unique and of great interest for tile general understanding of the o ptical behavior of these structures and related devices. We review our investigations of polariton propagation effects strongly governing tr ansmission of fs pulses perpendicular to II-VI waveguiding layers, sim ilar to those in respective laser structures, for low to high excitati on densities, being explained by the interference of simultaneously ex cited modes from four polariton branches involved. Second, exciton dif fusion properties can be deduced from results of transient-grating exp eriments. Extremely large exciton diffusion constants could be measure d in ultrapure ZnSe layers. For the first time, ultrafast time-resolve d laser mode and gain dynamics is determined for II-VI laser diode str uctures. Coupling of longitudinal ground modes and higher-order transv ersal modes results in a density-dependent temporal beat pattern which is well described in a model of weakly phase-coupled modes in II-VI r esonator cavities. Gain in laser diodes under optical pumping exhibits a complicated spectre-temporal shape with two subsequent stimulated-e mission peaks and kinetic- as well as spectral-hole-burning features, being explained on base of carrier heating and cooling effects during lasing. Challenges for the development of a microscopic theory of lasi ng in II-VI diodes are discussed.