Exciton Dynamics and Gain Mechanisms in Optically Pumped ZnSe-Based Laser Structures

Although lasing is meanwhile achieved in various ZnSe-based heterostructures, the underlying mechanisms are still seriously under debate. The gain spectra of various MBE-grown samples are measured using the variable-stripe-length method. A description of the gain spectra for low particle densities is possible in terms of the model of Ding et al. The responsible gain mechanism is assumed to be an induced recombination of strongly exchange-interacting localized excitons, which, however, may be a questionable precondition. By means of time-dependent measurements the localizing character of the active material is demonstrated. However, several indications are given that under certain circumstances more than one process contribute to lasing, in particular biexciton recombination seems to be involved in the gain mechanism.