Optical absorption, gain and lasing in ZnSe

Summary form only given. Different mechanisms were discussed to be relevant for the physical nature of gain in II-VI semiconductors. Since lasing was found to appear in the vicinity of the the exciton and according to the large exciton binding in comparison to the III-V materials different excitonic scattering processes (ex-ex, ex-LO phonon, biexcitons) were discussed, depending on the material composition, the geometry of the investigated heterostructures (bulk, quantum wells and superlattices) and on the temperature. Otherwise there are different experi ments for temperatures around and above 77K, were an electron-hole plasma recombination has been supported to be the dominant mechanism of gain and lasing as it is found for the III-V materials. In this paper we address this question from the theoretical point of view, whether excitonic absorption and gain can coexist in a dense electron-hole plasma at 77K. To give an answer a theoretical approach has to contain both (i) an appropriate description of the excitonic absorption including all relevant many-body effects and (ii) to guarantee the correct position of the chemical potential of carriers, fixing the transition from absorption to gain, and (iii) to include not only field driven but relaxed excitons too.