EXCITONIC PROPERTIES OF ZNSE (ZN,MG)SE QUANTUM-WELLS - A MODEL STUDY OF THE TENSILE-STRAIN-SITUATION/

We present a comprehensive study of the excitonic properties of ZnSe/( Zn,Mg)Se structures grown by molecular beam epitaxy. Magnetoabsorption is used to derive precise values of the exciton binding energies and reduced in-plane masses. The data demonstrate a remarkable enhancement of both quantities due to heavy-hole-light-hole coupling in the tensi le strained wells, independently verified by a calculation of the hole subband dispersions and the resulting reduced exciton masses in the f rame of the Luttinger Hamiltonian. The large exciton binding energies (approximate to 38 meV) signify a valence band offset of about 30% of the total band offset. The increased exciton stability as well as the accordingly reduced coupling to LO phonons result in dominant exciton contributions to the photoluminescence and optical absorption up to te mperatures of 240 K. At low temperatures, the localization of excitons on well thickness fluctuations, directly traced in time-resolved lumi nescence, gives rise to a dominant inhomogeneous broadening. A pronoun ced biexciton luminescence band is observed at elevated excitation den sities.