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 tensile strained wells, independently verified by a calculation of the hole subband dispersions and the resulting reduced exciton masses in the frame of the Luttinger Hamiltonian. The large exciton binding energies $\left(\approx 38\mathrm{meV}\right)$ 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 temperatures of 240 K. At low temperatures, the localization of excitons on well thickness fluctuations, directly traced in time-resolved luminescence, gives rise to a dominant inhomogeneous broadening. A pronounced biexciton luminescence band is observed at elevated excitation densities.