Excitonic Properties of ZnSe-ZnS Strained-Layer Superlattices and A Fibonacci Sequence

ABSTRACTExcitonic properties of ZnSe-ZnS strained-layer quantum wells (SLQWs) with type I band lineups are reviewed on the basis of our recent results of temperature- and strain-dependent photoluminescence and absorption spectra. In order to estimate the conduction and valence band offsets as a function of ZnSe well thickness, we have modified the “model-solid” theory in which the valence bands (heavy-hole band in ZnSe and light-hole band in ZnS) are relatively moved with strains. Temperature and high excitation dependent studies of the n=1 heavy-hole excitons suggest a localization of excitons and reveals the important evidence on scatterings of excitons with acoustic and optical phonons. The thermal quenching of the exciton emission is caused by thermal dissociation of quasi-two-dimensional excitons through electrons and holes, from which the activation energy for this dissociation is 4 times larger than Ea.3D (a binding energy of bulk exciton) of ZnSe. A new superlattice structure with a quasiperiodic crystal which is derived from a finite Fibonacci sequence, has been fabricated by a low-pressure MOCVD method and its photoluminescence properties are for the first time introduced.