EXCITONIC TRANSITIONS AND BAND-OFFSET CALCULATIONS IN A SHORT-PERIOD ZNS-ZNSE SUPERLATTICE

An investigation of the photoreflectance and photoluminescence spectra of a 45 period ZnS-ZnSe strained layer superlattice having well and b arrier widths of 3.3 and 3.7 nm, respectively, is reported. Heavy hole (e(1)hh(1)) and light hole (e(1)lh(1)) excitons are well resolved in the 2 K photoreflectance spectrum. The energies of these transitions a re calculated within the envelope function framework, generalized to s trained layers. The valence and conduction band offsets are the princi pal parameters in this calculation. Thus, two different approaches are set in competition to determine these quantities. The first is based on theoretical models while the second uses a ''semi-experimental'' me thod. The latter method gives a free-standing type-I superlattice with optimal agreement between photoreflectance measurements and theory. A lso the importance of a precise knowledge of the exciton binding energ y (enhanced because of the reduced dimensionality) for an accurate ban d offset determination is shown. This binding energy is estimated for the heavy hole exciton from a variational calculation.