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 barrier 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 are calculated within the envelope function framework, generalized to strained layers. The valence and conduction band offsets are the principal 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'' method. The latter method gives a free-standing type-I superlattice with optimal agreement between photoreflectance measurements and theory. Also the importance of a precise knowledge of the exciton binding energy (enhanced because of the reduced dimensionality) for an accurate band offset determination is shown. This binding energy is estimated for the heavy hole exciton from a variational calculation.