Excitonic properties of zinc-blende ZnSe/MgS superlattices studied by reflection spectroscopy

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Abstract
Excitonic properties of newly developed zinc-blende ZnSe/MgS superlattices (SL's) were measured by reflection spectroscopy. The modification of the excitonic peaks by the multiple reflection in the SL films was treated theoretically and a fitting method to estimate the exciton absorption peak positions and exciton linewidths was developed. Although zinc-blende MgS did not exist before, excellent optical properties were observed in the ZnSe/MgS SL"s. Excitonic structures were clearly observed from 13 K up to the measured room temperature. In spite of strong ionicity of MgS barrier layers in the ZnSe/MgS SL's, the reduction of exciton–LO-phonon coupling was clearly observed in narrower wells. This indicates that the quantum confinement effect on excitons is large due to the large band offsets and it overcomes the enhancement of exciton–LO-phonon scattering due to high ionicity in barrier layers.