Growth of ZnSe/ZnS strained-layer superlattices on Si substrates

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Abstract
The high-quality ZnSe-ZnS strained-layer superlattices (SLSs), as well as the ZnS layers, were successfully grown for the first time on Si substrates. Photoluminescence (PL) spectra of ZnS layers grown on Si showed an intense excitonic-emission line. In transmission electron microscopy analyses, no misfit dislocations and no moiré fringes were observed on the ZnS layer with a thickness of less than about 500 Å. We have also characterized ZnSe-ZnS SLSs grown on Si substrates. By the PL measurements, an intense excitonic-emission line, and no emissions due to deep levels, were observed. As the ZnSe well-layer thickness decreased, the peak of the line largely shifted towards the higher-energy side. This behavior may be related to the quantum size effect. In the temperature dependence of PL intensity, there appeared the thermal quenching process, which may be related to the thermal release of excitons in quantum wells. As the thickness of the ZnSe well-layer decreased, the activation energy abruptly increased at a ZnSe thickness of less than the three-dimensional exciton Bohr radius in bulk ZnSe. It is proposed that the dependence of the activation energy is due to the two-dimensional exciton behavior in quantum wells.