Morphologies and photoluminescence properties of gallium nitride‐based thin films grown on non‐single‐crystalline substrates were investigated. The films were directly grown on quartz glass and amorphous‐carbon‐coated graphite substrates by a molecular beam epitaxy apparatus which has dual nitrogen plasma cells. Co‐supplying of indium and gallium with simultaneous operation of the dual nitrogen plasma cells brought isolated and nano‐pillar‐shaped structures to the films. On the other hand, such structures were not obtained when the films were grown by the single plasma cell operation. Photoluminescence (PL) properties of the films greatly depended upon the morphologies. The intensities of the PL peaks emitted from the films which have such nano‐pillar shaped structures were quite intense although the peak energies shifted to lower energy sides compared with those of the films grown by the single plasma cell operation.

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CdZnS/ZnS/MgZnS separate-confinement heterostructures (SCHs) were grown on (100)-oriented GaAs substrates by low-pressure metalorganic chemical vapor deposition. Optical properties of SCHs were investigated by means of temperature-dependent photoluminescence (PL) spectroscopy in the temperature range of 4 to 300 K. In order to improve the crystalline quality of SCHs, a ZnS buffer layer was inserted prior to the growth of SCH structure on substrates. For a Cd 0.2 Zn 0.8 S/ZnS/Mg 0.25 Zn 0.75 S SCH structure with a ZnS buffer layer, which has the appropriate thickness of 100 nm, the decrease in PL intensity from 4 to 300 K was about two orders of magnitude. In comparison with the decrease observed for MQW structure, thermal quenching of the PL intensity was suppressed by about two orders of magnitude. It is expected that the suppression was attributed to the enhancement of carrier confinement by the insertion of a MgZnS cladding layer.Introduction II±VI semiconductors such as ZnS and ZnSe have intensively attracted attention both for optical devices in the ultraviolet (UV) spectral range and for basic research. Since ZnS has a large bandgap energy of 3.73 eV and an exciton binding energy of 36 meV, it is especially expected that the optical devices due to the radiative recombination of excitons or biexcitons can be realized in ZnS-based systems at RT. In fact, the excitonic stimulated emission was observed for different structures by various groups [1 to 3]. We also reported that the stimulated emission connected with the recombination of biexcitons was observed up to about 200 K [4]. In order to realize the biexcitonic stimulated emission at RT, it is important to enhance the carrier confinement. In ZnSe-based laser diodes (LD), Itoh et al. reported that a carrier overflow from an active layer was suppressed by the insertion of a Mg-compound cladding layer [7]. Therefore it is expected that the use of a MgZnS cladding layer leads to an enhancement of the carrier confinement in the quantum wells.In this study, we report the optical properties of CdZnS/ZnS multiple-quantum wells (MQWs) and CdZnS/ZnS/MgZnS separate confinement heterostructures (SCHs) by means of temperature-dependent photoluminescence (PL) measurements. We also report the improvement of crystalline quality in MgZnS mixed films by the insertion of a ZnS buffer layer. Furthermore, we demonstrate the enhancement of the luminescence intensity at RT from SCH structures grown on ZnS buffer layers.

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