MgS has been grown by molecular beam epitaxy in the zincblende crystal structure on GaAs ͑100͒ substrates using a technique where the sources are Mg and ZnS. Layers up to 134 nm thick have been grown without any degradation in the crystal structure. The lattice constant was found to be 0.5619Ϯ0.0001 nm and Poisson's ratio was estimated to be 0.425. The success of this growth technique has allowed the fabrication of MgS/ZnSe/MgS quantum wells that show sharp photoluminescence and transmission spectra indicating less than 1 ML fluctuations of the well widths. The small inhomogeneous broadening of the samples has allowed magneto-optical studies of the exciton absorption where the observation of higher excited exciton states have been observed and the exciton binding energies, E X , have been measured directly, notably E X (1s -2s) Ͼh LO in a 5 nm well. The full width at half maximum of the heavy-hole absorption transitions for this sample has been measured as a function of temperature and no broadening of the excitonic transitions has been observed up to 150 K showing that the exciton-LO phonon scattering has been suppressed.

Zinc blende MgS has been grown on GaAs by molecular beam epitaxy using a novel method where the sources were Mg and ZnS. A reaction at the surface results in the formation of MgS layers with a Zn content estimated by secondary ion mass spectrometry and Auger spectroscopy to be between 0.5% and 2%. Double crystal x-ray rocking curve measurements of ZnSe/MgS/ZnSe layers show layers with good crystallinity. Using this growth technique layers up to 67 nm thick have been grown. Photoluminescence measurements of MgS/ZnSe/MgS single-quantum-well structures show that the confinement of the heavy hole excitons can be as large as 430 meV for a 1.7 nm well.

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The wide bandgap II-VI semiconductors have unique properties which allow the possibility of suppressing the exciton-phonon scattering up to room temperature in quantum well structures designed so that the exciton excitation E1s→2s>hνLO. In particular, magnetic field and temperature dependent measurements are used to study the exciton binding energies and to investigate the exciton-LO phonon scattering processes of high quality ZnSe quantum wells in MgS grown by MBE. The small inhomogeneous broadening of the exciton transitions in these samples allows the observation of higher excited exciton states. Due to the large difference in band gap between ZnSe and MgS the exciton binding energy in a 5 nm well is found to be 43.9 meV, which is the largest reported for this material system. The FWHM of the heavy hole absorption transitions measured as a function of temperature shows that the scattering of the excitons by the LO phonons is partially suppressed. These results are compared with ZnS quantum wells where the exciton g-values have been measured and the exciton binding energies have been deduced from the exciton diamagnetic shifts. The results show the possibility of suppressing exciton-LO phonon scattering in these structures.

Magnetic field and temperature dependent measurements are used to study the excitonic properties of high quality ZnSe quantum wells in MgS barriers grown by molecular beam epitaxy. The small inhomogeneous broadening of the samples allows the observation of higher excited exciton states. Due to the large difference in band gap between ZnSe and MgS a value of 43.9 meV was measured for the exciton binding energy which is the largest reported for this material system. The full width at half maximum of the heavy hole transitions is measured as a function of temperature and the broadening of the excitonic transitions in narrow quantum wells is reduced compared to the ZnSe bulk value due to the expected reduction in the LO-phonon scattering.

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