Excitons with large binding energies in MgS/ZnSe/MgS and ZnMgS/ZnS/ZnMgS quantum wells

The wide bandgap II-VI semiconductors have unique properties which allow th e possibility of suppressing the exciton-phonon scattering up to room tempe rature in quantum well structures designed so that the exciton excitation E 1s-->2s > h nu (LO), In particular, magnetic field and temperature dependen t measurements are used to study the exciton binding energies and to invest igate the exciton-LO phonon scattering processes of high quality ZnSe quant um wells in MgS grown by MBE. The small inhomogeneous broadening of the exc iton transitions in these samples allows the observation of higher excited exciton states. Due to the large difference in band gap between ZnSe and Mg S 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 hol e absorption transitions measured as a function of temperature shows that t he scattering of the excitons by the LO phonons is partially suppressed. Th ese 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 suppres sing exciton-LO phonon scattering in these structures.