Magneto-optical investigations of II-VI DMS heterostructures: zinc(1-x-y) manganese(x) cadmium(y) selenium/zinc(1-x) manganese(x) selenium single quantum wells, zinc(1-x) cadmium(x) selenium/zinc(1-y) manganese(y) selenium type-I and cadmium selenide/zinc telluride based type-II superlattices.

摘要

This dissertation describes magneto-optical absorption measurements on Zn{dollar}sb{lcub}rm 1-x-y{rcub}{dollar}Mn{dollar}sb{lcub}rm x{rcub}{dollar}Cd{dollar}sb{lcub}rm y{rcub}{dollar}Se/Zn{dollar}sb{lcub}rm 1-x{rcub}{dollar}Mn{dollar}sb{lcub}rm x{rcub}{dollar}Se single quantum wells, and Zn{dollar}sb{lcub}rm 1-x{rcub}{dollar}Cd{dollar}sb{lcub}rm x{rcub}{dollar}Se/Zn{dollar}sb{lcub}rm 1-y{rcub}{dollar}Mn{dollar}sb{lcub}rm y{rcub}{dollar}Se type-I and CdSe/ZnTe based type-II superlattices. We first give a general presentation of the properties of diluted magnetic semiconductors, with emphasis on their striking magneto-optical properties. We then discuss the theoretical background of electronic states in semiconductor superlattices within the envelope function approximation. Next, we briefly discuss the experimental aspects of this investigation, including sample preparation and the apparatus for the magneto-optical experiments.; We then present a study of sp-d exchange interaction in quantum wells consisting of diluted magnetic semiconductors (DMSs) and either non-DMS or DMS barriers. The sp-d exchange interaction and its relation to the confinement effect of electrons and holes were studied for different quantum well thicknesses. The results show that the Zeeman splitting is not affected by the confinement effect itself, but is greatly influenced by the penetration of the wave functions into the non-magnetic layers.; We also present a detailed study of a series of Zn{dollar}sb{lcub}rm 1-x{rcub}{dollar}Cd{dollar}sb{lcub}rm x{rcub}{dollar}Se/Zn{dollar}sb{lcub}rm l-y{rcub}{dollar}Mn{dollar}sb{lcub}rm y{rcub}{dollar}Se type-I superlattices by magneto-absorption measurements. We present experimental evidence for the existence of localized excitons at above-barrier energies in type-I superlattices. We show conclusively that above-barrier excitons are localized in the barrier rather than in the well regions.; Superlattices based on CdSe/ZnTe (i.e., CdSe/ZnTe, Cd{dollar}sb{lcub}rm 1-x{rcub}{dollar}Mn{dollar}sb{lcub}rm x{rcub}{dollar}Se/ZnTe, and CdSe/Zn{dollar}sb{lcub}rm 1-x{rcub}{dollar}Mn{dollar}sb{lcub}rm x{rcub}{dollar}Te) are characterized by type-II band alignment. We have used these structures to demonstrate that type-II superlattices can exhibit type-I excitons, i.e., excitons which are confined in the same semiconductor layer (either in CdSe or CdMnSe, or in Zn{dollar}sb{lcub}rm 1-x{rcub}{dollar}Mn{dollar}sb{lcub}rm x{rcub}{dollar}Te in the above examples). Such spatially-direct excitons form in a type-II structure when one of the carriers (electron or hole) originates from a well, while the other (hole or electron) originates from a state localized in the barrier, which is typical for subbands at above-barrier energies. The type-I exciton transition between {dollar}Gammasb7{dollar} and {dollar}Gammasb6{dollar} bands in CdSe layers are also observed in those type-II superlattices.