Spin dependent carrier localization in Fe-based semimagnetic semiconductor heterostructures

Semimagnetic (or diluted magnetic) semiconductor heterostructures offer many unique opportunities for the study of spin dependent effects, including magnetic field induced quantum confinement and carrier spin lifetimes, In diluted magnetic semiconductors (DMS) such as Zn1-xFexSe, strong spin exchange interactions significantly modify the band structure in the presence of an applied magnetic field. This allows one to continuously and reversibly modify the band offsets in tailored heterostructures to selectively localize carriers according to their spin state, thereby providing another degree of freedom in tuning the spatial localization and overlap of carrier wave functions after the fact of growth. We review several examples which have been recently demonstrated in Zn1-xFexSe-based heterostructures grown by molecular beam epitaxy, including field tunable type-I-type-II transitions, the formation of a spin superlattice, and the continuous evolution of band alignment to the realization of a re-entrant type-I structure. Additional control over carrier confinement and lifetimes via carrier spin is possible in structures which consist of alternating layers of Zn1-xFexSe and Zn1-yMnySe. In such multiple quantum well systems, the heavy hole exciton simultaneously exhibits both Brillouin and Van Vleck paramagnetic behavior depending upon the spin state probed, Evidence is also observed for the formation of an electron spin population inversion which arises from the spin splitting of the electron states and the simultaneous spin separation of the holes into different layers of the structure.