Magneto-optical spectroscopy in diluted magnetic semiconductor-based quantum well structures.

摘要

Magneto-Optical spectroscopic techniques have been used to study diluted magnetic semiconductor (DMS) based quantum well structures. Two types of systems have been investigated.; a. Spin superlattices with alternating non-magnetic and magnetic layers, in which a tunable spin-dependent potential exists. The ZnSe/Zn{dollar}sb{lcub}0.99{rcub}{dollar}Fe{dollar}sb{lcub}0.01{rcub}{dollar}Se system, in which field induced spin splittings in both valence and conduction bands are much larger than the residual zero-field potentials, exhibits spin superlattice behavior. Low temperature magneto-reflectance experiments have been used to investigate the nature of these structures, verifying through field-dependent spin splittings and transition strengths, that they are in fact true spin superlattices, i.e. both the electrons and holes segregate according to their spin states.; The spin relaxation process in spin superlattice structures, both at zero field (no confining potential) and as a function of applied field (variable confining potential) have been studied. Evidence of an unexpectedly long hole spin relaxation time associated with the strain splitting of the valence band has been found. In addition, excitonic spin relaxation times which are unaffected by the strength of the spin-dependent confining potential were observed. It has been demonstrated that for excitons, spin flip via the magnetic ion-carrier exchange interaction is not the dominant spin relaxation mechanism, although it may play a more important role in the case of energetic hot carriers.; b. ZnTe/CdMnSe multiple quantum well structures have a type-II band alignment such that holes are subjected to strong confinement in the ZnTe layers ({dollar}simeq{dollar}0.7 eV) while electrons also experience strong confinement ({dollar}simeq{dollar}1.3 eV) in the CdMnSe layers. Two types of interband transitions have been observed in this system: (i) Type-II transitions between electrons confined in the CdMnSe layers and holes confined in the ZnTe layers. (ii) Type-I transitions associated with excitons formed between confined electrons and above the barrier hole states, both of which are localized in the CdMnSe layers. The position of the electrons and holes participating in both types of transitions has been verified by Zeeman Spectroscopy.