@phdthesis{Slobodskyy2005,
  author    = {Slobodskyy, Anatoliy},
  title     = {Diluted magnetic semiconductor Resonant Tunneling Structures for spin manipulation},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-18263},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2005},
  abstract  = {In this work we investigate magnetic resonant tunneling diode (RTD) structures for spin manipulation. All-II-VI semiconductor RTD structures based on [Zn,Be]Se are grown by molecular beam epitaxy. We observe a strong, magnetic field induced, splitting of the resonance peaks in the I-V characteristics of RTDs with [Zn,Mn]Se diluted magnetic semiconductors (DMS) quantum well. The splitting saturates at high fields and has strong temperature dependence. A phonon replica of the resonance is also observed and has similar behaviour to the peak. We develop a model based on the giant Zeeman splitting of the spin levels in the DMS quantum well in order to explain the magnetic field induced behaviour of the resonance.},
  subject      = {Resonanz-Tunneldiode},
  language  = {en}
}
@phdthesis{Knapp2019,
  author    = {Knapp, Alexander Gerhard},
  title     = {Resonant Spin Flip Raman-Spectroscopy of Electrons and Manganese-Ions in the n-doped Diluted Magnetic Semiconductor (Zn,Mn)Se:Cl},
  doi       = {10.25972/OPUS-18609},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-186099},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2019},
  abstract  = {Main focus of the present dissertation was to gain new insight about the interaction between magnetic ions and the conduction band of diluted magnetic semiconductors. This interaction in magnetic semiconductors with carrier concentrations near the metal-insulator transition (MIT) in an external magnetic field is barely researched. Hence, n-doped Zn1-xMnxSe:Cl samples were studied. Resonant Raman spectroscopy was employed at an external magnetic field between 1T and 7T and a temperature of 1.5K. The resulting magnetization of the material amplifies the splitting of states with opposite spins both in the valence and the conduction band. This is known as the "giant-Zeeman-effect". In this thesis, the resonance of the electron spin flip process, i.e. the enhancement of the signal depending on the excitation energy, was used as an indicator to determine the density of states of the charge carriers. The measured resonance profiles of each sample showed a structure, which consist of two partially overlapping Gaussian curves. The analysis of the Gaussian curves revealed that their respective maxima are separated independent of the magnetic field strenght by about 5 meV, which matches the binding energy of the donor bound exciton (D0, X). A widening of the full width at half maximum of the resonance profile was observed with increasing magnetic field. A detailed analysis of this behavior showed that the donor bound exciton spin flip resonance primarily accounts for the widening for all samples with doping concentrations below the metal insulator transition. A model was proposed for the interpretation of this observation. This is based on the fundamental assumptions of a spatially random distribution of the manganese ions on the group-II sublattice of the ZnSe crystal and the finite extension of the excitons. Thus, each exciton covers an individual quantity of manganese ions, which manifest as a local manganese concentration. This local manganese concentration is normally distributed for a set of excitons and hence, the evaluation of the distribution allows the determination of exciton radii Two trends were identified for the (D0, X) radii. The radius of the bound exciton decreases with increasing carrier concentration as well as with increasing manganese concentration. The determination of the (D0, X) radii by the use of resonant spin flip Raman spectroscopy and also the observation of the behavior of the (D0, X) radius depending on the carrier concentration, was achieved for the first time. For all samples with carrier concentrations below the metal-insulator transition, the obtained (X0) radii are up to a factor of 5.9 larger than the respective (D0, X) radii. This observation is explained by the unbound character of the (X0). For the first time, such an observation could be made by Raman spectroscopy.Beside the resonance studies, the shape of the Raman signal of the electron spin flip was analyzed. Thereby an obvious asymmetry of the signal, with a clear flank to lower Raman shifts, was observed. This asymmetry is most pronounced, when the spin flip process is excited near the (D0, X) resonance. To explain this observation, a theoretical model was introduced in this thesis. Based on the asymmetry of the resonantly excited spin flip signal, it was possible to estimate the (D0, X) radii, too. At external magnetic fields between 1.25T and 7T, the obtained radii lie between 2.38nm and 2.75nm. Additionally, the asymmetry of the electron spin flip signal was observed at different excitation energies. Here it is striking that the asymmetry vanishes with increasing excitation energy. At the highest excitation energy, where the electron spin flip was still detectable, the estimated radius of the exciton is 3.92nm. Beside the observations on the electron spin flip, the resonance behavior of the spin flip processes in the d-shell of the incorporated Mn ions was studied in this thesis. This was performed for the direct Mn spin flip process as well as for the sum process of the longitudinal optical phonon with the Mn spin flip. For the Stokes and anti-Stokes direct spin flip process and for the Stokes sum process, each the resonance curve is described by considering only one resonance mechanism. In contrast, resonance for the sum process in which an anti-Stokes Mn spin flip is involved, consists of two partially overlapping resonances due to different mechanisms. A detailed analysis of this resonance profile showed that for (Zn,Mn)Se at the chosen experimental parameters, an incoming and outgoing resonance can be achieved, separated by a few meV. Hereby, at a specific excitation energy range and a high excitation power, it was possible to achieve an inversion of the anti-Stokes to Stokes intensity, because only the anti-Stokes Mn spin flip process was enhanced resonantly.},
  subject      = {Raman-Spektroskopie},
  language  = {en}
}