Dynamics of the Spin Excitation Sepctrum in dimension reduced II-VI semiconductors
In our project have been studied exciton spin dynamic properties in wide-bandgap II-VI quantum wells, particulary in semimagnetic and nonmagnetic quantum wells. In time-resolved investigations we directly detected the formation of exciton magnetic polarons in semimagnetic barrier structures and determined the characteristical spin relaxation time in magntic Mn ions. Varying the sample structures, we achieved a modified arrangement of the energy bands. Thereby it was possible to study indirect type-II excitons in quantum-well structures and interface excitons on comparable conditions. By heating the spin system consisting Mn ions, for both exciton types was shown a significant reduction of the Riesen-Zeeman effect.
In semimagnetic quantum-well structures we observed an unexpected strong coupling between the optically generated excitons and the magnetic activated Mn Ions in doped quantum wells, which leds to a dramatically reduction of the exciton lifetime. Thereby the energy of the optically excited carriers had been directly transfered to the intra-atomic transitions of the magnetic ion. This transfer could be reduced in a magnetic field, whereby the remaining coupling brought about a nonradiant decay of the optically charged excitons. On account of the strong exciton coupling for the first time it was possible to carry out optical experiments for systematical studies of the d-d-exchange interaction of antiferromagnetic oriented Mn pairs in (Zn,Mn,Cd)Se structures and to determine an exactly value of the exchange constant.
In the case of nonmagnetic quantum wells we focussed our studies on the fine structure of the exciton ground state. In wide-bandgap II-VI structures we observed such a high electron-hole pair correlation, that the spin dynamic essentially could be determined by the excitons and their fine structure, while the spin relaxation of the single charge carriers was of secondary importance. In the context of our project for the first time successful have been resolved the fine structure of zero-dimensional excitons and detected fundamental properties of the electron-hole exchange interaction.
In our project have been studied exciton spin dynamic properties in wide-bandgap II-VI quantum wells, particulary in semimagnetic and nonmagnetic quantum wells. In time-resolved investigations we directly detected the formation of exciton magnetic polarons in semimagnetic barrier structures and determined the characteristical spin relaxation time in magntic Mn ions. Varying the sample structures, we achieved a modified arrangement of the energy bands. Thereby it was possible to study indirect type-II excitons in quantum-well structures and interface excitons on comparable conditions. By heating the spin system consisting Mn ions, for both exciton types was shown a significant reduction of the Riesen-Zeeman effect.
In semimagnetic quantum-well structures we observed an unexpected strong coupling between the optically generated excitons and the magnetic activated Mn Ions in doped quantum wells, which leds to a dramatically reduction of the exciton lifetime. Thereby the energy of the optically excited carriers had been directly transfered to the intra-atomic transitions of the magnetic ion. This transfer could be reduced in a magnetic field, whereby the remaining coupling brought about a nonradiant decay of the optically charged excitons. On account of the strong exciton coupling for the first time it was possible to carry out optical experiments for systematical studies of the d-d-exchange interaction of antiferromagnetic oriented Mn pairs in (Zn,Mn,Cd)Se structures and to determine an exactly value of the exchange constant.
In the case of nonmagnetic quantum wells we focussed our studies on the fine structure of the exciton ground state. In wide-bandgap II-VI structures we observed such a high electron-hole pair correlation, that the spin dynamic essentially could be determined by the excitons and their fine structure, while the spin relaxation of the single charge carriers was of secondary importance. In the context of our project for the first time successful have been resolved the fine structure of zero-dimensional excitons and detected fundamental properties of the electron-hole exchange interaction.
Henneberger, Fritz Prof. Dr. sc. nat. (Details) (Experimental Physics / Physical Foundations of Photonics)
Financer
DFG: Sachbeihilfe
Duration of project
Start date: 01/1995
End date: 07/1999
