Spin-Effekte von optisch erzeugten Ladungsträgern in Halbleitern

Today?s semiconductor-electronics and opto-electronics are mainly based on the Coulomb-interaction between the charge of electrons. But electrons own beneath their charge also the spin as an additonal property. The electron-spin is a pure quantum mechanical property which has no classical analogon. It can only be in one of the two states ?spin-up? or ?spin-down?, respectively. About 75 years after the introduction of the spin into physics by Goudsmith and Uhlenbeck in 1925 and its correct description in the relativistical quantum mechanics by Dirac in1930, the property ?spin? gets into the modern semiconductor and information technology. With thin metallic film systems, there have been already succesfull developments in the field of magneto-electronics, e.g. the GMR- and TMR effects. Also the ?Magnetic Random Acces Memory? (MRAM) is subject to intense research. All these application make use of the quantum mechanical property ?spin?, but are base on metallic systems only. A semiconductor based spin-electronic (?Spintronic?) has the advantage of easy integration into the conventional electronics. Also a connection with opto-electronics is possible. One of the main prerequisites for spin-based electronic is the efficient and controlled injection of carrier spin currents. By coherent control of two laser light-fields spin-polarized currents can be generated in semiconductors. These currents are based on the interference of quantum mechanical (opical) transitions and are a makroscopic manifestation of a pure quantum mechanical phenomen, which is shown in this work. A different approach to influence spin-related effects in semiconductors is due a controllable symmetry reduction by internal or external applied electrical fields in semiconductor heterostructures. The resulting anisotropic spin-effects are measured by spin quantum beat spectroscopy in magnetic fields. The spin-depahsing mechanism electron-hole pairs with parallel spin-orientation, so called ?dark excitions? are investigated in semiconductor quantum dots. Those quantum dots are often suggested to play a role in a prosper quantum-computing technology, because of the long decoherece times of their carrier spins. Dark excitons are excited by two-photon absorption by an ultrashort laser pulse and the converion of the dark excitons (J=2) to bright excitons (J=1) is measured time-resolved under different conditions.Today?s semiconductor-electronics and opto-electronics are mainly based on the Coulomb-interaction between the charge of electrons. But electrons own beneath their charge also the spin as an additonal property. The electron-spin is a pure quantum mechanical property which has no classical analogon. It can only be in one of the two states ?spin-up? or ?spin-down?, respectively. About 75 years after the introduction of the spin into physics by Goudsmith and Uhlenbeck in 1925 and its correct description in the relativistical quantum mechanics by Dirac in1930, the property ?spin? gets into the modern semiconductor and information technology. With thin metallic film systems, there have been already succesfull developments in the field of magneto-electronics, e.g. the GMR- and TMR effects. Also the ?Magnetic Random Acces Memory? (MRAM) is subject to intense research. All these application make use of the quantum mechanical property ?spin?, but are base on metallic systems only. A semiconductor based spin-electronic (?Spintronic?) has the advantage of easy integration into the conventional electronics. Also a connection with opto-electronics is possible. One of the main prerequisites for spin-based electronic is the efficient and controlled injection of carrier spin currents. By coherent control of two laser light-fields spin-polarized currents can be generated in semiconductors. These currents are based on the interference of quantum mechanical (opical) transitions and are a makroscopic manifestation of a pure quantum mechanical phenomen, which is shown in this work. A different approach to influence spin-related effects in semiconductors is due a controllable symmetry reduction by internal or external applied electrical fields in semiconductor heterostructures. The resulting anisotropic spin-effects are measured by spin quantum beat spectroscopy in magnetic fields. The spin-depahsing mechanism electron-hole pairs with parallel spin-orientation, so called ?dark excitions? are investigated in semiconductor quantum dots. Those quantum dots are often suggested to play a role in a prosper quantum-computing technology, because of the long decoherece times of their carrier spins. Dark excitons are excited by two-photon absorption by an ultrashort laser pulse and the converion of the dark excitons (J=2) to bright excitons (J=1) is measured time-resolved under different conditions.