| The motivation for this dissertation is based in the emerging fields of spintronics and quantum computation, and two different topics are explored within this framework. The first topic deals with spin-injection into the narrow-gap semiconductor InAs, which is viewed as one possible fundamental building block of semiconductor spintronics. Experimental techniques were developed to investigate the circular polarization characteristics of mid-infrared radiation from InAs-based light-emitting diodes. The circular polarization degree was measured for several structures and is related to the spin-polarization of injected electrons, which were spin-aligned with a II-VI diluted magnetic semiconductor, CdMnSe. Spire-injection into the InAs-based samples is dominated by band structure effects, as well as the finite ratio of spin relaxation and recombination times. These conclusions are based on analysis with a detailed rate equation model, which was developed and incorporates some of the aspects of spin-injection ignored in previous studies.; The second topic: concerns the internal structure of negatively charged excitons in semiconductor quantum clots arising from monolayer well-width fluctuations in narrow, quasi-two-dimensional quantum well systems. Electron spins (the negatively charged exciton provides two, either anti-symmetrically or symmetrically coupled) in quantum dots are viewed as important systems to understand on the way to realistic implementations of quantum-computational applications. Ensemble and single dot photoluminescence (PL) was studied extensively through so-called mu-PL techniques, which were developed as part of this investigation. In addition, optically detected resonance (ODR) spectroscopy was developed and implemented for ensembles and single dots. This technique monitors (small) resonant changes of the photoluminescence induced by far-infrared radiation. Optically detected resonance spectroscopy of single quantum dots was achieved for the first time to the best knowledge of the author. The well-width dependence of the ensemble ODR was studied extensively, and the importance of the combination of magnetic translational invariance and cylindrical symmetry for the internal transitions of the negatively charged exciton in wide quantum wells is demonstrated. Theoretical predictions regarding the selection rules dictated by the above symmetries have been verified. |
