This thesis work aims at a better understanding of magneto-optical properties of dilute nitrides and II-VI diluted magnetic semiconductor quantum structures. The thesis is divided into two parts. The first part gives an introduction of the research fields, together with a brief summary of the scientific results included in the thesis. The second part consists of seven scientific articles that present the main findings of the thesis work. Below is a short summary of the thesis. Dilute nitrides have been of great scientific interest since their development in the early 1990s, because of their unusual fundamental physical properties as well as their potential for device applications. Incorporation of a small amount of N in conventional Ga(In)As or Ga(In)P semiconductors leads to dramatic modifications in both electronic and optical properties of the materials. This makes the dilute nitrides ideally suited for novel optoelectronic devices such as light emitting devices for fiber-optic communications, highly efficient visible light emitting devices, multi-junction solar cells, etc. In addition, diluted nitrides open a window for combining Si-based electronics with III-V compounds-based optoelectronics on Si wafers, promising for novel optoelectronic integrated circuits. Full exploration and optimization of this new material system in device applications requires a detailed understanding of their physical properties. Papers I and II report detailed studies of effects of post-growth rapid thermal annealing (RTA) and growth conditions (i.e. presence of N ions, N2 flow, growth temperature and In alloying) on the formation of grown-in defects in Ga(In)NP. High N2 flow and bombardment of impinging N ions on grown sample surface is found to facilitate formation of defects, such as Ga interstitial (Gai) related defects, revealed by optically detected magnetic resonance (ODMR). These defects act as competing carrier recombination centers, which efficiently decrease photoluminescence (PL) intensity. Incorporation of a small amount of In (e.g. 5.1%) in GaNP seems to play a minor role in the formation of the defects. In GaInNP with 45% of In, on the other hand, the defects were found to be abundant. Effect of RTA on the defects is found to depend on initial configurations of Gai related defects formed during the growth. In Paper III, the first identification of an interfacial defect at a heterojunction between two semiconductors (i.e. GaP/GaNP) is presented. The interface nature of the defect is clearly manifested by the observation of ODMR lines originating from only two out of four equivalent <111> orientations. Based on its resolved hyperfine interaction between an unpaired electronic spin (S=1/2) and a nuclear spin (I=1/2), the defect is concluded to involve a P atom at its core with a defect/impurity partner along a <111> direction. Defect formation is shown to be facilitated by N ion bombardment. In Paper IV, the effects of post-growth hydrogenation on the efficiency of the nonradiative (NR) recombination centers in GaNP are studied. Based on the ODMR results, incorporation of H is found to increase the efficiency of the NR recombination via defects such as Ga interstitials. In Paper V, we report on our results from a systematic study of layered structures containing an InGaNAs/GaAs quantum well, by the optically detected cyclotron resonance (ODCR) technique. By monitoring PL emissions from various layers, the predominant ODCR peak is shown to be related to electrons in GaAs/AlAs superlattices. This demonstrates the role of the SL as an escape route for the carriers confined within the InGaNAs/GaAs single quantum well. The last two papers are within a relatively new field of spintronics which utilizes not only the charge (as in conventional electronics) but also the quantum mechanical property of spin of the electron. Spintronics offers a pathway towards integration of information storage, processing and communications into a single technology. Spintronics also promises advantages over conventional charge-based electronics since spin can be manipulated on a much shorter time scale and at lower cost of energy. Success of semiconductor-based spintronics relies on our ability to inject spin polarized electrons or holes into semiconductors, spin transport with minimum loss and reliable spin detection. In Papers VI and VII, we study the efficiency and mechanism for carrier/exciton and spin injection from a diluted magnetic semiconductor (DMS) ZnMnSe quantum well into nonmagnetic CdSe quantum dots (QD’s) by means of spin-polarized magneto PL combined with tunable laser spectroscopy. By means of a detailed rate equation analysis presented in Paper VI, the injected spin polarization is deduced to be about 32%, decreasing from 100% before the injection. The observed spin loss is shown to occur during the spin injection process. In Paper VII, we present evidence that energy transfer is the dominant mechanism for carrier/exciton injection from the DMS to the QD’s. This is based on the fact that carrier/exciton injection efficiency is independent of the width of the ZnSe tunneling barrier inserted between the DMS and QD’s. In sharp contrast, spin injection efficiency is found to be largely suppressed in the structures with wide barriers, pointing towards increasing spin loss.

Der vorliegende Beitrag untersucht das Dreiecksverhältnis zwischen ökologischer Nachhaltigkeit, wirtschaftlichem Wachstum und liberaler Demokratie und stellt fest, dass dieses sich in den westlichen Konsumgesellschaften im Angesicht der zunehmenden lebensweltlichen Manifestation der "Grenzen des Wachstums" grundlegend neu konfiguriert. Dabei zeichnen sich tatsächlich die Konturen einer "demokratischen Postwachstumsgesellschaft" ab - allerdings unter gänzlich anderen Vorzeichen, als es der überwiegende Teil der Transformationsforschung ersehnt. In der Absicht, einen Beitrag zur Rückkopplung der normativen und sich als transformativ verstehenden Teile der Nachhaltigkeitsforschung an die sozialwissenschaftliche Analyse moderner Gesellschaften zu leisten, zeigt der Beitrag zunächst, wie im Bereich umweltpolitischer und demokratiebezogener Diskurse zentrale Narrative, die über Jahrzehnte die Debatte bestimmt haben, heute ihre Glaubwürdigkeit verlieren und sich damit das Feld für eine Neujustierung der Dreiecksbeziehung eröffnet. Anschließend wird aus gesellschaftstheoretischer Perspektive ausgeleuchtet, wie die Demokratie im Zeichen moderner Subjektivitätsverständnisse und bestenfalls noch moderater Wachstumsraten zunehmend zu einem Mittel der "nachhaltigen" Verteidigung nicht-nachhaltiger Lebensstile wird. Entschiedener denn je, so zeigt sich, erheben moderne Konsumgesellschaften die "Politik der Nicht-Nachhaltigkeit" zu ihrem Prinzip.

To avoid irreversible damage to the climate system and biosphere, the majority of the world’s countries must reduce rates of resource throughput. However, the socio-economic conditions for satisfying basic human needs at low resource use have received scant empirical attention. I apply cross-country panel analysis and dynamic linear modelling to explore how different dimensions of inequality affect countries’ abilities to deliver a good life for all at sustainable levels of carbon consumption. My results suggest that inequalities reduce socio-ecological performance, with income inequality reducing the proportion of carbon channelled into meeting basic needs and wealth inequality increasing the carbon-intensity of expenditure. Overall, this study highlights the importance of reducing inequalities in a resource-constrained world. Social media summary. Income inequality raises the carbon cost of meeting basic human needs at the national and global scales.