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Charge transport and electroluminescence mechanisms in Si-rich Si oxynitride/silicon oxide (SRON/SiO2) superlattices deposited on p-type Si substrate are reported. The superlattice structures were deposited by plasma-enhanced chemical-vapor deposition and subsequently annealed at 1150 °C to precipitate and crystallize the Si excess into Si nanocrystals. The dependence of the electrical conduction on the applied voltage and temperature was found to be well described by a Poole-Frenkel transport mechanism over a wide voltage range. On the other hand, the observed dependence of the electroluminescence on the SRON layer thickness is a clear proof of quantum confinement and was attributed to an excitonic radiative recombination taking place in the confined states within the Si quantum dots. A model is proposed based on thermal hopping of electrons between the quantum dots acting as trap states (Poole-Frenkel). A correlation between carrier transport and electroluminescence has been established considering impact ionization of high-kinetic energy electrons on the Si quantum dots.

28th European Photovoltaic Solar Energy Conference and Exhibition; 142-146, We present the first crystalline Si-based tandem solar cell device consisting of a monolithically interconnected c-Si wafer bottom and a Si nanocrystal (NC) top solar cell. The major part of this work has been realised within a European consortium in the frame of the FP7 project NASCEnT. Within this project we have been able to (i) develop new nanomaterials with photovoltaic compatible technologies, to (ii) improve the theoretical understanding of transport, recombination and dopant incorporation in these quantum confined absorber materials and to (iii) design devices which enable us to prove quantum confinement. In this publication we show that although solid phase crystallisation at 1100 °C for around 30 min is necessary to generate Si NCs of proper quality the wafer bottom cell as well as the c-SiC(n+) tunnel recombination junction layer can withstand such harsh conditions. Besides simulations to determine the influence of the high thermal budget on dopant profiles in wafer and c-SiC lifetime measurements on parallel processed wafers still show minority carrier lifetimes of 600 μs. The bifacial character of the tandem device enables us to clearly distinguish between bottom and top cell contributions. With a NC layer thickness of initially 3 nm Voc values as high as 978 mV could be achieved at 1 sun illumination from the front-side. Under rear-side illumination the short circuit current Jsc is with 1.0 mA/cm2 4 times higher that under front side illumination due to the better absorption and carrier lifetime of the bottom cell but still limited by the series resistance of the intrinsic NC absorber material. However, at 510 mV the Voc is much lower, indicating the difference in Voc is due to photogenerated voltage in the NC top cell which can only be created by illumination with low-wavelength light, i.e. front illumination. This very first tandem solar cell device including quantum dot absorber layers produced with photovoltaic compatible processes is the next step to successfully overcome the Shockley-Queisser limit for wafer based Si solar cells.

27th European Photovoltaic Solar Energy Conference and Exhibition; 35-40, Silicon nanocrystals (Si NCs) embedded in Si-based dielectrics provide a Si-based high band gap material (1.7 eV) and enable the construction of all-crystalline Si tandem solar cells. However, Si nanocrystal formation involves high-temperature annealing which deteriorates the properties of any previously established selective contacts. The inter-diffusion of dopants during high-temperature annealing alters Si NC formation and limits the built-in voltage. Furthermore, most devices presented so far also involve electrically active bulk Si and therefore do not allow a clear separation of the observed photovoltaic effect of the quantum dot layer from that of the bulk Si substrate. A membrane route is presented for quantum dot based p-i-n solar cells to overcome these limitations. In this approach, the formation of both selective contacts is carried out after high-temperature annealing and therefore not affected by the latter. P-i-n solar cells are investigated with Si NCs embedded in silicon carbide in the intrinsic region. Open-circuit voltages of up to 370 mV are shown for the NC layer. An optical model of the device is presented for improving the cell current. Finally device failure due to damaged insulation layers is analysed by electron beam induced current measurements.

26th European Photovoltaic Solar Energy Conference and Exhibition; 22-27, We present an overview of the project NASCEnT and the first results we were able to achieve after one year of project duration. The overall objective of the project is to develop new nano-materials with new production technologies and to fabricate silicon quantum dot (Si QD) materials for all-silicon tandem solar cells to achieve increased efficiencies. The understanding of electrical transport and recombination mechanisms in these newly developed nano-materials will enable us to design novel solar cell structures that help to overcome the efficiency limits of conventional solar cell concepts. So far we developed simple device structures and process sequences for both material systems (Si QDs in silicon oxide and silicon carbide) and tested a pin solar cell structure. Another objective of the project is to ensure the compatibility of the newly developed technologies with high-throughput processing leading to further cost-reduction. Within the scope of this project the novel concept of band gap-tuneable quantum dot superlattices is to be exploited in combination with a wafer-based high efficiency silicon solar cell as well as with a thin-film solar cell structure. The outcome of the project will be significant progress in solar cell evolution and will lead to higher efficiencies for solar cells and to ongoing cost-reductions from both a short-term and a long-term perspective.

26th European Photovoltaic Solar Energy Conference and Exhibition; 454-460, Silicon carbide (SiC) is a promising host material for silicon quantum dots (Si QDs), which are being investigated as absorber materials for tandem solar cells based solely on crystalline silicon. Amorphous silicon carbide (a-SiC) films are deposited by plasma-enhanced chemical vapour deposition (PECVD) and annealed under the same conditions usually used to precipitate Si QDs. During annealing, the films shrink by 20%, and some a-SiC transforms into SiC nanocrystals (nc-SiC) about 3 nm in size. P-type doping with boron is found to inhibit SiC crystallisation and lower conductance as compared to intrinsic films. N-type doping with phosphorus on the other hand promotes SiC crystallisation and leads to a higher conductance. The trends in conductance are ascribed solely to the effect of the dopant on crystallisation. Al, Ti, Cr, Ni20%Cr, and ITO are all found to form Ohmic contacts to the SiC films on deposition, with no change in contact properties brought about by sintering at 425°C. Temperature-dependent conductivity measurements on intrinsic SiC films reveal two distinct activation energies; 65 meV below 200 K, and 158 meV above 200 K.

Petroleum systems located at passive continental margins received increasing attention in the last decade mainly because of deep- and ultra‐deep-water hydrocarbon exploration and production. The high risks associated with these settings originate mainly from the poor understanding of inherent geodynamic processes. The new priority program SAMPLE (South Atlantic Margin Processes and Links with onshore Evolution), established by the German Science Foundation in 2009 for a total duration of 6 years, addresses a number of open questions related to continental breakup and post‐breakup evolution of passive continental margins. 27 sub‐projects take advantage of the exceptional conditions of the South Atlantic as a prime “Geo‐archive.” The regional focus is set on the conjugate margins located east of Brazil and Argentina on one side and west of Angola, Namibia and South Africa on the other (Figure 1) as well as on the Walvis Ridge and the present‐day hotspot of Tristan da Cunha. The economic relevance of the program is demonstrated by support from several petroleum companies, but the main goal is research on fundamental processes behind the evolution of passive continental margins.

Aim of the study: Only a minority of fourth year medical students participate in surgical large lectures. The underlying causes are unknown. Strategies to ensure students´ participation are lacking. The aim of our investigation was to evaluate why students do not participate large lectures in order to develop strategies to bring them back to the lecture hall.Methods: Students and teachers of the Surgical Department of the medical University of Marburg were interviewed by a standardized questionnaire. Causes of absence and suggestions for improving the participation at the lectures were suggested for choice using a 7 point Likkert scale ranging from "very low" to "very high" agreement. In addition, interviews were animated to give free text answers. Additionally, an internal benchmarking with the best utilized lecture at the medical university was performed. To exclude low acceptance of lectures as a local problem, a survey among representative students from 27 of 35 German medical universities was also performed.Results: Overall results showed a good agreement between students and teachers concerning their perceptions at surgical lectures. All 22 putative causes which may explain the low participation rate and all 16 but one suggested improvements showed no differences between students and teachers greater than two points on the Likkert scale. Both groups, the students and the teachers, are convinced that surgical lectures should be maintained. They recommended that excellent teaching should be rewarded. Several organizational nuisances, for example overlapping lectures, are pointed out to be the leading cause for to missing surgical lectures in Marburg. While students hesitate, teachers decided clearly that examinations are an essential part of the teaching strategy. The main differences between surgical and benchmarked lectures were attendance sheets and final examinations. According to information from other medical universities in Germany empty lecture halls are common. Conclusion: Low participation in surgical lectures is a general problem. Nevertheless, lectures are desired by students and teachers. The interview of students and teachers of the Surgical Department of the medical University of Marburg outlined that the improvement of participation in surgical lectures has several conditions. In face of the introduction of the new approbation guidelines organisational nuisances should be avoided and joins of lectures of different departments is needed to avoid redundancies. Excellent teaching should be rewarded. The contents of surgical lectures need to be examined. Ziel der Studie: Eine Unterrichtsform kann nur wirksam werden, wenn sie besucht wird. Somit ist ein ausreichender Besuch einer bestimmten Unterrichtsform eine notwendige - wenn auch nicht hinreichende - Bedingung für ihre Wirksamkeit. Das Lehrangebot "Vorlesung" wird an vielen Universitäten schlecht genutzt. Was sind die Gründe hierfür und was muss sich ändern?Methode: Studierende und Lehrende der Chirurgischen Kliniken der Philipps-Universität Marburg wurden systematisch mit einer 7-stufigen Likert-Skala (von 0 = "trifft gar nicht zu" bis 6 = "trifft vollständig zu") nach den Gründen für den geringen Vorlesungsbesuch gefragt. Hierzu wurden einerseits mögliche Gründe und Änderungsvorschläge vorgegeben, zusätzlich bestand die Möglichkeit zu Freitextantworten. Des Weiteren erfolgte ein internes Benchmarking mit einer anderen Klinik unserer Fakultät, die einen signifikant besseren Vorlesungsbesuch verzeichnen kann. Um zu überprüfen ob es sich bei dem schlechten Besuch chirurgischer Vorlesungen um ein deutschlandweites Problem handelt, wurde eine zusätzliche Umfrage unter Vertretern der Fachschaften von 27 der 35 deutschen medizinischen Fakultäten durchgeführt. Ergebnisse: Bei der Befragung in Marburg wich im Median bei keinem von 22 angebotenen möglichen Gründen für schlechten Vorlesungsbesuch, und nur bei einem von 16 angebotenen Änderungsvorschlägen die Einschätzung der Studierenden und der Lehrenden um mehr als 2 Skalenpunkte voneinander ab: Studierende und Lehrende sind nicht der Auffassung, dass Vorlesungen überflüssige Lehrveranstaltungen sind (Median: 1). Gemeinsam besteht die Auffassung, dass gute Lehre der Dozenten belohnt werden sollte (Median: 5 bzw. 6). Es werden verschiedene organisatorische Missstände des Studienablaufs, wie z.B. die Überschneidung von Lehrveranstaltungen, als Hauptursachen für den schlechten Vorlesungsbesuch angesehen. Die Vorlesungen der unterschiedlichen klinischen Fächer sollten besser aufeinander abgestimmt werden. Während die Studierenden unentschieden waren (Median 3), ob die Inhalte der Vorlesungen in Prüfungen abgefragt werden sollten, befürworteten dies die Lehrenden (Median 5,5). Im Vergleich mit einer anderen Klinik im Fachbereich mit signifikant höheren Besucherzahlen zeigt sich als wesentlicher Unterschied, dass dort Anwesenheitskontrollen und eine Abschlussprüfung stattfinden. An 19 von 27 Fakultäten liegt der Vorlesungsbesuch nach Einschätzung der Fachschaftsvertreter bei =70% und an 5 Universitäten mit >40 bis