Silicon carbide is a very promising semiconductor material for high-power, highrequency, and high-temperature applications. SiC distinguishes from traditional narrow bandgap semiconductors, such as silicon, in that common doping impurities in SiC have activation energies larger than the thermal energy kT even at room temperature. This causes incomplete ionization of such impurities, which leads to strong temperature and frequency dependence of the semiconductor junction differential admittance and, if carrier freeze-out effects are not taken into account, errors in doping profiles calculated from capacitance-voltage data. Approaches commonly used to study the influence of incomplete impurity ionization on the junction admittance are based on the truncated space charge approximation and/or the small-signal approximation. The former leads to impurity ionization time constant and occupation number errors, while the latter fails if the measurement ac signal amplitude is larger than kT/q. In this work, a new reverse bias Schottky junction admittance model valid for the general case of an arbitrary temperature, measurement signal frequency and amplitude, and doping occupation number and time constant distributions is developed. Results of junction admittance calculations using the developed model are compared with the results of traditional models. Based on the general model, a new method of admittance spectroscopy data analysis is created and used to determine impurity parameters more accurately than allowed by traditional approaches. Incomplete impurity ionization is investigated for the case of nitrogen donors and aluminum and boron acceptors in 4H- and 6H-SiC. It is shown that the degree of carrier freeze-out is significant in heavily N-doped 6H-SiC and in Al- and B-doped SiC. Frequency dispersion of the junction admittance is shown to be significant at room temperature in N- and B-doped SiC. Junction capacitance calculations as a function of applied dc bias show that calculated doping profiles deviate from the actual impurity concentration profiles if the impurity ionization time constant is comparable with the ac signal period. This is the case for N- and B-doped SiC with certain values of the impurity activation energy and capture cross-section. Validity of the new model and its predictions are successfully tested on experimental admittance data for N- and B-doped SiC Schottky diodes.

This thesis focuses on the effects of dopant compensation on the electrical properties of crystalline silicon relevant to the operation of solar cells. We show that the control of the net dopant density, which is essential to the fabrication of high-efficiency solar cells, is very challenging in ingots crystallized with silicon feedstock containing both boron and phosphorus such as upgraded metallurgical-grade silicon. This is because of the strong segregation of phosphorus which induces large net dopant density variations along directionally solidified silicon crystals. To overcome this issue, we propose to use gallium co-doping during crystallization, and demonstrate its potential to control the net dopant density along p-type and n-type silicon ingots grown with silicon containing boron and phosphorus. The characteristics of the resulting highly-compensated material are identified to be: a strong impact of incomplete ionization of dopants on the majority carrier density, an important reduction of the mobility compared to theoretical models and a recombination lifetime which is determined by the net dopant density and dominated after long-term illumination by the boron-oxygen recombination centre. To allow accurate modelling of upgraded-metallurgical silicon solar cells, we propose a parameterization of these fundamental properties of compensated silicon. We study the light-induced lifetime degradation in p-type and n-type Si with a wide range of dopant concentrations and compensation levels and show that the boron-oxygen defect is a grown-in complex involving substitutional boron and is rendered electrically active upon injection of carriers through a charge-driven reconfiguration of the defect. Finally, we apply gallium co-doping to the crystallization of upgraded-metallurgical silicon and demonstrate that it allows to significantly increase the tolerance to phosphorus without compromising neither the ingot yield nor the solar cells performance before light-induced degradation.

Institutional fight against doping in sport The diploma thesis with the title Institutional fight against doping in sport deals with the problematic issues of using banned substances and banned methods in sport or any other violation of anti-doping rule from the point of view of establishing international institutions with worldwide scope of activity with the aim of elimination of doping in sport. After the general introduction into the problematic issues of doping with the description of the historical roots of this unfair sporting practice there is a part focusing on the basic instruments of the fight against doping. A principle of strict liability of a sportsman for a violation of anti-doping rule is described, as well as the list of banned substances and banned methods, the process of testing, the therapeutic use exemption, the whereabouts and the athlete biological passport. In the following part the instruments of the public international law which were concluded by Council of Europe and UNESCO are analysed. The fight against doping in sport is transported through these international conventions on the level of intergovernmental cooperation which reflects the important non-governmental institutions and binds itself to international coordination. The main part of the thesis is contributed to...

Diamond is a unique material with many exceptional properties. It has therefore been proven to be an important material for many applications. Moreover, the introduction of dopant species into the gas phase during the CVD growth process has been shown to strongly influence not only the properties and morphology of diamond, but also the growth rate. The purpose with the theoretical part of the present study has been to support and explain the experimental observations regarding the effect of various dopants (nitrogen, phosphorous, sulphur, and boron) on the diamond growth rate. Commonly observed H-terminated diamond surfaces [(111), (110) and (100)-2×1], were thereby carefully investigated using density functional theory under periodic boundary conditions. Based on the assumption that the hydrogen abstraction reaction is the growth rate-limiting step, both the thermodynamic and kinetic aspects of the diamond growth process were found to be severely affected by various dopants. More specifically, the results showed that nitrogen and phosphorous dopants (positioned within the 2nd, 3rd or 4th carbon layer) will cause an enhancement in the growth rate (as compared with non-doped situations). On the other hand, any growth rate improvement does only occur when positioning boron in the 2nd, and sulphur in the 4th, atomic carbon layer. With boron, and sulphur, positioned within the other atomic carbon layers, the growth rates were observed to decrease. In addition, the main purpose with the experimental part of the present study has been to investigate the effect of one specific dopant precursor (TMB) on the boron-doped diamond growth process. The result has shown that the increasing mass flow of TMB will not affect the mechanism of the HFCVD growth process of boron doped diamond. However, a linear boron carrier concentration in the diamond film vs. mass flow rate of TMB was observed.

The nonlinear optical properties of a semiconductor-doped glass (SDG) channel waveguide were measured on a picosecond time-scale; namely, fluence-dependent changes in the absorption and the refractive index as well as the relaxation time of the nonlinearity. Slower, thermally-induced changes in the refractive index were also observed. The saturation of the changes in the absorption and the refractive index with increasing optical fluence is explained using a plasma model with bandfilling as the dominant mechanism. The fast relaxation time of the excited electron-hole plasma (20 ps) is explained using a surface-state recombination model. A figure of merit for a nonlinear directional coupler fabricated in a material with a saturable nonlinear refractive index is presented. The measured nonlinear change in the refractive index of the SDG saturates below the value required to effect fluence-dependent switching in a nonlinear directional coupler. Experiments with a channel-waveguide directional coupler support this prediction. However, absorption switching due to differential saturation of the absorption in the two arms of the directional coupler was observed.

No description available.

The doping culture represents an issue for sport and for society. Normative debates on doping have been mainly concerned with questions of the justifiability of doping. The practice of assigning responsibility for doping behaviour has chiefly been individual-based, focusing mainly on the individual athlete’s doping behaviour. The overarching aim of this thesis is to investigate the relevance and the importance of the ideas of responsibility in relation to ethical debates on doping. The more specific aim is to examine the possibility of broadening the scope of responsibility beyond the individual athlete, and to sketch a theoretical framework within which this expansion could be accommodated. In the first study, it is argued that bioethicists have a moral/professional responsibility to start out from a realistic and up-to-date view of genetics in ethical debates on gene doping, and that good bioethics requires good empirics. In study 2, the role played by affective processes in influencing athletes’ attitudes towards doping behaviour is investigated, both on an individual and on a collective level. It is concluded that an exclusive focus on individual-level rule violation and sanctions may entail overlooking the greater social picture and would prove to be ineffective in the long term. In study 3, the common doping-is-cheating arguments are examined and it is argued that they fail to capture vital features of people’s moral responses to doping behaviour. An alternative account of cheating in sport is presented in terms of failure to manifest good will and respect. It is concluded that putting cheating in the broader context of human interpersonal relationships makes evident the need to broaden the scope of moral responsibility and agency beyond the individual athlete. In study 4, the particular case of assigning responsibility for doping to sports physicians is used to examine the current individual-based approach to responsibility. This approach underestimates the scope of the responsibility by leaving out a range of other actors from the discourse of responsibility. The central conclusion of the thesis is that transforming the current doping culture requires broadening the scope of responsibility to include individuals and groups of individuals other than the athletes themselves.

No description available.

The AsF6- anion, in the crystalline polymer electrolyte PEO6:LiAsF6, was replaced with the larger N(SO2CF3)2- anion. This produced an increase in the room temperature ionic conductivity of 1.5 orders of magnitude. It is believed that the enhancement is the result of the disruption of the electrostatic field around the lithium ions. The presence of the large and asymmetrical N(SO2CF3)2- ion creates a greater number of defects and thus enhances conductivity. These results demonstrate for the first time the enhancement lithium ion conductivity in a crystalline polymer electrolyte by isovalent doping. XF6- anions, in the crystalline polymer electrolyte system PEO6:LiXF6, were replaced by another anion of similar size and shape. A continuous solid solution was obtained for PEO6:(LiAsF6)1-x(LiSbF6)x. These results represent the first continuous solid solution demonstrated in the field of crystalline polymer electrolytes. They also show for the first time an enhancement of conductivity caused only by the size of the dopant anion. The enhancement is believed to originate from changes in the length of the crystal axis and changes in the potential landscape around the lithium ions. The structures of the glyme complexes monoglyme:LiAsF6, hexaglyme:LiAsF6, octaglyme:LiAsF6, undecaglyme:LiAsF6 and dodecaglyme:LiAsF6 have been solved. There structures are discussed and compared to that of PEO6:LiAsF6. The properties of these complexes together with those of diglyme:LiAsF6, triglyme:LiAsF6 and tetraglyme:LiAsF6 were investigated. Triglyme:LiAsF6 has been shown to demonstrate high ionic conductivity of 10-5.5 Scm-1 at 30oC as well as a high transport number of 0.8. These complexes demonstrate the control that crystal structure has over ionic conductivity. These complexes are neither ceramic nor polymeric. A number of the complexes show plastic crystal like solid-solid phase transitions.

Doctor of Philosophy / Department of Chemistry / Viktor Chikan / Semiconducting nanoparticles have emerged in the past few decades as an interesting material with great potential in various interdisciplinary applications such as light-emitting devices, solar cells and field-effect transistors, mostly notably for their size-dependent electronic structure and properties. Manipulation of their electronic-optical characters through defects control is one of the most important approaches towards realization of these applications. This thesis focuses on understanding the role of defects, including their impact on carrier density and conductivity at both room and elevated temperature, their impact on growth kinetics of colloidal nanoparticles and new opportunities for dopant control. To achieve these goals, colloidal CdSe quantum dots are doped with gallium atoms and important changes in electronic and optical properties of the material are reported, which shows a significant impact on the growth kinetics of quantum dots, and reveals clues about the mechanism of the gallium dopant incorporation into the CdSe. It is shown that the gallium doping significantly impacts the conductivity of CdSe thin film made of the quantum dots as well as the photoluminescence and chemical reactivity of the quantum dots, in agreement with the expected n-type character. P3HT/CdSe hybrid cells are constructed with Ga-, In- and Sn-doped CdSe QDs, demonstrating high conductivity and stronger electronic coupling which leads to enhanced charge separation and transport efficiency, both essential for hybrid inorganic-organic solar cells. This work also demonstrates a novel heating method that can drastically improve size distribution control of colloidal nanoparticle synthesis. Sub-2-nm ultra-small CdSe QDs are prepared with the induction (magnetic) heating and show excellent agreement of its emission profile compared with natural sunlight. The impact of extreme high heating rate on the development of more accurate nucleation and growth theories are also discussed. Finally, this study also investigates the stabilization of charges from intrinsic defects by looking for altered blinking behaviors of CdSe nanorods (NRs) under different polar environments. TMOS-PTMOS gradient films are prepared with infusion withdrawal dip-coating technique. Although no significant differences are observed of the fluorescence statistics of these NRs, permanent bleaching induced by exciting laser light is discovered, which significantly lowers raw blinking spot count and increases the “off” time of these fluorophores.