Role of dopant concentration and starting reagents in the dosimetric performance of MgB4O7:Ce, Li
Igor V. PlokhikhIlia I. SadykovОlga V. SafonovaŁukasz KondrackiE.G. YukiharaLily BossinD. J. Gawryluk
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Abstract The kinetics of reduction (n doping) of fibrillar films of polyacetylene (PA) by a large excess of organoalkaline electron donors in solution was studied. The doping rate is proportional to dopant concentration and inversely proportional to the square of film thickness (in a range 100–1000 microns). This means that the kinetics of reduction is entirely controlled, in these experiments, by the interfibrillar diffusion of dopants, leading to macroscopic doping inhomogeneity if the reaction is stopped before completion. The maximum doping level achieved at the end of the reaction is mainly controlled by the redox potential of the dopant. Homogeneously doped thick films, at various doping levels, were prepared using a suitable set of dopants in various solvents.
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The ability to incorporate a dopant element into silicon nanocrystals (NC) and quantum dots (QD) is one of the key technical challenges for the use of these materials in a number of optoelectronic applications. Unlike doping of traditional bulk semiconductor materials, the location of the doping element can be either within the crystal lattice (c-doping), on the surface (s-doping) or within the surrounding matrix (m-doping). A review of the various synthetic strategies for doping silicon NCs and QDs is presented, concentrating on the efficacy of the synthetic routes, both in situ and post synthesis, with regard to the structural location of the dopant and the doping level. Methods that have been applied to the characterization of doped NCs and QDs are summarized with regard to the information that is obtained, in particular to provide researchers with a guide to the suitable techniques for determining dopant concentration and location, as well as electronic and photonic effectiveness of the dopant.
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This is the first book to describe thoroughly the many facets of doping in compound semiconductors. Equal emphasis is given to the fundamental materials physics and to the technological aspects of doping. The author describes in detail all the various techniques, including doping during epitaxial growth, doping by implantation, and doping by diffusion. The key characteristics of all dopants that have been employed in III–V semiconductors are discussed. In addition, general characteristics of dopants are analyzed, including the electrical activity, saturation, amphotericity, auto-compensation and maximum attainable dopant concentration. The timely topic of highly doped semiconductors is discussed as well. Technologically important deep levels are summarized. The properties of deep levels are presented phenomenologically. The final chapter is dedicated to the experimental characterization of impurities.
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The process of p-type doping for GaN nanowires is investigated using calculations starting from first principles. The influence of different doping elements, sites, types, and concentrations is discussed. Results suggest that Mg is an optimal dopant when compared to Be and Zn due to its stronger stability, whereas Be atoms are more inclined to exist in the interspace of a nanowire. Interstitially-doped GaN nanowires show notable n-type conductivity, and thus, Be is not a suitable dopant, which is to be expected since systems with inner substitutional dopants are more favorable than those with surface substitutions. Both interstitial and substitutional doping affect the atomic structure near dopants and induce charge transfer between the dopants and adjacent atoms. By altering doping sites and concentrations, nanowire atomic structures remain nearly constant. Substitutional doping models show p-type conductivity, and Mg-doped nanowires with doping concentrations of 4% showing the strongest p-type conductivity. All doping configurations are direct bandgap semiconductors. This study is expected to direct the preparation of high-quality GaN nanowires.
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Abstract Dopants and defects are important in semiconductor and magnetic devices. Strategies for controlling doping and defects have been the focus of semiconductor physics research during the past decades and remain critical even today. Co-doping is a promising strategy that can be used for effectively tuning the dopant populations, electronic properties, and magnetic properties. It can enhance the solubility of dopants and improve the stability of desired defects. During the past 20 years, significant experimental and theoretical efforts have been devoted to studying the characteristics of co-doping. In this article, we first review the historical development of co-doping. Then, we review a variety of research performed on co-doping, based on the compensating nature of co-dopants. Finally, we review the effects of contamination and surfactants that can explain the general mechanisms of co-doping.
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Doping strategy has been applied in lots of areas holding promising performance for many functions. Here, we systemically report the main trends in structural, electronic properties and chemical bonding for V doped into 2H-NbSe2 in two types of doping by means of the first-principles PBE-GGA calculations. To investigate the stability of the doped system with changing concentration of V atoms, 2 × 2 × 1, 3 × 3 × 1 and 4 × 4 × 1 2H-NbSe2 supercells have been taken into consideration. Results show that it is easier to be doped as the concentration of dopant V is lower and the substituted doping structure is more stable than that of the dopant embedded into the interlayer. In addition, it is found that the dopant V atom forms a covalent bond with the surrounding Se atoms in both of the two doping structures, which can explain the variations of the structural parameters after V atom is doped into 2H-NbSe2. Moreover, what leads to the variation of the electronic structures is that the asymmetric structure and the more energetic Se atoms firstly near the dopant V atom after V is doped into 2H-NbSe2 in both of the two doping types. Our calculation results can provide good theoretical knowledge for the subsequent experiments.
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As well as understanding the location of dopants in optical materials, it is also important to understand how much dopant can be added to a given material. A method for calculating the maximum concentration of dopants has been developed, and applied to dopants in mixed metal fluorides for optical and nuclear clock applications. Applications to rare earth doping in YLiF4, and Th doping in LiCaAlF6/LiSrAlF6 are described, and compared with available experimental data.
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Abstract We review the state of the art in the field of semiconductor nanocrystal (SC NC) doping, with emphasis on cationic doping for modified optical and magnetic properties. Doping has the potential to greatly expand the already vast technological promise of SC NCs by allowing for the introduction of dopant‐specific or dopant‐modified properties. In the last several years, tremendous progress has been made with respect to both the understanding and implementation of SC NC–doping strategies. Here, we review the prevailing theoretical models (the “dopant extrusion model” and the “sticky surface model”) underpinning the current understanding of the process of dopant ion incorporation during NC growth. Further, we review the general synthetic approaches that have been developed in the context of this understanding, as well as many specific examples of SC NC–dopant systems, revealing both the successes and those that have fallen short in either achieving doping or fully demonstrating that doping was achieved. In support of this aim, we also provide a summary of the characterization methods (spectroscopic, structural, and chemical) that are critical for critiquing the doped system. We have necessarily focused on cationic doping as anionic doping has yet to be realized in a similar fashion. Further, the topic of electronic doping is only briefly addressed. While examples are reasonably abundant with respect to transition metal and lanthanide doping for modified magnetic/optical and optical properties respectively, permanent electronic doping of SC NCs has yet to be demonstrated. Finally, we identify (in addition to anionic and electronic doping) the topic areas that remain to be explored in this field of SC NC doping.
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Non-equilibrium Approach to Doping of Wide Bandgap materials by Molecular Beam Epitaxy. Final Report
It is well known that it has been difficult to obtain good bipolar doping in a wide bandgap semiconductors. Developed a new doping technique, involving use of a standard dopant, together with a ''co-dopant'' used to facilitate the introduction of the dopant, and have vastly alleviated this problem.
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