1,721,277 research outputs found
Preface of the Special Issue: Special Issue: III-Nitride Nanostructures Preface
No full textSemiconductors of group III-V, in particular III-Nitrides and their compounds,have shown an increasing interest from the scientific community in the last years.
Electronic transitions in low dimensional semiconductor structures measured by surface photovoltage spectroscopy
No full textAim of the present contribution is to review several results obtained by the application of surface photovoltage spectroscopy method to low dimensional semiconductors. Photo-induced electronic transitions have been detected in: heterostructures based on III-nitrides, Si-based nanostructures (nanowires and nanocrystals) and nanoporous Ge layers. The effect of two-dimensional electron gas and of quantum confinement on the energy of band-to-band transitions in these structures has been studied. The results show that Surface Potovoltage Spectroscopy is a flexible and non-destructive method capable to reveal phase changes, Burstein Moss effects, doping-related features, light trapping and quantum confinement effects in low dimensional structures that can be useful for several optoelectronic applications
Nanostructured surfaces investigated by quantitative morphological studies
No full textThe morphology of different surfaces has been investigated by atomic force microscopy and quantitatively analyzed in this paper. Two different tools have been employed to this scope: The analysis of the height-height correlation function and the determination of the mean grain size, which have been combined to obtain a complete characterization of the surfaces. Different materials have been analyzed: SiOxNy, InGaN/GaN quantum wells and Si nanowires, grown with different techniques. Notwithstanding the presence of grain-like structures on all the samples analyzed, they present very diverse surface design, underlying that this procedure can be of general use. Our results show that the quantitative analysis of nanostructured surfaces allows us to obtain interesting information, such as grain clustering, from the comparison of the lateral correlation length and the grain size
Multi-characterization study of interface passivation quality of amorphous sub-stoichiometric silicon oxide and silicon oxynitride layers for photovoltaic applications
No full textSi solar cells have achieved a world record efficiency of 26.7% as a result of both improvement of Si ingot growth and optimal passivation of surfaces and interfaces. In this framework, a clear understanding of the electronic, optical, structural and passivation properties of innovative Si based layers is mandatory. The present study reports on the characterization of amorphous sub-stoichiometric silicon oxide (a-SiOx) and silicon oxynitride (a-SiOxNy) layers and their surface passivation properties. The layers have been deposited on float zone Si wafers (2 Ω cm, (100)-oriented, 250 μm thick) by plasma enhanced chemical vapour deposition (PECVD) adding increasing fractions of N2O and CO2to the SiH4flux during deposition to increase the energy band gap of the layers. Composition, optical properties, light induced electronic transitions and minority carrier lifetimes of Si wafers passivated with these layers have been investigated by Fourier-transform infrared spectroscopy (FTIR), spectral ellipsometry, surface photovoltage (SPV) spectroscopy and photo conductance decay (PCD). The overall characterization of the layers has allowed us to understand the effect of increasing N2O and CO2flux ratios during deposition on the interface properties. The present study establishes the importance of the approach of using multiple characterization methods in the evaluation of the passivation capability of layers that combine large optical band gap and surface passivation
The electrical conductivity of hydrogenated nanocrystalline silicon investigated at the nanoscale
No full textAbstract
Hydrogenated nanocrystalline silicon (nc-Si:H) is a multiphase, heterogeneous material, composed of Si nanocrystals embedded in an amorphous matrix. It has been intensively studied in the last few years due to its great promise for photovoltaic and optoelectronics applications.
The present paper aims to study the current transport mechanisms in nc-Si:H by mapping the local conductivity at the nanoscale. The role of B doping in nc-Si:H is also investigated.
Conductivity maps are obtained by atomic force microscopy using a conductive tip. Differences and similarities between intrinsic and doped nc-Si:H conductivity maps were observed and these are also explained on the basis of recently published computational studies
Iron related precipitates in multicrystalline silicon by conductive atomic force microscopy
Full text linkMulticrystalline silicon (mc-Si) is a widely used material for photovoltaic applications. The presence of metallic contaminated grain boundaries strongly affects the crystal electronic properties enhancing electron-hole recombination, thus reducing the solar cell performance. The present study aims to investigate the electrical activity of metallic contaminated grain boundaries in mc-Si. Two sets of mc-Si wafers, contaminated with iron and aluminium, respectively, were analyzed. The wafers presented grain boundaries whose density and character were characterized by Electron Backscatter Diffraction (EBSD), while their electrical activity was analyzed using Conductive Atomic Force Microscopy (c-AFM). The grain boundary density decreases along the ingot height and the most common coherent grain boundaries have the character Σ3n. The grain boundary electrical activity is mostly due to metallic precipitates located at the grain boundaries. In particular, iron precipitates enhance the current contrast at the grain boundaries. Both fixed voltage maps and current-voltage characteristics at the grain boundaries were measured to understand and clarify the transport phenomena at grain boundaries decorated with metallic impurities. The current profiles measured by c-AFM across a grain boundary were modelled by assuming the contribution of a Coulombic potential introduced by the positively charged precipitate. Quantitative parameters regarding the segregated iron-related precipitates are estimated from the model. The results of this study, based on local electrical characterization and appropriate modelling, will contribute to improving the understanding of the recombination at iron precipitates at grain boundaries in mc-Si
Electronic transitions at defect states in Cz p-type silicon
No full textPoint and extended defects introduced in p-type Cz Si by oxygen precipitation and plastic
deformation have been investigated with electrical and optical methods. Different materials soxygen
precipitated and/or deformed Cz Si and Fz Sid were examined in order to separate the role of oxygen
precipitation, plastic deformation, and metallic contamination on the radiative and nonradiative
electronic transitions at defect centers. A deep hole trap, named T1, has been associated with
dislocation-related impurity centers; additional deep traps have been related to contamination by
grown-in transition metals and to clusters involving oxygen atoms
Cap 10, Superconduttività, Cap11 Diamagnetismo e Paramagnetismo
No full textSince the publication of the first edition over 50 years ago, Introduction to Solid State Physics has been the standard solid state physics text for physics students. The author's goal from the beginning has been to write a book that is accessible to undergraduates and consistently teachable. The emphasis in the book has always been on physics rather than formal mathematics. With each new edition, the author has attempted to add important new developments in the field without sacrificing the book's accessibility and teachability
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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