Evidence of formation of Si-C bonds during growth of Si-doped III-V semiconductor compounds

In this work, we demonstrate that Si-C bonds are formed in III-V semiconductor compounds grown by chemical beam epitaxy. Our results suggest that the formation of Si-C bonds occurs in III-V epitaxial layers with acceptor Carbon residual concentration and high Si concentrations (>10(17) cm(-3)). The main consequence of Si-C bonds is the generation of defects along [111] direction. These defects produce carrier concentration saturation, reduction of electrical mobility, crystal quality degradation, and surface defects. (C) 2005 American Institute of Physics.861

Surface morphologies in GaAs homoepitaxy: Mound formation and evolution

Atomic force microscopy has been used to observe surface morphologies during growth of GaAs films on GaAs(001) by chemical beam epitaxy. Mound formation is observed at the beginning of GaAs growth as a function of the surface prior to deposition. GaAs substrates exhibit a large density of pits and cracks after usual thermal treatment employed for oxide desorption. On this kind of surface mounds form and coalesce as film thickness increases; surface planarization is eventually achieved-at this point, morphologies are typically those expected from two-dimensional growth. In this sense we observe that monolayer island size distribution is determined by the kinetic conditions used for the growth; nucleation sites and island spatial distribution, however, are strongly influenced by the topography of the initial surface where the film is deposited even for films thousands of monolayers thick. The final morphologies present wide terraces and few monolayer islands on top of them independent of growth conditions. This picture agrees with theoretical results where negligible step edge barriers are considered.5841947195

Evidence of Be3P2 formation during growth of Be-doped phosphorus-based semiconductor compounds

In this work, we present evidence that Be3P2 microcrystals are formed in Be-doped phosphorus-based semiconductor compounds grown by chemical beam epitaxy. Our results suggest that microcrystal formation occurs when high Be concentrations (> 10(18) cm(-3)) and temperatures higher than 500 degrees C are used for crystal growth. The main consequence of Be3P2 formation is a high phosphorus consumption close to these microcrystals that causes a large density of P vacancies in the semiconductor layer. This results in reduced electrical mobility, lattice parameter reduction, and poor crystalinity of the film in general. (c) 1999 American Institute of Physics. [S0003-6951(99)01624-1].74243669367

Spatial ordering in InP/InGaP nanostructures

We report the observation of a spatially-ordered bidimensional array of self-assembled InP quantum dots grown on slightly In-rich InGaP layers. The alignment of InP dots is observed along [100] and [010] directions. This effect is enhanced when 2degrees off vicinal substrates are used; it is also strongly dependent on growth temperature. Our results suggest that the density and size of CuPt-type atomically ordered regions as well as compositional modulation of InGaP layers play an important role on the spatial alignment of InP/InGaP quantum dots. (C) 2003 American Institute of Physics.82203523352

Embracing Monogenic Parkinson's Disease: The MJFF Global Genetic PD Cohort

Background: As gene-targeted therapies are increasingly being developed for Parkinson's disease (PD), identifying and characterizing carriers of specific genetic pathogenic variants is imperative. Only a small fraction of the estimated number of subjects with monogenic PD worldwide are currently represented in the literature and availability of clinical data and clinical trial-ready cohorts is limited. Objective: The objectives are to (1) establish an international cohort of affected and unaffected individuals with PD-linked variants; (2) provide harmonized and quality-controlled clinical characterization data for each included individual; and (3) further promote collaboration of researchers in the field of monogenic PD. Methods: We conducted a worldwide, systematic online survey to collect individual-level data on individuals with PD-linked variants in SNCA, LRRK2, VPS35, PRKN, PINK1, DJ-1, as well as selected pathogenic and risk variants in GBA and corresponding demographic, clinical, and genetic data. All registered cases underwent thorough quality checks, and pathogenicity scoring of the variants and genotype–phenotype relationships were analyzed. Results: We collected 3888 variant carriers for our analyses, reported by 92 centers (42 countries) worldwide. Of the included individuals, 3185 had a diagnosis of PD (ie, 1306 LRRK2, 115 SNCA, 23 VPS35, 429 PRKN, 75 PINK1, 13 DJ-1, and 1224 GBA) and 703 were unaffected (ie, 328 LRRK2, 32 SNCA, 3 VPS35, 1 PRKN, 1 PINK1, and 338 GBA). In total, we identified 269 different pathogenic variants; 1322 individuals in our cohort (34%) were indicated as not previously published. Conclusions: Within the MJFF Global Genetic PD Study Group, we (1) established the largest international cohort of affected and unaffected individuals carrying PD-linked variants; (2) provide harmonized and quality-controlled clinical and genetic data for each included individual; (3) promote collaboration in the field of genetic PD with a view toward clinical and genetic stratification of patients for gene-targeted clinical trials. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Vertical stacks of InAs quantum wires in an InP matrix

In this work, multilayered films-consisting of layers of self-assembled InAs quantum wires separated by InP spacers-were deposited on (0 0 1) InP substrates. We studied the vertical alignment of the nanostructures by using cross-section transmission electron microscopy (XTEM). A clear relation between the geometry of the wire cross-section and the stacking angles was observed. For asymmetric wires the stacking angle with respect to the growing direction is larger. Moreover, XTEM shows that the strain field generated by two nanowires can induce the nucleation of a unique wider nanowire in the subsequent InAs layer. Similarly to quantum-dot multilayers systems, this mechanism could produce uniform width distribution for the self-assembled nanowires. (C) 2003 Elsevier Science B.V. All rights reserved.254416711

Growth of Be-doped homoepitaxial GaAs films on rough substrates

We present a study of morphologies - obtained by atomic force microscopy - of Be-doped humoepitaxial GaAs films grown by chemical beam epitaxy. The results show that the dopant on the surface may significantly affect the shape and size of the structures present in the film morphologies only when a large-scale roughness is observed in the initial surface for growth. Heavily doped samples (p similar to 4 x 10(19) cm(-3)) grown on these rough substrates present an anisotropic aspect ratio in the shape of the surface structures. This behavior suggests that the effect of the presence of Be atoms is different for adatom movement along different crystallographic directions on the surface. (C) 1999 Elsevier Science B.V. All rights reserved.20541671364