Study of the optical and structural properties of multi quantum well structures grown on high-index surfaces
The MOVPE overgrowth of high [01@?1]-oriented ridges confined at sides by facets related to {n11} crystallographic planes is reported. We studied the influence of the side tilt on the thickness of the AlGaAs and GaAs epitaxial layers grown under the condition of the kinetic growth mode. The multi quantum well (MQW) structures were prepared on the sides of ridges tilted at 54.7^o, 45^o and 30^o to (100). The sidewall surface morphologies before and after epitaxial growth were evaluated and compared. We observed no tendency towards planarization towards a neighbouring high-index crystallographic plane, such as (211) and (311). We also showed that the quantum wells of the MQW structure make a smooth transition over the edge between the top surface and the facet as both AlGaAs and GaAs grew at similar rates on the surfaces.
OMVPE fabrication of continuous transitions between GaAs/AlGaAs quantum wells and V-groove quantum wires
The fabrication of defect-free and continuous transitions between AlGaAs/GaAs quantum wells (QWs) and quantum wires (QWRs) using organo-metallic vapor phase epitaxy on variable-width V-grooved substrates is demonstrated. The basic idea of our approach is developed using a Monte-Carlo simulation of the self-limiting growth on tapered grooves. A detailed surface and cross-sectional atomic force microscopy study reveals the high quality of the resulting coupled quantum structures. In particular, we demonstrate the efficient control, brought about by this experimental technique, on the well-wire transitions.
Access to antenatal care and children’s cognitive development: a comparative analysis in Ethiopia, Peru, Vietnam and India
ObjectivesEarly life interventions are considered essential for reducing the burden of health inequalities over the life course. This paper tests this issue empirically focusing on whether access to antenatal care can later reduce children’s health and educational inequalities.MethodsData came from the Young Lives Project for Ethiopia, Peru, Vietnam, and the State of Andhra Pradesh in India. We selected children born in early 2001/2002 and who were followed longitudinally in 2006/2007. We used multilevel mixed effects linear regression models to estimate the parameters of interest.ResultsWe found a positive and significant relationship between mothers’ access to antenatal care and their children’s cognitive development in all countries. In addition, we found a positive and significant relationship between antenatal care and children’s cognitive development for stunted children but only in Peru and Vietnam.ConclusionsWe conclude that (1) antenatal care has the potential to change the negative consequences of early nutritional deficiencies on later cognitive development in Peru and Vietnam; (2) differentials in the quality of antenatal care services could explain the cross-country differentials in the role of early life interventions found here.