The use of a high-growth-temperature GaAs spacer layer is demonstrated to significantly improve the performance of 1.3μm multilayer self-assembled InAs∕InGaAs dot-in-a-well lasers. The high-growth-temperature spacer layer inhibits threading dislocation formation, resulting in enhanced electrical and optical characteristics. Incorporation of these spacer layers allows the fabrication of multilayer quantum-dot devices emitting above 1.3μm, with extremely low room-temperature threshold current densities and with operation up to 105°C.

The growth temperature of spacer layers (SPLs) is investigated as a means to obtain identical layers for multilayer quantum dot (QD) structures. A 5-layer 1.3-μm InAs∕GaAs QD structure with 50-nm GaAs SPLs served as a model system. It is found that the growth temperature of the GaAs SPLs has pronounced effects on both the structural and optical properties of the InAs QDs. For GaAs SPLs grown at a low temperature of 510°C, dislocations are observed in the second and subsequent layers, a result of significant surface roughness in the underlying spacer layer. However by increasing the growth temperature to 580°C for the final 35nm of the 50-nm GaAs SPLs, a much smoother surface is achieved, allowing the fabrication of essentially identical, defect free QD layers. The suppression of defect formation enhances both the room-temperature photoluminescence efficiency and the performance of 1.3-μm multilayer InAs∕GaAs QD lasers. An extremely low continue-wave room-temperature threshold current density of 39A∕cm2 is achieved for an as-cleaved 5-layer device with emission at 1.306μm and ground state operation up to 100°C.

We present the 1.55 μm GaInNAs/GaAs multiple quantum well (QW) heterostructures with a GaNAs or a GaInNAs barrier and space layer (BSL). The stronger improvement of photoluminescence efficiency has been observed with increasing N concentration in a GaNAs BSL, instead of increasing N composition in GaInNAs QWs, to achieve room-temperature emission above 1.5 μm for GaInNAs/GaNAs multiple QW structure, when the nitrogen concentration in GaInNAs QW is as high as 3%. A further enhancement of photoluminescence intensity and a remarkable reduction of emission linewidth of GaInNAs multiple QWs have been demonstrated by using a GaInNAs quaternary BSL. These effects of a GaInNAs BSL could be understood in terms of the improvement of structural properties of GaInNAs QWs, resulting from the reduction of the strain at QW/BSL interface. These results present a variable approach to further developing GaAs-based light sources in the telecommunication-wavelength range near 1.55 μm.

Organic micro-contaminants (OMCs) enter in freshwaters and interact with other contaminants such as carbon nanoparticles, becoming a problem of unknown consequences for river ecosystems. Carbon nanoparticles (as fullerenes C60) are good adsorbents of organic contaminants and their interaction can potentially affect their toxicity to river biofilms. We tested the C60 interactions with selected OMCs and their effects on river biofilms in different short-term experiments. In these, river biofilms were exposed to C60 and three OMCs (triclosan, diuron, or venlafaxine) and their respective mixtures with fullerenes (C60 + each OMC). The effects were evaluated on structural, molecular, and functional descriptors of river biofilms. Our results showed that C60 did not cause toxic effects in river biofilms, whereas diuron and triclosan significantly affected the heterotrophic and phototrophic components of biofilms and venlafaxine affected only the phototrophic component. The joint exposure of C60 with venlafaxine was not producing differences with respect to the former response of the toxicant, but the overall response was antagonistic (i.e., decreased toxicity) with diuron, and synergistic (i.e., increased toxicity) with triclosan. We suggest that differences in the toxic responses could be related to the respective molecular structure of each OMC, to the concentration proportion between OMC and C60, and to the possible competition between C60 pollutants on blocking the receptors of the biological cell membranes. We conclude that the presence of C60 at low concentrations modified the toxicity of OMC to river biofilms. These interactions should therefore be considered when predicting toxicity of OMC in river ecosystems.

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Primary degeneration of the granular layer of the cerebellum is an autosomal recessive disorder exhibiting characteristic clinical features: hypotonia, strabismus, delayed motor development, nonprogressive ataxia, delayed language development with dysarthria and mental retardation. We studied fourteen children, seven of each gender. Neuroimaging tests including pneumoencephalography, computed tomography (CT) and magnetic resonance imaging (MRI) showed severe cerebellar atrophy in all. MRI best demonstrated the cerebellar lesion, revealing great uniformity amongst the cases. Vertebrobasilar angiography was performed in two cases and showed marked hypoplasia of the cerebellar arteries, predominantly the posterior inferior cerebellar artery (PICA) and its branches. Necropsy was performed in three cases; cerebellar atrophy with loss of granular cells and diverse abnormalities of the Purkinje cells was found in two. The third, the sister of one of the other two cases, had a similar but shorter clinical course and died at three months of age. Her sister, who died at 5 years of age, presented a severe cerebellar atrophy with typical changes in the granular cell layer and Purkinje cells. In the third patient, who lived three months, only focal cerebellar folial atrophy with no microscopic changes in the granular cell layers was present. Though this case cannot objectively be included in the cerebellar atrophy syndrome with granular cell loss, her family history and clinical picture suggest the same disease. The findings observed in our series and the study of cases described in the literature, suggest that there are several forms of this disease which differ mainly in severity and neurological evolution. The cerebellar lesion seems to be a progressive atrophic process with the most severe changes during the early years of life.

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This work focuses on the influence of the growth temperature on the structural and optical quality of GaInNAs/GaAs and GaInAs/GaAs multi-quantum wells with similar lattice mismatch, studied by transmission electron microscopy and photoluminescence. We have found compositional fluctuations in all the GaInNAs samples, which vary from negligible to very strong over the temperature range studied (360-460 • C). In comparison, at the same growth temperature, GaInAs heterostructures appear more homogeneous. It is proposed therefore that the introduction of N in the structure could be responsible for the enhanced phase separation. A broadening of the photoluminescence peak in GaInNAs structures when raising the growth temperature has also been found associated with the increase in composition fluctuations. Moreover, a kinetically limited Stranski-Krastanow growth mode has been observed in both GaInAs and GaInNAs structures, taking place at lower temperature in GaInNAs quantum wells. We suggest that the enhancement of this growth mode is a consequence of the increased phase separation. The influence of the introduction of N into the GaInAs alloy on the compositional fluctuations and 3D growth mode is discussed.