Determination of free-carrier and phonon-assisted absorptions for Si-doped GaSb thin layers

International audiencePhotothermal deflection spectroscopy is used in order to investigate near- and sub-band gap absorption of Si-doped GaSb epilayers deposited by MBE on a semi-insulating GaAs substrate. The optical absorption spectra show an extra absorption on the transparency region below the bandgap due to free-carrier absorption. However, for energies above the gap, we notice a linear behavior of the square root of the absorption coefficient versus the heating beam energy, which is attributed to phonon-assisted absorption. From interpolation of the phonon absorption to low energies we have determined the free-carrier absorption that is found to follow the Drude law

Investigation of electrical and optothermal properties of Si-doped GaSb epitaxial layers by the Hall effect, PL measurement and photothermal deflection spectroscopy

International audienceThe aim of this work is to investigate the influence of Si-doping on the optical, thermal and electrical properties of GaSb epitaxial layers. Such an influence was quantified through photoluminescence (PL), mirage effect (photothermal spectroscopy) and Hall effect measurements. Several GaSb samples, grown by Molecular Beam Epitaxy (MBE) on (100)-oriented GaAs semiinsulating substrates, with different Si-doping levels ranging from 4.95E16 at.cm-3 up to 8.11E19 at.cm-3 were tested. As a comparison, the same measurements were also performed on a GaSb non intentionally doped layer. The Hall effect data shows a monotonic decrease in carrier mobility when the hole concentration increase. The effect of band-to-band, band-impurity transitions on the PL gap E0 and the influence of high impurity concentration on the PL and absorption spectra have been also studied. Finally, the optical absorption changes induced by Si-doping on GaSb samples were investigated by photothermal deflection. It was shown that this technique allows a very precise deduction of the real interband gap energy of a semiconductor material as GaSb. Thermal conductivities were also deduced from the photothermal deflection measurements. The found values are very low due to the thermal resistivity of the layer-substrate interface but also due to the lattice-mismatch between GaSb epilayers and the GaAs substrate. However, the contribution of the free carriers to the thermal conductivity, with a high p-doping level (p>10E19 cm-3), could be highlighted

Success of anti-CD20 monoclonal antibody treatment for severe autoimmune hemolytic anemia caused by warm-reactive immunoglobulin A, immunoglobulin G, and immunoglobulin M autoantibodies in a child: a case report

Abstract Background Autoimmune hemolytic anemia is rare in children. First-line therapies for this disease consist of corticosteroids and intravenously administered immunoglobulin that are effective in most patients. However, a small proportion of cases (5 to 10%) is refractory to these therapies and may represent a medical emergency, especially when hemolysis is due to warm immunoglobulin M. Recently, reports of the use of rituximab in adult autoimmune diseases have shown promising results. In children, there are few studies on the use of rituximab in the treatment for autoimmune hemolytic anemia, especially on its long-term efficacy and adverse effects. Case presentation Here, we report the case of a 10-year-old Tunisian girl with refractory acute autoimmune hemolytic anemia caused by warm-reactive immunoglobulin A, immunoglobulin G, immunoglobulin M, and C3d autoantibodies. First-line treatments using corticosteroids and intravenously administered immunoglobulin were ineffective in controlling her severe disease. On the other hand, she was successfully treated with rituximab. In fact, her hemolytic anemia improved rapidly and no adverse effects were observed. Conclusions The case that we report in this paper shows that rituximab could be an alternative therapeutic option in severe acute autoimmune hemolytic anemia with profound hemolysis refractory to conventional treatment. Moreover, it may preclude the use of plasmapheresis in such an urgent situation with a sustained remission