[en] Ferromagnetic (FM) nanostructures embedded in semiconductors are attracting interest because their physical properties could be used in new devices such as memories, sensors or more generally involving 'spintronics'. In this work, we present results on the synthesis and the characterization of nanosized MnAs ferromagnets buried in GaAs. These nanocrystals can be formed either by single Mn implantation or by Mn+As co-implantation at room temperature into GaAs wafers followed by thermal annealing. High-resolution transmission electron microscopy and diffraction analysis show that the MnAs precipitates exhibit the regular hexagonal structure with a 3m orientation relationship with respect to the matrix. The mean diameters of the nanocrystals range from 9 to 13 nm depending on the annealing conditions. Magnetization measurements by superconducting quantum interference device magnetometry reveal an FM state. Upon warming, a progressive transition to a superparamagnetic state is evidenced, probably due to the distribution of individual blocking temperatures, resulting both from the size distribution of the nanocrystals and from dipolar interactions. Curie temperatures in the range of 360 K are measured, significantly higher than for bulk MnAs

[en] We have realized 150 μmx150 μm pixels using ion implantation followed by photolithography, metallic contact evaporation and chemical etching on about 200 μm thick GaAs epitaxial layers. These layers were grown on n⁺ and p⁺ substrates by an already described Chemical Reaction technique, which is economical, non-polluting and can attain growth rates of several microns per minute. The mesa p⁺/i/n⁺ pixel were characterized using current-voltage and capacitance-voltage measurements. The charge collection efficiency was evaluated by photoconductivity measurements under typical conditions of standard radiological examinations

[en] Hydrogen diffusion in InP:Zn, protected by an undoped GaInAs epilayer, has been performed from a hydrogen plasma exposure. Passivation of shallow acceptors occurs in the hydrogen diffused region of InP:Zn. Secondary ion mass spectrometry, transport measurements and thermal annealing experiments indicate the existence of neutral Zn,H pairs in InP:Zn,H. We find that these pairs have a relatively higher thermal stability than in GaAs:Zn. This is interpreted with the help of the microscopic description of the Zn,H complexes. (author) 15 refs., 4 figs

[en] We studied the epitaxial growth of CeO₂ thin films as a function of deposition temperature (200-800 deg. C), r.f. magnetron power (25-125 W) and anode-cathode distance (2-6 cm). The films were grown on Si(111) substrates by on-axis r.f. magnetron sputtering of a cerium oxide target in an Ar plasma. The crystalline quality of the films was investigated using X-ray diffraction and Raman spectroscopy. Our results show that the crystalline quality of the films can be improved by a post-growth rapid thermal annealing

[en] To be used for X-ray imaging, semiconductor materials must exhibit good and uniform electronic properties. Epitaxial layers are therefore better adapted than bulk materials which contain dislocations, precipitates and point defects in variable concentrations depending on the growth mode and the nature of the material. However, they have to be thick enough to absorb photons efficiently. We produced thick epitaxial layers using a proprietary technique and made p/i/n (200-300 μm thick) diodes with this new material. These diodes are characterized by a large reverse current, which can originate from electron emission from deep level defects present in the depleted region or be a leakage current. In order to answer this question, we performed a characterization of the defects present in the material. Here, we describe results obtained from X-ray diffraction, X-ray topography, time resolved photoluminescence and resistivity measurements. We also investigated the possible effect of hydrogen. From these observations, we deduced that defects exhibiting an electrical role are in negligible concentration and concluded that the high reverse current observed is a leakage current.