Pure and Aluminum doped Zinc Oxide Nanoparticles (AZO NPs) with various doping concentrations were synthesized using an original aqueous chemical process under atmospheric pressure and moderate temperature, using only deionized water as a solvent with a filtration step followed by heat treatment.The X-Ray Diffraction (XRD), Raman and Field Emission Scanning Electron Microscopy- Energy-Dispersive X-ray Spectroscopy (FESEM-EDS) analysis of nanoparticles reveals a hexagonal wurtzite structure, with a size around 60 nm and the presence of aluminum in our samples. Optical investigations demonstrate that the material is of high quality, with few deep structural defects, since Photoluminescence (PL) is largely dominated by excitonic emission at low temperatures.

In order to analyze why the CIGS (CuInGaSe2) - based solar cells efficiency decrease for wide band gap (high Ga content), we have performed a series of samples by PVD using the three stage process. The average compositions of our solar cells range from x = 0 to x = 0.88, as measured by X-ray diffraction. An important feature of this process is to create a double Ga gradient into the absorber, which contributes to improve efficiencies, and this has a major impact on the determination of the sample composition from x-ray diffraction data. We have developed a model in order to assess this impact and question the validity of the compositions extracted from x-ray data. This model allows to get some information about gradient shapes. Using our model, we have obtained some insights on the evolution of the gallium gradient in samples with increasing Ga content, and we determine that this gradient is less pronounced when increasing the amount of gallium. It is a well known fact that this gradient assists the extraction of photocreated carriers, and the modifications of the gallium profile that we have determined may explain, for some part, the degradation of solar cells efficiency for high gallium compositions.

InSe is a promising material in many aspects where the role of excitons is decisive. Here we report the sequential appearance in its luminescence of the exciton, the biexciton, and the P-band of the exciton-exciton scattering while the excitation power increases. The strict energy and momentum conservation rules of the P-band are used to reexamine the exciton binding energy. The new value >= 20 meV is markedly higher than the currently accepted one (14 meV), being however well consistent with the robustness of the excitons up to room temperature. A peak controlled by the Sommerfeld factor is found near the bandgap (similar to 1.36 eV). Our findings supported by theoretical calculations taking into account the anisotropic material parameters question the pure three-dimensional character of the exciton in InSe, assumed up to now. The refined character and parameters of the exciton are of paramount importance for the successful application of InSe in nanophotonics.

Lead halide perovskites, used to produce photovoltaic devices, have been thesubject of a huge research effort these last years. This is due to the spectac-ular improvement of the conversion effciency results within a short amount oftime. However, some issues have been identified, which include stability, leaduse and cost of some precursors. It has recently been shown that low purity, lowcost PbI2 could be succesfully used in the synthesis of the MAPbI3 perovskite,provided that HCl is added during the synthesis to prevent solubility problems.Thus, it is of high interest to provide information pertaining to the materialquality, in relation with the HCl additions performed during synthesis. In thiswork, we have grown three sets of samples with different HCl to (PbI 2 + MAI)molar ratios (R HCl ), where PbI2 and methylamine iodide (MAI) are the precur-sors of the perovskite. We used RHCl = 0 (no HCl), 0.5 and 1.2 . We performedx-ray diffraction, transmittance and 77K photoluminescence experiments in or-der to assess the material structural and optoelectronic properties and foundthat an optimum HCl concentration must be used. HCl introduction clearlyhas a beneficial effect both on domain sizes and photoluminescence intensityat RHCl = 0.5, but lead to subsequent degradation of the perovskite quality athigher RHCl .

We report on the growth of GaSe films by molecular beam epitaxy on both (111)B GaAs and sapphire substrates. X-ray diffraction reveals the perfect crystallinity of GaSe with the c-axis normal to the substrate surface. The samples grown under Ga rich conditions possess an additional gallium film on top of the monochalcogenide layer. This metallic film shows two normal-to-superconducting transitions which are detected at T c ≈ 1.1 K and 6.0 K. They correspond likely to the β and α-phases of gallium in the form of bulk and droplets respectively. Our results demonstrate that van der Waals epitaxy can lead to future high quality hybrid superconductor/monochalcogenide heterostructures.

Optical investigations and strain effect in AlGaN/GaN epitaxial layers