There is a growing interest in the recent years toward developing wide gap semiconductor nanostructures, and a lot of efforts have been dedicated to ZnO. In order to design core shell structures, a larger bandgap material is needed, which would ideally be similarly environment friendly. ZnS is an interesting possibility and although some efforts were devoted to it in the literature, its properties are not yet fully understood and precisely measured. In this work, we make a thorough analysis of high quality ZnS epilayers, in order to precisely determine the basic optical properties related to excitons and impurities in ZnS. We have made the first precise quantitative determination of residual strain using high-resolution x-ray diffraction. This allows us to demonstrate that, as it was hypothesized in most previous works, thermoelastic strain originating from the layer-substrate expansion coefficient mismatch is responsible for shifts and splitting of exciton photoluminescence lines. The identification of the bound excitons’ optical transitions is analyzed through their temperature/power dependence, in order to precisely assess their exact nature. Combined with the careful determination of donor and acceptor ionization energies in our ZnS sample, we discard the possibility of sodium as the main residual acceptor, as it has often been proposed in the literature.

We have produced thin film samples of cubic ZnS by the chemical bath method. These samples were synthesized using zinc chloride, thiourea, sodium citrate and ammonia solutions at varied deposition time from 24h to 96h. X-ray diffraction (XRD), transmittance and photoluminescence (PL) analyses provided the physical characteristics of cubic ZnS films with crystal plane orientations (2 0 0) and (2 2 2), lattice parameters of 5.648 Å and an atomic plane distance d=1.412 Å. The grain size calculed are 16.53 nm and 17.12 nm. PL revealed deep defects in the gap with peaks in the visible, with prominent emissions at 430 nm (blue) and 510 nm (green). The measured transmittance of the films is 88.6%.

A number of factors have been identified that influence the intensity of photoluminescence in a 4H-SiC:V sample. A photoluminescence temperature study shows trapping behaviour. An unexpected dependence of epitaxial growth rate on VCl 4 presence has been demonstrated.

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.

This paper discusses the results of high temperature resistivity and Hall effect studies of Mg-doped GaN and AlxGa1−xN epilayers (0.05 < x < 0.23). The studied samples were grown by molecular beam epitaxy on low temperature buffers of GaN and AlN deposited on a sapphire substrate. The experiments were carried out at temperatures ranging from 300 up to 1000 K. Up to a certain critical temperature TC (around 800 K), a typical increase of the conduction processes due to the excitation of impurity states has been observed with an activation energy of about EA = 200 meV. However, at this critical temperature TC, an annealing effect was observed in all the investigated samples. At this critical temperature, the increase in the free carrier concentration as a function of time leads to an irreversible decrease in the samples’ resistivity of more than 60%. The observed temperature dependences of the electrical transport properties are analyzed in the frame of an impurity model including shallow donors and Mg-related acceptors (with EA ∼ 200 meV). In some cases, an additional conduction channel not related to free carriers in the valence band must be taken into account. This can lead to an incorrect determination of hole concentration in the valence band, an important parameter in the process of radiative recombination.

Context : agriculture is one of the major cause of the climate change. In France, agriculture is responsible for 19 % of the national GHG emissions caused by 3 gases : N2O (50%), CH4 (40%) et CO2(10%). Agriculture is doubly concerned since it already faces dramatic consequences, due to climate change, like decrease of crop yields. That motivates the transition toward a new agriculture paradigm, known as agroecology. Agroforestry is one of the agroecologic practice, which combines trees and cereal crops. Growing trees and roots will sequester carbon in soils allowing to mitigate the carbon impact of the cultivated parcell. These practices require careful studies of the GHG of the cultivated parcel which would be sustained by new gaz sensor technologies : cheap, robust and sensitive.