P. Marie

Defects induced in GaN by europium implantation

We have investigated structural and electrical properties of defects introduced during room temperature europium implantation into GaN. Two geometries, random and channeled implantation, were used. Rutherford backscattering and channeling analysis reveals that implantation induces a significantly lower concentration of defects, in the case of channeled implantation. These defects generate a perpendicular expansion of the GaN lattice in the implanted region, as evidenced by x-ray diffraction. From deep-level transient spectroscopy, beside intrinsic defects with energy levels below the conduction band, one additional electron trap, labeled Eu2, is observed at an energy (Ec−0.36eV). It is believed that this defect in n‐GaN is europium related.

Statistical properties of intermittent maps with unbounded derivative

We study the ergodic and statistical properties of a class of maps of the circle and of the interval of Lorenz type which present indifferent fixed points and points with unbounded derivative. These maps have been previously investigated in the physics literature. We prove in particular that correlations decay polynomially, and that suitable limit theorems (convergence to stable laws or central limit theorem) hold for Holder continuous observables. Moreover, we show that the return and hitting times are exponentially distributed in the limit.

Structural characterisation of BaTiO3 thin films deposited on SrRuO3/YSZ buffered silicon substrates and silicon microcantilevers

We report on the progress towards an all epitaxial oxide layer technology on silicon substrates for epitaxial piezoelectric microelectromechanical systems. (101)-oriented epitaxial tetragonal BaTiO3 (BTO) thin films were deposited at two different oxygen pressures, 5.10 2 mbar and 5.10 3 mbar, on SrRuO3/Yttria-stabilized zirconia (YSZ) buffered silicon substrates by pulsed laser deposition. The YSZ layer full (001) orientation allowed the further growth of a fully (110)-oriented conductive SrRuO3 electrode as shown by X-ray diffraction. The tetragonal structure of the BTO films, which is a prerequisite for the piezoelectric effect, was identified by Raman spectroscopy. In the BTO film deposited at 5.10 2 mbar strain was mostly localized inside the BTO grains whereas at 5.10 3 mbar, it was localized at the grain boundaries. The BTO/SRO/YSZ layers were finally deposited on Si microcantilevers at an O2 pressure of 5.10 3 mbar. The strain level was low enough to evaluate the BTO Young modulus. Transmission electron microscopy (TEM) was used to investigate the epitaxial quality of the layers and their epitaxial relationship on plain silicon wafers as well as on released microcantilevers, thanks to Focused-Ion-Beam TEM lamella preparation

Pronounced crystallization of silicon layers deposited with high deposition rates at temperatures ⩽200 °C

Abstract Silicon layers were grown at 200 °C by reactive magnetron sputtering in a hydrogen-rich plasma (80% dilution). The samples were examined by Raman and infrared spectroscopies, as well as by transmission electron microscopy and optical transmission. In addition to the pronounced crystallization induced by the interactions with the H-based radicals, the incremental crystallization observed on the sample deposited in the region close to the cathode, where the radical density is high, appears due to the contribution of the incorporated Si nanopowders created in the surrounding plasma. The formation of these particles appeared, therefore, spatially limited because of its dependence on the radical density that is inhomogeneously distributed in the cathode-substrate separating area. To some extent, this allows one to control their insertion, the growth rate and layer compactness, through variation of electrodes spacing, r.f. power and plasma pressure. The occurrence of both particle creation in the plasma and columnar growth in the bulk attests of the key role played by the highly sticking and reactive SiH2.

Si-rich Al2O3 films grown by RF magnetron sputtering: structural and photoluminescence properties versus annealing treatment

Silicon-rich Al2O3 films (Six(Al2O3)1−x) were co-sputtered from two separate silicon and alumina targets onto a long silicon oxide substrate. The effects of different annealing treatments on the structure and light emission of the films versus x were investigated by means of spectroscopic ellipsometry, X-ray diffraction, micro-Raman scattering, and micro-photoluminescence (PL) methods. The formation of amorphous Si clusters upon the deposition process was found for the films with x ≥ 0.38. The annealing treatment of the films at 1,050°C to 1,150°C results in formation of Si nanocrystallites (Si-ncs). It was observed that their size depends on the type of this treatment. The conventional annealing at 1,150°C for 30 min of the samples with x = 0.5 to 0.68 leads to the formation of Si-ncs with the mean size of about 14 nm, whereas rapid thermal annealing of similar samples at 1,050°C for 1 min showed the presence of Si-ncs with sizes of about 5 nm. Two main broad PL bands were observed in the 500- to 900-nm spectral range with peak positions at 575 to 600 nm and 700 to 750 nm accompanied by near-infrared tail. The low-temperature measurement revealed that the intensity of the main PL band did not change with cooling contrary to the behavior expected for quantum confined Si-ncs. Based on the analysis of PL spectrum, it is supposed that the near-infrared PL component originates from the exciton recombination in the Si-ncs. However, the most intense emission in the visible spectral range is due to either defects in matrix or electron states at the Si-nc/matrix interface.

Volume charge carrier number fluctuations probed by low frequency noise measurements in InN layers

Bulk conduction in molecular beam epitaxial InN layers has been confirmed using low frequency noise measurements versus temperature. A generation-recombination process has been identified at low temperatures 100 K and attributed to a trap with a discrete energy level in the band gap. The energy position of this trap has been determined to be around 52 meV below the conduction band minimum.

Effect of swift heavy ions on the photoluminescence properties of Si/SiO2 multilayers

Si/SiO2 multilayers were prepared by reactive magnetron sputtering of a pure silica target and irradiated at 300K at GANIL with Kr and Pb ions whose energies were 9MeV (Se=0.72keVnm−1) and 4.6MeV per nucleon (Se=2.25keVnm−1), respectively. After a postannealing treatment, the films exhibit luminescence in the visible spectral range at room temperature. A blueshift of the photoluminescence with the increasing Se is noticed and is ascribed to a decrease in the Si grain size and/or to a decrease in the interface width.