Olivier Debieu

Microstructural, electrical, and optical properties of undoped and Nd3+-doped SiOx/SiNy multilayers fabricated by reactive radio frequency magnetron co-sputtering have been investigated with regard to thermal treatment. This letter demonstrates the advantages of using SiNy as the alternating sublayer instead of SiO2. A high density of silicon nanoclusters of the order 1019 nc/cm3 is achieved in the SiOx sublayers. Enhanced conductivity, emission, and absorption are attained at low thermal budget, which are promising for photovoltaic applications. Furthermore, the enhancement of Nd3+ emission in these multilayers in comparison with the SiOx/SiO2 counterparts offers promising future photonic applications.

By means of ADE-FDTD method, this paper investigates the electromagnetic modelling of a rib-loaded waveguide composed of a Nd³⁺ doped Silicon Rich Silicon Oxide active layer sandwiched between a SiO₂ bottom cladding and a SiO₂ rib. The Auxilliary Differential Equations are the rate equations which govern the levels populations. The Finite Difference Time Domain (FDTD) scheme is used to solve the space and time dependent Maxwell equations which describe the electromagnetic field in a copropagating scheme of both pumping (λ _pump = 488 nm) and signal (λ _signal = 1064 nm) waves. Such systems are characterized by extremely different specific times such as the period of electromagnetic field ~ 10^-15 s and the lifetimes of the electronic levels between ~ 10^-10s and ~ 10^-4 s. The time scaling method is used in addition to specific initial conditions in order to decrease the computational time. We show maps of the Poynting vector along the propagation direction as a function of the silicon nanograin (Si-ng) concentrations. A threshold value of 10²⁴ Si-ng m^-3 is extracted below which the pump wave can propagate so that a signal amplication is possible.

We examined and compared the electrical properties of silica (SiO₂) and silicon oxynitride (SiO _x N _y ) layers embedding silicon nanoclusters (Sinc) integrated in metal-insulator-semiconductor (MIS) devices. The technique used for the deposition of such layers is the reactive magnetron sputtering of a pure SiO₂ target under a mixture of hydrogen/argon plasma in which nitrogen is incorporated in the case of SiO _x N _y layer. Al/SiO _x N _y -Sinc/p-Si and Al/SiO₂-Sinc/p-Si devices were fabricated and electrically characterized. Results showed a high rectification ratio (>10⁴) for the SiO _x N _y -based device and a resistive behavior when nitrogen was not incorporating (SiO₂-based device). For rectifier devices, the ideality factor depends on the SiO _x N _y layer thickness. The conduction mechanisms of both MIS diode structures were studied by analyzing thermal and bias dependences of the carriers transport in relation with the nitrogen content.

In this article, the microstructure and photoluminescence (PL) properties of Nd-doped silicon-rich silicon oxide (SRSO) are reported as a function of the annealing temperature and the Nd concentration. The thin films, which were grown on Si substrates by reactive magnetron co-sputtering, contain the same Si excess as determined by Rutherford backscattering spectrometry. Fourier transform infrared (FTIR) spectra show that a phase separation occurs during the annealing because of the condensation of the Si excess resulting in the formation of silicon nanoparticles (Si-np) as detected by high-resolution transmission electron microscopy and X-ray diffraction (XRD) measurements. Under non-resonant excitation at 488 nm, our Nd-doped SRSO films simultaneously exhibited PL from Si-np and Nd³⁺ demonstrating the efficient energy transfer between Si-np and Nd³⁺ and the sensitizing effect of Si-np. Upon increasing the Nd concentration from 0.08 to 4.9 at.%, our samples revealed a progressive quenching of the Nd³⁺ PL which can be correlated with the concomitant increase of disorder within the host matrix as shown by FTIR experiments. Moreover, the presence of Nd-oxide nanocrystals in the highest Nd-doped sample was established by XRD. It is, therefore, suggested that the Nd clustering, as well as disorder, are responsible for the concentration quenching of the PL of Nd³⁺.

We report on the microstructure and photoluminescence (PL) properties of Nd-doped SiO2 thin films containing silicon nanoparticles (Si-np) as a function of the annealing temperature and the Nd concentration. The thin films, which were grown on Si substrates by reactive magnetron co-sputtering, contain the same Si excess. Fourier transform infrared (FTIR) spectra show that a phase separation occurs during the annealing due to the agglomeration of the Si excess resulting in the formation of Si-np. Besides, after annealing, the films exhibit PL from excitonic states confined in Si-np. We showed that the intensity of the PL of Nd3+ ions that occurs at ∼0.92, 1.06, and 1.4 μm is maximal at low Nd concentration and while well-passivated Si-np are formed. FTIR and x-ray measurements showed that the increase in the Nd incorporation has detrimental effects on the PL of Nd3+ because of the formation of Nd2O3 nanocrystals and inherent disorder in the SiO2 host matrix. PL excitation measurements demonstrate that the PL of Nd3+ ions is nonresonant and follows the excitation of Si-np giving new evidence of the energy transfer from Si-np toward the rare earth ions.