We present a multimode longitudinal pumping scheme for integrated rare-earth doped waveguide amplifiers which
allows an efficient use of low cost multimode pump sources. The scheme is based on evanescent pump light coupling
from a multimode low loss waveguide, which is gradually transferred to a single mode Si-nc sensitized Er<sup>3+</sup> doped active
core. Population inversion is ensured along the whole amplifier length, thus overcoming the main limitation of
conventional single mode pump butt-coupling in case of strongly absorbing active materials. Great flexibility in
controlling the pump power intensity values within the active core is also provided.
We propose this pumping scheme at 477 nm for Si-nanocluster sensitized Erbium doped waveguide amplifiers, in
which top pumping by LED arrays is limited by the low pump intensity values achievable within the active region.
The coupling between the multimode waveguide and the active core has been numerically studied for slab waveguide
structures using a 2D split-step finite element method.
Numerical simulation results, based on propagation and population-rate equations for the coupled Er<sup>3+</sup>/Si-nanoclusters
system, show that high pump intensities are indeed achieved in the active core, ensuring good uniformity of the
population inversion along the waveguide amplifier.
Although longitudinal multimode pumping by high power LEDs in the visible can potentially lead to low-cost integrated
amplifiers, further material optimization is required. In particular, we show that when dealing with high pump intensities,
confined carrier absorption seriously affects the amplifier performance, and an optimization of both Si-nc and Er<sup>3+</sup>
concentrations is necessary.
A Conductive Atomic Force Microscope (C-AFM) has been used to investigate the nanometer scale electrical properties of Metal-Oxide-Semiconductor (MOS) memory devices with Silicon nanocrystals (Si-nc) embedded in the gate oxide. This study has been possible thanks to the high lateral resolution of the technique, which allows to characterize areas of only few hundreds of nm<sup>2</sup> and, therefore, the area that contains a reduced number of Si-nc. The results have demonstrated the capability of the Si-nc to enhance the gate oxide electrical conduction due to trap assisted tunneling. On the other hand, Si-nc can act as trapping centers. The amount of charge stored in Si-nc has been estimated through the change induced in the barrier height measured from the I-V characteristics. The results show that only ~20% of the Si-nc are charged. These nanometer scale results are consistent with those obtained during the macroscopic characterization of the same structures. Therefore, C-AFM has been shown to be a very suitable tool to perform a detailed investigation of the performance of memory devices based on MOS structures with Si-nc at such reduced scale.