Anna Muscara

Quantitative determination of the clustered silicon concentration in substoichiometric silicon oxide layer

We present an analytical methodology, based on electron energy loss spectroscopy (EELS) and energy-filtered transmission electron microscopy, which allows us to quantify the clustered silicon concentration in annealed substoichiometric silicon oxide layers, deposited by plasma-enhanced chemical vapor deposition. The clustered Si volume fraction was deduced from a fit to the experimental EELS spectrum using a theoretical description proposed to calculate the dielectric function of a system of spherical particles of equal radii, located at random in a host material. The methodology allowed us to demonstrate that the clustered Si concentration is only one half of the excess Si concentration dissolved in the layer.

Design and Electro-Optical Characterization of Si-Based Resonant Cavity Light Emitting Devices

The fabrication and characterization of electrically pumped silicon/silicon dioxide (Si/SiO2) Fabry-Perot microcavities is reported. The active region of these devices consists of an Er-implanted silicon-rich oxide (SRO:Er) film placed in the center of a λ-cavity polysilicon spacer. The structures have been designed in order to enhance the electroluminescence signal at 1540 nm, which is an important wavelength for telecommunication systems, and to achieve high directionality and high-purity spectra. The active region design allows the Er-implanted SRO film to be driven electrically. These Si-based resonant cavity light emitting diodes are fabricated by chemical vapor deposition on a silicon substrate. Microcavities with a quality factor ranging from 50 to 118, depending on the number of Si/SiO2 pairs constituting the dielectric mirrors, have been fabricated. Low operating voltages and electrical stability have been achieved. The emitted power versus current flowing in the active medium was measured for the structures with different quality factors. An enhancement of the electroluminescence signal at the selected emission wavelength was achieved with a proper design.

High Efficiency Light Emission Devices in Silicon

We report on the fabrication and performances of the most efficient Si-based light sources. The devices consist of MOS structures with erbium (Er) implanted in the thin gate oxide. The devices exhibit strong 1.54 μm electroluminescence at 300K with a 10% external quantum efficiency, comparable to that of standard light emitting diodes using III-V semiconductors. Emission at different wavelenghts has been achieved incorporating different rare earths (Ce, Tb, Yb, Pr) in the gate dielectric. The external quantum efficiency depends on the rare earth ions incorporated and ranges from 10% (for an Tb doped MOS) to 0.1% (for an Yb doped MOS). RE excitation is caused by hot electrons impact and oxide wearout limits the reliability of the devices. Much more stable light emitting MOS devices have been fabricated using Er-doped SRO (Silicon Rich Oxide) films as gate dielectric. These devices show a high stability, with an external quantum efficiency reduced to 0.2%. In these devices Er pumping occurs part by hot electrons and part by energy transfer from the Si nanostructures to the rare earth ions, depending by Si excess in the film. Si/SiO 2 Fabry-Perot microcavities have been fabricated to enhance the external quantum emission along the cavity axis and the spectral purity of emission from the films that are used as active media to realize a Si based RCLED (resonant cavity light emitting diode). These structures are realized by chemical vapour deposition on a silicon substrate. The microcavities are tuned at different wavelengths: 540nm, 980nm and 1540nm (characteristic emission wavelengths respectively for Tb, Yb and Er). The reflectivity of the microcavities is of 97% and the quality factor ranges from 60 (for the cavity tuned at 980nm) to 95 (for the cavities tuned at 540nm and 1540nm).

Si-based resonant cavity light-emitting devices

We report on the fabrication and characterization of Si/SiO2 Fabry-Perot microcavities. These structures are used to enhance the external quantum emission along the cavity axis and the spectral purity of emission from Rare earth doped and undoped SiOx (x <= 2)films that are used as active media to fabricate a Si based RCLED (Resonant Cavity Light emitting Devices). These structures are fabricated by chemical vapour deposition on a silicon substrate. The microcavities are tuned at different wavelengths: 540nm, 980nm, 1540nm, 780nm and 850nm (characteristic emission wavelength respectively for Tb, Yb and Er and Silicon Rich Oxide (SRO)). The reflectivity of the microcavities is of 97% and the factor quality ranges from 50 (for the cavity tuned at 540nm) to 95 (for the cavities tuned at 980nm and 1540nm) and 150 (for the cavity tuned at 780nm and 850 nm). These cavities have been characterized by TEM analysis to evaluate films uniformity, thickness and densification after annealing process for temperature ranging from 800° to 1100°C. The reflectivity and photoluminescence spectra show resonant wavelengths in agreement with the calculated values. A new structure to electrically pump the active media has been designed. The electrical properties of the active media have been analysed. An enhancement of the photoluminescence signal of twenty times have been achieved for the selected emission wavelength.