Maria Eloisa Castagna

Si-based materials and devices for light emission in silicon

Abstract We report on the fabrication and performances of extremely 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 (EL) at 300 K with a 10% external quantum efficiency, comparable to that of standard light-emitting diodes using III–V semiconductors. Er 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 silicon rich oxide (SRO) films as gate dielectric. These devices show a high stability, with an external quantum efficiency reduced to 1%. In these devices, Er pumping occurs by energy transfer from the Si nanostructures to the rare-earth ions. Finally, we have also fabricated MOS structures with Tb- and Yb-doped SiO 2 which show room temperature EL at 540 nm (Tb) and 980 nm (Yb) with an external quantum efficiency of a 10% and 0.1%, respectively.

Highly Efficient Low Reverse Biased 4H-SiC Schottky Photodiodes for UV-Light Detection

Ultraviolet light detection has a wide range of scientific and industrial applications. In particular, SiC photodiodes have been proposed because of their robustness even in harsh environments, high quantum efficiency but excellent visible blindness, very low dark current, and high speed. Here, we report on the electrical and optical performances of high efficient large area 4 H-SiC Schottky photodiodes working in the photovoltaic regime. We demonstrate that the high signal-to-noise ratio along with the low operating reverse voltage in spite of the large sensitive area makes them suitable in low power consumption applications requiring high sensitivity down to 250 nm.

Influence of the matrix properties on the performances of Er-doped Si nanoclusters light emitting devices

We investigated the properties of light emitting devices whose active layer consists of Er-doped Si nanoclusters (nc) generated by thermal annealing of Er-doped SiOx layers prepared by magnetron cosputtering. Differently from a widely used technique such as plasma enhanced chemical vapor deposition, sputtering allows to synthesize Er-doped Si nc embedded in an almost stoichiometric oxide matrix, so as to deeply influence the electroluminescence properties of the devices. Relevant results include the need for an unexpected low Si excess for optimizing the device efficiency and, above all, the strong reduction of the influence of Auger de-excitation, which represents the main nonradiative path which limits the performances of such devices and their application in silicon nanophotonics.

Quantum Dot Materials and Devices for Light Emission 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. Er 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 1%. In these devices Er pumping occurs by energy transfer from the Si nanostructures to the rare earth ions.

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.

Inductive Integrated Biosensor With Extended Operative Range for Detection of Magnetic Beads for Magnetic Immunoassay

Biosensors are prominent in several areas, such as medical diagnosis, food preparation, pharmaceutical industries, and clinical analysis; high performances are required in spite of attaining accuracy, sensitivity, low cost, easy handling, and portability, but the major parameter that is always representing a challenge for biosensors is specificity. High sensitivity and specificity can be obtained by combining appropriate transduction methods together with immunoassay techniques. In this paper, integrated inductive biosensors for the magnetic immunoassay process, which use magnetic beads as markers for biomolecules, are presented with potential applications to proteins and DNA measurements. The working principle and a dedicated fabrication technology, which also embeds thermal actuation and control, are described; in particular, an improved sensing architecture is proposed here, which allows one to expand the microsensor operative field toward very low bead concentrations. The sensor characterization results are presented together with the analytical model of the transduction principle; a detection limit of approximately 300 beads has been demonstrated. The microsensor is also capable of operating by measuring up to 450 000 beads with a good linearity. Therefore, the sensor architecture proposed here has been demonstrated for wide operating field with high resolution and good linearity; the results proposed confirm the suitability of the devices developed for magnetic immunoassay applications.

Si-based rare earth doped light emitting devices

We report on the fabrication and performances of highly efficient Si-based light sources. The devices consist of MOS structures with erbium (Er) implanted in the thin gate oxide. The devices exhibit strong 1540 nm 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. 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 different pumping mechanisms for the Er ions are simultaneously operating: Er can be excited by direct hot electron impact (like in stoichiometric oxide MOS) and by energy transfer from excited Si nanostructures, depending on the Si excess in the film. We propose a model to describe the electrical conduction mechanism in a Silicon Rich Oxide film. The electrical characteiristics can be fitted by a Schottky emission mechanism at low electrical fields and by a SCLC(Space Charge Limited Conduction) model for high elctrical fields. Data obtained from C-V measurements confirm the proposed model.

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.

Electrically actuated microfluidic biosensors: A novel silicon 48 microwells device for biosensing applications

In this paper, we described a miniaturized microfluidic device able to electro-loading small volumes (200nl) of biologic samples via ElectroWetting on Dielectric (EWoD) actuation and detect DNA via polymerase chain reaction (PCR). The miniaturized silicon-based chip contains 48 microchambers properly chemically treated for EWOD process. The device was designed to contain also integrated temperature sensors and heaters for the thermal cycling of PCR (Polymerase Chain Reaction) reaction. The system here proposed is a very appealing potential solution for genetic point-of-care (PoC) applications.