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Stacking Faults (SFs) are the main defect of 3C-SiC material and in this work a detailed study of this typology of defect is presented. We studied the behavior of SFs with High Resolution XRD and STEM analysis. The homo-epitaxial growth was proposed as a solution for the reduction of SFs density in 3C-SiC material and the influence of the growth condition on the SFs density was studied. The knowledge of the mechanism of SFs reduction is crucial for the development of a high quality material for devices fabrication.

In this paper the influence of point defects generated by the ion implantation process in 4H-SiC DIMOSFET has been studied in detail. The point defects generated by the source or body implantation process have been detected by micro-photoluminescence and the effect of these defects on the electrical characteristics of the DIMOSFET has been studied. In particular it has been observed that a reduction of the source ion implanted dose produces a large reduction of point defects in the source region and a considerable improvement of the electrical characteristic of the DIMOSFET.

Ultraviolet (UV) monitoring is of great interest in the healthcare field to prevent excessive UV exposure risks. In the last years silicon carbide (SiC) has emerged as a suitable material for the fabrication of UV detectors. In this paper we propose a 4H-SiC Schottky photodiode with a continuous very thin Ni2Si layer operating at 0V, properly designed for UV radiation monitoring.

The on resistance increment observed when the device is operated at high drain-source voltages is one the topics that limits the performance of the AlGaN/GaN HEMT devices. In this paper, the physical mechanisms responsible of the RDSon degradation are investigated. The dynamic RDSon transient method is used in order to get insight to characterize the traps states. By calculating the Arrhenius plot associated with the RDSon transients an activation energy of 0.86eV was extracted, that can be correlated to the traps due to the incorporation of Carbon inside the buffer. This hypothesis was further supported by the analyses performed on a simpler structure (TLM). By applying a negative substrate bias the effect of only the buffer traps was studied. A fairly close value of the activation energy (0.9eV) to the one extracted when analyzing the RDSon transient was obtained.

Compound semiconductors (and mainly at the moment SiC and GaN) power devices have practically shown a quantum leap in the performances of power devices and the possibility to enlarge the use of power electronics at very high voltages, high temperature and high power. However, the status of SiC and GaN devices today is much less mature than that of Si power devices in terms of manufacturability, material quality, process control, cost and reliability. In this paper activities on SiC and GaN power devices at STMicroelectronics will be presented and the perspectives of a large adoption of compound semiconductors power devices highlighted.

We report on the fabrication and performance of Si-based light sources. The devices consist of MOS structures with erbium (Er)-doped silicon rich oxide (SRO) film as gate dielectric. The devices exhibit electroluminescence (EL) at 1.54 μm at room temperature with a 0.2% external quantum efficiency. These devices show a high stability due to the silicon excess in the film. The Er-doped SRO films have been introduced in a Si/SiO 2 Fabry–Perot Microcavity in order to increase the spontaneous emission rate, the extraction efficiency and the spectral purity at the resonant wavelength. The active medium in the cavity has been electrically pumped and the conduction mechanisms have been analyzed. The EL spectra have also been acquired and compared with photoluminescence (PL) ones for the same resonant cavity light-emitting device (RCLED). The EL and PL peak intensities of the on-axis emission at the resonant wavelength are over 20 times above that of the similar Er-doped SRO film without a cavity. The Si-based RCLEDs exhibit different quality factors, ranging from 60 to 170. The spectra shape and intensity have been correlated with the quality factor. A high directionality of the emitted light, due to the presence of the resonant cavity, has also been observed: the overall luminescence is confined within 10° cone from the sample normal.

Gene expression profiles are unveiling a wealth of new potential drug targets for a wide range of diseases, offering new opportunities for drug discoveries. The emerging challenge, however, is the effective selection of the myriad of targets to identify those with the most therapeutic utility. Numerical clustering has became a commonly used method to investigate and interpret gene expression data sets but it is often inadequate to infer the genes' and proteins' role and point to candidate genes for drug development. This review illustrates how clustering methods based on semantic characteristics, such as gene ontologies, could be used to extract more knowledge from genomic data and improve drug target and discovery processes.

We present our calculations of the optical absorption for dipole direct transitions in the tight binding zone folding scheme for single wall carbon nanotubes. We have applied the Fermi's golden rule by calculating the electric dipole matrix element and we provide an analytical expression for it. We have calculated the optical absorption of semiconducting zig-zag SWNTs equally distributed and with gaussian distribution of the diameters, where collisional broadening of the density of states was taken into account. The calculated behavior is in agreement with optical density measurements for SWNTs. Our analytical calculations will be useful for the analysis of the optical emission and absorption from single wall carbon nanotubes. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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. They exhibit strong 1.54 μm electro-luminescence (EL) at 300 K with a 10% external quantum efficiency, comparable to that of standard light emitting diodes using III–V semiconductors. Emission at different wavelengths has been achieved incorporating different rare earths (terbium (Tb) and ytterbium (Yb)) in the gate dielectric. The external quantum efficiency depends on the rare-earth ions incorporated and ranges from 10% (for a 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 silicon rich oxide (SRO) 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 partially by hot electrons and partially by energy transfer from the Si nanostructures to the rare-earth ions, depending on 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 fabricate a Si-based resonant cavity light emitting diode (RCLED). These structures are fabricated by chemical vapour deposition on a silicon substrate. The microcavities are tuned at different wavelengths (nm): 540, 980 and 1540 (characteristic emission wavelengths, respectively, for Tb, Yb and Er). The reflectivity of the microcavities is about 97% and the quality factor ranges from 60 (for the cavity tuned at 980 nm) to 95 (for the cavities tuned at 540 and 1540 nm).

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 SiO2 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.

We monitored the defect migration and interaction with impurities and dopant atoms using in situ (leakage current, I L ) and ex situ deep level transient spectroscopy (DLTS) techniques. n-Type and p-type Si samples were implanted with He or Si at energies of 0.04–10 MeV to doses of 10 9 –10 14 cm −2 and dose rates of 10 7 –10 12 cm −2 s −1 and the depth profiles of the room temperature (RT) stable complexes studied. Through I L we monitored defect diffusion effects in reverse biased junctions, during and after implantation and observed that I L is mostly given by vacancy-type defects in both n-type and p-type Si. When the implantation dose is above a threshold ( 2×10 13 He cm −2 for 1 MeV He) a strong difference arises in the defect generation in p-type Si, suggesting a different defect evolution due to the B presence.

Photodetection in the ultraviolet (UV) region has drawn extensive attention owing to its various applications in industrial, environmental, and even biological fields. In this letter, we report on the morphological and electro-optical characteristics of continuous thin metal film Ni 2 Si/4H-SiC photodiodes properly designed for the realization of an extremely compact digital sensor suited to measure the total sun UV radiation for environmental UV light monitoring.

The combination of BF 2 ion implantation and excimer laser annealing has been used to fabricate ultra-shallow junctions, with depths below 100 nm and high electrical activation. Secondary ion mass spectrometry and spreading resistance profiling analysis have been performed to investigate B atomic transport and electrical activation in these samples. The structural analysis of the material irradiated by excimer laser and of the corresponding samples annealed by conventional methods, was carried out by Transmission Electron Microscopy. The latter technique enabled us to detect the presence of microcavities, induced by the implanted fluorine, which are detrimental with respect to the electrical activation issue. We have found that the use of ion implantation and excimer laser annealing results in ultra-shallow junctions with an electrically active peak concentration higher than the levels normally achieved by conventional annealing cycles.

This paper reviews some fundamental aspects of point defect migration and agglomeration in crystalline Si. Both in-situ and ex-situ measurements were used to reach this target. Room temperature (RT) diffusivities of 1.5×10−15 and 3.0×10 −13 cm 2 / s for I and V, respectively, were obtained using in-situ leakage current measurements, performed during and just after ion implantation. To follow the defect evolution and clustering upon annealing, ex-situ optical and electrical measurements were used. Low temperature (300–500°C) annealing causes the formation of point-like defects, while higher temperatures (500–800°C) are necessary to have defect clustering. Finally, a well-defined dose (1×10 13 Si / cm 2 in pure Si) temperature (650°C) and time thresholds exist for the transition from I-clusters to extended {3 1 1} defects. When the transition takes place, both the optical and electrical defect properties undergo a dramatic change, suggesting an abrupt structural transition in the evolution from I-cluster to {3 1 1} defects. Kinetic lattice Monte-Carlo simulations used to model the defect agglomeration and growth confirm these results.

We have designed and fabricated novel Si-based optoelectronic devices. To this aim, different Si-based optical sources have been made and their performances at room temperature compared. Er-doped Si p–n junctions, operating at 1.54 μm and exhibiting an efficiency of 0.05% at room temperature, have been integrated with planar Si rib waveguides using either epitaxial Si or silicon on insulators (SOI) wafers. Optical characterization of these waveguides reveals very low transmission losses (below 1 dB/cm). However, Er-doping of the waveguide core, needed for the realization of the light source, results in a large increase of the losses as a consequence of absorption by the free electrons introduced by the rare earths. These losses can be suppressed when the junction is reverse biased and the whole Er profile is embodied in the depletion layer. Since this also allows efficient pumping of Er ions by hot carriers, the performances of the diodes and of the waveguides can be suitably combined. This optimized structure has also been used to design electrically pumped optical amplifiers and lasers, whose performances have been simulated.

Formation condition and annealing kinetics of self-interstitial (I) clusters in ion implanted Si have been investigated. Deep level transient spectroscopy (DLTS) and photoluminescence (PL) measurements were performed on both p-type Czochralski Si samples implanted with Si ions at energies ranging from 40 keV to 1.2 MeV. They reveal that I-clusters form for implantation fluences above 1012 cm−2 and annealing temperatures higher than 550°C. Analysis of the annealing kinetics at temperatures in the range 550–700°C reveals that I-clusters dissociate with an energy depending on the implantation dose. The characteristic dissociation energy is ∼2.3 eV for 1×1012 cm−2 implants, and this value increased towards the typical {311} extended defects dissociation energy value (∼3.8 eV) by increasing the implantation fluence. Finally, the transition from I-clusters to {311} defects was followed using PL and DLTS in combination with transmission electron microscopy analysis. A PL line at 1375 nm has been associated to {311} extended defects and a threshold dose and annealing temperature for the extended defects formation identified.

We have investigated the electrical transport and luminescence of Si dots embedded in SiO 2 . The dots have been obtained by high temperature annealing of silicon rich oxides prepared by chemical vapor deposition. Transmission electron microscopy analysis demonstrates the presence of crystalline Si dots with grain radii down to 1 nm. The data of luminescence and electrical transport appear correlated with the dot size distribution. Moreover, the analysis of the electrical characteristics of metal-oxide–semiconductor capacitors with silicon rich oxide films indicates that such systems may reversibly store charge, thus exhibiting the function of a memory.

We have investigated the electrical properties of terbium ions incorporated in crystalline Si. Silicon p+-n junctions were realized in n-type epitaxial or Czochralski-grown Si, having an O concentration of ∼1015 and 7×1017/cm3, respectively. These junctions were implanted with 5 MeV Tb ions to fluences in the range 6×1011–6×1012/cm2. Some epitaxial Si samples were also coimplanted with O in order to provide a concentration of ∼1018 O/cm3 in the region where Tb sits. Annealing at temperatures between 800 and 1000 °C and times ranging from 5 s to 30 min was performed. Deep-level transient spectroscopy, current–voltage, capacitance–voltage, and carrier lifetime measurements were used to characterize the levels introduced by Tb ions in the Si band gap. It is found that in a highly pure epitaxial Si, Tb introduces several donor levels at energies comprised between 0.15 and 0.53 eV from the conduction band. Interaction between Tb and O produces severe modifications in the distribution of deep levels related to ...

Formation, thermal evolution and annealing kinetics of self-interstitial clusters in ion implanted Si have been investigated. Deep level transient spectroscopy measurements performed on epitaxial and Czochralski Si samples implanted with Si ions at energies of 145 keV or 1.2 MeV reveal that these clusters are formed for fluences above 1012/cm2 and annealing temperatures higher than 550°C. Interstitial clusters introduce seven well defined levels in the Si band gap at EV + 0.33 eV, EV + 0.52 eV, EC − 0.58 eV, EC − 0.50 eV, EC − 0.37 eV, EC − 0.29 eV and EC − 0.14 eV. Analysis of the annealing kinetics at temperatures in the range 550–700°C reveal that the clusters undergo Ostwald ripening and anneal out with a characteristic dissociation energy of ∼2.3 eV for a Si fluence of 1 × 1012/cm2. Furthermore, their annealing temperature increases with implantation fluence. These results indicate that small interstitial clusters act as the source of interstitial supersaturation that drive transient enhanced dopant diffusion in the absence of extended defects.

We have analyzed the room temperature migration properties of ion beam generated self-interstitials and vacancies in crystalline Si using deep level transient spectroscopy and in situ leakage current measurements. Silicon p+-n junctions, formed by B diffusion in n-type epitaxial Si wafers, were implanted at room temperature with 2.5 MeV He ions to fluences in the range 1×10 9 –1×10 12 cm −2 . Diodes were reverse biased and leakage current was measured both during and immediately after ion implantation. At the beam turn-off, leakage current decreases by about a factor of 2 in times as long as few days. Ex situ deep level transient spectroscopy measurements show that the main contribution to leakage current is given by vacancy-type defects, i.e. phosphorous-vacancy and divacancy complexes. Hence, the leakage reduction at the beam turn off has been associated to the recombination of vacancy clusters by residual free interstitials. Assuming a diffusion limited recombination process, a value of 1.5×10−15 cm2/s has been determined for the interstitial diffusivity. When the dose rate of the beam is increased, a faster transient, lasting up to 1000 s, is revealed by the in situ measurements and it has been tentatively associated with the annihilation of residual free vacancies by migration to interstitial sinks or by trapping at impurity atoms (O, C).

Erbium implantation in silicon has recently emerged as a promising method to tailor the optical properties of Si towards the achievement of a light emission at 1.54 μm. In this paper we will review our recent work on this subject. In particular a detailed investigation of the non-radiative processes, competing with the radiative emission of Er in Si will be presented. Among these processes, an Auger de-excitation with the energy released to free carriers will be demonstrated to be extremely efficient, with an Auger coefficient C A ~4.4×10 −13 cm 3 s −1 . Using the knowledge on the material properties, an efficient Er implanted light emitting diode has been fabricated. It will be shown that by exciting Er within the depletion region of reverse biased p + -n + Si diodes in the breakdown regime it is possible to avoid Auger quenching and to achieve high efficiency. Moreover, at the switch off of the diode, when the depletion region shrinks, the excited Er ions become suddenly embedded within the neutral heavily doped region of the device. In this region Auger de-excitation with free carriers sets in and quenches the luminescence rapidly. This allows modulation of the light emitting devices at frequencies as high as a few MHz. These data will be presented and discussed.

The enormous progress of communication technologies in the last years has increased the demand for efficient and low-cost optoelectronic functions. For several present and future applications, photonic materials—in which light can be generated, guided, modulated, amplified, and detected—need to be integrated with standard electronic circuits in order to combine the information-processing capabilities of electronics data transfer and the speed of light. Long-distance communications, local-area-networks data transfer, and chip-to-chip or even intrachip optical communications all require the development of efficient optical functions and their integration with state-of-the-art electronic functions. Silicon is the material of choice for reliable and low-cost optoelectronic integrated circuits because it is the leading semiconductor in the electronic arena and since a wellestablished processing technology exists for this material. However Si is characterized by an indirect bandgap and by a weak electro-optic effect. It is therefore not suitable for the implementation of fundamental optical functions such as light emission and modulation. At the moment, hybrid integration of compound-semiconductor optical functions with Si electronic functions is providing the gateway from electronic to photonic technology. However several strategies are being considered to engineer the optical functions of Si and to realize fully Si-based or at least Si-compatible optoelectronics.

A detailed investigation on the excitation and deexcitation processes of ${\mathrm{Er}}^{3+}$ in Si is reported. In particular, we explored Er pumping through electron-hole pair recombination and Er deexcitation through Auger processes transferring energy to either free or bound electrons and holes. Since Er donor behavior would result in a free-carrier concentration varying along its profile, experiments have been performed by embedding the whole Er profile within previously prepared $n$-doped or $p$-doped regions. Multiple P (B) implants were performed in $n$-type ($p$-type) Czochralski Si samples in order to realize uniform dopant concentrations from $4\ifmmode\times\else\texttimes\fi{}{10}^{16}$ to $1.2\ifmmode\times\else\texttimes\fi{}{10}^{18}/{\mathrm{cm}}^{3}$ at depths between 0.5 and 2.5 \ensuremath{\mu}m below the surface. These samples have been subsequently implanted with 4 MeV $3.3\ifmmode\times\else\texttimes\fi{}{10}^{13}{\mathrm{E}\mathrm{r}/\mathrm{c}\mathrm{m}}^{2}$ and annealed at 900 \ifmmode^\circ\else\textdegree\fi{}C for 30 min. Free electrons or holes concentrations in the region where Er sits were measured by spreading resistance profiling. It has been found that the release of electrons or holes from shallow donors and acceptors, occurring at temperatures between 15 and 100 K, produces a strong reduction of both time decay and luminescence intensity at 1.54 \ensuremath{\mu}m. These phenomena are produced by Auger deexcitation of the ${\mathrm{Er}}^{3+}$ intra-$4f$ electrons with energy transfer to free carriers. The Auger coefficient of this process has been measured to be ${C}_{A}\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}{\mathrm{cm}}^{3}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ for both free electrons and free holes. Moreover, at 15 K (when the free carriers are frozen and the donor and acceptor levels occupied) the ${\mathrm{Er}}^{3+}$ time decay has been found to depend on the P (or B) concentrations. This is attributed to an impurity Auger deexcitation to electrons (or holes) bound to shallow donors (acceptors): the efficiency of this process has been determined to be two orders of magnitude smaller with respect to the Auger deexcitation with free carriers. Furthermore, at temperatures above 100 K a nonradiative back-transfer decay process, characterized by an activation energy of 0.15 eV, is seen to set in for both $p$-type and $n$-type samples. This suggests that the back-transfer process, which severely limits the high-temperature luminescence efficiency, is always completed by a thermalization of an electron trapped at an Er-related level to the conduction band. Finally, by analysis of the pump power dependence of time decay and luminescence yield at 15 K, we have found that excitation of Er through the recombination of an electron-hole pair is a very efficient process, characterized by an effective cross section of $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}{\mathrm{cm}}^{2}$ and able to provide an internal quantum efficiency as high as 10% at low temperatures (15 K) and pump powers (below 1 mW). This efficiency is significantly reduced when, at higher temperatures and/or high pump powers, strong nonradiative decay processes set in. These phenomena are investigated in detail and their impact on device operation perspectives are analyzed and discussed.

We have investigated the role of the metal-semiconductor back contact on the performances of thin film modules consisting of single junction a-Si:H photovoltaic (PV) cells deposited with p-i-n configuration. We find that an adequate choice of the back contact helps reducing the barrier height of the junction improving the contact conductivity. For this purpose Mo has shown to be effective. Moreover we find that Mo, as refractory material, has additional beneficial effects reducing the formation of defects leading to the decrease of recombination losses. We have then fabricated a PV module on flexible substrate for indoor energy harvesting applications using Mo as back contact. An efficiency of 6% is obtained at 300 lux under F12 spectrum illumination.

We have investigated the transition from small interstitial clusters to {311} defects in ion-implanted Si. Czochralski Si wafers were implanted with 1.2 MeV Si ions to fluences in the range 1012–5×1013/cm2 and annealed at temperatures of 600–750 °C for times as long as 15 h. Photoluminescence and transmission electron microscopy analyses allowed us to analyze the transition of small interstitial clusters, formed by the agglomeration of the excess interstitials introduced by the beam, into {311} defects. It is found that {311} defects form only at fluences ⩾1013/cm2 and at temperatures above 600 °C. When {311} are observed in transmission electron microscopy, the luminescence spectrum is dominated by a sharp signal at 1376 nm which has been correlated with optical transitions occurring at or close to these defects. At lower temperatures or at lower fluence, no extended defects are observed in transmission electron microscopy and the luminescence spectrum present two broad signatures arising from carrier re...

In this work, we report on the improvement of microarray sensitivity provided by a crystalline silicon substrate coated with thermal silicon oxide functionalized by a polymeric coating. The improvement is intended for experimental procedures and instrumentations typically involved in microarray technology, such as fluorescence labeling and a confocal laser scanning apparatus. The optimized layer of thermally grown silicon oxide (SiO(2)) of a highly reproducible thickness, low roughness, and fluorescence background provides fluorescence intensification due to the constructive interference between the incident and reflected waves of the fluorescence radiation. The oxide surface is coated by a copolymer of N,N-dimethylacrylamide, N-acryloyloxysuccinimide, and 3-(trimethoxysilyl)propyl methacrylate, copoly(DMA-NAS-MAPS), which forms, by a simple and robust procedure, a functional nanometric film. The polymeric coating with a thickness that does not appreciably alter the optical properties of the silicon oxide confers to the slides optimal binding specificity leading to a high signal-to-noise ratio. The present work aims to demonstrate the great potential that exists by combining an optimized reflective substrate with a high performance surface chemistry. Moreover, the techniques chosen for both the substrate and surface chemistry are simple, inexpensive, and amenable to mass production. The present application highlights their potential use for diagnostic applications of real clinical relevance. The coated silicon slides, tested in protein and peptide microarrays for detection of specific antibodies, lead to a 5-10-fold enhancement of the fluorescence signals in comparison to glass slides.

We have determined the room-temperature diffusivity of self-interstitials and vacancies in Si. Silicon p+−n junctions were realized in n-type epitaxial Si wafers, having an O and C content ⩽1015/cm3, and implanted at room temperature with 2.5 MeV He ions to fluences in the range 1×109–1×1012/cm2. The junctions were reverse biased at −30 V, in order to embody the entire damage profile of the ion in the depletion layer, and in situ leakage measurements were performed during and just after implantation. It is found that the leakage current increases monotonically during implantation while, at the beam turn off, it decreases by about a factor of 2 for times as long as 1 day. Ex situ deep level transient spectroscopy measurements show that the main contribution to leakage current is due to the deep levels introduced in the band gap by phosphorous–vacancy and divacancy complexes. This allowed us to associate the leakage current reduction at the beam turn off to the recombination of vacancy-type complexes by res...

We provide direct evidence that Er ions incorporated in the depletion layer of a p+–n+ Si junction are efficiently pumped through an impact excitation process with hot carriers. The carriers were accelerated by the electric field present in the depletion layer after being produced by either Zener breakdown of the junction at ∼5 V or by irradiating the diode with an argon laser. Measurements of the electroluminescence yield at 1.54 μm as a function of the reverse bias voltage (and for a constant current through the device) reveal that excitation of Er only occurs at voltages above 1 V, demonstrating that impact is the pumping mechanism. Moreover, we have found that Er ions are only excited within ∼15 nm from the edges of the depletion layer leaving a dark, ∼50 nm thick, region in the central part of the depletion region. Monte Carlo calculations confirmed that only close to the depletion layer edges the energy gained by the carriers in the electric field is high enough to impact excite Er.

We fabricated and characterized an electro-optic Si-based amplitude light modulator working at 1.5 μm. It is a Bipolar Mode Field-Effect transistor (BMFET) integrated within a Si rib waveguide. The devices, 100 μm long, were fabricated using epitaxial Si wafers and standard clean room processing. The light is absorbed during its travel in the device optical channel when a plasma of free carriers, electrically driven, is generated and placed inside the channel. We experimentally monitored the plasma formation and localization in the device using standard Emission Microscopy analysis. The optical characterization in static conditions provides a modulation depth of ~ 90%, well above the 25% minimum required to consider a device a modulator. Furthermore, dynamical measurements show a modulation depth of 65% at 100KHz of operation frequency. Finally, an experimental evidence of a frequency threshold, at about 500 KHz, is observed in the plasma behavior. Theoretical considerations and experimental data suggest that at frequencies below threshold the dominant phenomenon is the plasma generation/recombination, while above threshold the carrier drift leads the plasma motion and redistribution in the device channel.

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.

We report on the fabrication and characterization of Si/SiO 2 Fabry-Perot microcavities. These structure 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: 540 nm, 980 nm, 1540 nm, 780 nm and 850 nm (characteristic emission wavelength respectively for Tb, Yb and Er and Silicon Rich Oxide (SRO)). The reflectivity of the microcavities is of 97% and the quality factor ranges from 50 (for the cavity tuned at 540nm) to 95 (for the cavities tuned at 980 nm and 1540 nm) and 150 (for the cavity tuned at 780 nm and 850 nm). These cavities have been characterized by TEM analysis to evaluate film 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.

The multigenic program underlying neuronal apoptosis is mostly unknown. To study the program, we used genome-scale screening by oligonucleotide microarrays during serum and potassium deprivation-induced apoptosis of cerebellar granule neurons. From the 8740 genes interrogated by the arrays, 423 genes were found to be regulated at both the transcriptional and the posttranscriptional level and segregated into distinct clusters. Semantic clustering based on gene ontologies showed coordinated expression of genes with common biological functions and metabolic pathways. Among the genes implicated in apoptotic cerebellar granule neurons, 70 were in common with those differentially expressed in cortical neurons exposed to amyloid beta-protein, indicating the existence of common mechanisms responsible for neuronal cell death. Our results offer a genomic view of the changes that accompany neuronal apoptosis and yield new insights into the underlying molecular basis.

Bacterio-rhodopsin purple membrane (PM) thin films have been prepared by selfassembling (SA) technique. Morphological properties of the layers were inspected by Scanning Electron Microscopy (SEM) and Scanning Force Microscopy (SFM) highlighting the presence of densely packed PM films. Reflectance Uv-vis spectra on these films revealed the typical bR absorption at 570 nm. By using a tungsten lamp illuminations (250-350 mW) chopped at 0.5Hz, photoelectric responses were detected. Differential (light-on and light-off) photocurrent signals of up to 1 μA/cm2 were obtained upon light exposure.

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/SiO2 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).

The implementation of efficient Si optical functions has attracted a considerable interest in the last years since it would allow the use of Si technology for the realisation of integrated optoelectronic (OE) devices. We have fabricated and characterised a novel Si-based light modulator working at the standard communication wavelength of 1.54 mum. It consists of a three terminal Bipolar Mode Field Effect Transistor (BMFET) integrated in a silicon rib waveguide realised on epitaxial (epi) Si wafers. The optical channel of the modulator is embodied within its vertical electrical channel. Light modulation is obtained through the formation of a plasma of carriers, inside the optical channel, that produces an increase of the absorption coefficient. Modulation is achieved by moving the plasma inside and outside the optical channel by properly changing the bias of the control electrode. The devices have been fabricated using clean room processes fully compatible with ULSI technology. Electrical characterisation shows a strong channel conductivity modulation. Optical measurements confirm the plasma formation in the channel. The distribution of the plasma under different bias conditions has been directly derived from Emission Microscopy analysis. The devices exhibit modulation depths ranging from 68% up to 83% depending on the bias conditions.

The implementation of efficient Si-based optical functions has attracted a considerable interest in the last years since it would allow the use of the Si technology for the realization of integrated optoelectronic devices. We have fabricated and characterized a novel Si-based light modulator working at the standard communication wavelength of 1.54 micrometers . It consists of a three terminal Bipolar Mode Field Effect Transistor integrated with a silicon RIB waveguide on epitaxial Si wafers. The optical channel of the modulator is embodied within its vertical electrical channel. Light modulation is obtained through the formation of a plasma of carriers, inside the optical channel, that produces an increase of the absorption coefficient. Fast modulation is achieved by moving the plasma inside and outside the optical channel by properly biasing the control electrode. The devices have been fabricated using clean room processing. Detailed electrical characterization and device simulation confirm that strong conductivity modulation and plasma formations in the channel are achieved. The plasma distribution in the device under different bias conditions has been directly derived from Emission Microscopy analysis. The expected device performances in terms of modulation depth and speed will be presented and discussed.

In many applications the need of galvanic isolation for safety or functional requirements is very high. In this paper a new isolated opto-coupler device concept is presented. Our approach combines an isolation technology with the integration of a silicon-based optical transmission system. This new concept enhances design, flexibility, performances and reliability of the devices, resulting in space and cost saving. In the first section two isolation technologies will be presented. Subsequently, the transmission system will be elucidated. At last a case of application in the field of power devices will be presented.

During the last decade, many studies have addressed the use of synthetic diamond as sensing material for deep UV photon detection. Solar missions, as the Solar Orbiter and the Solar Probe will require UV photon detectors with unprecedented sensitivity at wavelengths (lambda) 230 nm and 107 above 400 nm), its very low dark current level avoids the use of cooling systems, has a high UV responsivity and it is radiation hard and chemically inert. This paper is a review of our recent results on the electro- optical properties of diamond and a comparative analysis and characterization of the performances of different diamond- based photodetectors in the vacuum UV. In addition, we will describe some of the photodetectors that are under development for space applications and that will exploit the properties of diamond.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We review the results of several experiments aimed to elucidate the thermal evolution of the self-interstitial excess introduced by Si-ion implantation in crystalline Si. Deep-level transient spectroscopy and photoluminescence measurements were used to monitor how those interstitials are stored into stable point-like defect structures just after implantation, evolve into defect clusters upon annealing at intermediate temperatures, and are annealed out, releasing the stored self-interstitials upon annealing at larger temperatures. It is shown that although dopant atoms and impurities (C and O) are not the main constituents of these clusters, the impurity content has a large effect on the early stage of cluster formation, at low fluence and low temperatures, and can affect their dissociation kinetics. A stable residual damage, electrically characterized by two signatures at ${E}_{v}+0.33\mathrm{eV}$ and ${E}_{v}+0.52\mathrm{eV}$ and exhibiting two broad signatures in the photoluminescence spectrum, is present for doses $g~{10}^{12}/{\mathrm{cm}}^{2}$ and annealing $g~600\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ This residual damage, formed by interstitial clusters, is stable to temperatures as high as $750\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and anneals out with an activation energy of \ensuremath{\sim}2.3 eV. It is suggested that these clusters store the interstitials that drive transient enhanced diffusion at low implantation doses and/or low temperatures, when no extended defects are formed. Finally, when {311} extended defects form the luminescence spectrum is dominated by a sharp signal at 1376 nm, which we correlate with optical transitions occurring at or close to these defects. Dose and temperature thresholds for the transition from small clusters to extended defects have been observed and will be discussed.

We present an ‘on lattice’ Monte Carlo study of defect clustering in a Si matrix. The simulations are based on local interaction models, which allows us to reliably include the energetics of defects obtained by tight binding molecular dynamic calculations. In particular the dependence of cluster stability and reactivity on cluster size and geometrical configuration is considered. Proper accelerated algorithms have been implemented in order to extend simulations to macroscopic time scales. Our simulations show that the stability of specific cluster configurations strongly affects the kinetic evolution of the defect ensemble.

The use of graphene grown by chemical vapor deposition to fabricate solution-gated field-effect transistors (SGFET) on different substrates is reported. SGFETs were fabricated using graphene transferred on poly(ethylene 2,6-naphthalenedicarboxylate) substrate in order to study the influence of using a flexible substrate for pH sensing. Furthermore, in order to understand the influence of fabrication-related residues on top of the graphene surface, a fabrication method was developed for graphene-on-SiO2 SGFETs that enables to keep a graphene surface completely clean of any residues at the end of the fabrication. We were then able to demonstrate that the electrical response of the SGFET devices to pH does not depend either on the specific substrate on which graphene is transferred or on the existence of a moderate amount of fabrication-related residues on top of the graphene surface. These considerations simplify and ease the design and fabrication of graphene pH sensors, paving the way for developing low cost, flexible, and transparent graphene sensors on plastic. We also show that the surface transfer doping mechanism does not have significant influence on the pH sensing response. This highlights that the adsorption of hydroxyl and hydronium ions on the graphene surface due to the charging of the electrical double layer capacitance is responsible for the pH sensing mechanism.