Ge dots embedded in Si offer the possibility of Si-based light detection at 1.3-1.55 μm. In this communication, we report a very efficient photo-detector based on a Si/SiGe heterojunction bipolar transistor structure with 10 Ge dot layers (8 ML Ge each) incorporated in the basecollector junction. The device structures were grown using low-temperature molecular beam epitaxy, and fabricated for both normal and edge incidence with no electrical contact to the base. The processed Ge-dot transistor detectors revealed a rather low dark current density, 0.01 mA/cm2 at -2 V. Photoconductivity measurements were performed at room temperature. At 1.31 μm, responsivity values of 50 mA/W at normal incidence have been directly measured at Vce = -4 V, without involving any rescaling factor due to light coupling. This value is a ∼250-fold increase compared to a reference p-i-n diode with the same dot layer structure, due to the current amplification function of the transistor. For a rib waveguide device, a very high responsivity value of about 470 mA/W (Vce = -4V) has been obtained at 1.31 μm. Measurements were also performed at 1.55 μm, and the photo-response of the waveguide phototransistor was 25 mA/W, which is again a large improvement compared with the reference waveguide photodiode (∼1 mA/W). Moreover, time-resolved photoconductivity measurements have been carried out. The results have indicated that the device frequency performance is primarily limited by the emitterbase junction capacitance.

Two distinct mechanisms for the endotaxial growth of quantum dots in the Sn/Si system were observed by means of analytical transmission electron microcopy. Both mechanisms operate simultaneously during temperature and growth rate modulated molecular beam epitaxy combined with ex situ thermal treatments. One of the mechanisms involves the creation of voids in Si, which are subsequently filled by Sn, resulting in quantum dots that consist of pure α-Sn. The other mechanism involves phase separation and leads to substitutional solid solution quantum dots with a higher Sn content than the predecessor quantum well structures possess. In both cases, the resultant quantum dots possess the diamond structure and the shape of a tetrakaidecahedron. (Sn,Si) precipitates that are several times larger than the typical (Sn,Si) quantum dot possess an essentially octahedral shape.

Although silicon is known as a poor emitter of light, recent work has demonstrated silicon light emission efficiencies in the range normally associated with III-V semiconductors. The present paper explores the light emission efficiency potential of silicon as well as the scope for implementing silicon optical functions into high density integrated circuits.

Prospects of laser operation in erbium doped silicon has been analyzed by a Shockley-Read-Hall (SRH) model. Erbium atoms have been considered to be introducing strong recombination centers in the silicon lattice. Electron-hole recombination at these sites were considered to be the source of erbium excitation. A two level system was considered for calculation of optical gain and the laser threshold. For a laser cavity of 300 μm with mirror reflectivities of 90%, and an optimistic absorption coefficient of 5 cm-1, a population inversion of 1.4×1018/cm3 was estimated as the threshold value. Achievement of the lasing condition was found feasible, but only for certain conditions of erbium activation. Effects of nonradiative deexcitation routes have been analyzed. On the assumption of 1019/cm3 of active erbium sites, linear increase of optical power in the laser cavity has been estimated for injected carrier densities above 1018/cm3.

The performance of poly-Si0.7Ge0.3 as a thermo-electric material that is fully process compatible with IC fabrication in silicon been fully analyzed and characterized. The application is in on-chip thermal stabilization of a micromachined platform in silicon. A Seebeck coefficient α= -174 μV/K and a figure of merit z= 0.173 has been obtained for n-type material. Measurements indicate a cooling capability of 2.1 K below ambient temperature.

The effects of annealing time on continuous-wave (CW) and nanosecond time-resolved (TR) photoluminescence (PL) spectra of silicon-ion-implanted Borosilicate glass (BSO:Si+) annealing at 500°C are characterized. A broadband CWPL of the as-implanted BSO:Si+ at 450-530 nm is observed, and the luminescent peak is found to slightly red-shift after annealing for 90 min. The increasing CWPL intensity reveals that the natural oxygen vacancy (NOV, ΞSi Si-SiΞ) related irradiative defect is highly activated during 30-min annealing, however, which abruptly decreases with the annealing lengthens to 60-min or longer. The TRPL analysis indicates a non-radiative recombination process with a sub-picosecond lifetime for the blank BSO and the as-implanted BSO:Si+ samples, which gradually disappears as the BSO:Si+ is long-term annealed. The irradiative luminescent lifetime of the 60-min annealed BSO:Si+ is lengthened from 1.7 ns to 2.8 ns, which reveals that the density of the NOV defect is decreasing by at least one order of magnitude. A longer irradiative decay with nearly identical lifetime is also found in all annealed BSO:Si+. The ratios of TRPL peak intensities for different samples correlate well with those observed in CWPL measurement, however, the weighting factors of TRPL intensities for the latter two decaying components are vicissitudinous each other in different samples BSO:Si+. This interprets a significant evolution among different decaying mechanisms during the annealing process.

Hydrogen passivation of non-radiative defects increases the luminescence intensity from silicon nanocrystals. In this study, photoluminescence (PL) and time-resolved PL were used to investigate the chemical kinetics of the hydrogen passivation process. Isochronal and isothermal annealing sequences were used to determine the reaction kinetics for the absorption and desorption of hydrogen, using the generalised consistent simple thermal (GST) model proposed by Stesmans for Pb defects at planar Si/SiO2 interfaces. This included determination of the activation energies and rate constants for the forward and reverse reactions as well as the associated spread in activation energies. The reaction kinetics determined from such measurements were found to be in excellent agreement with those for the passivation of Pb defects at planar Si/SiO2 interfaces, suggesting the nanocrystal emission process is also limited by such defects. These results provide useful model data as well as insight into the processing conditions needed to achieve optimum passivation in H2. As an extension to the work, a preliminary study into passivation by atomic hydrogen was pursued via a post-metallization Al anneal (alneal). A considerable gain in luminescence efficiency was achieved over the previously optimised passivation in H2.

An entirely new method to fabricate optically active and carrier-mediated excitable erbium complexes on silicon is presented. The Er-Si-O nano-complexes are formed by spin-coating a Si (100) substrate with an ErC13 solution, followed by a rapid thermal oxidation and annealing sequence (RTOA). Intense room-temperature luminescence is observed from the Er-Si-O nano-complexes, with a line width as narrow as 4 meV at room temperature. The Er emission at 1.53 μm can be excited both directly and through photo carriers. Formation and optical activation of the Er-Si-O nano-complexes are discussed. In addition, an application of the wet chemical synthesis technique to incorporation of the Er-Si-O nano-complexes into nano-porous silicon waveguides is demonstrated.

In the present work, a quantitative understanding of the Er-doped Si nanocrystals interaction is reported. We present a model based on an energy level scheme taking into account the coupling between each Si nanocrystal and the neighboring Er ions. By fitting the steady state and time resolved luminescence signals at both the 1.54 and 0.98 μm Er lines we were able to determine a value of 3×10-15 cm3 s-1 for the coupling coefficient. Moreover, a strong cooperative up-conversion mechanism, active between two excited Er ions and characterized by a coefficient of 7×10-17 cm3 s-1, will be shown to be active in the system, demonstrating that each Si nanocrystal can actually excite more than one Er ion.

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).

We report on efficient electronic energy transfer from excitons confined in silicon (Si) nanocrystals to molecular oxygen (MO). The remarkable photosensitizing properties of Si nanocrystal assemblies result from a broad energy spectrum of photoexcited excitons, a long triplet exciton lifetime and a highly developed surface area. Quenching of photoluminescence (PL) of Si nanocrystals by MO physisorbed on their surface is found to be most efficient when the energy of excitons coincides with the triplet-singlet splitting energy of oxygen molecules. Spectroscopic analysis of the quenched PL spectrum evidences that energy transfer is accompanied by multi-phonon emission. From time-resolved measurements the characteristic time of energy transfer is found to be in the range of microseconds. The dependence of PL quenching efficiency on the surface termination of nanocrystals is consistent with short-range resonant electron exchange mechanism of energy transfer. The energy transfer to oxygen molecules in the gaseous phase at elevated temperatures is demonstrated.

Europium oxide has been doped into sodium borosilicate (NBS) glasses (8Na2O-32B2O3- 60SiO2- xEu2O3) at various concentration levels. The glass raw materials were calcined at 800°C and melted at 1380°C and transparent glasses with slightly red color were obtained by quenching the melt in air. Thermal analyses and other experimental results showed excellent glass forming capability with Tg around 480 to 520°C at various doping concentrations. A typical deformation temperature of the europium-doped NBS glasses is around 570-660°C with densities around 2.45 to 2.6 g/cm3. The doped NBS glasses were further heat-treated at 560°C for phase-separation. Scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), thermomechanical analysis (TMA), optical absorption spectrometer and fluorescence emission spectrometer were used to explore properties of the glasses.

We study sensitization of the 4I13/2 – 4I15/2 Er3+ luminescence at 1.54 μm in silicon-rich silicon oxide (SRSO) in the whole range of blue-green pump wavelengths. We show that, in general, defects due to excess Si in silica act as luminescence sensitizers. They cause a wide excitation band with a long wave length limit of 600 nm. For monochromatic excitation the maximum luminescence yield is still smaller than for resonant excitation within the 4f shell of Er without additional Si. The large enhancement of the excitation cross section for electrical excitation reported in the literature is plausible, however, as the wide excitation band makes good use of the wide energy distribution of hot carriers. We suggest that the dominant factors, which limit the excitation efficiency of Er3+, are distance dependence of the transfer rate and little spectral overlap of the interacting states.

Si nanocrystals (Si-nc) embedded in amorphous silica matrix have been obtained by thermal annealing of substoichiometric SiOx films, deposited by PECVD (plasma enhanced chemical vapour deposition) technique with different amount of Si concentrations (42 and 46 at.%). Both nucleation and evolution of Si-nc together with the changes of the amorphous matrix have been studied as a function of the annealing temperature. The comparison of x-ray absorption measurements in Total Electron Yield (TEY) mode at the Si k-edge with photoluminescence (PL), FTIR and Raman spectra, allowed clarifying the processes of Si-nc formation and structural evolution as a function of the annealing temperature and Si content.

Sensitization of Er3+ photoluminescence in SiO2 layers by silicon nanocrystals has been investigated under resonant and nonresonant pulsed optical pumping. We observed that the very efficient channel of erbium excitation introduced by the nanocrystals can be saturated when very high pulsed photon flux is used. While this channel is saturated, tuning to the resonant excitation wavelength results in an increase of erbium-related photoluminescence, indicating that direct and indirect excitations can take place simultaneously.

Time-resolved variable stripe length (VSL) experiments on a set of silicon nanocrystal waveguides obtained by plasma enhanced chemical vapor deposition (PECVD) have revealed a fast recombination dynamics (20 ns) related to population inversion under 6 ns optical pumping at 355 nm. Modal gain values about 10 cm-1 have been measured at 760 nm by VSL technique for the fast recombination component while optical losses about 15 cm-1 are measured for the integrated signal in the slow (lifetime of about 10 μs) recombination tail. Threshold behavior in the emission intensity together with a pumping length and pumping power dependence of both the intensity and the time duration of the fast recombination component has been observed. These results are explained within an effective four level model to describe the strong competition among different Auger processes and stimulated emission.

Si nanocrystals (NCs) consisting of small crystals from 1 to 20 nm were formed by pulsedlaser deposition (PLD) in inert Ar gas and reactive O2 gas. The oxygen content of the Si NCs increases with increasing O2 ambient pressure and nearly SiO2 stoichiometry is obtained when O2 pressure is higher than 100 mTorr. The optical absorption of the Si NCs shows an indirect band transition. Broad PL spectra are observed from Si NCs. The peak position and intensity of the PL band at 1.8–2.1 eV are dependent on excitation laser intensity, while intensity changes and blue shifts are observed after oxidation and annealing. The PL band at 2.55 eV displays vibronic structures with periodic spacing of 97 ± 9 meV, while no peak shift is found before and after oxidation and annealing. The as-deposited Si NCs show a polycrystal structure and crystallinity improves after annealing. Combined with the PL of Si NCs obtained by crumbling electrochemical-etched porous Si layer, the results give strong evidence that the PL band at 1.8–2.1 eV is due to the quantum confinement effect (QCE) in Si NC core while the PL band at 2.55 eV is related to the localized surface states at SiOx/Si interface.

Interface formation in Yb/Si(111) system has been investigated by AES and EELS spectroscopy and in situ Hall measurements at room temperature. It was found that interface formation process may be divided into five stages: 1) two-dimensional growth of Yb, 2) intermixing and formation of two-dimensional Yb silicide, 3) formation of 3D silicide islands, 4) growth of Yb on 3D silicide islands, 5) coalescence of 3D Yb – Yb silicide islands and formation of continuos Yb film. We attribute the observed character of conductivity in Yb/Si(111) system to the evolution of morphological and electrical properties of the growing Yb layer (2D Yb, silicide, metal) rather than to the changes within the space charge layer under the surface. Some amplitude oscillations have been observed in sheet conductivity, hole mobility and surface hole concentration within the coverage range below 6 ML where formation of a continuos Yb silicide film completes. Conductivity oscillations are explained by transition from semiconductor-type conductivity at the first growth stages (two-dimensional Yb growth) to metal-like conductivity of 2D and 3D Yb silicide films.

In this presentation, we described a study on preparation and microstructure of Au (Ru) nano-particles embedded in SiO2 matrices, which were prepared as advanced display materials by using Sol-gel method. Both microstructure and composition of these micro/nano-particles composites were characterized by HRTEM (high resolution transmission electron microscope), EMP (electron microprobe) and nano-probe EDS (energy dispersive X-ray spectroscopy). Experimental results showed that the products have multi-levels in structure like nebulae. The aggregation of Au/Ru nano-particles can be extremely diminished by using SiO2 micro-particles as matrices. Distortions of the atomic lattices of Au and Ru nano-crystallites were often observed in the surface of these nano-particles. Moreover, nano-EDS measurements revealed that Au and Ru nano-particles are always separately embedded in SiO2 matrices, no alloy of them is observed.

We have exploited the interaction between erbium ions and silicon nanoclusters to produce a photodetector for use in the spectral region around 1.5 μm. The device consists of an MOS structure in which the oxide layer has been implanted with both erbium and silicon and annealed to produce silicon nanocrystals around 3 nm in diameter. Upon illumination with a 1480 nm laser diode, the well-known interaction between the nanocrystals and the rare-earth ions results in a transfer of excitation from the erbium ion to nearby silicon nanocrystals. The resultant modification of the conductivity of the oxide layer enables a current to flow when a voltage is applied.