Integration of photonic devices on silicon (Si) substrates is a key method in enabling large scale manufacturing of Si-based photonic–electronic circuits for next generation systems with high performance, small form factor, low power consumption, and low cost. Germanium (Ge) is a promising material due to its pseudo-direct bandgap and its compatibility with Si-CMOS processing. In this article, we present our recent progress on achieving high quality germanium-on-silicon (Ge/Si) materials. Subsequently, the performance of various functional devices such as photodetectors, lasers, waveguides, and sensors that are fabricated on the Ge/Si platform are discussed. Some possible future works such as the incorporation of tin (Sn) into Ge will be proposed. Finally, some applications based on a fully monolithic integrated photonic–electronic chip on an Si platform will be highlighted at the end of this article.

A system combining photovoltaic (PV) and solar thermal approaches is designed to convert solar energy to electricity with high efficiency across the full solar spectrum. Concentrated solar spectrum is split into two parts: PV and thermal. The PV part of the spectrum is further split into several subbands directed to bandgap appropriate solar cells on an inexpensive Si substrate. Epitaxial Ge on Si is used as a virtual substrate for III-V semiconductor growth. At long and very short wavelengths where PV efficiency is low, solar radiation is directed to a high temperature thermal storage tank for electricity generation using heat engines. The potential of using PV waste heat due to thermalization of high energy photoelectrons for electricity generation is also investigated. Detailed optical and thermal analysis show that with optimized design and neglecting optical component loss, system power conversion efficiency can reach 56%, including more than 16% absolute contribution from thermal storage.

A compact, single element concentrator comprising a near linear array of prisms has been designed to simultaneously split and concentrate the solar spectrum. Laterally aligned solar cells with different bandgaps are devised to be fabricated on a common Si substrate, with each cell absorbing a different spectral band optimized for highest overall power conversion efficiency. Epitaxial Ge on Si is used as a low cost virtual substrate for III-V materials growth. Assuming no optical loss for the prism concentrator, no shadowing and perfect carrier collection for the solar cells, simulations show that 39% efficiency can be achieved for a parallel four-junction (4PJ) InGaP-GaAs-Si-Ge cell under 200X concentration, and higher efficiency is possible with more junctions.

We characterized the optical nonlinearities of CdSe nanocrystals surrounded by rod-like CdS shells with ultrafast measurements of time-resolved photoluminescence. We measured the exciton-exciton interaction to be, depending on structure details, attractive or repulsive, by as much as 29 meV, due to the unique band alignment in the CdSe/CdS. This feature makes CdSe/CdS dot/rods promising gain media for solution-processable lasers, as it appears combined with 80% photoluminescence quantum yield, narrow size and shape distributions and the antenna effect of the CdS rod shell enhancing optical absorption by more than a factor 50 with respect to bare dots.

This study concerns the acquisition of the meaning of adversative connectives in French and German children from 7; 8 to 9; 11. French mais has both a substitutive and a contrastive use which is expressed by two different connectives in German, i.e. sondern and aber. 36 French and 36 German children were tested in a completion and a judgement task. Two hypotheses are confirmed: (a) substitutive but is easier to process and hence is acquired earlier than contrastive but; (b) the interpretation of contrastive but-sentences depends on their inferential complexity relative to a given context. A third assumption about the facilitative effect of lexical differentiation in German was only partially supported by the data. This issue needs further investigation with more languages and younger children.

Superior caval venous syndrome is one of the late problems known to occur after Mustard repair of complete transposition. Reoperation may leave residual stenosis, and carries substantial risk for the patient. It is now feasible to use intravascular stents to overcome systemic venous baffle obstructions, and such an approach is probably more effective. The purpose of our study therefore, was to assess immediate and medium term results of inserting stents subsequent to gradual balloon enlargement of acquired atresia of the intraatrial baffle in patients who had undergone an atrial switch operation. We investigated five patients with complete obstruction of the superior caval venous pathway at perforation of the atretic segment was achieved using a guide wire technique. The procedure was successful in all patients. Gradual angioplasty was performed and intravascular stents were implanted. The pressure in the superior caval vein dropped to normal values, symptoms improved, and the patency of the newly created venoatrial communication was proven at mid-term follow-up. Thus critical obstructions at the superior caval venous pathway after the Mustard procedure can be reopened by interventional catheterization. Implantation of balloon-expandable intravascular stents is safe and effective in the acute relief of the obstructions, but careful long-term follow-up is mandatory.

Er-based optical amplification continues to be the ideal low noise, WDM crosstalk free, broadband candidate for waveguide amplifiers. Design analysis of the applicability of Er-Doped Waveguide Amplifiers (EDWAs) for micron-scale integrated photonics in a planar lightwave circuit concludes: (i) an >80× increase in gain efficiency, and (ii) a >40×increase in device shrink can be realized, for a high index contrast EDWA (with a core-cladding index difference of δn=0.1↔0.7), compared to a conventional Er-doped fiber amplifier. The materials challenge now is to establish a robust materials system which meets this high index difference design requirement while simultaneously leveraging the capability of silicon (Si) processing: a host platform for EDWAs must be found which can integrate with Si Microphotonics. Silicon nitride (Si3N4), silicon oxide (SiO2) and a miscible silicon oxynitride alloy (SiON) of the two meet this materials challenge. We present the results of reactive and conventional magnetron sputtering based materials characterization for this high index host system. Room temperature and 4 K photo-luminescence studies for annealed samples show the reduction of non-radiative de-excitation centers while maintaining an amorphous host structure. Atomic force microscopy shows less than 1 nm peak-to-peak roughness in deposited films. Prism coupler measurements show a reliable reproducibility of host index of refraction with waveguide scattering loss <2 dB/cm. We conclude that the SiON host system forms an optimal waveguide core for an SiO2-clad EDWA. Initial gain measurements show a gain coefficient of approximately 3.9 dB/cm.

We present a high speed, high responsivity, tensile strained Ge p-i-n photodetector selectively grown on Si platform that covers the whole C band and a large part of the L band for high capacity optical communications. The device shows a 3dB bandwidth of 2.5GHz and its responsivities at 1310nm and 1550nm are comparable to commercial InGaAs photodetectors currently used in telecommunications. The device has promising applications in Si microphotonics such as the fiber-to-the-home technology.

We have fabricated the first CMOS process compatible high-responsivity Ge p-i-n diodes for 1.55 μm wavelengths. The thermal expansion mismatch between Ge epilayers and Si substrates was used to engineer tensile strain upon cooling from the growth temperature. This 0.2% tensile strain results in a lowering of the direct transition energy in Ge by 30 meV and extends the responsivity curve to near 1.6μm.

The effect of microstructures on the photoluminescence of Er2O3thin films has been systematically studied in this paper. The Er2O3 film was fabricated via reactive sputtering of Er metal in an Ar/O2 atmosphere. The as-deposited thin film contained both amorphous and polycrystalline structures, which showed weak photoluminescence at 1.55 µm. Annealing at an elevated temperature from 650 to 1050 °C in O2 ambient significantly incorporated oxygen into the lattice and strongly promoted crystalline grain growth, which in turn dramatically induced the transaction of photoluminescence from 1.55 µm to 1.541 µm. The ideal large crystal Er2O3 structure with fcc-Er2O3 and bcc-Er2O3 precipitates was obtained by conducting a two-step annealing (650 °C for 5 hours followed by 1020 °C for 2 hours) which resulted in a sharp photoluminescence peak at 1.541 µm. Further significant enhancement of PL at 1.541 µm was achieved via RTA at 1050 °C for 30 seconds to introduce more fcc-Er2O3 precipitates into the bcc-Er2O3 matrix.

A new approach for one-dimensional photonic bandgap formation is introduced. The method consists of wafer bonding and delamination, which is capable of stacking single crystalline semiconductor layers on non-crystalline insulator layers. Si and SiO2 layers with sub-wavelength periodicity are successfully stacked to form photonic crystals consisting of 3 pairs without a defect layer and of 4.5 pairs with a defect layer. The transmittance spectra are well reproduced by transfer matrix calculations. This clearly verifies the potential of the wafer bonding and delamination method.

Results of new electron nuclear double resonance (ENDOR) experiments on the thermal donors (NL8) in silicon are presented. Hyperfine interactions (hf) with 17O were observed. Two types of oxygen were found, of each type there are at least two oxygen atoms. The size and tensor orientations of their hf interactions are consistent with the presence of four oxygen atoms with approx. <111>-symmetry in the core of the thermal donors.