CuInS 2 -based thin-film solar cells are presented with 11.1% total area efficiency or 12.5% active area efficiency. This is the best efficiency reported so far for this type of solar cell. The technology is based on a sequential process using d.c. magnetron sputtering of the metals and sulphurization in elemental sulphur vapour without the use of a toxic gas. Absorber layers and solar cells with precursor atomic copper to indium ratios between 1.0 and 1.8 are analysed. The best cells with fewest defects are made from the most copper-rich CuIn precursor layers. The solar cell performance, however, decreases only slowly for small deviations of the Cu/In ratio from the optimum value.
Two dimensional photonic crystal waveguides in high index materials enable integrated optical devices with an extremely small geometrical footprint on the scale of micrometers. Slotted waveguides are based on the guiding of light in low refractive index materials and a field enhancement in this particular region of the device. In this letter we experimentally demonstrate electro-optic modulation in slotted photonic crystal waveguides based on silicon-on-insulator substrates covered and infiltrated with nonlinear optical polymers. A photonic crystal heterostructure is used to create a cavity, while simultaneously serving as an electrical connection from the slot to the metal electrodes that carry the modulation signal. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3156033͔Electrically driven optical modulation in silicon photonics typically relies on interactions between the optical mode and a free carrier plasma via either carrier depletion, injection, or accumulation. 1-3 The achievable modulation speed using these methods is limited by the time constants related to the injection or removal of carriers from the optical waveguide. In contrast, modulation via nonlinear optical ͑NLO͒ polymers accesses the electronic polarization of the organic molecules, which allows extremely high modulation speeds extending up to frequencies in the terahertz range. 4 Furthermore, molecular engineering of organic molecules has led to extremely high Pockels-coefficients in polymers exceeding 300 pm/V, 5 which is ten times the value available in lithiumniobate, the standard inorganic material used in electro-optic ͑EO͒ applications. Photonic devices based on a hybrid material system merging silicon and polymer are therefore attractive since they combine the strong light confining abilities of silicon with the superior NLO properties of polymers.All-optical and EO-modulation in such hybrid silicon and NLO-polymer systems has been demonstrated for slotted photonic wire based Mach-Zehnder and ring-resonator modulators. 6-8 Concepts based on slotted photonic crystal ͑PhC͒ waveguides can exploit slow light mechanisms or high quality factor cavities to achieve very compact device dimensions and have been discussed recently. 9-11 We propose a concept using a double heterostructure cavity 11-13 in a slotted silicon PhC waveguide, infiltrated with NLO-polymer to operate as an EO-modulator. Figure 1 shows a scanning electron micrograph of the structure. The 150 nm wide slot in the center of the waveguide is filled with NLO-polymer ͑n poly = 1.63͒ and the strong overlap between the optical field and the polymer makes the effective index of the propagating mode very sensitive to any refractive index changes in EOpolymer. The PhC features a background doping density of 10 15 cm −1 and therefore serves as an electrical conductor from the metallic contact pads to the slot, while keeping the optical field away from the metal regions and hence preventing additional losses. The double heterostructure design of the PhC ͑a = 410 nm, r / a = 0....
The realization of an integrated delay line using tapered Bragg gratings in a drop-filter configuration is presented. The device is fabricated on silicon-on-insulator (SOI) rib waveguides using a Deep-UV 248 nm lithography. The continuous delay tunability is achieved using the thermo-optical effect, showing experimentally that a tuning range of 450 ps can be obtained with a tuning coefficient of -51 ps/°C. Furthermore the system performance is considered, showing that an operation at a bit rate of 25 Gbit/s can be achieved, and could be extended to 80 Gbit/s with the addition of a proper dispersion compensation.
The absorption coefficient of crystalline silicon is an important input for designing solar cells and extracting recombination parameters from device measurements. Since many contradicting measurements have been published, an assessment of data is given based on device measurements and on the discussion of experiments in the literature. An absorption coefficient for the ultraviolet to infrared spectral range is proposed, based on the results of three groups. These data can be described semiempirically by the theory of direct and indirect band transitions. This formulation enables the determination of the optical absorption in crystalline silicon at an arbitrary temperature. The interpretation and design of solar cells for operation at temperatures above room temperature is now possible.
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