Modelling of photonic wire Bragg Gratings

Some important properties of photonic wire Bragg grating structures have been investigate. The design, obtained as a generalisation of the full-width gap grating, has been modelled using 3D finite-difference time-domain simulations. Different types of stop-band have been observed. The impact of the grating geometry on the lowest order (longest wavelength) stop-band has been investigated - and has identified deeply indented configurations where reduction of the stop-bandwidth and of the reflectivity occurred. Our computational results have been substantially validated by an experimental demonstration of the fundamental stop-band of photonic wire Bragg gratings fabricated on silicon-on-insulator material. The accuracy of two distinct 2D computational models based on the effective index method has also been studied - because of their inherently much greater rapidity and consequent utility for approximate initial designs. A 2D plan-view model has been found to reproduce a large part of the essential features of the spectral response of full 3D models

DISLOCATION DEFECT STATES IN SILICON

Une méthode de spectroscopie par capacité transitoire a été utilisée pour l'étude des niveaux d'énergie introduits dans le silicium par déformation plastique à 770°C. Une grande variété de niveaux a été observée avec un niveau prépondérant à E(Ec-0.68eV) après déformation. La variation de la configuration des dislocations par une double déformation ne change pas les spectres de capacité observés après une simple déformation. Après recuit à 900°C les spectres se simplifient et montrent seulement deux niveaux d'énergie dominant à E(Ec-0.38eV) et H(Ev+0.35eV).Capacitance transient spectroscopy has been used to study the defect states introduced into silicon by plastic deformation at 770°C. A large variety of defect states are observed with a prominent state at E(Ec-0.68eV) after deformation. Varying the dislocation structure by a two stage deformation procedure did not change the observed capacitance spectra after deformation. Upon annealing at 900°C the spectra simplify to two dominant states at E(Ec-0.38eV) and H(Ev+0.35eV)

Growth of epitaxial YbBa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e7\u3c/sub\u3e superconductor by liquid-gas-solidification processing

Superconductive films of YbBa2Cu3O7 have been epitaxially grown on SrTiO3 substrate by a novel liquid-gas-solidification process. A layer of metallic YbBa2Cu3 melt was coated on the substrate and in situ oxidized. The oxide films grown on the SrTiO3 (100) substrate are epitaxially oriented in structure with the c axis normal to the plane film. Values of T c (R =0) of 82 K with a transition width of 1 K have been achieved. The critical current density J c is typically 105 A/cm2 at 50 K and 104 A/cm2 at 77 K

Athermal high-index-contrast waveguide design

We present generalized design rules for athermal performance and materials compatibility in high-index-contrast (HIC) waveguides. Thermal stability of integrated photonic devices is one critical limitation in the development of commercially viable integrated optoelectronic circuits. Thermooptically neutral designs are achieved by choosing a cladding material whose thermooptic coefficient is opposite to that of the waveguide core. We derive analytical expressions of athermal conditions for both symmetric and asymmetric channel waveguide structures. The equations apply to general HIC systems such as silicon-on-insulator and SiN-based structures

Efficient high-speed near-infrared Ge photodetectors integrated on Si substrates

We have fabricated Ge/Si heterojunction photodetectors with high responsivities of 550 mA/W at 1.32 mu m and 250 mA/W at 1.55 mu m and time responses shorter than 850 ps. High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition followed by cyclic thermal annealing. The beneficial effect of the post-growth thermal annealing on the electrical properties of Ge epilayers, due to the reduction of threading-dislocation densities, is confirmed by the dramatic enhancement of the performance of the photodetectors. (C) 2000 American Institute of Physics. [S0003-6951(00)03410-0]