Alexandre Giguere

Effect of Thermal Annealing on the Kinetics of Rehydroxylation of Eu3+:La2O3 Nanocrystals

Europium-doped lanthanum oxide (5 mol % Eu(3+):La(2)O(3)) was prepared by calcining europium-doped lanthanum hydroxide (5 mol % Eu(3+):La(OH)(3)) previously synthesized by a simple hydrothermal method. Interestingly, we observed different emission Eu(3+) signatures depending on the phase of the host (lanthanum oxide or hydroxide) by cathodoluminescence. Taking into account that lanthanum oxide easily rehydroxylates in air, for the first time, we report the use of cathodoluminiscence as a novel characterization technique to follow the lanthanum oxide rehydroxylation reaction versus time according to different annealing procedures. Additionally, differential thermal-thermogravimetric analysis, infrared spectroscopy, and X-ray diffraction techniques were used to identify the phases formed from the Eu(3+):La(OH)(3) depending on temperature and to study the evolution of La(2)O(3) to La(OH)(3) versus time. The results showed that the higher the temperature and the longer the annealing time, the higher the resistance to rehydroxylation of the Eu(3+):La(2)O(3) sample.

Waveguide-coupled drop filters on SOI using quarter-wave shifted sidewalled grating resonators.

We report on the design, fabrication, and demonstration of waveguide coupled channel drop filters at 1550 nm, on a silicon-on-insulator (SOI) substrate. These devices rely on resonant power transfer from a bus waveguide to side-walled Bragg resonators with quarter-wave shifts in the middle. By employing a second mirror resonator, and a tap-off waveguide, reflections along the bus waveguide can be reduced, leading to realization of circulator-free resonance filters. These devices were fabricated on SOI using e-beam lithography and inductively coupled plasma (ICP) etching. Fabricated devices with two coupled cavities are demonstrated to have rejection ratios greater than 20 dB and 3-dB bandwidths of 110 GHz, close to the values predicted by numerical modeling. We also demonstrate power tap-off at resonance of around 16 dB.

Fabrication of p-type porous GaN on silicon and epitaxial GaN

Porous GaN layers are grown on silicon from gold or platinum catalyst seed layers, and self-catalyzed on epitaxial GaN films on sapphire. Using a Mg-based precursor, we demonstrate p-type doping of the porous GaN. Electrical measurements for p-type GaN on Si show Ohmic and Schottky behavior from gold and platinum seeded GaN, respectively. Ohmicity is attributed to the formation of a Ga2Au intermetallic. Porous p-type GaN was also achieved on epitaxial n-GaN on sapphire, and transport measurements confirm a p-n junction commensurate with a doping density of ∼1018 cm−3. Photoluminescence and cathodoluminescence confirm emission from Mg-acceptors in porous p-type GaN.

Design and Demonstration of Apodized Comb Filters on SOI

We report on the design, modeling, and characterization of apodized comb filters in the silicon-on-insulator platform. These devices are based on sampled gratings, wherein the comb response is generated by a convolution of a regular grating by a predetermined periodic sampling function. We show that dual and complementary apodization of the etch depth in the marks and spaces ensures a near-zero dc index change over the length of the device and avoids the unwanted sidelobes obtained in a single apodized device. Comb filters with a 40-dB side-mode suppression ratio, a 92-GHz clear bandwidth, 200-GHz channel spacing, and a 120-dB/dec rolloff have been theoretically proposed. An experimental demonstration of the fabricated devices is also presented, and the performance is compared with the numerical simulations.

Waveguide coupled drop filters on SOI using vertical sidewalled grating resonators

A vertical grating resonator coupled drop filter with 20 dB channel extinction and 37% dropped channel tapping efficiency is proposed. We also show that by employing coupled cavities a flat-top filter response can be obtained.

EFFECTIVE GaN SURFACE PASSIVATION BY PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION OF SILICON OXIDE

We report on an effective and stable process for GaN surface passivation by plasma enhanced chemical vapor deposition (PECVD) of silicon oxide (SiOx). Metal–oxide–semiconductor (MOS) capacitors were fabricated on unintentionally doped n-GaN layers grown by OMVPE on sapphire substrates and characterized using capacitance–voltage (C–V) and current–voltage (I–V) measurements. A high level of surface potential modulation, a small voltage shift, a small hysteresis, and no evident frequency dispersion are observed on C–V characteristics, indicating a high SiOx/GaN interface quality with a low electronic surface state density.

Hybrid III–V silicon evanescent lasers with vertical sidewalled gratings

A hybrid III–V silicon evanescent laser with sidewalled gratings as the feedback element, and having 60% waveguide confinement is proposed. The device is fabricated using e-beam lithography, and low-temperature plasma assisted direct bonding.

Demonstration of waveguide-coupled sidewalled grating filters on SOI

We report on the demonstration of waveguide coupled side-walled grating filter fabricated on SOI using e-beam lithography. We obtain a dropped channel extinction of 20 dB and a flat top response using coupled cavities.