M. Gioffrè

Cu/p-Si Schottky barrier-based near infrared photodetector integrated with a silicon-on-insulator waveguide

In this letter, a near infrared all-silicon (all-Si) photodetector integrated into a silicon-on-insulator waveguide is demonstrated. The device is based on the internal photoemission effect through a metal/Si Schottky junction placed transversally to the optical field confined into the waveguide. The technological steps utilized to fabricate the device allow an efficiently monolithic integration with complementary metal-oxide semiconductor compatible structures. Preliminary results show a responsivity of 0.08 mA/W at 1550 nm with a reverse bias of 1 V and an efficient behavior both in C and L band. Finally, an estimation of bandwidth for GHz range is deduced.

Fabrication and characterization of a porous silicon based microarray for label-free optical monitoring of biomolecular interactions

We have fabricated a microarray of porous silicon Bragg reflectors on a crystalline silicon substrate using a technological process based on standard photolithography and electrochemical anodization of the silicon. The array density is of 170 elements/cm2 and each element has a diameter of 200 μm. The porous silicon structures have been used as platform to immobilize an amino terminated DNA single strand probe. All fabrication steps have been monitored by spectroscopic reflectometry, optical and electron microscopy, and Fourier transform infrared spectroscopy. A label-free detection method has been employed to investigate the hybridization between micromolar DNA probe and its complementary target. Due to fast and low cost production, good reproducibility, and high quality optical features, this platform could be adopted also for other different microarray applications such as proteomics and medical diagnostics.

Silicon resonant cavity enhanced photodetector based on the internal photoemission effect at 1.55μm: Fabrication and characterization

In this paper, the realization and the characterization of a resonant cavity enhanced (RCE) photodetector, completely silicon compatible and working at 1.55μm, are reported. The detector is a RCE structure incorporating a Schottky diode and its working principle is based on the internal photoemission effect. Taking advantage of a Cu∕Si Schottky diode fed on a high reflectivity Bragg mirror, an improvement in responsivity at 1.55μm is experimentally demonstrated.

A 2.5 ns switching time Mach­Zehnder modulator in as-deposited a-Si:H

A very simple and fast Mach-Zehnder electro-optic modulator based on a p-i-n configuration, operating at λ = 1.55 μm, has been fabricated at 170 °C using the low cost technology of hydrogenated amorphous silicon (a-Si:H). In spite of the device simplicity, refractive index modulation was achieved through the free carrier dispersion effect resulting in characteristic rise and fall times of ~2.5 ns. By reverse biasing the p-i-n device, the voltage-length product was estimated to be V(π)∙L(π) = 40 V∙cm both from static and dynamic measurements. Such bandwidth performance in as-deposited a-Si:H demonstrates the potential of this material for the fabrication of fast active photonic devices integrated on standard microelectronic substrates.

Cavity Enhanced Internal Photoemission Effect in Silicon Photodiode for Sub-Bandgap Detection

In this paper, a new approach for the near infrared sub-bandgap detection in Si-based devices is investigated. In particular, the design, the realization and the characterization of a back illuminated silicon resonant cavity enhanced Schottky photodetectors, working at 1.55 μm, are reported. The photodetectors are constituted by Fabry-Perot microcavity incorporating a Schottky diode. The working principle is based on the internal photoemission effect enhanced by cavity effect. Performances devices in terms of responsivity, free spectral range, finesse and estimated bandwidth are reported.

Tunable two-dimensional hexagonal phase array in domain engineered z-cut lithium niobate crystal

An optical phase array with tunable phase step is demonstrated. The phase array consists of a two-dimensional hexagonal lattice of inverted ferroelectric domains fabricated on a Z-cut lithium niobate substrate. The electro-optically tunable phase step is obtained by the application of an external electric field along the z axis of the crystal via transparent electrodes. Theoretical analysis and experimental results are presented, showing that a tunable and flexible adaptive optical illuminator device can be realized by combining the electro-optic tunability with the Talbot effect. Generation of a multiplicity of light patterns is shown.

Mid-infrared tunable two-dimensional Talbot array illuminator

We report the realization and characterization of a tunable, two-dimensional Talbot array illuminator for mid-infrared (MIR) wavelengths. A phase array, prepared by deposing tin-doped indium oxide electrodes on a square-lattice-geometry poled LiNbO3 sample, is illuminated by a difference-frequency generator emitting at 3 μm. Then, combining the electro-optic with the Talbot effect allows generation of a variety of light patterns under different values of distance and external electric field. Several potential applications with great relevance to the MIR spectral region are discussed.

Thickness measurement of thin transparent plates with a broad-band wavelength scanning interferometer

A novel broad-band telecom laser source is used to make a lateral-shear scanning-wavelength interferometer for measuring the thickness of thin plates. We show that the wide tunability range allows us to detect samples down to tens of microns with a relative uncertainty of less than 0.5%. A comparable accuracy in the thickness characterization of double-layer structures is also demonstrated. In turn, the wide tunability range needs the dispersion law of the materials to be taken into account in the model for correct thickness evaluation, although simultaneous measurement of dispersion and thickness are in principle possible with this technique.

Electro-optical effect in hydrogenated amorphous silicon-based waveguide-integrated p-i-p and p-i-n configurations

Abstract. A p-i-p configuration of an electro-optical modulator based on hydrogenated amorphous silicon (a-Si:H) is characterized and compared with an a-Si:H based p-i-n modulator. In particular, we estimate the performances in terms of optical losses, voltage-length product, and bandwidth at λ=1550  nm for waveguide-integrated p-i-p versus p-i-n configurations. Both devices are fabricated on a silicon substrate by plasma enhanced chemical vapor deposition at low temperature ensuring the back-end integration with a CMOS microchip. We demonstrate a factor of merit for the p-i-p waveguide integrated Fabry-Perot resonator of Vπ×Lπ=19  V×cm allowing the design of shorter devices with respect to p-i-n structure.

Photoluminescence characterization of ZnO nanowires functionalization

Nanostructured photoluminescent materials are optimal transducers for optical biosensors due to their capacity to convert molecular interactions in light signals without contamination or deterioration of the samples. In recent years, nanostructured biosensors with low cost and readily available properties have been developed for such applications as therapeutics, diagnostic and environmental. Zinc oxide nanowires (ZnO NWs) is material with unique properties and due to these they were widely studied in many fields as electronics, optics, and photonics. ZnO NWs can be either grown independently or deposited on solid support, such as glass, gold substrates and crystalline silicon. Vertical aligned ZnO forest on a substrate shows specific advantages in photonic device fabrication. ZnO NWs are typically synthesized by such techniques classified as vapour phase and solution phase synthesis. In particular, hydrothermal methods have received a lot of attention and have been widely used for synthesis of ZnO NWs. This technique shows more crystalline defects than others due to oxygen vacancies, so as the material shows intense photoluminescence emission under laser irradiation. ZnO NWs surface is highly hydrolysed, so it is covered by OH reactive groups, and standard biomodification chemistry can be used in order to bind bioprobes on the surface. In this work, we present our newest results on synthetic nanostructured materials characterization for optical biosensors applications. In particular, we characterize the ZnO NWs structure grown on crystalline silicon by SEM images and the biomodification by photoluminesce technique, fluorescence microscopy, water contact angle and FT-IR measurements.