Vito Sorianello

Design optimization of single and double layer Graphene phase modulators in SOI.

In this paper we report on an electro-refractive modulator based on single or double-layer graphene on top of silicon waveguides. The graphene layers are biased to the transparency condition in order to achieve phase modulation with negligible amplitude modulation. By means of a detailed study of both the electrical and optical properties of graphene and silicon, as well as through optimization of the geometrical parameters, we show that the proposed devices may theoretically outperform existing modulators both in terms of V(π)L and of insertion losses. The overall figures of merit of the proposed devices are as low as 8.5 and 2dB∙V for the single and double layer cases, respectively.

Low-temperature germanium thin films on silicon

We discuss thermal evaporation of Germanium thin films as a suitable route to realizing near-infrared detectors integrated on a Silicon platform. We study the structural properties of samples grown at various substrate temperatures by X-ray diffraction and transmission electron microscopy, showing that Ge thin films are amorphous when deposited below 225°C, mono-crystalline between 225 and 400°C, poly-crystalline above 450°C. We further investigate their optical and electrical properties using differential optical absorption spectroscopy, Hall and photocurrent measurements. Finally, with the evaporated Ge thin films we demonstrate near-infrared photodiodes with low dark current density and good responsivity at 1.55 μm.

High responsivity near-infrared photodetectors in evaporated Ge-on-Si

Germanium is considered the most suitable semiconductor for monolithic integration of near-infrared detectors on silicon photonic chips. Here we report on Ge-on-Si near-infrared photodetectors fabricated by thermal evaporation, demonstrating the use of phosphorus spin-on-dopant to compensate the acceptor states introduced by dislocations. The detectors exhibit 1.55 μm responsivities as high as 0.1 A/W, more than two orders of magnitude larger than in undoped devices and comparing well with state-of-the-art p-i-n photodiodes. This approach enables simple and low-cost monolithic integration of near-infrared sensors with silicon photonics.

Germanium-on-Glass solar cells: fabrication and characterization

We report on Germanium on Glass solar cells realized by wafer bonding, layer splitting and epitaxial regrowth. We provide a detailed description of the layer transfer process and discuss the material characterization. The solar cells are fabricated and tested to extract the most significant figures of merit, evaluating their performance versus device area and operating temperature. The cells exhibit typical conversion efficiencies exceeding 2.4% under AM1.5 irradiation and a maximum efficiency of 3.7% under concentrated excitation. This Germanium on Glass approach is promising in terms of added flexibility in multi-junction engineering and allows a significant cost reduction thanks to the re-usability of the Ge substrates.

Near-infrared absorption of germanium thin films on silicon

Using differential optical absorption spectroscopy of germanium thin films epitaxially grown on silicon, we accurately evaluate the near-infrared absorption versus wavelength and temperature. The results allow for optimized design and realization of Ge-on-Si photodetectors.

Graphene-silicon phase modulators with gigahertz bandwidth

V. Sorianello, M. Midrio,G. Contestabile,I. Asselberg,J. Van Campenhout,C. Huyghebaerts,I. Goykhman,A. K. Ott,A. C. Ferrari,M.Romagnoli Consorzio Nazionale per le Telecomunicazioni (CNIT), National Laboratory of Photonic Networks, Via G. Moruzzi 1, 56124 Pisa, Italy Consorzio Nazionale per le Telecomunicazioni (CNIT), University of Udine, Via delle Scienze 206, 33100 Udine, Italy Consorzio Nazionale per le Telecomunicazioni (CNIT), Scuola Superiore Sant’Anna, via G. Moruzzi 1, 56124 Pisa, Italy IMEC, Kapeldreef 75, 3001 Leuven, Belgium Cambridge Graphene Centre, Cambridge University, 9 JJ Thomson Avenue, Cambridge CB3 OFA, UK

Germanium near infrared detector in silicon on insulator

The authors demonstrate near infrared photodetectors in evaporated germanium on silicon-on-insulator waveguides. The authors achieve peak responsivities as high as 1A∕W and dark current densities as low as 40nA at a reverse bias of 1V. Owing to the low deposition temperature, this technology allows for simple and low cost monolithic integration with silicon.

Investigation of Static and Dynamic Characteristics of Optically Controlled Field Effect Transistors

In this paper, we report on an optically controlled field effect transistor (OCFET). The device is based on a modified MOSFET geometry with a Germanium layer interposed between the gate oxide and the gate metal contact. The investigation is performed using the technology computer aided design tool. We describe the principle of operation and investigate the static and dynamic properties of the OCFET under near infrared light at 1.55 μm. Device performance in terms of both ON/OFF current ratio and switching times are studied versus design parameters such as Germanium doping and lifetime as well as gate bias voltage and optical power. Strategies toward best operating conditions and satisfactory tradeoff are investigated and discussed along with future perspective and possible fundamental limitations.

300 nm bandwidth adiabatic SOI polarization splitter-rotators exploiting continuous symmetry breaking

Adiabatic polarization splitter-rotators are investigated exploiting continuous symmetry breaking thereby achieving significant device size and losses reduction in a single mask fabrication process for both SOI channel and ridge waveguides. A crosstalk lower than -25 dB is expected over 300nm bandwidth, making the device suitable for full grid CWDM and diplexer/triplexer FTTH applications at 1310, 1490 and 1550nm.

Near-Infrared Ge-on-Si Power Monitors Monolithically Integrated on SOI Chips

We realize and test power monitors monolithically integrated on silicon-on-insulator optical chips. The devices consist of near-infrared waveguide photodetectors in evaporated germanium with front-end transimpedance amplifiers. The power monitors operate with signals as small as 10 nW, with errors below 0.2% and 2% at 1 and 0.1 ¿W , respectively.