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Graphene integrated photonics provides several advantages over conventional Si photonics. Single layer graphene (SLG) enables fast, broadband, and energy-efficient electro-optic modulators, optical switches and photodetectors (GPDs), and is compatible with any optical waveguide. The last major barrier to SLG-based optical receivers lies in the low responsivity - electrical output per optical input - of GPDs compared to conventional PDs. Here we overcome this shortfall by integrating a photo-thermoelectric GPD with a Si microring resonator. Under critical coupling, we achieve $>$90% light absorption in a $\sim$6 $��$m SLG channel along the Si waveguide. Exploiting the cavity-enhanced light-matter interaction, causing carriers in SLG to reach $\sim$400 K for an input power of $\sim$0.6 mW, we get a voltage responsivity $\sim$90 V/W, demonstrating the feasibility of our approach. Our device is capable of detecting data rates up to 20 Gbit/s, with a receiver sensitivity enabling it to operate at a 10$^{-9}$ bit-error rate, on par with mature semiconductor technology. The natural generation of a voltage rather than a current, removes the need for transimpedance amplification, with a reduction of the energy-per-bit cost and foot-print, when compared to a traditional semiconductor-based receiver., 11 pages, 5 figures

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 mu m. 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.

Epitaxial growth of germanium on silicon produces large misfit and threading dislocation densities which dramatically affect electronic properties of Ge. For this reason, TCAD standard models and parameters, optimized for bulk Ge, fail when applied to Ge epilayers. In this work we describe a novel approach for the simulation of highly defected germanium films grown by thermal evaporation. We also take into account the gradient of defect concentration depending on the germanium thickness. The proposed model is successfully employed for TCAD simulations of Ge-on-Si pn heterojunction photodiodes, demonstrating good agreement with experimental data. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report oil novel pn Ge photodetectors fabricated oil glass The fabrication consists of wafer bonding and layer splitting. followed by a low-temperature epitaxial growth of Ge The photodiodes are characterized in terms of dark current and responsivity, and their performance compared with devices realized on either Ge or Si The minimum current density is 50 mu A/cm(2) at 1 V reverse bias. the responsivity is 0.2 A/W in the photovoltaic mode, with a maximum of 0 28 A/W at 1.55 micron at a reverse voltage of 5 V (C) 2009 Elsevier

We report on a novel near infrared SiGe phototransistor fabricated by a standard silicon photonics foundry. The device is first investigated by simulations. The fabricated devices are characterized in terms of current-voltage characteristics at different optical power. Typical phototransistors exhibit 1.55µm record responsivity at low optical power exceeding 232A/W and 42A/W at 5V and 1V bias, respectively. A differential detection scheme is also proposed for the dark current cancellation to significantly increase the device sensitivity.

We report on the fabrication and characterization of a novel near infrared phototransistor provided with a Germanium optical gate and fabricated by means of a commercially available silicon photonics foundry.

We report on the fabrication and characterization of a near infrared junction field effect phototransistor provided with a Germanium gate and fabricated in a silicon photonics foundry. The maximum device responsivity exceeds 36A/W with a dark current of 33μA at 2V.

We report on the simulation of Optically Controlled Field Effect Transistors (OCFET) based on a MOSFET with a Germanium gate. We study the static and dynamic characteristics of the device under near infrared light at 1.55 μm and investigate its operation as a digital inverter.

Threading dislocations in germanium thin films on silicon introduce acceptor states in the germanium bandgap close to the valence band. Thus, highly defected germanium thin films spontaneously exhibit a p-type behavior. Here we report on spin-on-dopant diffusion of phosphorus in thermally evaporated, highly defected germanium thin films. We demonstrate effective compensation of the acceptor states associated to dislocations by means of post-growth doping. We discuss phosphorus diffusion in these highly defected films and pinpoint the benefits of spin-on-doping by realizing and testing near-infrared photodiodes in evaporated Ge on Si, achieving high responsivities which compare well with those of state-of-the-art Ge p-i-n photodiodes. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

"Thermal evaporation of germanium (Ge) on silicon (Si) has proved to be a suitable technique for the fabrication of high responsivity, low-cost, near-infrared pn detectors. Such results rely on low-temperature diffusion of n-type dopants. The corresponding transport phenomena are quite involved and cannot be described by standard models for pn junctions because of rather large defect concentration density in the Ge layer. In this paper, we report on fabrication, characterization, and simulation of defected Ge on Si photodiodes. For the simulations, we developed a technology computer aided design model and hereby demonstrate its ability to reproduce the measured optoelectronic characteristics of the devices. "

Technology roadmaps identify the transmission bottleneck as one of the major challenges at high frequencies and in compact geometries. Increasing bandwidth and massive data processing prompt for the use of optics over short distances, down to board-to-board, chip-to-chip and even intra-chip. In this framework, optical to electric converters are key elements. We investigate the feasibility of an optically controlled field effect transistor (FET), a device capable of switching when driven by light (rather than voltage) thanks to a photosensitive gate. We develop a physical model in order to simulate with TCAD the modulation of FET channel conductivity, using drift-diffusion with optical generation. Current modulation of more than one order of magnitude with 1 µW optical power and time response lower than 100 ps can be achieved. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

"We perform an extensive micro-Raman analysis of Germanium thin films physically evaporated on several substrates including silicon, silicon oxide and glass. We investigate the dependence of crystal quality on thin film deposition parameters such as substrate temperature and growth rate. We also study the continuous transitional change of the material structure from amorphous to crystalline phases. Ge films obtained by this simple and low cost technique are a viable solution towards the realization of virtual substrates and devices. (C) 2010 Elsevier B.V. All rights reserved."

We report on pn Ge solar cells grown on Ge substrates and transferred onto glass by wafer bonding. They perform similarly to cells on the native Ge substrate, whereas their energy conversion efficiency compares well with state-of-the-art stand alone Ge photovoltaic cells. We propose Germanium layer transfer and wafer bonding for the realization of effective multi-junction solar cells and versatile multi-stack engineering.

"\"We report on the fabrication and operation of optical power monitors monolithically integrated on silicon-on-insulator optical chips. The devices consist of near-infrared waveguide pn heterojunction photodiodes in evaporated germanium. The low temperature growth of Ge is compatible with silicon waveguide technology. The photodetectors exhibit typical responsivities of 10-30 mA\\\/W; the power monitors are used with front-end trans-impedance amplifiers based on commercially available operational amplifiers and can operate with optical signals as small as 10 nW, with errors below 0.2% and 2% at 1 and 0.1 mu W, respectively. (C) 2010 Elsevier B.V. All rights reserved.\""

"Using conventional and polarization-dependent Raman spectroscopy we investigate the structural properties of Germanium films thermally evaporated on Silicon under various conditions. The analysis suggests that the Ge films can be crystalline, amorphous and poly-oriented, depending on the substrate temperature. We use both comparison with Raman spectra of Ge films grown on amorphous substrates and polarization-dependent Raman measurements to demonstrate that in the 250-450 degrees C interval, crystalline Ge films are epitaxial. This result is validated by means of large angle X-ray diffraction measurements. We employ these films to fabricate and characterize near infrared heterojunction photodiodes that exhibit high responsivities and low dark current densities. (C) 2011 Elsevier B.V. All rights reserved."

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 10nW, with errors below 0.2% and 2% at 1 and 0.1 mu W, respectively.

Ge-on-glass photodetectors is fabricated by wafer bonding and layer splitting, followed by the epitaxial growth of pn structures. The detectors exhibit a remarkably low dark current density of 50 muA/cm 2 at 1 V reverse bias and responsivities as high as 0.33 and 0.43 A/W at 1.52 and 1.3 mum, respectively. This approach can be readily extended to other substrates, enabling the integration of Ge on different platforms.

We investigate the temperature dependence of p-i-n photodetectors realized in germanium on silicon. The dark current increases by a factor 1.6-1.9 every 10 degrees C and is typically dominated by generation in the space charge region, with diffusion contributing in the best samples. The near infrared (NIR) responsivity decreases with temperature in devices with a large defect-density, but is more stable in high-quality photodiodes. These findings provide a relevant insight on the design of Ge-on-Si NIR detectors to be operated above room temperature. (C) 2008 Elsevier B.V. All rights reserved.

We report the integration of near-infrared waveguide photodetectors in polycrystalline Germanium with Silicon on Insulator optical chips for power monitor applications. We discuss design and fabrication of the devices as well as their characterization in terms of dark current, responsivity and signal to noise ratio. [DOI: 10.2971/jeos.2009.09030]

We report on near-infrared waveguide photodetectors realized in germanium evaporated at low temperature on silicon-on-insulator optical chips. We discuss the fabrication and integration and show experimental results in terms of dark current, responsivity and signal to noise ratio. (C) 2008 Elsevier B.V. All rights reserved.

We investigate the temperature dependence of germanium on silicon p-i-n photodetectors in terms of both dark current density and near-infrared responsivity. The dark current increases by nearly a factor 1.6 every 10 degrees C, consistently with carrier generation in the space charge region. The responsivity has a complex trend, its temperature variation depending on wavelength and on the germanium quality. Detectors with a large defect density in the active layer exhibit a reduced responsivity as the temperature increases.

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. (C) 2008 American Institute of Physics.

We investigate the temperature dependence of p-i-n photodetectors realized in germanium on silicon. The dark current increases by a factor 1.6÷1.9 every 10oC and is typically dominated by generation in the space charge region, with diffusion contributing in the best samples. The NIR responsivity decreases with temperature in devices with a large defect-density, but is more stable in high quality photodiodes. These findings provide a relevant insight on the design Ge-on-Si NIR detectors to be operated above room temperature