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We demonstrate novel near-infrared waveguide photodetectors in polycrystalline germanium deposited on silicon-on-insulator at low temperatures. We present the design, fabrication, and characterization of two photodiodes and their comparison. Without optimization, at 1.55 /spl mu/m, we measured wall-plug and effective responsivities as high as 30 mA/W and in excess of 150 mA/W, respectively.

PbS colloidal quantum dots (CQDs) are attractive materials for the realization of simple, low-cost, high responsivity near-infrared photodetectors due to the large tunability of their optical properties together with their solution processability. In this work we propose multiple PbS CQD photoconductive devices with different spectral sensitivity realized on silicon substrates. We characterized the devices in terms of dark current, responsivity and response speed. Eventually, we discuss an algorithm for wavelength measurement of a quasi-monochromatic radiation based on linear combination of photocurrents from different photodetectors.

Germanium-based photodetectors represent the state-of-the-art in Near Infrared (NIR) detection systems when it comes to the monolithic integration with silicon electronics and CMOS compatibility. Germanium-on-silicon devices have been widely studied and several different photodetection schemes have been employed, such as Shottky junctions, pn diodes and phototransistors. Typically, germanium-based photodetectors provide a sensitivity spectrum ranging from the visible to the near infrared (NIR) and their responsivity at shorter wavelengths can be slightly tuned by the applied bias due to the varying extension of the electric field inside the Ge film. In this paper we propose a novel Ge-on-Si photodetector architecture whose spectral response can be completely switched from the visible to the NIR with the application of a proper bias. We provide Technology Computer Aided Design (TCAD) simulations of the device showing how the photodetection performance depend on different fabrication parameters. Finally, we show preliminary results obtained on sample devices.

The fabrication of germanium-based near infrared photo-resistors on a flexible substrate is reported. The devices were fabricated using plasma enhanced chemical vapor deposition of amorphous germanium on an insulating stack layer of silicon nitride and silicon oxide on a flexible polyimide thin film. The deposited films were annealed using a pulsed laser at different pulse rates and laser energy densities to investigate the effects of germanium recrystallization on the characteristics of the photo-resistors. Electrical and opto-electrical responses of the films have been measured and reported. Surface characterization via scanning electron and atomic force microscopy was used to evaluate the variations in surface roughness of the annealed material versus the amorphous germanium layers. Power spectral density analysis was performed to investigate the effect of laser annealing on the crystalline structure of the germanium samples. Providing a low-temperature processing flow, this work lays the foundation for the development of infrared sensors above flexible substrates with potential applications in wearable electronics among others.

In this paper we report on recrystallized amorphous hydrogenated germanium (a-Ge:H) thin film on polyimide to fabricate flexible near infrared (NIR) light sensitive resistors that can be used in flexible electronics. In this work we investigate the effect of pulsed excimer laser annealing of a-Ge:H thin films for fabrication of low temperature photo-detectors operating in the NIR.

In this letter, we report on high responsivity fire detectors based on PbS colloidal quantum dots photoconductors. The devices operate in the near infrared and are equipped with a visible light silicon filter for wavelength selectivity. Devices are fabricated by a simple, low cost, and silicon compatible process based on drop casting of a ligand exchanged solution of PbS nanoparticles. The photodetectors exhibit responsivity as high as 20 A/W at 1-V bias. We exploit the combination of their high responsivity and spectral response for the development of a novel fire detector able to detect a small flame at a distance exceeding 15 m in ambient illumination.

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)

Colloidal quantum dots have recently attracted lot of interest in the fabrication of optoelectronic devices due to their unique optical properties and their simple and low cost fabrication. PbS nanocrystals emerged as the most advanced colloidal material for near infrared photodetectors. In this work we report on the fabrication and characterization of PbS colloidal quantum dot photoconductors. In order to make devices suitable for the monolithic integration with silicon electronics, we propose a simple and low cost process for the fabrication of photodetectors and investigate their operation at very low voltage bias. Our photoconductors feature high responsivity and detectivity at 1.3 μm and 1 V bias with maximum values of 30 A/W and 2·1010 cmHz1/2W−1, respectively. Detectivity close to 1011 cmHz1/2W−1 has been obtained resorting to bridge sensor readout.

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)

The fabrication and characterization of near infrared photodetectors integrated on silicon substrates are reported on where the active layer is a thermally evaporated polycrystalline germanium. Recent results are presented in the effort to enhance the optoelectronic properties of the poly-Ge film in terms of uniformity for multiple device integration, speed and responsivity. In particular we demonstrate a 16 pixel linear array, a speed of photoresponse of about 650 ps and an enhancement of responsivity by a factor of four. The fabrication process, including substrate cleaning and preparation, requires temperatures lower than 300 degrees C being fully compatible with silicon technology. (C) 2000 Elsevier Science S.A. All rights reserved.

"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. "

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 demonstrate fast and efficient germanium-on-silicon p-i-n photodetectors for optical communications, with responsivities as high as 0.89 and 0.75 A/W at 1.3 and 1.55 mum, respectively, time response 2.5 Gb/s integrated receivers for the second and third fiber spectral windows. (C) 2002 American Institute of Physics.

We invesyigate the noise in Ge/Si photodiodes. The noise performance is characterized by current voltage characteristics and spectral analysis and the results compared with reference Ge/Ge photodetectors. Both thermal and shot noise are of the same order, while Ge/Si devices exhibit a significantly larger 1/f noise.

We report on the fabrication and characterization of Ge solar cells on glass realized by layer transfer and epitaxial regrowth. These devices exhibit typical conversion efficiency exceeding 2.4% under AM1.5 irradiation and maximum efficiency of 3.7% under concentrated excitation. This approach enables flexible and affordable multi-junction engineering for solar energy conversion.

"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 demonstrate Ge/Si heterojunction photodetectors based on high quality epitaxial germanium grown on silicon. Germanium deposited by ultra-high-vacuum chemical vapor deposition (UHV-CVD) undergoes thermal annealing cycles which reduce the number of dislocations and, thus, improve the overall quality. The photodetectors exhibit record responsivity of 0.55 A/W and a sub-ns photoresponse at 1.3 mum. We describe the fabrication process as well as a complete optoelectronic characterization of the devices. (C) 2001 Elsevier Science 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.

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].

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 review near-infrared detectors in germanium grown on silicon. We discuss pn and pin photodiodes based on Ge deposited on Si by a number of techniques, including thermal evaporation; the optical and electronic characterization of Ge-on-Si heterostructures using various approaches to minimize the density of defects; and compatibility issues with standard fabrication processes for Si electronics. We describe in greater detail the most promising devices realized by us and operating either at normal incidence or in guided-wave geometries, with applications to high-speed optical receivers, as well as image sensors.

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.

We investigate and characterize p-i-n near-infrared photodiodes fabricated in Ge-on-Si by reduced-pressure chemical vapor deposition, a technology compatible with silicon processing. The detectors exhibit remarkably low dark current densities of 1mA/cm(2) at unity reverse bias and high responsivities of 200 mA/W at 1.55 mu m. We evaluated their small-signal resistance, capacitance, and bandwidth as well as eye-diagrams at 2.5 and 10 Gbit/s.

The authors demonstrate a two-dimensional array of Si-integrated photodetectors equipped with readout electronics and operating in the near infrared. The chip is realized in polycrystalline Ge on a silicon complementary metal oxide semiconductor circuitry and includes 512 pixels, 64 analog to digital converters, dark current cancellation, and test/calibration facilities. They describe its design, fabrication, characterization, and operation as a near-infrared image sensor.

We demonstrate near-infrared Ge-on-Si photodiodes designed to minimize the dark current density and fabricated by chemical vapor deposition. The p-i-n detectors exhibit record low dark currents of 7 nA at 1-V reverse bias with responsivities close to the theoretical maximum. An excellent performance is ascertained,even for very low reverse voltages.

We report on the first silicon-integrated 2-D light-sensitive array equipped with complementary-metal-oxide-semiconductor addressing and readout electronics and operating in the near infrared. The chip includes 64 times 8 pixels, 64 analog-to-digital converters, cancellation circuitry for dark current, and facilities for test/calibration. We describe its architecture and fabrication, its electronic and optoelectronic characterization, as well as its operation as a near-infrared camera

We report on fast p-i-n photodetectors operating in the near infrared and realized in pure germanium on silicon. The diodes were fabricated by chemical vapor deposition at 600 degrees C without affecting the crystal quality and allowing the integration with standard silicon processes. We demonstrate responsivities of 0.4 and 0.2 A/W at 1.3 and 1.55 mu m, respectively, as well as operation at 10 Gbit/s. (c) 2006 American Institute of Physics.

We report on fast p-i-n near infrared photodetectors in pure germanium on silicon. The diodes were fabricated by chemical vapor deposition at 600 degrees C followed by thermal annealing at 900 degrees C. We also verified that bypassing the thermal treatment did not have significant effects on the resulting crystal quality, allowing to considerably reducing the thermal budget hence simplify the integration with silicon. We demonstrate the operation of photodiodes with responsivities of 0.4 and 0.2A/W at 1.3 and 1.55 mu m, respectively, as well as open-eye diagrams at 10 Gbit/s. (c) 2006 Elsevier B.V. All rights reserved.

Using a guided wave configuration, we demonstrate a novel polyGe-on-Si heterostructure photodetector realized on a silicon-on-insulator by a low deposition temperature process. Without further detector optimization, at 1.55 mu m we measured wall-plug responsivities as high as 15 mA/W with an effective responsivity in excess of 300 mA/W. Device operation was demonstrated up to 2.5 Gbit/s. (C) 2005 American Institute of Physics.

Based on cascading between coupled-modes in planar guides, we undertook a study of spatial optical solitons in this novel geometry encompassing two waveguides and orthogonal eigenmodes.

Combining reverse proton exchange and uniform periodic poling in LiNbO3 planar waveguides, we demonstrate low-energy spatial optical solitons by second-harmonic generation at room temperature, with a threshold as low as 23 pJ/mum at 1.5 mum. (C) 2004 Optical Society of America.

Low-threshold spatial optical solitons are observed for the first time in buried planar waveguides obtained by reverse-proton-exchanged periodically poled LiNbO3.

We describe a linear array of Ge-Si heterojunction photodiodes monolithically integrated on a complementary metal-oxide-semiconductor (CMOS) integrated circuit for detection and imaging in the near infrared. Detectors are realized by thermal evaporation of Ge films at the end of the standard CMOS process on substrates held at low temperature (300/spl deg/C). Each of the 64 detectors is connected to a front-end stage for photocurrent integration and analog-to-digital conversion.

In this paper we review the recent achievements of germanium on silicon technologies for the fabrication of near infrared photodetectors.

We report on a fast polycrystalline germanium-on-silicon heterojunction photodetector for the near-infrared. The device exhibits a pulse response faster than 200 ps, allowing operation at 2.5 Gbit/s as testified by open eye diagrams. This polycrystalline device, with responsivities of 16 and 5 mA/W at 1.3 and 1.55 mum, respectively, and dark currents of 1 mA/cm(2), is entirely integrable on standard silicon electronics and is an appealing low-cost candidate for fiber-to-the-home communication networks. (C) 2003 American Institute of Physics.

With second-harmonic generation in surface and buried planar waveguides achieved by direct and reverse proton exchange in lithium niobate, we demonstrate a novel kind of quadratic spatial simulton: The transverse-electric fundamental input and the transverse-magnetic second-harmonic waves nonlinearly couple two superimposed planar waveguides, permitting transverse localization of light at room temperature and at excitations as low as 340 nJ in 20-ps pulses. (C) 2003 Optical Society of America.

Near infrared (NIR) detectors, operating in the 1.3– 1.6 μm region, are key elements in a number of applications ranging from optical communications to remote sensing. InGaAs and Ge are currently the materials of choice for the fabrication of NIR detectors due to their good absorption and transport properties. However, as the required performances increase (bit-rate in optical communications, number of pixels in imaging, etc.), it becomes more and more important to reduce the separation from detectors and driving/biasing and amplifying electronics, by integrating the two components on the same chip. We demonstrate an array of NIR detectors monolithically integrated with standard silicon CMOS readout electronics. The employed low temperature process allowed the integration of the detectors as the last step of chip fabrication. The integrated micro-system consists of a linear array of 120×120 μm 2 pixels, an analog CMOS multiplexer and a transimpedance amplifier. The chip exhibits a good photoresponse in the NIR, with responsivities as high as 43 V / W at 1.3 μm , dark currents of 1 mA / cm 2 and inter-pixel cross-talk better than −20 dB .

Si based optoelectronic devices have recently successfully entered the market of optical communications, This fact is stimulating renewed efforts in the design of optoelectronic components based on the well-established Si technology. In this paper, the motivations supporting these efforts and the major obstacles to be overcome are presented. Moreover, an overview of the state of the art of different classes of silicon based optoelectronic devices (waveguides, detectors, light sources etc.) is given. (C) 2002 Elsevier Science B.V. All rights reserved.

Integration of near infrared (NIR) photodetectors on a silicon substrate is a key step for the fabrication of an all silicon based NIR transceiver. To this extent, polycrystalline germanium (poly-Ge) technology is attractive due to the low deposition temperature and cost. Poly-Ge detectors demonstrated broad response, covering the whole NIR spectrum to 1.55 micron, fast, subnanosecond, speed and excellent versatility. In this work we present our recent results on the integration of a poly-Ge photodetector on a SOI silicon waveguide. The use of a waveguide for light in-coupling is appealing for telecom applications where signal is transported on an optical fibre, but, at the same time, it allows to increase detector responsivity. In fact, in this device the light is absorbed into the thin sensitive layer of the poly-Ge/Si heterojunction in a distributed way, during propagation. This releases the strong constraint of the absorption length being smaller than photocarrier collection length typical of normal incidence photodetectors. In the paper, both design issues and experimental results are reported.

We present a technology for the integration of high performance near-infrared Ge P-I-N photodetectors on Si for Si microphotonics. High quality Ge epilayers were grown on Si by a two-step ultrahigh-vacuum / chemical-vapor-deposition (UHV/CVD) process. Two-step UHV/CVD allows the epitaxial growth of Ge on Si without islanding. Threading-dislocations in Ge epilayers were reduced by cyclic thermal annealing. The reduction of threading-dislocations can be understood in terms of thermal stress induced dislocation glide and reactions. We found that sessile threading-dislocations are not permanent and can be removed.