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We report on an epitaxial Ge-on-Si dual-band photodetector grown on a Si p-n junction, to form two photodiodes connected in a back-to-back configuration. The device responsivity can be tuned, with an external bias, to cover wavelengths within the visible and near-infrared spectral regions.

Flame sensing and early fire detection are primary features in modern security and surveillance systems. Optical detection systems are widely developed and offer the highest sensitivity and selectivity but they are still expensive and show a high power budget. Here we propose a low-cost, low-power flame detector based on PbS colloidal quantum dots. We show detector operation with a 21 nW total power dissipation and the ability to detect the flame of a candle at 20 m with a 5 dB signal to noise ratio (SNR).

High sensitivity photodetectors based on PbS colloidal quantum dots have been demonstrated by several research groups in the last years with performance comparable to commercial III–V semiconductor devices. Nevertheless, investigation of the noise performance of such new photodetectors is still lacking. Here we report on the characterization of PbS colloidal quantum dot near infrared photoconductors including a preliminary analysis of noise power spectra. Devices have been characterized focusing on the low frequency regime (up to 10 kHz) investigating the noise dependence on the voltage bias.

In this paper we outline a novel design of a wireless sensor wearable band for tracking patient movements. This technology and design has potential applications for rehabilitation of stroke survivors who suffer from spasticity in their upper extremities. This technology could be used to track patient movement performed in a non-clinical environment, such as inside the comfort of their home. Data on their treatment progress could be transmitted wirelessly both to the clinician and to the patient. This technology could help realize increased monitoring of the patient, quantitative data on patient improvement over time and decreased health care costs. In this paper we demonstrated a preliminary prototype which can track and distinguish classes of movement of a user performing elbow flexion exercises while seated at a table. A study was completed with 6 participants with classification accuracies up to 88%.

A novel fully wearable system based on a smart wristband equipped with stretchable strain gauge sensors and readout electronics have been assembled and tested to detect a set of movements of a hand crucial in rehabilitation procedures. The high sensitivity of the active devices embedded on the wristband do not need a direct contact with the skin, thus maximizing the comfort on the arm of the tester. The gestures done with the device have been auto-labeled by comparing the signals detected in real-Time by the sensors with a commercial infrared device (Leap motion). Finally, the system has been evaluated with two machine-learning algorithms Linear Discriminant Analysis (LDA) and Support Vector Machine (SVM), reaching a reproducibility of 98% and 94%, respectively.

We report on the fabrication and characterization of Schottky barrier transistors on polycrystalline silicon. The transistors were realized exploiting Cr-Si and Ti-Si Schottky barrier with a low thermal budget process, compatible with polymeric, ultraflexible substrates. We obtained devices with threshold voltages as low as 1.7 V (for n channel) and 4 V (for p channel) with channel lengths ranging from 2 to 40 μm. Resulting on/off ratios are as high as 5 · 103. The devices showed threshold voltages and subthreshold slopes comparable with already published N- and P-MOS devices realized with the same process on polyimide substrates thus representing a cheaper and scalable alternative to ultraflexible transistors with doped source and drain.

The FAMU experiment aims to accurately measure the hyperfine splitting of the ground state of the muonic hydrogen atom. A measurement of the transfer rate of muons from hydrogen to heavier gases is necessary for this purpose. In June 2014, within a preliminary experiment, a pressurized gas-target was exposed to the pulsed low-energy muon beam at the RIKEN RAL muon facility (Rutherford Appleton Laboratory, UK). The main goal of the test was the characterization of both the noise induced by the pulsed beam and the X-ray detectors. The apparatus, to some extent rudimental, has served admirably to this task. Technical results have been published that prove the validity of the choices made and pave the way for the next steps. This paper presents the results of physical relevance of measurements of the muon transfer rate to carbon dioxide, oxygen, and argon from non-thermalized excited mu-p atoms. The analysis methodology and the approach to the systematics errors are useful for the subsequent study of the transfer rate as function of the kinetic energy of the mu-p currently under way., Comment: 15 pages, 3 figures, 2 tables

We report on the epitaxial growth of Cu(In,Ga)Se2 (CIGS) thin films on n-type Ge substrates using the Pulsed Electron Deposition (PED) technique. Single-crystal films with smooth interface and no dislocations were obtained at a substrate temperature of 300°C with thickness above 1.5μm. CIGS/Ge epilayers were characterized in terms of Transmission Electron Microscopy, X-Ray Diffraction and Photoluminescence. Preliminary results are very promising for a variety of potential applications as absorber layer in single and multi-junction thin-film solar cells.

"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 degrees C, mono-crystalline between 225 and 400 degrees C, poly-crystalline above 450 degrees 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 mu m. (C) 2011 Optical Society of America"

"\"Using a low-temperature process, we thermally evaporated Ge thin films on Si substrates and investigated both structural and electrical properties of samples grown at various temperatures. The characterization included X-ray diffraction, atomic force microscopy and Hall measurements and aimed at determining a suitable temperature range in terms of crystal quality and transport properties. Finally, we employed Ge films on Si to fabricate near infrared photodiodes and test them in terms of dark current and responsivity. (C) 2010 Elsevier B.V. All rights reserved.\""

It is described a photodetector structure (1,1′,1"), comprising a silicon-based waveguide (2) in which optical signals to be detected travel in a given direction (X) and are confined therein; a germanium-based layer (4) disposed on a portion of the silicon-based waveguide (2), the germanium layer (4) including a first mesa (10) defining an active region having a length (L) along the signal propagating direction (X) and a width (W) in a direction (Z) substantially perpendicular to the propagating direction (X) so that an evanescent tail of the propagating optical signal in the waveguide (2) is coupled into the active region, and a second mesa (30; 40) separated by a distance d from the first mesa (10) in said direction (Z) substantially perpendicular to the signal propagating direction. The photodetector further includes a first (7) and a second metallic contact (9a,9b) having opposite polarities, the first metallic contact (7) being located on the active region of the first mesa (10) and the second metallic contact (9a, 9b) being located on said second mesa (30), said first and second contact being used to collect electrons generated by light absorption to obtain an output electric signal.

We carried out second-harmonic generation in quasi-phase-matched a-phase lithium niobate channel waveguides realized by proton exchange and surface periodic poling. Owing to a limited ferroelectric domain depth, we could observe the interplay between second-harmonic generation and self-phase modulation due to cascading and cubic effects, resulting in a nonlinear resonance shift. Data reduction allowed us to evaluate both the quadratic nonlinearity in the near infrared as well as the depth of the uninverted domains. (c) 2007 Optical Society of America.

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.

we describe the NIRCAM2, i.e. the first two-dimensional array of 64x8 pixels equipped with readout electronics. The chip includes 64 analog to digital converters, dark current cancellation circuitry and test/calibration facilities. We report on its fabrication, electronic as well as optoelectronic characterization, operation as a CMOS near infrared image sensor.

In recent years, several Ge-on-Si technologies for the fabrication of near infrared photodetectors on Si substrates were proposed. In particular, using a low temperature (300 °C) technique, we have demonstrated poly-Ge_on_Si detectors with high speed and good NIR responsivity. The low process temperature allows the monolithic integration of the detectors as a final step in the fabrication of Si CMOS integrated circuits. After an introduction on poly-Ge, we describe a novel integrated chip (NIRCAM-1) designed as a readout/control circuit for arrays of 64 (32) poly-Ge_on_Si photodetectors. The photodiodes, monolithically integrated (wirebonded with a hybrid approach) on the IC, generate a photocurrent which is then ADC converted after subtraction of the dark component, thus allowing a convenient digital readout of the array. The extensive optoelectronic characterization of the IC is presented

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 µm 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

The term "near infrared" or NIR is most commonly used with reference to a wavelength spectral range between 0.7 and 2.0um. This portion of infrared is of paramount importance in several applications, first among them optical communications with transmission windows located at 0.85, 1.3 and 1.55um, corresponding to GaAs-based laser emission and to two minima in attenuation for standard silica fibers, respectively. Moreover, wavelength division multiplexing for high capacity links encourages to using the whole interval between 1.3 and 1.6ƒÝm (S, C and L bands). Due to the growing demand for wideband internet and massive data transmission, applications have shifted from long-haul point-to-point connections to local networks down to subscribers, softening the specifications and opening entire new markets. Besides communications, NIR spectroscopy is employed in remote sensing of the environment, monitoring of industrial processes, biology and medicine. For example, water has absorption lines which allow to detect its content in the flora for fire prevention, various gas species exhibit NIR absorption bands useful for emission or toxicity analysis. In addition, NIR spectroscopy has been exploited for DNA sequencing, brain activity mapping and cancer detection. However, since optical fiber communications remains the main field driving research in NIR detectors, this chapter will focus on NIR detectors on silicon from the receiver standpoint.Among semiconductor materials, SiGe alloys have allowed to fabricate novel, highly performative electronic devices such as heterojunction bipolar and field-effect transistors ( ), opening new perspectives also in NIR optoelectronics by exploiting the band gap of germanium (0.66eV), much lower than of silicon (1.12eV) which is otherwise useless for detection at these wavelengths. Numerous NIR devices have been proposed, from emitters to waveguides, couplers, modulators and detectors . The centrosymmetry and the indirect nature of Si, Ge and SiGe pose important limitations to SiGe devices as compared to III-V's; nevertheless, exploiting a few structurally related modifications such as quantum confinement, acceptable performances have been foreseen, with the significant advantage of the compatibility with the unsurpassed silicon VLSI technology. The key of success of SiGe-based optoelectronics is the ability to conveniently compromise between material performance and monolithic integration. The fabrication of embedded optoelectronics and electronics in the same process does considerably reduce alignment and interconnection problems, offering improved reliability, yield, compactness and reduced parasitics. Conversely, monolithic integration with SiGe requires heteroepitaxy, which is known to be critical for lattice mismatched materials such as Si and Ge, with mismatch of about 4% . In the specific case of photodetectors, material quality requirements are less stringent than in other devices, thus encouraging towards the realization of innovative and competitive devices.This chapter is organized as follows. After a short introduction on photodetector operation and figures of merit in Section 2, Section 3 deals with SiGe technology for photodiodes, focusing on the quality of both strained and relaxed epilayers, their optical and electrical characteristics and their bearing in device performances. Design strategies and fabrication are discussed in Section 4 along with an overview of the most relevant approach

A photodetector structure includes a silicon-based waveguide in which optical signals to be detected travel in a given direction and are confined therein and a germanium layer disposed in contact with a portion of the silicon-based waveguide so that an evanescent tail of the propagating optical signal in the waveguide is coupled into the germanium layer. In addition, the germanium layer includes a mesa having a length along the signal propagating direction and a width in a direction substantially perpendicular to the propagating direction, in which the width of said mesa is smaller than its length. The photodetector also comprises a first and a second metal contacts, the first metallic contact being located on the germanium layer, the said second metallic contact being located on the silicon-based waveguide, the first and second contacts being used to collect electrons generated by light absorption to obtain an output electric signal.

In the past two decades SiGe has been the material of choice for the realization of near infrared (NIR: 0.7-2ƒÝm) optoelectronic devices based on silicon and its technology, and several groups have developed high performance NIR photodetectors fabricated on Si substrates [ ]. Nevertheless, the existing gap between a good device and its monolithic integration with VLSI electronics on silicon had not been filled until recently, when we demonstrated the first silicon integrated circuit (IC) capable of NIR detection. [2] This was fabricated using a standard technology, but adopting a low temperature approach towards polycrystalline Ge deposition. A low thermal budget, in fact, allows monolithic integration of poly-Ge/Si heterojunction photodiodes with VLSI silicon electronics as a back-end process. After an introduction on both silicon-based NIR photodetectors and compatibility issues, we describe the novel poly-Ge deposition process and discuss the performance of poly-Ge_on_Si devices. Finally, we illustrate linear arrays of NIR detectors integrated with silicon CMOS electronics (front-end, addressing, A/D conversion and readout), demonstrating their operation and the full compatibility with standard Si CMOS technology.

A device for stabilizing the operating wavelength () of an electro-optical component having a nominal operating wavelength (0) by a wavelength influencing circuit adapted to be driven by a control signal. The device comprises a semiconductor photodiode adapted to be impinged upon by the radiation generated and/or processed by the component and to generate an output signal which is indicative of a difference of the wavelength of the radiation (() with respect to the nominal operating wavelength (0, i). The semiconductor photodiode includes a plurality of layers jointly defining two opposite diodes generating opposite photocurrents as a result of radiation impinging onto the photodiode. The opposite photocurrents are adapted to generate the control signal to effect the stabilization action.

We show that the direct epitaxial growth of Ge on Si is a viable technology for the integration of near-infrared photodetectors on Si for Si microphotonics. This conclusion is based on a study of the electronic properties of threading-dislocations in p-n junction and an experimental demonstration of the performance of Ge p-i-n photodiode made from Ge grown directly on Si. At 1.3 μm, we measured a responsivity of 550 mA/W. With the addition of SiO2 anti-reflection coating, we measured a maximum external responsivity of 770 mA/W.

We have investigated the integration of Ge p-i-n and n-i-p heterojunction photodiodes on Si. Recognizing the crucial role of interface defects at the Ge/Si interface on the performance of photodetectors, we have designed and fabricated high-performance n-i-p Ge photodiodes on p(+)-Si substrates. These photodiodes exhibit short-circuit responsivities of 0.3 and 0.2 A/W at 1.3 and 1.55 mum, respectively, reverse dark currents of 20 mA/cm(2) and response times of 800 ps.

We report the fabrication of e cient near-infrared photodetectors based on polycrystalline Ge ® lms on Sih100i. In view of integration with Si electronics, metal± semiconductor± metal photodiodes have been realized, for the ® rst time to the best of our knowledge, by low-temperature evaporation. The experiments performed on non-optimized devices indicate a substantial sensitivity at both 1.32 and 1.55 mm, with a responsivity as high as 16mAW¡1 at 1.32 mm with 0.2 V bias, and a time response of about 4 ns.