Photodetectors are of great interest in several technological applications thanks to their capability to convert an optical signal into an electrical one through light-matter interactions. In particular, broadband photodetectors are used in multiple applications such as environmental monitoring, imaging, fire detection, and astronomical observations. We present a two-dimensional photodiode heterojunction based on reduced graphene oxide (rGO) deposited on an n-type Silicon substrate. We report on the electro-optical properties of the device that have been measured in dark and light conditions into a spectral range from UV to IR. The room temperature current-voltage (I-V) measurements of rGO/n-Si photodetector exhibits a reverse saturation current linearly dependent on the light power. The main figures of merit of the photodetector such as linearity and responsivity have been evaluated and compared with the recent progress obtained substituting the rGO with a graphene single layer (Gr) on the similar n-Si substrate. The photoconductive properties and analysis of the two devices are presented and discussed. Finally, the experimental results demonstrate the feasibility of the rGO/n-Si and Gr/n-Si device to detect light from UV to IR light, nominating graphene-based heterojunction as a novel candidate for the realization of new broadband photodetectors.

Terahertz (THz) technology has recently attracted wide scientific and technological interests in quantum science, where the need of fast and sensitive photodetectors prospects fascinating impacts in quantum computing, quantum metrology and optical communications. In this work, we demonstrate that quantum dot single electron transistors (SETs) based on InAs/InAs0.3P0.7 axially heterostructured nanowires integrated with planar on-chip nano-antennas, behave as highly sensitive zero-bias photo-thermoelectric detectors at 0.6 THz. The detector photoresponse can be optimized by electrostatic gating, taking advantage of the SET transport characteristics that clearly reflects energy quantization and single-electron tunneling in the dot.

For the future JET deuterium-tritium (DT) campaigns numerous gamma-ray diagnostics, in particular the JET Gamma-ray Camera (GC) and the JET Gamma-ray Spectrometer (GS), were upgraded in the last few years. The upgrade of GC and GS included replacement of detector modules in order to allow operation at expected high count rate of ~0.5 Mcps on the scintillator front surface of 506 mm2 for each GC crystal and 7 squared inches for GS as well as to improve energy resolution to equal or better than 5% at gamma-ray energy above 1.1 MeV for both diagnostics. Within the JET4 Enhancements Project, performance of a number of photodetectors including multi-pixel photon counter (MPPC), PIN diode and photomultiplier tube (PMT) connected to scintillators was investigated. Upgraded detector modules are based on fast scintillators with a decay time of about 20 ns, LaBr3:Ce and CeBr3, coupled to MPPC and PMT for GC and GS, respectively. Results on energy resolution obtained with upgraded diagnostics, already installed at JET, are presented and compared to those collected in laboratory conditions.

We demonstrate a THz detector that is made of high-quality graphene and is based on the photo-thermoelectric (PTE) effect: absorbed THz light leads to hot-carriers that generate a photoresponse at a junction between two graphene regions with different carrier density, ideally a pn-junction. Our photodetector combines a device geometry that is optimized for the PTE effect with an antenna that focuses the THz light at the pn-junction. We find that the noise-equivalent power (NEP) at room temperature is < 200 mathrm{pW}/sqrt{mathrm{Hz}}, while the response time is < 40 ns (limited by the measurement setup)-many orders of magnitude faster than commercial room temperature detectors.

Simulations and phantom measurements are used to evaluate the ability of time- domain diffuse optical tomography using Mellin-Laplace transforms to quantify the absorption perturbation of centimetric objects immersed at depth 1-2 cm in turbid media. We find that the estimated absorption coefficient varies almost linearly with the absorption change in the range of 0-0.15 cm-1 but is underestimated by a factor that depends on the inclusion depth (~2, 3 and 6 for depths of 1.0, 1.5 and 2.0 cm respectively). For larger absorption changes, the variation is sublinear with ~20% decrease for ??a = 0.37 cm-1. By contrast, constraining the absorption change to the actual volume of the inclusion may considerably improve the accuracy and linearity of the reconstructed absorption.

We device plasmonic, bolometric and thermoelectric antenna-coupled Terahertz photodetectors based on black phosphorus and hybrid van der Walls heterostructures, showing 20000 signal to noise ratios and 100pW/Hz1/2 noise equivalent powers in the 0.3-3 THz frequency range.

We characterized the single-photon timing response function of various silicon photomultipliers (SiPMs) over a broad (500-1100 nm) spectral range. We selected two SiPM manufacturers, and we investigated two active areas, i.e., a small (1-1.69 mm(2)) and a large (9 mm2) one, for each of them. We demonstrate that selected SiPMs are suitable for time-resolved diffuse optics (DO) applications where a very large detection area and sensitivity down to single photons are crucial to detecting the very faint return signal from biological tissues, like the brain, thus allowing replacement of photomultiplier tubes and opening the way to a novel generation of DO multichannel instrumentation. Due to our custom front-end electronics, we show the world's best single-photon timing resolution for SiPMs, namely, 57-ps full-width at half maximum for Hamamatsu 1.69 mm(2) and 115 ps for Excelitas 9 mm(2). Even further, we provide a thorough spectral investigation of the full single-photon timing response function, also detailing diffusion tails' time constants and dynamic range. The achieved insight and the reported performance open the way to a widespread diffusion of SiPMs not just in many-photon regimes (e.g., PET) but at single-photon counting regimes like DO as well.

We present the experimental investigation of the coherence properties of the light produced by parametric down conversion in the macroscopic regime, also including pump depletion. In particular, we compare the results obtained in very similar geometric conditions by using two nonlinear crystals having different lengths. We observe that the number of generated photons, the size of spatio-spectral coherence areas, and the number of modes in the photon number statistics exhibit a similar behavior in the two crystals as a function of pump mean power, even if we notice that the absolute values are different. The available theory of parametric down conversion cannot account for these differences.

In this paper, design, fabrication and characterization of an all-silicon photodetector (PD) at 1550 nm, have been reported. Our device is a surface-illuminated PD constituted by a Fabry-Perot microcavity incorporating a Cu/p-Si Schottky diode. Its absorption mechanism, based on the internal photoemission effect (IPE), has been enhanced by critical coupling condition. Our experimental findings prove a peak responsivity of 0.063 mA/W, which is the highest value obtained in a surface-illuminated IPE-based Si PD around 1550 nm. Finally, device capacitance measurements have been carried out demonstrating a capacitance &lt; 5 pF which has the potential for GHz operation subject to a reduction of the series resistance of the ohmic contact.

We investigate the possibility of using linear detectors that exhibit a response to dark just resolved from that corresponding to a single detected photon to reconstruct the photon-number statistics of pulsed fields containing sizeable numbers of photons per pulse. We demonstrate that by applying a self-consistent procedure to analyze the output pulses of such detectors, we can properly measure statistical distributions of the number of detected photons and photon number correlations. The lack of fulfillment of such minimal requirements impairs the possibility of reliable shot-by-shot determinations of photon numbers. © 2011 World Scientific Publishing Company.

We propose a near infrared all-silicon integrated photodetector based on the internal photoemission effect. Device is charactered by a responsivity of 0.08 mA/W at 1550 nm for a reverse bias of 1 V. © 2011 IEEE.

Ge thin films are epitaxially grown onto (1 0 0) Si substrates by DC-Pulsed Magnetron Sputtering. Relaxed single crystalline layers, with slightly misoriented domains are identified by XRD, TEM and HREM. Planar defects and threading dislocations are the relevant lattice imperfections. As-deposited Ge films are p-type without the need for intentional doping, even in the absence of grain boundaries. A pronounced flatness in the near IR absorption spectra is evident, in the absence of strong interfacial strain. This could be traced to a bandgap narrowing effect due to intragap states related to defects in the interfacial region. Photoconductive response around ? = 1.5 ?m is flat and an equivalent responsivity R eff| Vbias = -1V = 1.0088 A/W at ? = 1.5 ?m has been estimated. DC-Pulsed Magnetron Sputtering is therefore an attractive solution, deserving further development, to build near-infrared C-MOS compatible photodetectors, particularly suitable for low-speed applications. © 2010 Elsevier B.V. All rights reserved.

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.

In this paper we discuss strategies for the development of fast photodetectors suitable for operation in the lambda > 850 nm near-infrared (NIR) spectral region in the ITER core LIDAR Thomson scattering (TS) system. Detection of this spectral range is necessary if a Nd:YAG laser operating at the fundamental wavelength (lambda = 1.06 mu m) will be used as the input laser source. Different types of NIR photodetectors are potentially suitable for use in ITER LIDAR TS: the transferred electron (TE) InGaAsP/InP hybrid photodiodes and microchannel plate photomultipliers (MCP PMTs), the In(x)Ga(1-x)As MCP image intensifiers and PMTs, and the detectors based on transmission Si photocathodes. But their characteristics of either sensitivity, active area or speed of response, do not match the ITER specifications and all devices require some developmental work. For each of these detector types we review the characteristics of devices presently available and suggest a realistic development strategy suitable to extend their performances to meet the ITER specifications. Finally the expected performance of the ITER LIDAR TS system for different detector choices are compared by calculating the expected signal-to-noise ratio of the measured plasma temperature and density.

In this paper the realization and the characterization of a new kind of resonant cavity enhanced photodetector (RCE), fully compatible with silicon microelectronic technologies and working at 1.55 ?m, are reported. © 2010 Springer Science+Business Media B.V.

In this paper, the design of a novel photodetector at 1.55 ?m, working at room temperature and completely silicon compatible, is reported. The device is a resonant cavity enhanced (RCE) structure incorporating a silicon photodetector based on the internal photoemission effect. In order to quantify the performance of photodetector, quantum efficiency including the image force effect, bandwidth and dark current as a function of bias voltage is numerically calculated. A comparison among three different Schottky barrier silicon photodetectors, having as metal layers gold, silver or copper respectively, is proposed. The highest efficiency (0.2%) but also the highest dark current is obtained with metal having the lowest barrier, while for all devices, values of the order of 100 GHz and 100 MHz were obtained, respectively, for the carrier transit time limited 3 dB bandwidth and bandwidth efficiency.

The experimental characterization of an innovative optical system for detection of carbon monoxide (CO) is reported. In this system a photodetector based on gallium nitride (GaN) and an UV light source are integrated. The gas flows between the light source and the GaN photodetector. The UV light source consists of a spark produced by an arc discharge which induced transitions in the gas, causing a modification of the light intensity as a function of gas composition. These transitions modify the fraction of light in the UV spectral region which is detected by the GaN-photodetector, as a function of the species concentration. By virtue of its structural properties, gallium nitride (GaN) allows to operate at high temperature and high speed and to work insitu in the exhaust manifold of combustion engines at temperatures as high as 600°C, at which the deposited organic residuals on the detector can be oxidized. This assures the clear surface needed for a real time optical measurement of the species concentration to be used for a closed loop control of the fuel injection process. The system was applied to the detection of CO with concentration between 0-2,4% in a buffer of pure nitrogen gas, showing an increase in the measured photocurrent as a function of the above gases. © 2006 IEEE.