Photosensitive Devices Research Articles

Photovoltaic properties of Pt/BiFeO3 thin film/fluorine-doped tin oxide capacitor

We study the photovoltaic properties of the Pt/BiFeO3 (BFO) thin film/fluorine-doped tin oxide capacitor and obtain the open circuit voltage (Voc) of 0.44 V and short circuit photocurrent (Jsc) of 0.14 mA/cm2 under purple laser illumination. As compared to the BFO film with random orientations, the BFO film with a strong preferred orientation exhibits larger photovoltaic output as a result of its larger spontaneous polarization in the unpoled state. We further demonstrate that there is remarkable influence of external electric field poling on the photovoltage in the two polycrystalline BFO films, and the larger net change of the photovoltage after positive and negative poling in the highly preferred oriented BFO film is believed to be due to its improved crystalline structure. Our experiment results indicate that the responsiveness to external electric field and photovoltaic performance of the narrow-band-gap BFO film can be optimized by structural modification, making it possible to apply in the photosensitive and other optoelectronic devices.

High-Sensitivity Photodetectors Based on Multilayer GaTe Flakes

Optoelectronic devices based on layered materials such as graphene have resulted in significant interest due to their unique properties and potential technological applications. The electric and optoelectronic properties of nano GaTe flakes as layered materials are described in this article. The transistor fabricated from multilayer GaTe shows a p-type action with a hole mobility of about 0.2 cm(2) V(-1) s(-1). The gate transistor exhibits a high photoresponsivity of 10(4) A/W, which is greatly better than that of graphene, MoS2, and other layered compounds. Meanwhile, the response speed of 6 ms is also very fast. Both the high photoresponsivity and the fast response time described in the present study strongly suggest that multilayer GaTe is a promising candidate for future optoelectronic and photosensitive device applications.

Ferroelectric photovoltaic properties of Ce and Mn codoped BiFeO3 thin film

Photovoltaic properties of multiferroic (Ce, Mn) codoped BiFeO3 (BCFMO) thin films grown on low cost ITO coated corning glass substrate have been investigated. The transient response of photovoltaic current of the BCFMO thin film in metal-multiferroic-metal (MMM) capacitor configuration is found to be strongly dependent on both the intensity of incident laser light (λ = 405 nm) varying from 15 mW/cm2 to 160 mW/cm2 and thickness of the BCFMO film (110 to 305 nm). Current density-voltage (J-V) measurement shows an exponential increase in photoinduced open circuit voltage and linear increase in short circuit photocurrent with increase in intensity of illuminating light. Almost 240 fold enhancement in photo-induced current is observed in BCFMO thin film of 110 nm thickness. Present work suggests that multiferroic BCFMO thin film deposited on ITO coated corning glass substrate using chemical solution deposition technique exhibits strong photovoltaic response that can be exploited efficiently for the light harvesting and photosensitive device application.

The KM3NeT neutrino telescope: Status and prospects

The KM3NeT Collaboration intends to build and operate a deep-sea research infrastructure that will host as its main facility a neutrino telescope of several cubic kilometres. The infrastructure will be distributed in three sites located near Toulon, France (40km offshore and seabed at 2500m), Capo Passero (80km offshore and seabed at 3500m) and Pylos, Greece (20km offshore and seabed between 2500 and 5000m). In this contribution we describe the technological choices made for the basic components of the three-dimensional array of photo-sensitive devices in which the telescope will consist. The Digital Optical Modules (DOMs) will use a 17in. pressure-resistant sphere to accommodate 31 photomultipliers (PMTs) with a 3in. photocathode each. These DOMs will be installed in detector units (DUs) consisting of vertical strings anchored to the seabed and kept taut by the appropriate buoyancy. These DUs will be deployed by means of launching vehicles that will allow several of them to be deployed in the same campaign. The main features of the telescope and its technical components, the science it can do and the recent progress made towards its construction will be described here.

Mathematical model of aerial photosystem based on photosensitive devices with charge transfer transfer

Mathematical model of aerial photosystem based on photosensitive devices with charge transfer transfer

Исследование линейности аэрофотосистем, построенных на основе фоточувствительных приборов с переносом заряда

Исследование линейности аэрофотосистем, построенных на основе фоточувствительных приборов с переносом заряда

ZnO nanoparticles as a luminescent down-shifting layer for photosensitive devices

The optical properties of ZnO nanoparticles (NPs) fabricated by three different methods were studied by the UV-excited continuous wave photoluminescence in order to estimate their down-shifting (DS) efficiency. Such a luminescent layer modifies the incident solar radiation via emitting wavelengths better matching the spectral response of the underlying photosensitive device (photodiode), thereby increasing its efficiency. Some of the studied ZnO NPs were subsequently deposited on the front side of commercial silicon photodiodes and the external quantum efficiency (EQE) characteristics of the final devices were measured. Through comparison of the photodiode's EQE characteristics before and after the deposition of the ZnO NPs layer, it was concluded that for the photodiode with a low UV sensitivity (about 8%), the ZnO luminescent layer produces a down-shifting effect and the EQE in the UV and blue range improves by 16.6%, while for the photodiodes with a higher initial UV sensitivity (about 50%), the EQE in this range decreases with the ZnO layer thickness, due to the effects competing with DS, like the diminution of the ZnO layer transmittance and an increasing diffusion.

Plasmon-induced photoexcitation of “hot” electrons and “hot” holes in amorphous silicon photosensitive devices containing silver nanoparticles

We report on a plasmon-induced photocurrent in photosensitive devices based on hydrogenated amorphous silicon (a-Si:H) containing silver nanoparticles (NPs). The photocurrent is measured in a spectral region corresponding to optical transitions below the band gap of a-Si:H. Photoexcitation of “hot” electrons in the NPs or in defect states present in the vicinity of the NPs, resulting from plasmon decay in the NPs, is often cited as being responsible for this effect. In this study, we demonstrate that plasmon induced photogeneration of “hot” holes is also able to contribute to a photocurrent. A bifacial symmetrical transparent device was prepared in order to compare the internal quantum efficiency of both processes, the first based on the photogeneration of “hot” electrons and the second based on the photogeneration of “hot” holes.

Upgrade of the CMD-3 BGO Endcap Calorimeter

The BGO endcap calorimeter was successfully operated in the CMD-2 detector at the VEPP-2M collider. It consists of 680 BGO crystals each with a size of 25×25×150 mm3, arranged in two identical endcaps, with a total crystal weight of 450 kg. The light readout used vacuum phototriodes. The endcap calorimeter has now been upgraded to work in the CMD-3 detector at new collider VEPP-2000. The major part of the endcap calorimeter, the BGO crystals, remains the same. The main upgrade is the use of silicon PIN photodiodes and new electronics. Main reason to change photosensitive device is the strong non-uniform magnetic field in the endcap calorimeter volume so the vacuum photosensitive devices cannot operate in such magnetic fields. Also the available space for the endcap calorimeter space had to be reduced. The Hamamatsu PIN photodiode S3590-08 was chosen as the optimal solution, as they are insensitive to magnetic fields and are both compact and stable. An order of magnitude larger capacitance of silicon photodiodes requires design and produce new custom electronics. The upgrade is expected to bring an overall improvement of parameters. The endcap calorimeter has been installed in the detector and participates in data taking which started at 2010. The preliminary data analysis shows an improvement of the energy resolution compare to the CMD-2 detector.

VSiPMT for underwater neutrino telescopes

Underwater neutrino telescopes are nowadays considered among the most important aims in the field of astroparticle physics. Their structure consists of a cubic-kilometer three-dimensional array of photosensitive devices aimed at the detection of the Cherenkov light emitted by charged particles produced by high energy neutrino interactions with the Earth.To date, a crucial role in this kind of experiments has been played by PhotoMultiplier Tubes (PMTs), however they suffer from many drawbacks such as linearity-to-gain relationship and difficulty in single photon counting. The next generation of experiments will require further improvements in photon detectors performances, therefore alternatives to PMTs are currently under study.In particular the most promising development in this field is represented by the rapidly emerging CMOS p-n Geiger-mode avalanche photodiode technology (G-APD or SiPM), that will allow the detection of high-speed single photons with high gain and linearity. In order to overcome the limit of small sensitive surfaces we suggest an innovative design for a modern hybrid, high gain, silicon based Vacuum Silicon Photomultiplier Tube (VSiPMT) based on the combination of a SiPM with a hemispherical vacuum glass PMT standard envelope. In this work we describe the full SiPM characterization realized by our group and we present the results of our Geant4-based simulations of electron backscattering over the SiPM surface.

A large surface photomultiplier based on SiPMs

Light detection through photosensitive devices represents one of the key issues for a large variety of experiments. In the recent years, Silicon PhotoMultipliers (SiPMs) based on limited Geiger-mode avalanche have been extensively studied in view of their future applications. However, their use is strongly limited by their small sensitive surfaces and by the fact that any increment in the surface turns out into an increase of the dark count rate. In the present work we describe the dark count rate reduction obtained by using a FPGA-based logical circuit for fast pre-processing of pulses from a 3×3 matrix of SiPMs. The prototype we developed supports two SiPMs: we show that a rate reduction from 6.6Mcps (Mega counts per second) down to 0.436Mcps at the lowest threshold (0.5 photon-equivalent) and from 1.2kcps down to 0.02cps for the highest threshold (3.5 photon-equivalent) is obtainable.

Noise Performance of a Regulated Cascode Transimpedance Amplifier for Radiation Detectors

A low noise transimpedance amplifier (TIA) is used in radiation detectors to transform the current pulse produced by a photo-sensitive device into an output voltage pulse with a specified amplitude and shape. We consider here the specifications of a PET (positron emission tomography) system. We review the traditional approach, feedback TIA, using an operational amplifier with feedback, and we investigate two alternative circuits: the common-gate TIA, and the regulated cascode TIA. We derive the transimpedance function (the poles of which determine the pulse shaping); we identify the transistor in each circuit that has the dominant noise source, and we obtain closed-form equations for the rms output noise voltage. We find that the common-gate TIA has high noise, but the regulated cascode TIA has the same dominant noise contribution as the feedback TIA, if the same maximum transconductance value is considered. A circuit prototype of a regulated cascode TIA is designed in a 0.35 μm CMOS technology, to validate the theoretical results by simulation and by measurement.

Solid-State Solar Simulator

This paper presents an efficient, low-cost, and versatile LED-based solar simulator intended to produce a well-characterized spectrum for tests of solar cells and other photosensitive devices. Three major design aspects are addressed: LED spectra, power converters for LED drive, and control. The visible light of a standard solar spectrum is simulated using six LED colors. The number of LEDs and their placement for uniformity are addressed. Boost converters under current-mode control are used to achieve reproducible LED brightness through adjustable currents, or equivalent radiant-flux commands. The independent control of the six colors can simulate a range of different light sources and solar spectra. Uniformity tests verify that the system achieves standard spectral uniformity requirements over an area of 100 mm × 100 mm in simulations and 100 mm × 50 mm in experiments. LEDs in the proposed simulator consume less power and reduce the simulator size compared to the available state of the art. The user-friendly interface also allows active control of the simulated spectrum.

Successive Spray Deposition of P3HT/PCBM Organic Photoactive Layers: Material Composition and Device Characteristics

AbstractControlling the active layer composition in organic electronic devices represents one of the major challenges in their fabrication. In particular, the composition of mixed donor/acceptor active layers for photosensitive device applications is known to strongly influence device performance. Here, an alternative approach for the preparation of organic heterojunction photoactive layers by successive spray deposition of the donor material, poly(3‐hexylthiophene) (P3HT), and acceptor material, [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM), is reported. Optical absorption spectra, X‐ray reflectivity, and cross‐sectional transmission electron microscopy investigations are used to indicate the penetration of PCBM into a previously deposited P3HT layer and the spontaneous formation of a bulk heterojunction (BHJ) within the active layer, which provides the large interfacial area needed for efficient exciton dissociation. It is shown that organic photodiodes composed of photoactive layers prepared using this fabrication method exhibit a performance comparable to conventional BHJ devices in which the active layer is rigorously blended in advance. Moreover, separate handling of the individual materials and their deposition from distinct solutions enables an enhanced control of the active layer composition and hence increases the ability of tuning device characteristics.

The Fabrication of La<sub>0.9</sub>Sr<sub>0.1</sub>CoO<sub>3</sub> Thin Films and its LITV Effect Applications

High quality La0.9Sr0.1CoO3 (LSCO) thin films grown on 5° vicinal cut LaAlO3 (LAO) (100) substrates were deposited by pulse laser deposition (PLD). Laser induced thermoelectric voltage (LITV) was detected instantly with fast response time and extremely narrow full width at half maximum (FWHM) when 248 nm pulse laser radiated on the surface of LSCO thin films. These merits of LSCO thin films make it one ideal material to fabricate light detectors and photosensitive device. With the increase of pulse laser energy, the peak voltages increase linearly, so LSCO thin films can be used to make high precision laser energy/power meter.

Structural, electronic and optical properties of titania nanotubes

This review paper describes primarily recent theoretical calculations with some supporting experimental findings on titania nanotubes. Nanotubes with different types and sizes are discussed in detail in terms of existing theoretical and experimental achievements. Both classical and quantum mechanical simulations are focused on. The properties of these nanotubes have been treated within first principle density functional electronic structure simulation methods. In this paper, we pay particular attention to computational aspects, but when appropriate, relationships with experimental results on titania nanostructures will be mentioned. First, the structural properties of titania nanotubes are reviewed, focusing from experimental growth mechanism to possible theoretical stable structure and orientation. Second, the electronic structure of nanotubes is discussed in terms of band gap modifications of titania and photocatalytic efficiencies in photoelectrochemical devices. Finally, current computational limitations and future directions are described with respect to the performances of nanotube titania based photosensitive devices.

Cadmium Sulfide Nanostructures for Photovoltaic Devices

Cadmium sulfide (CdS) nanostructures have been found to be attractive for possible applications in semiconductor lasers, light emitting diodes, photovoltaic cells, display devices and biological sensing. The present paper reviews our work on the potential of CdS based nanostructures and composites for photovoltaic and photosensitive devices. The realization of a hybrid photovoltaic device has been demonstrated by the dispersion of multi-walled carbon nanotube (MWCNT)–CdS nanocomposites in a conducting polymer [poly(3-hexylthiophene)] (P3HT) matrix. An improved photovoltaic effect has been observed in MWCNT–CdS/P3HT composite over control P3HT polymeric device. An improved photocurrent spectrum with broadband response (visible to near-infrared region) has been demonstrated in the Ge/CdS core–shell heterojunction nanowires, making them useful candidates for nanowire heterojunction solar cells.

Light Concentrators for Silicon Photomultipliers

Photosensitive devices represent a key solution for several current and future categories of experiments in which photon detection is the crucial point for the observation of physical phenomena. Astro particle experiments for instance, one of the most promising observation channels for High Energy Physics, typically study energetic phenomena in which charged particles originating from the interactions or decays of primary particles radiate Cherenkov or fluorescence light, which is then detected by photosensitive devices. In these fields of applications, the Silicon Photomultipliers (SiPM) devices based on the limited Geiger-mode avalanche (generally G-APD, Geiger Avalanche Photons Detectors), are extensively under study. Unfortunately, applications of SiPMs are very limited by their small sensitive surfaces. In order to overcome the limits of the small dimensions of the sensitive area of SiPM devices, different solutions are reported. In particular it is discussed the use of Optical Concentrators with the correct refraction index, characteristic and geometry for the improvement of the sensitive surface dimensions of a SiPM device.

Optimized Design of Sun Position Detection Sensor

With the object of optical sensor detects the position of the sun, the working principle of the sun position detection system based on four photosensitive devices was analyzed.The sensitive part of this type of sensors was analyzed with optimization. Silicon photocells were selected as optical elements . The main factors and interactions between them which affect the accuracy of the sensor were analyzed using the idea of orthogonal experiment and related software , the optimal combination for the size of the sensor structure was got.

Adaptation to the Scene in Color Imaging

In the field of digital imaging, there are pixel topologies whose color detection capability relies on the Silicon absorption properties rather than on the presence of a Color Filter Array (CFA) deposited on top of the pixels. The spectral response of the different color channels is thus not always determined a priori as in the case of a CFA, but it depends on the way photocarriers are collected from the Silicon bulk. In some cases, the spectral responses can be tuned so that the sensor has pixels with an adjustable color space. Color space tunability potentially enables new features to be implemented at pixel level. In this paper, the discussion and the experimental results are focused on the Transverse Field Detector (TFD), a CMOS photosensitive device for imaging applications that performs color detection without color filters. Thanks to the innovative working principle, based on the generation of transverse electric fields in a depleted region of a semiconductor active layer, the color space of a TFD can be real-time adjusted by means of voltage tuning. Three different applications of color space tunability are discussed: the increase/decrease of color saturation, the implementation of white balance by tunable spectral responsivities, and the improvement of interleaved imaging for high dynamic range sensors.