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15 pages, 1193 KiB

Open AccessArticle

Identification and Quantification of Explosives in Nanolitre Solution Volumes by Raman Spectroscopy in Suspended Core Optical Fibers

by Georgios Tsiminis, Fenghong Chu, Stephen C. Warren-Smith, Nigel A. Spooner and Tanya M. Monro

Sensors 2013, 13(10), 13163-13177; https://doi.org/10.3390/s131013163 - 30 Sep 2013

Cited by 38 | Viewed by 8810

Abstract

A novel approach for identifying explosive species is reported, using Raman spectroscopy in suspended core optical fibers. Numerical simulations are presented that predict the strength of the observed signal as a function of fiber geometry, with the calculated trends verified experimentally and used [...] Read more.

A novel approach for identifying explosive species is reported, using Raman spectroscopy in suspended core optical fibers. Numerical simulations are presented that predict the strength of the observed signal as a function of fiber geometry, with the calculated trends verified experimentally and used to optimize the sensors. This technique is used to identify hydrogen peroxide in water solutions at volumes less than 60 nL and to quantify microgram amounts of material using the solvent’s Raman signature as an internal calibration standard. The same system, without further modifications, is also used to detect 1,4-dinitrobenzene, a model molecule for nitrobenzene-based explosives such as 2,4,6-trinitrotoluene (TNT). Full article

(This article belongs to the Special Issue Photodetectors)

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34 pages, 907 KiB

Open AccessArticle

Currents Induced by Injected Charge in Junction Detectors

by Eugenijus Gaubas, Tomas Ceponis and Vidas Kalesinskas

Sensors 2013, 13(9), 12295-12328; https://doi.org/10.3390/s130912295 - 12 Sep 2013

Cited by 10 | Viewed by 6196

Abstract

The problem of drifting charge-induced currents is considered in order to predict the pulsed operational characteristics in photo-and particle-detectors with a junction controlled active area. The direct analysis of the field changes induced by drifting charge in the abrupt junction devices with a [...] Read more.

The problem of drifting charge-induced currents is considered in order to predict the pulsed operational characteristics in photo-and particle-detectors with a junction controlled active area. The direct analysis of the field changes induced by drifting charge in the abrupt junction devices with a plane-parallel geometry of finite area electrodes is presented. The problem is solved using the one-dimensional approach. The models of the formation of the induced pulsed currents have been analyzed for the regimes of partial and full depletion. The obtained solutions for the current density contain expressions of a velocity field dependence on the applied voltage, location of the injected surface charge domain and carrier capture parameters. The drift component of this current coincides with Ramo’s expression. It has been illustrated, that the synchronous action of carrier drift, trapping, generation and diffusion can lead to a vast variety of possible current pulse waveforms. Experimental illustrations of the current pulse variations determined by either the rather small or large carrier density within the photo-injected charge domain are presented, based on a study of Si detectors. Full article

(This article belongs to the Special Issue Photodetectors)

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11 pages, 273 KiB

Open AccessArticle

Visible Light Communication System Using an Organic Bulk Heterojunction Photodetector

by Belén Arredondo, Beatriz Romero, José Manuel Sánchez Pena, Agustín Fernández-Pacheco, Eduardo Alonso, Ricardo Vergaz and Cristina De Dios

Sensors 2013, 13(9), 12266-12276; https://doi.org/10.3390/s130912266 - 12 Sep 2013

Cited by 60 | Viewed by 10462

Abstract

A visible light communication (VLC) system using an organic bulk heterojunction photodetector (OPD) is presented. The system has been successfully proven indoors with an audio signal. The emitter consists of three commercial high-power white LEDs connected in parallel. The receiver is based on [...] Read more.

A visible light communication (VLC) system using an organic bulk heterojunction photodetector (OPD) is presented. The system has been successfully proven indoors with an audio signal. The emitter consists of three commercial high-power white LEDs connected in parallel. The receiver is based on an organic photodetector having as active layer a blend of poly(3-hexylthiophene) (P3HT) and phenyl C61-butyric acid methyl ester (PCBM). The OPD is opto-electrically characterized, showing a responsivity of 0.18 A/W and a modulation response of 790 kHz at −6 V. Full article

(This article belongs to the Special Issue Photodetectors)

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38 pages, 3026 KiB

Open AccessArticle

Theoretical Analysis of Interferometer Wave Front Tilt and Fringe Radiant Flux on a Rectangular Photodetector

by Robert Smith and Franz Konstantin Fuss

Sensors 2013, 13(9), 11861-11898; https://doi.org/10.3390/s130911861 - 6 Sep 2013

Cited by 6 | Viewed by 9031

Abstract

This paper is a theoretical analysis of mirror tilt in a Michelson interferometer and its effect on the radiant flux over the active area of a rectangular photodetector or image sensor pixel. It is relevant to sensor applications using homodyne interferometry where these [...] Read more.

This paper is a theoretical analysis of mirror tilt in a Michelson interferometer and its effect on the radiant flux over the active area of a rectangular photodetector or image sensor pixel. It is relevant to sensor applications using homodyne interferometry where these opto-electronic devices are employed for partial fringe counting. Formulas are derived for radiant flux across the detector for variable location within the fringe pattern and with varying wave front angle. The results indicate that the flux is a damped sine function of the wave front angle, with a decay constant of the ratio of wavelength to detector width. The modulation amplitude of the dynamic fringe pattern reduces to zero at wave front angles that are an integer multiple of this ratio and the results show that the polarity of the radiant flux changes exclusively at these multiples. Varying tilt angle causes radiant flux oscillations under an envelope curve, the frequency of which is dependent on the location of the detector with the fringe pattern. It is also shown that a fringe count of zero can be obtained for specific photodetector locations and wave front angles where the combined effect of fringe contraction and fringe tilt can have equal and opposite effects. Fringe tilt as a result of a wave front angle of 0.05° can introduce a phase measurement difference of 16° between a photodetector/pixel located 20 mm and one located 100 mm from the optical origin. Full article

(This article belongs to the Special Issue Photodetectors)

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25 pages, 1218 KiB

Open AccessArticle

A Comparative Analysis between Active and Passive Techniques for Underwater 3D Reconstruction of Close-Range Objects

by Gianfranco Bianco, Alessandro Gallo, Fabio Bruno and Maurizio Muzzupappa

Sensors 2013, 13(8), 11007-11031; https://doi.org/10.3390/s130811007 - 20 Aug 2013

Cited by 89 | Viewed by 11537

Abstract

In some application fields, such as underwater archaeology or marine biology, there is the need to collect three-dimensional, close-range data from objects that cannot be removed from their site. In particular, 3D imaging techniques are widely employed for close-range acquisitions in underwater environment. [...] Read more.

In some application fields, such as underwater archaeology or marine biology, there is the need to collect three-dimensional, close-range data from objects that cannot be removed from their site. In particular, 3D imaging techniques are widely employed for close-range acquisitions in underwater environment. In this work we have compared in water two 3D imaging techniques based on active and passive approaches, respectively, and whole-field acquisition. The comparison is performed under poor visibility conditions, produced in the laboratory by suspending different quantities of clay in a water tank. For a fair comparison, a stereo configuration has been adopted for both the techniques, using the same setup, working distance, calibration, and objects. At the moment, the proposed setup is not suitable for real world applications, but it allowed us to conduct a preliminary analysis on the performances of the two techniques and to understand their capability to acquire 3D points in presence of turbidity. The performances have been evaluated in terms of accuracy and density of the acquired 3D points. Our results can be used as a reference for further comparisons in the analysis of other 3D techniques and algorithms. Full article

(This article belongs to the Special Issue Photodetectors)

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20 pages, 510 KiB

Open AccessArticle

A Phenomenological Model for the Photocurrent Transient Relaxation Observed in ZnO-Based Photodetector Devices

by James C. Moore and Cody V. Thompson

Sensors 2013, 13(8), 9921-9940; https://doi.org/10.3390/s130809921 - 5 Aug 2013

Cited by 101 | Viewed by 10486

Abstract

We present a phenomenological model for the photocurrent transient relaxation observed in ZnO-based metal-semiconductor-metal (MSM) planar photodetector devices based on time-resolved surface band bending. Surface band bending decreases during illumination, due to migration of photogenerated holes to the surface. Immediately after turning off [...] Read more.

We present a phenomenological model for the photocurrent transient relaxation observed in ZnO-based metal-semiconductor-metal (MSM) planar photodetector devices based on time-resolved surface band bending. Surface band bending decreases during illumination, due to migration of photogenerated holes to the surface. Immediately after turning off illumination, conduction-band electrons must overcome a relatively low energy barrier to recombine with photogenerated holes at the surface; however, with increasing time, the adsorption of oxygen at the surface or electron trapping in the depletion region increases band bending, resulting in an increased bulk/surface energy barrier that slows the transport of photogenerated electrons. We present a complex rate equation based on thermionic transition of charge carriers to and from the surface and numerically fit this model to transient photocurrent measurements of several MSM planar ZnO photodetectors at variable temperature. Fitting parameters are found to be consistent with measured values in the literature. An understanding of the mechanism for persistent photoconductivity could lead to mitigation in future device applications. Full article

(This article belongs to the Special Issue Photodetectors)

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19 pages, 1873 KiB

Open AccessArticle

Photo-Detectors Integrated with Resonant Tunneling Diodes

by Bruno Romeira, Luis M. Pessoa, Henrique M. Salgado, Charles N. Ironside and José M. L. Figueiredo

Sensors 2013, 13(7), 9464-9482; https://doi.org/10.3390/s130709464 - 22 Jul 2013

Cited by 48 | Viewed by 12321

Abstract

We report on photo-detectors consisting of an optical waveguide that incorporates a resonant tunneling diode (RTD). Operating at wavelengths around 1.55 μm in the optical communications C band we achieve maximum sensitivities of around 0.29 A/W which is dependent on the bias [...] Read more.

We report on photo-detectors consisting of an optical waveguide that incorporates a resonant tunneling diode (RTD). Operating at wavelengths around 1.55 μm in the optical communications C band we achieve maximum sensitivities of around 0.29 A/W which is dependent on the bias voltage. This is due to the nature of RTD nonlinear current-voltage characteristic that has a negative differential resistance (NDR) region. The resonant tunneling diode photo-detector (RTD-PD) can be operated in either non-oscillating or oscillating regimes depending on the bias voltage quiescent point. The oscillating regime is apparent when the RTD-PD is biased in the NDR region giving rise to electrical gain and microwave self-sustained oscillations Taking advantage of the RTD’s NDR distinctive characteristics, we demonstrate efficient detection of gigahertz (GHz) modulated optical carriers and optical control of a RTD GHz oscillator. RTD-PD based devices can have applications in generation and optical control of GHz low-phase noise oscillators, clock recovery systems, and fiber optic enabled radio frequency communication systems. Full article

(This article belongs to the Special Issue Photodetectors)

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21 pages, 872 KiB

Open AccessArticle

Electric Field and Current Transport Mechanisms in Schottky CdTe X-ray Detectors under Perturbing Optical Radiation

by Adriano Cola and Isabella Farella

Sensors 2013, 13(7), 9414-9434; https://doi.org/10.3390/s130709414 - 22 Jul 2013

Cited by 21 | Viewed by 8411

Abstract

Schottky CdTe X-ray detectors exhibit excellent spectroscopic performance but suffer from instabilities. Hence it is of extreme relevance to investigate their electrical properties. A systematic study of the electric field distribution and the current flowing in such detectors under optical perturbations is presented [...] Read more.

Schottky CdTe X-ray detectors exhibit excellent spectroscopic performance but suffer from instabilities. Hence it is of extreme relevance to investigate their electrical properties. A systematic study of the electric field distribution and the current flowing in such detectors under optical perturbations is presented here. The detector response is explored by varying experimental parameters, such as voltage, temperature, and radiation wavelength. The strongest perturbation is observed under 850 nm irradiation, bulk carrier recombination becoming effective there. Cathode and anode irradiations evidence the crucial role of the contacts, the cathode being Ohmic and the anode blocking. In particular, under irradiation of the cathode, charge injection occurs and peculiar kinks, typical of trap filling, are observed both in the current-voltage characteristic and during transients. The simultaneous access to the electric field and the current highlights the correlation between free and fixed charges, and unveils carrier transport/collection mechanisms otherwise hidden. Full article

(This article belongs to the Special Issue Photodetectors)

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Graphical abstract

9 pages, 432 KiB

Open AccessArticle

Performance Enhancement of a GaAs Detector with a Vertical Field and an Embedded Thin Low-Temperature Grown Layer

by Marc Currie, Pouya Dianat, Anna Persano, Maria Concetta Martucci, Fabio Quaranta, Adriano Cola and Bahram Nabet

Sensors 2013, 13(2), 2475-2483; https://doi.org/10.3390/s130202475 - 18 Feb 2013

Cited by 8 | Viewed by 7786

Abstract

Low temperature growth of GaAs (LT-GaAs) near 200 °C results in a recombination lifetime of nearly 1 ps, compared with approximately 1 ns for regular temperature ~600 °C grown GaAs (RT-GaAs), making it suitable for ultra high speed detection applications. However, LT-GaAs detectors [...] Read more.

Low temperature growth of GaAs (LT-GaAs) near 200 °C results in a recombination lifetime of nearly 1 ps, compared with approximately 1 ns for regular temperature ~600 °C grown GaAs (RT-GaAs), making it suitable for ultra high speed detection applications. However, LT-GaAs detectors usually suffer from low responsivity due to low carrier mobility. Here we report electro-optic sampling time response measurements of a detector that employs an AlGaAs heterojunction, a thin layer of LT-GaAs, a channel of RT-GaAs, and a vertical electric field that together facilitate collection of optically generated electrons while suppressing collection of lower mobility holes. Consequently, these devices have detection efficiency near that of RT-GaAs yet provide pulse widths nearly an order of magnitude faster—~6 ps for a cathode-anode separation of 1.3 μm and ~12 ps for distances more than 3 μm. Full article

(This article belongs to the Special Issue Photodetectors)

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Review

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35 pages, 1896 KiB

Open AccessReview

Development of an Amorphous Selenium-Based Photodetector Driven by a Diamond Cold Cathode

by Tomoaki Masuzawa, Ichitaro Saito, Takatoshi Yamada, Masanori Onishi, Hisato Yamaguchi, Yu Suzuki, Kousuke Oonuki, Nanako Kato, Shuichi Ogawa, Yuji Takakuwa, Angel T. T. Koh, Daniel H. C. Chua, Yusuke Mori, Tatsuo Shimosawa and Ken Okano

Sensors 2013, 13(10), 13744-13778; https://doi.org/10.3390/s131013744 - 11 Oct 2013

Cited by 49 | Viewed by 12639

Abstract

Amorphous-selenium (a-Se) based photodetectors are promising candidates for imaging devices, due to their high spatial resolution and response speed, as well as extremely high sensitivity enhanced by an internal carrier multiplication. In addition, a-Se is reported to show sensitivity against wide variety of [...] Read more.

Amorphous-selenium (a-Se) based photodetectors are promising candidates for imaging devices, due to their high spatial resolution and response speed, as well as extremely high sensitivity enhanced by an internal carrier multiplication. In addition, a-Se is reported to show sensitivity against wide variety of wavelengths, including visible, UV and X-ray, where a-Se based flat-panel X-ray detector was proposed. In order to develop an ultra high-sensitivity photodetector with a wide detectable wavelength range, a photodetector was fabricated using a-Se photoconductor and a nitrogen-doped diamond cold cathode. In the study, a prototype photodetector has been developed, and its response to visible and ultraviolet light are characterized. Full article

(This article belongs to the Special Issue Photodetectors)

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37 pages, 1229 KiB

Open AccessReview

A Comprehensive Review of Semiconductor Ultraviolet Photodetectors: From Thin Film to One-Dimensional Nanostructures

by Liwen Sang, Meiyong Liao and Masatomo Sumiya

Sensors 2013, 13(8), 10482-10518; https://doi.org/10.3390/s130810482 - 13 Aug 2013

Cited by 769 | Viewed by 31936

Abstract

Ultraviolet (UV) photodetectors have drawn extensive attention owing to their applications in industrial, environmental and even biological fields. Compared to UV-enhanced Si photodetectors, a new generation of wide bandgap semiconductors, such as (Al, In) GaN, diamond, and SiC, have the advantages of high [...] Read more.

Ultraviolet (UV) photodetectors have drawn extensive attention owing to their applications in industrial, environmental and even biological fields. Compared to UV-enhanced Si photodetectors, a new generation of wide bandgap semiconductors, such as (Al, In) GaN, diamond, and SiC, have the advantages of high responsivity, high thermal stability, robust radiation hardness and high response speed. On the other hand, one-dimensional (1D) nanostructure semiconductors with a wide bandgap, such as β-Ga₂O₃, GaN, ZnO, or other metal-oxide nanostructures, also show their potential for high-efficiency UV photodetection. In some cases such as flame detection, high-temperature thermally stable detectors with high performance are required. This article provides a comprehensive review on the state-of-the-art research activities in the UV photodetection field, including not only semiconductor thin films, but also 1D nanostructured materials, which are attracting more and more attention in the detection field. A special focus is given on the thermal stability of the developed devices, which is one of the key characteristics for the real applications. Full article

(This article belongs to the Special Issue Photodetectors)

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45 pages, 701 KiB

Open AccessReview

Progress in Infrared Photodetectors Since 2000

by Chandler Downs and Thomas E. Vandervelde

Sensors 2013, 13(4), 5054-5098; https://doi.org/10.3390/s130405054 - 16 Apr 2013

Cited by 218 | Viewed by 19593

Abstract

The first decade of the 21st-century has seen a rapid development in infrared photodetector technology. At the end of the last millennium there were two dominant IR systems, InSb- and HgCdTe-based detectors, which were well developed and available in commercial systems. While these [...] Read more.

The first decade of the 21st-century has seen a rapid development in infrared photodetector technology. At the end of the last millennium there were two dominant IR systems, InSb- and HgCdTe-based detectors, which were well developed and available in commercial systems. While these two systems saw improvements over the last twelve years, their change has not nearly been as marked as that of the quantum-based detectors (i.e., QWIPs, QDIPs, DWELL-IPs, and SLS-based photodetectors). In this paper, we review the progress made in all of these systems over the last decade plus, compare the relative merits of the systems as they stand now, and discuss where some of the leading research groups in these fields are going to take these technologies in the years to come. Full article

(This article belongs to the Special Issue Photodetectors)

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