Visible Light Detection Research Articles

Novel III-V Nitride Polymorphs in the P42/mnm and Pbca Phases.

In this work, the elastic anisotropy, mechanical stability, and electronic properties for P42/mnm XN (XN = BN, AlN, GaN, and InN) and Pbca XN are researched based on density functional theory. Here, the XN in the P42/mnm and Pbca phases have a mechanic stability and dynamic stability. Compared with the Pnma phase and Pm-3n phase, the P42/mnm and Pbca phases have greater values of bulk modulus and shear modulus. The ratio of the bulk modulus (B), shear modulus (G), and Poisson’s ratio (v) of XN in the P42/mnm and Pbca phases are smaller than those for Pnma XN and Pm-3n XN, and larger than those for c-XN, indicating that Pnma XN and Pm-3n XN are more ductile than P42/mnm XN and Pbca XN, and that c-XN is more brittle than P42/mnm XN and Pbca XN. In addition, in the Pbca phases, XN can be considered a semiconductor material, while in the P42/mnm phase, GaN and InN have direct band-gap, and BN and AlN are indirect wide band gap materials. The novel III-V nitride polymorphs in the P42/mnm and Pbca phases may have great potential for application in visible light detectors, ultraviolet detectors, infrared detectors, and light-emitting diodes.

Visible Light Detection and Memory Capabilities in MgO/HfO₂ Bilayer-Based Transparent Structure for Photograph Sensing

Photograph response in transparent devices has been a hot area of investigation, with several material systems being used to generate a response to illumination. In this study, we propose an ITO/MgO/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /ITO bilayer (BL) transparent resistive switching (RS) device that exhibits a photograph response through defect engineering in the switching layer, which resulted in a subsurface active RS location in the formed conductive filament, thus reducing the loss of oxygen through the polycrystalline electrode. We observe that the switching performance is enhanced in the ITO/MgO/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /ITO BL device as compared to the ITO/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /ITO single-layer device with the insertion of MgO layer between the ITO top electrode and HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> RS layer. The device shows excellent ON/ OFF ratio (~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> ), high and stable dc electrical set and optical reset endurance (>1000 cycles without degradation), excellent retention (>10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> s at 85 °C), high transparency (>85% transmittance in the visible spectrum), and a response time of 30 μs for the optical reset. This study lays the foundation for future work involving oxide defect-based optical functionalization in RS devices with the possibility for being used in photograph sensing.

Photoresponse properties of CdSe thin film photodetector

In the present investigation, the performance of highly sensitive photodetector based on CdSe thin film has been demonstrated. The cadmium selenide (CdSe) films were deposited successfully by spray pyrolysis method on glass substrate. The as-deposited films were used as visible light detector. Further, the structural, morphological, and optical properties of CdSe films were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy, and optical absorption spectrophotometer. The XRD studies show that the produced samples are polycrystalline in nature. A UV–Visible absorbance spectrum indicates direct allowed transition with bandgap about 1.75 eV. The SEM micrographs depict uniformly distributed well defined uneven hexagonal grains. The CdSe film-based photodetector exhibits high responsivity, detectivity and shows an ultrafast photoresponse. The excellent photoresponse and high photosensitivity of CdSe film makes it a strong candidate for high-performance photodetectors.

Possible detection of visible light and γ rays from a swarm of ball lightning.

It is shown that a simultaneous, 15-min-long registration of visible light and an increase in the rate of γ ray count at Aragats Space Environmental Center on September 1, 2020 [A. Chilingarian et al., Phys. Rev. Res. 1, 033167 (2019)10.1103/PhysRevResearch.1.033167] could be the registration of visible light and γ rays from a swarm of ball lightning. The information from several reports about visual observation of swarms of objects, described by witnesses as balls or ball lightning, in thunderclouds and about the fall of a large number of such objects from thunderclouds is presented. Illustrative examples of location and parameters of ball lightning are also presented.

Design and Implementation of a Compact Single-Photon Counting Module

A compact single-photon counting module that can accurately control the bias voltage and hold-off time is developed in this work. The module is a microcontroller-based system which mainly consists of a microcontroller, a programmable negative voltage generator, a silicon-based single-photon avalanche diode, and an integrated active quench and reset circuit. The module is 3.8 cm × 3.6 cm × 2 cm in size and can communicate with the end user and be powered through a USB cable (5 V). In this module, the bias voltage of the single-photon avalanche diode (SPAD) is precisely controllable from −14 V ~ −38 V and the hold-off time (consequently the dead time) of the SPAD can be adjusted from a few nanoseconds to around 1.6 μs with a setting resolution of ∼6.5 ns. Experimental results show that the module achieves a minimum dead time of around 28.5 ns, giving a saturation counting rate of around 35 Mcounts/s. Results also show that at a controlled reverse bias voltage of 26.8 V, the dark count rate measured is about 300 counts/s and the timing jitter measured is about 158 ps. Photodetection probability measurements show that the module is suited for detection of visible light from 450 nm to 800 nm with a 40% peak photon detection efficiency achieved at around 600 nm.

Photosensor Based on Split Gate TMD TFET Using Photogating Effect for Visible Light Detection

This paper reports a highly-sensitive and low power photosensor based on split gate tunnel field effect transistor (TFET) structure for visible light detection in wavelength ranging from 450-750 nm. The TFET based sensing device utilizes the photogating effect in a portion of transition metal dichalcogenide (TMD) channel. The optically tunable workfunction contrast between the two gates of dual material gate (DMG) TFET achieves significant gains in the overall device characteristics. It demonstrates high photo-to-dark current ratio of the order of 10 8 and variation in responsivity in the range between 10 3 AmW -1 to 10 -5 AmW -1 for V gs = -0.9 V. This paper further discusses the photodetector performance based on the position of the photogate on the tunneling or auxiliary side, the gate splitting ratio between the photosensing region and the metal, and the n-TFET based device design. The device performance has been analyzed using the analytical model for the optically controlled workfunction. This hybrid device consisting of an ultrathin channel sensitized with absorbing semiconductors while exploiting the characteristics of TFET leads to a new generation of highly sensitive photodetectors.

A micromachined vector light sensor

We report the design, fabrication, and performance characteristics of a novel microfabricated light sensor designed to determine the intensity and direction of an incident light source. The device structure comprises several light sensors that are integrated onto a pyramid base. The direction to the light source is estimated using the ratios of the signals from the lights sensors that are facing different directions. We demonstrate that this “vector light sensor”, is capable of measuring both the intensity and the direction of light from a source. The three-dimensional structure of the sensor is created based on well-known silicon microfabrication techniques and uses photodiodes for the detection of visible light. The signals from the photodiodes were read and processed based on a simple algorithm to experimentally verify the device performance. In addition to the direction, the distance to a light source may be estimated by simple triangulation of data from two vector light sensors. The small size and low power consumption of the individual sensors make them suitable for applications where passive distance and direction estimation is required. Furthermore, it is envisioned that arrayed sensors can directly provide light-field information in a plane.

Paper based organic–inorganic hybrid photodetector for visible light detection

Photodetectors based on organic–inorganic hybrid are promising which can combine the merits like function tunability of organic materials as well as broadband absorption, excitonic mechanisms and high carrier mobility of inorganic materials. Flexible thin film photodetectors based on inorganic WSe2 nanosheets and organic PANI by tuning composition are developed by simple, cost effective solution blending process. The fabricated hybrid thin films on filter paper substrate manifest visible light detection with high responsivity, fast photoswitching and high specific detectivity. In addition, the performance of hybrid film is retained even after 400 bending cycles. In case of WSe2-PANI hybrid films, the enhanced photoresponse is due to change in work function between PANI and WSe2 nanosheets, local electric fields are formed at WSe2-PANI interface thereby generating a greater number of photogenerated electrons. Compared with other hybrid-based photodetectors, this work advocates huge development in future applications in wearable electronics, security surveillance, high-performance optoelectronics, etc.

Ag2BiI5 perovskite thin films: Studies on structure, morphology, composition and optoelectronic properties for visible photodetector application

Solution-processed lead halide perovskites have gained considerable attention for the last few years and intense research is going on to find a suitable replacement for lead to reduce the effects of its toxicity, poor stability in ambient conditions, and negative impact on the environment. Herein, we present the synthesis of silver bismuth iodide (SBI) thin films by spin coating of silver iodide and bismuth iodide dissolved in N, N-dimethyl formamide followed by annealing in vacuum. We investigated the effect of bismuth iodide concentration on the SBI perovskite crystal structure and properties. X-ray diffraction analysis revealed the Ag2BiI5 phase with a hexagonal crystal structure. Vibrational spectral analysis by Raman spectroscopy for SBI thin films is reported for the first time. Detailed analysis of the composition and chemical states of the SBI thin films are also described. The Ag2BiI5 perovskites possess a band gap of 1.71 eV which makes them useful for optoelectronic applications. Morphology, optical and electrical properties of the perovskites are influenced by the bismuth iodide concentration. Here, we developed a highly sensitive and reproducible silver bismuth pentaiodide (Ag2BiI5) based visible light detector. The detector showed good responsivity, sensitivity as well as an incident light intensity-dependent behavior when illuminated with 532 nm laser suggesting them as a suitable candidate for various optoelectronic applications.

Structural Design and Pyroelectric Property of SnS/CdS Heterojunctions Contrived for Low‐Temperature Visible Photodetectors

AbstractThe traditional photodetectors based on photoelectric effect exhibit inferior response or even out of operation with the decrease of temperature. However, cryogenic visible light detection is increasingly demanded in deep space and polar exploration. Herein, a self‐powered visible photodetector coupling pyroelectricity and photoelectricity to optimize the cryogenic detecting performance is designed in which hydrothermally grown CdS nanorod array is covered by SnS nanoflakes. The choice of SnS allows the detector with strong visible light absorption and great photoelectric conversion efficiency, while the CdS nanorod structure with pyroelectricity can effectively modulate the behavior of photogenerated carriers at low temperatures. It is found that the response characteristics of the photodetector are dominated by the combination of pyroelectric and photoelectric effects, which becomes more significant with the reduced temperature. Specifically, at 130 K temperature, the photoresponse current under 650 nm light is improved by 7.5 times as that at room temperature, while the ratio of pyroelectric current to photocurrent can be increased to 400%. Meanwhile, the responsivity and detectivity are as high as 10.4 mA W−1 and 3.56 × 1011 Jones, respectively. This work provides a promising approach to develop high‐performance self‐powered visible photodetectors with low‐temperature operating capability.

The role of CdS doping in improving SWIR photovoltaic and photoconductive responses in solution grown CdS/PbS heterojunctions

Low cost short wavelength infrared (SWIR) photovoltaic (PV) detectors and solar cells are of very great interest, yet the main production technology today is based on costly epitaxial growth of InGaAs layers. In this study, layers of p-type, quantum confined (QC) PbS nano-domains (NDs) structure that were engineered to absorb SWIR light at 1550 nm (Eg = 0.8 eV) were fabricated from solution using the chemical bath deposition (CBD) technique. The layers were grown on top of two different n-type CdS intermediate layers (Eg = 2.4 eV) using two different CBD protocols on fluoride tin oxide (FTO) substrates. Two types of CdS/PbS heterojunction were obtained to serve as SWIR PV detectors. The two resulting devices showed similar photoluminescence behavior, but a profoundly different electrical response to SWIR illumination. One type of CdS/PbS heterojunction exhibited a PV response to SWIR light, while the other demonstrated a photo-response to SWIR light only under an applied bias. To clarify this intriguing phenomenon, and since the only difference between the two heterojunctions could be the doping level of the CdS layer, we measured the doping level of this layer by means of the surface photo voltage (SPV). This yielded different polarizations for the two devices, indicating different doping levels of the CdS for the two different fabrication protocols, which was also confirmed by Hall Effect measurements. We performed current voltage measurements under super bandgap illumination, with respect to CdS, and got an electrical response indicating a barrier free for holes transfer from the CdS to the PbS. The results indicate that the different response does, indeed, originate from variations in the band structures at the interface of the CdS/PbS heterojunction due to the different doping levels of the CdS. We found that, unlike solar cells or visible light detectors having similar structure, in SWIR photodetectors, a type I heterojunction is formed having a barrier at the interface that limits the injection of the photo-exited electrons from the QC-PbS to the CdS side. Higher n-doped CdS generates a narrow depletion region on the CdS side, with a spike like barrier that is narrow enough to enable tunneling current, leading to a PV current. Our results show that an external quantum efficiency (EQE) of ∼2% and an internal quantum efficiency (IQE) of ∼20% can be obtained, at zero bias, for CBD grown SWIR sensitive CdS/PbS-NDs heterojunctions.

Colloidal Quantum-Dots/Graphene/Silicon Dual-Channel Detection of Visible Light and Short-Wave Infrared

Integration of infrared detectors with current silicon-based imagers would not only extend their spectral sensing range but also enables numerous applications including thermal imaging, machine vis...

A smartphone-based dual detection mode device integrated with two lateral flow immunoassays for multiplex mycotoxins in cereals

In this study, a smartphone-based quantitative dual detection mode device, integrated with gold nanoparticles (GNPs) and time-resolved fluorescence microspheres (TRFMs) lateral flow immunoassays (LFIA) for multiplex mycotoxins in cereals were established. The most frequently used visible light and fluorescence detection modes were integrated in one device. A user-friendly application was self-written to rapidly quantify results. GNPs-LFIA and TRFMs-LFIA were used to detect aflatoxin B1 (AFB1), zearalenone (ZEN), deoxynivalenol (DON), T-2 toxin (T-2), and fumonisin B1 (FB1). The visible limits of detection (vLODs) were 10/2.5/1.0/10/0.5, 2.5/0.5/0.5/2.5/0.5 μg/kg for the two methods, respectively. The quantitative limits of detection (qLODs) were 0.59/0.24/0.32/0.9/0.27, 0.42/0.10/0.05/0.75/0.04 μg/kg, respectively. The recoveries of both LFIAs ranged from 84.0%-110.0%. A parallel analysis in 30 naturally contaminated cereal samples was conducted by liquid chromatography–tandem mass spectrometry (LC-MS/MS), the results showed good consistency, indicating the practical reliability of the established methods. The developed two smartphone-based LFIAs provide a promising technique for multiplex, highly sensitive, and on-site detection of mycotoxins.

Passive Visible Light Detection Of Humans.

This paper experimentally investigates passive human visible light sensing (VLS). A passive VLS system is tested consisting of one light emitting diode (LED) and one photodiode-based receiver, both ceiling-mounted. There is no line of sight between the LED and the receiver, so only reflected light can be considered. The influence of a human is investigated based on the received signal strength (RSS) values of the reflections of ambient light at the photodiode. Depending on the situation, this influence can reach up to . The experimental results show the influence of three various clothing colors, four different walking directions and four different layouts. Based on the obtained results, a human pass-by detection system is proposed and tested. The system achieves a detection rate of 100% in a controlled environment for 21 experiments. For a realistic corridor experiment, the system keeps its detection rate of 100% for 19 experiments.

Tungsten Dichalcogenide Nanoflake/InGaZnO Thin‐Film Heterojunction for Photodetector, Inverter, and AC Rectifier Circuits

AbstractHeterojunction PN diode and inverter circuits are fabricated and presented, combining two‐dimensional WSe2 nanoflake and amorphous InGaZnO (a‐IGZO) thin film on a glass substrate. A heterojunction p‐WSe2/n‐IGZO diode exhibits rectifying characteristics and effectively responds to red light (λ = 620 nm) under a reverse bias. The combination of a heterojunction PN diode and IGZO field effect transistor (FET) leads to a diode‐load inverter showing a peak voltage gain of about 12 at a supply voltage of 5 V. The same integration from the PN diode and n‐FET displays the capability of visible light detection when a reverse‐bias voltage is applied to the PN diode. Furthermore, after oxygen plasma treatment on the PN diode, it shows dramatically enhanced on/off rectification ratio of ≈5 × 105 due to the hole doping effect on the WSe2 nanoflake. Such an improved PN diode leads to an alternating current rectifier circuit as integrated with IGZO FET.

Facile assembly of single α-MoO3 microbelt/β-Ni(OH)2 heterojunction ultraviolet–visible detector with fast switching characteristics

In this paper, we report a simple, low-cost, facile fabrication of single α-MoO3 Microbelt/β-Ni(OH)2 heterostructure. The heterostructure consisting of α-MoO3 microbelt and β-Ni(OH)2 nanosheets is grown using aqueous method. The device based on the α-MoO3 microbelt/β-Ni(OH)2 heterostructure shows the fast switching characteristics with broad spectrum detection. The ultraviolet response is due to the β-Ni(OH)2 layer, and the visible light detection can be attributed to the existence of substantial gap states in the α-MoO3 microbelt, which can produce light response in the visible region. The results will provide a new way for fabrication of high-performance broad spectral detection device.

Room-temperature liquid diffused separation induced crystallization for high-quality perovskite single crystals

Large single crystals serve as an ideal platform for investigating intrinsic material properties and optoelectronic applications. Here we develop a method, namely, room-temperature liquid diffused separation induced crystallization that uses silicone oil to separate the solvent from the perovskite precursors, to grow high-quality perovskite single crystals. The growth kinetics of perovskite single crystals using this method is elucidated, and their structural and optoelectronic properties are carefully characterized. The resultant perovskite single crystals, taking CH3NH3PbBr3 as an example, exhibit approximately 1 µs lifetime, a low trap density of 4.4 × 109 cm−3, and high yield of 92%, which are appealing for visible light or X-ray detection. We hope our findings will be of great significance for the continued advancement of high-quality perovskite single crystals, through a better understanding of growth mechanisms and their deployment in various optoelectronics. The diffused separation induced crystallization strategy presents a major step forward for advancing the field on perovskite single crystals.

Investigations on the effects of rGO incorporation on the photosensitivity of (Cd:Zn)S nanocrystalline thin film-based visible photodetectors by hydrothermal synthesis

Reduced graphene oxide-incorporated cadmium zinc sulphide (rGO–CZS) thin films were synthesised on glass substrates by hydrothermal-assisted chemical bath deposition. The effect of the rGO concentration (0.5–2 wt%) on the photosensitivity of the films was established along with the structural, morphological and optical properties of the composite films. The structural investigations by XRD analysis ensured that the prepared samples are nanocrystalline with hexagonal structure of cadmium zinc sulphide. Scanning electron microscopy showed aggregated sphere-like CZS nanoparticles enveloped with rGO flakes. The average particle size attained from TEM image is approximately 8 nm. The presence of various functional groups was scanned by FTIR analysis. Further, we established the characteristics of the rGO–CZS nanocomposite films as visible-light photodetectors. The photosensitivity, photo response and detectivity of the devices were found to increase with rGO concentration. (2 wt%) rGO–CZS detector exhibits highest photosensitivity of the order of 106, photoresponse of 18.5 mA/W and specific detectivity of 2.08 × 1012 Jones. This work demonstrates fast and simple preparation process of rGO–CZS visible-light detectors with high sensitivity, responsivity and good stability. The enhancement of sensitivity and responsivity can be attributed to the excellent electron conductivity and mobility due to the warm interfacial contact between CZS nanoparticles and the rGO sheet.

HfS2/MoTe2 vdW heterostructure: bandstructure and strain engineering based on first-principles calculation.

In this study, a multilayered van der Waals (vdW) heterostructure, HfS2/MoTe2, was modeled and simulated using density functional theory (DFT). It was found that the multilayers (up to 7 layers) are typical indirect bandgap semiconductors with an indirect band gap varying from 0.35 eV to 0.51 eV. The maximum energy value of the valence band (VBM) and the minimum energy value of the conduction band (CBM) of the heterostructure were found to be dominated by the MoTe2 layer and the HfS2 layer, respectively, characterized as type-II band alignment, leading to potential photovoltaic applications. Optical spectra analysis also revealed that the materials have strong absorption coefficients in the visible and ultraviolet regions, which can be used in the detection of visible and ultraviolet light. Under an external strain perpendicular to the layer plane, the heterostructure exhibits a general transition from semiconductor to metal at a critical interlayer-distance of 2.54 Å. The carrier effective mass and optical properties of the heterostructures can also be modulated under external strain, indicating a good piezoelectric effect in the heterostructure.

Implementation challenge and analysis of thermal image degradation on R-CNN face detection

Face detection systems with color cameras were rapidly evolving and have been well researched. In environments with good visibility they can reach excellent accuracy. But changes in illumination conditions can result in performance degradation, which is the one of the major limitations in visible light face detection systems. The solution to this problem could be in using thermal infrared cameras, since their operation doesn't depend on illumination. Recent studies have shown that deep learning methods can achieve an impressive performance on object detection tasks, and face detection in particular. The goal of this paper is to find an effective way to take advantages from thermal infrared spectra and provide an analysis of various image degradation influence on thermal face detection performance in a system based on R-CNN with special accent on implementation on a hardware platform for video signal processing that institute Vlatacom has developed, called vVSP.