Photodiode Research Articles

Interaction between laser phase-locking and laser pointing for a space gravitational wave interferometer

We have conducted both theoretical and experimental investigations into the interaction between laser phase-locking and laser pointing techniques, which are crucial for space gravitational wave detection missions. Both techniques are essential for minimizing phase noise in the space interferometer, as the laser phase is the carrier of gravitational wave information. Introducing phase noise from either technique can significantly degrade the mission’s performance. To date, both techniques have been studied independently. Our research reveals the interaction that the laser phase-locking technique is sensitive to the laser pointing technique. The laser phase-locking technique suppresses one phase information from the quadrant photo diode (QPD) and disrupts the differential wave sensing (DWS) function for the laser pointing technique. Such circumstances indicate a need for re-evaluation of the current designs for both techniques.

Suppressing the Dark Current Under Forward Bias for Dual‐Mode Organic Photodiodes

AbstractTremendous research efforts are developed to suppress the reverse dark current (Jd) and enhance the responsivity of organic photodiodes (OPDs). The functional layers of traditional OPDs usually follow the principle of energy level alignment to make unobstructed photo‐carriers transport under reverse bias, but this inevitably leads to a large forward Jd. Herein, a universal strategy is proposed to manipulate the carrier dynamics and effectively suppress the forward Jd of OPDs, that is, tuning the energy level and electron traps of the anode interface layers (AILs). The bandgap and electron traps of typical organometallic chelate AIL (PEIE‐Co) can be well controlled by adjusting the component ratio of PEIE and metal ions. The wide bandgap increases the carrier injection barrier under reverse and forward bias, endowing OPD with a much lower Jd; the electron traps induce hole tunneling injection by capturing photo‐generated electrons under forward bias, thereby enabling the photomultiplication effect. The obtained OPD exhibits photoconductive/photomultiplication working mode at reverse/forward bias and the specific detectivity approaches ≈1013/1012 Jones, showing promise for adaptively detecting faint and strong light. This study presents an intelligent strategy to achieve dual‐mode OPDs, paving the way for the multifunctional development of photodetectors.

Simple three-stage control scheme achieving interrupt-free integrated polarization stabilization

It is a long-outstanding challenge to achieve low-complexity interrupt-free integrated polarization stabilization of infinitely changing light. Integrated phase shifters have finite tuning range and experience abrupt switching or reset when reaching the limits of their tuning ranges during the polarization stabilization process. We propose a three-stage interrupt-free integrated polarization stabilization scheme with nested electronic-photonic loops (NEPL) and dimensionality reduction (DR) method. Based on the NEPL structure, only three Mach-Zehnder interferometer (MZI) stages are needed to achieve interrupt-free polarization stabilization scheme. The input state is first constrained into a predetermined range using a nested loops with the first MZI stage and then processed by regular two-stage scheme. Throughout the entire operation, all phase shifters are tuned continuously without any pause, abrupt switching or reset. Furthermore, a DR method is introduced to reduce the control complexity and enhance control speed and accuracy of the regular two-stage scheme. A detailed analysis of the proposed design is provided, and its effectiveness is verified using electronic-photonic co-simulation in the Cadence platform. This scheme consists of only phase shifters, couplers and photodiodes (PDs) with simple electronic controllers, and can be implemented in various material systems and process platforms. To the best of our knowledge, this is the first three-stage interrupt-free polarization stabilization scheme reported in the literature.

Direct characterisation of AM-to-PM phenomena in fast Si and InGaAs photodiodes

The direct measurement method of AM-to-PM phenomena in fast silicon and InGaAs photodiodes is described. The setup is simple, relatively inexpensive and allows fast and precise measurements not only in a laboratory environment. During sample tests, the authors have found that the influence of bias voltage on the phase shift of an optical signal conversion is significant. The reported effect together with the influence of modulation depth on phase shift (AM-to-PM conversion) has a negative impact on an optical signal reception especially in coherent applications. The authors show that, with our proposed setups, it is possible to find optimal bias voltage and optimal optical power in order to reduce electrical phase noise of the photodetector.

Ideal Photothermal Materials Based on Ge Subwavelength Structure.

Photothermal materials often prioritize solar absorption while neglecting thermal radiation losses, which diminishes thermal radiation conversion efficiency. This study addresses this gap by introducing a germanium (Ge) subwavelength structure (SWS) designed to optimize both solar absorption and infrared emissivity. Using a self-masked reactive ion etching (RIE) technique, we achieved a peak absorption of 98.8% within the 300 nm to 1800 nm range, with an infrared emissivity as low as 0.32. Under solar illumination of 1000 W/m2, the structure's temperature increased by 50 °C, generating a heating power of 800 W/m2. Additionally, it demonstrated good mechanical and thermal stability at high temperatures and possessed a hydrophobic angle of 132°, ensuring effective self-cleaning. These characteristics make the Ge SWS suitable for application in solar panels, displays, sensors, and other optoelectronic devices.

A Wireless Miniature Injectable Device with Memory-Assisted Backscatter for Multimodal Animal Physiological Monitoring.

This paper introduces a wirelessly powered multimodal animal physiological monitoring application-specific integrated circuit (ASIC). Fabricated in the 180 nm process, the ASIC can be integrated into an injectable device to monitor subcutaneous body temperature, electrocardiography (ECG), and photoplethysmography (PPG). To minimize the device size, the ASIC employs a miniature receiver (Rx) coil for wireless power receiving and data communication through a single inductive link operating at 13.56 MHz. We propose a folded L-shape Rx coil with improved coupling to the transmitter (Tx) coil, even in the presence of misalignment, and enhanced quality factor. The ASIC functions alternatively between recording and sleeping modes, consuming 2.55 μW on average. For PPG measurements, a reflection-type PPG sensor illuminates an LED with tunable current pulses. A current-input analog frontend (AFE) amplifies the current of a photodiode (PD) with 30.8 pARMS current input-referred noise (IRN). The ECG AFE captures ECG signals with a configurable gain of 45-80 dB. The temperature AFE achieves 0.02 ̊C inaccuracy within a sensing range between 27-47 ̊C. The AFE outputs are sequentially digitized by a 10-bit successive approximation register (SAR) analog-to-digital converter (ADC) with an effective number of bits (ENOB) of 8.79. To improve the reliability of data transmission, we propose a memory-assisted backscatter scheme that stores ADC data in an off-chip memory and transmits it when the coupling condition is stable. This scheme achieves a package loss rate (PLR) lower than 0.2% while allowing 24-hour data storage. The device's functionality has been evaluated by in vivo experiments.

Graphene, graphene oxide or modified graphene in polyaniline based nanocomposites—features and technical highlights

Polyaniline is a remarkable conjugated polymer having valuable structural and physical characteristics. Nevertheless, polyaniline has poor solubility and structural durability which had limited its practical utilization. Consequently, polyaniline has been reinforced with carbonaceous and inorganic nanoparticles to enhance its processability and physical properties, such as electrical/thermal conductivity and thermal/mechanical stability. Accordingly, polyaniline has been applied as a valuable matrix material to form nanocomposites with graphene which is a one atom thick nanosheet of hexagonally arranged carbon atoms. Subsequently, graphene as well as modified graphene forms have been utilized as important nanoadditives for the polyaniline matrix. This state-of-the-art review article has been designed to investigate the fabrication, characteristics, and applications of the polyaniline and graphene/modified graphene based nanomaterials. Potential enhancements in the physical characteristics of the pristine polyaniline upon graphene reinforcement seemed to be reliant upon the matrix-nanofiller interactions, interface formation, and synergetic effects between polyaniline-graphene. Subsequently, practical aspects of the polyaniline/graphene nanocomposites have been discussed regarding their applications in the fields of solar cells, supercapacitors, and sensors. According to the literature analysis, dye sensitized solar cell based on polyaniline/graphene and polyaniline/graphene oxide exhibited superior power conversion efficiencies ∼2.0-7.6 % and open circuit voltage ∼500-800 mV. Supercapacitor electrodes based on polyaniline/graphene oxide and polyaniline/reduced graphene oxide showed significantly high values of specific capacitance and capacitance retention of ∼1100-1900 Fg−1 and ∼80-98 %, respectively, during >5000-6000 cycles. Besides, the polyaniline/graphene oxide depicted superior sensitivity and response time for gas sensors (∼20 % and 50 s, respectively) and humidity sensors (>90 % and 4-7 s, respectively) and low detection limits for biosensors.

Transformation of Engineered Copper Oxide Nanoparticles in Surface Waters.

Copper oxide nanoparticles (CuO-NPs) are widely used for their catalytic properties, conductive capacity, and innovations in the fields of superconductors, alloys, and solar energy sensors. To better understand the impact of water chemistry on the stability of CuO nanoparticles, a series of measurements were carried out on nanoparticles suspended in pure water, natural water, and water enriched with natural organic matter fulvic acid (FA). ICP-MS characterization in single-particle mode (SP-ICP-MS) was performed to determine the stability or transformation of nanoparticles in contrasting water conditions. We first observed that particle sedimentation was very fast in pure Milli-Q water. The addition of FA favored the dissolution of CuO-NPs with an increase in the dissolved copper concentration, for both Milli-Q water and natural water. The presence of FA also reduced the size of CuO-NPs (i.e., less aggregation) measured in natural water. By comparing signals of single particles, FA decreased nanoparticle numbers as well, confirming the increase in dissolution of CuO-NPs over time. The transformation products of CuO-NPs are important in the ecological context since the uptake and toxicity of parent nanoparticles differ from those of the chemical species in solution. Further considerations are needed on the fate of released NPs to better assess their exposure pathways to aquatic organisms and potential environmental risks.

Optimizing optoelectronics performance: theoretical and experimental study on ZnO thin film for Al/ZnO/p-Si photodiode

Abstract In this paper, a ZnO photodiode in a p-n heterojunction configuration is fabricated on a p-type Si substrate focusing specifically on ZnO/p-Si heterojunction photosensitive devices and photodiodes (PDs) using Al contacts. Through an experimental and theoretical analysis approach aims to evaluate the effects of important parameters, including ZnO layer thickness, defect density, and contact materials, on PD’s efficiency. Numerical analysis simulations comparatively examine the experimentally fabricated device performance at a 5 nm ZnO layer thickness by balancing photon absorption and carrier formation while minimizing carrier transport limitations. Experimentally process, an Atomic Layer Deposition (ALD) system was used to grow ZnO interlayers on one side of the polished Si wafer. Then, Al metallic contacts were created on the ZnO layers using a hole array mask. The PDs were then subjected to electrical characterization using I-V and I-t measurements under various illumination densities. Al/ZnO/p-Si PD’s device with active performance has been produced and analyzed with electrical parameters such as barrier height, photocurrent, spectral response, ideality factor and EQE were derived, analyzed and studied. In conclusion, this work provides a comprehensive understanding of the performance of Al/ZnO/p-Si PD at varying illumination intensities and offering a detailed analysis of key parameters influencing device efficiency for future optoelectronics applications.

Separation of planar and edge contributions to total capacitance for accurate doping concentration determination in square silicon photodiodes

Accurately determining the doping concentrations of silicon photodiodes (PDs) is crucial for optimizing their performance in various applications. This study presents a methodology for separating the planar and edge contributions to the total capacitance of square silicon PDs with guard rings. Through capacitance-voltage measurements, we distinguished planar capacitance, which reflects the bulk properties of the silicon PD, from edge capacitance, influenced by device geometry and fringing fields. We demonstrated that the fabricated PDs with guard rings surrounding the active area could be effectively modeled using a coxial-like structure to estimate edge capacitance. Doping concentrations, depletion widths, and resistivities were determined through linear fitting of the inverse square of the measured capacitance per unit area as a function of the reverse bias voltage. All parameters obtained from the full depletion voltage Vd , determined by the intersection of the linear fits for V < Vd and V > Vd , demonstrated agreement within 1σ. Our results underscore the importance of accounting for edge effects to accurately determine doping concentrations from 1/C 2 vs. V plots.

Acpro: fusion of embedded ambient light sensor and image sensor for visible light positioning

Abstract With the increasing demand for indoor positioning, visible light positioning (VLP) systems have become an optics technologies research hotspot due to their high accuracy and avoidance of electromagnetic interference. However, current photodiode (PD)-based and image sensor (IS)-based VLP systems still suffer from high costs at the receiver, and the problem of the trade-off between field of view (FoV) and positioning accuracy. Therefore, we propose a smartphone-based low-cost, and high-precision VLP system, Acpro. The system combines the smartphone’s embedded ambient light sensor and IS as the receiver for the positioning. First, for the low sampling rate of the ambient light sensor, we use the frequency aliasing characteristic to identify the LED’s beacon through the dynamic undersampling principle. Then, to increase the FoV and positioning accuracy, we use the standard distance information corrected by the IS to improve the noise distance calculated by the ambient light sensor. Further, the corrected distance information is used for positioning. Extensive results show that our system can achieve sub-meter positioning accuracy.

Structural and dynamical properties of two dimensional disordered metal chalcogenides AB (A [formula omitted] Zn, Cd; B [formula omitted] S, Se): A classical molecular dynamic study

In recent years, the synthesis of two-dimensional (2D) materials, particularly the crystalline and disordered phases of 2D transition metal chalcogenides (TMCs), has gained considerable attention due to their wider electronic band gaps. This distinctive feature is pivotal in shaping their potential applications in solar cells, sensors, field-effect transistors (FETs), and photocatalysis for water decomposition. In the present study, we report molecular dynamics simulation of 2d disordered configuration of ZnX and CdX (X: S, Se) compounds using the Stillinger–Weber potential. We have explored their structural features by calculating their radial distribution functions and ring statistics. These systems are thermodynamically stable. The disordered network with numerous voids in these compounds play a pivotal role in lowering their melting temperature compared to their 2D crystalline counterparts, which falls within the range of 600 K to 700 K. The phonon density of states for all these systems shows a higher number of lower frequency (acoustic) modes than optical modes, which is understandably due to the presence of open regions and 2-fold sites in such systems.

Harnessing the potential of electrospun TiO2 nanofibers and nanoparticles enriched with natural dyes: a path towards affordable aolutions for low-cost electronic devices

Abstract This study evaluates the morphological effects of TiO2 nanoparticles, nanofibers, and a bilayer configuration on electronic devices, such as Dye-Sensitized Solar Cells (DSSCs) and UV sensors. Cost-efficient natural dyes—curcumin, coffee beans, and banana peel—were used as sensitizers for nanomaterial films. TiO2 nanoparticles were synthesized using the sol–gel technique, while nanofibers were produced via electrospinning. Characterization techniques, including Scanning Electron Microscopy (SEM), Energy Dispersive x-ray Spectroscopy (EDS), and x-ray Diffraction (XRD), confirmed the formation and dimensions of the TiO2 nanostructures. UV–visible spectroscopy was used to determine the optical properties of the samples. TiO2 nanofibers and nanoparticles exhibited high surface-area-to-volume ratios, with nanofibers having a diameter of 20 nm and particles measuring 50 nm. A binder-free, low-temperature paste was prepared using TiO2 nanoparticles and nanofibers to develop thin films. The turmeric dye showed peak absorption at 470 nm with a band gap energy of 2.06 eV when loaded on a TiO2 bilayer film. This study aims to develop electronic devices that reduce costs and enhance performance by using low-cost, efficient, and economically viable dyes. TiO2 nanofiber and nanoparticle films show promise for cost-effective and high-performance electronic devices.

Hybrid trap detector sensitive at visible and telecom wavelengths

Abstract We have developed a transmission trap detector sensitive over a wide optical wavelength range. The developed device takes advantage of the smooth reflectance profile of silicon photodiodes. The detector is based on two 10 mm size photodiodes – a Si photodiode and an InGaAs photodiode. The constructed hybrid trap detector is sensitive at the wavelength range from 400 nm up to 1600 nm. The detector is designed to provide a tool for countermeasures against attacks to secure quantum communication.

Comparison of piperine content, antimicrobial and antioxidant activity of Piper chaba root and stem

Piper chaba (locally known as “Choi Jhal”) is used traditionally as spices and folk medicine in different parts of Bangladesh. One of the most important bioactive compounds in this plant is piperine. In this study, the amount of piperine in P. chaba root and stem was investigated and the optimal solvent for piperine extraction at room temperature was also studied. High performance liquid chromatography (HPLC) was operated using a reverse phase column where methanol and water (70:30) were used as mobile phase. The detection was performed using photo diode array (PID) detector at a wavelength of 345 nm. The standard piperine showed linearity between 0.005 % and 0.04 % and the correlation co-efficient found for the linearity was 0.9933. The percentage of relative standard deviation (RSD) for both retention time and peak area were less than 2.0 %. The theoretical plate number (N) > 3000 and a tailing factor (T) < 1.5 were found in the acceptable range. The recovery percentage (%) of standard piperine was 99.16 %. Low value of co-efficient of variation and standard deviation are recognized for high precision of the method. The highest amount of piperine was found in root extracted with methanol (MR) amounting to 1.75 % in the root powder. The maximum amount of piperine in the stem was 1.59 % when extracted with methanol (MS). The piperine quantification in other extract like n-hexane root (HR), ethyl acetate root (ER), n-hexane stem (HS), ethyl acetate stem (ES) were 0.76 %, 1.69 %, 0.33 % and 1.46 % respectively. Methanol has given the highest yield of piperine compared to ethyl acetate and n-hexane for both root and stem. The developed method was simple, rapid, economic and validated in terms precision, accuracy and recovery. This selective method is found to be repeatable, accurate and successfully utilized for the Piper extract in marketed and pharmaceutical samples with well chromatographic conditions. The ethyl acetate extract of root and stem showed promising DPPH (1, 1-diphenyl-2-picrylhydrazyl) free radical scavenging activity with an IC50 value of 39.62 ± 0.95 μg/mL and 43.85 ± 1.50 μg/mL respectively. The study reports potential antibacterial activity and antifungal activity of P. chaba root and stem extracts. These outcomes revealed that different extracts of P. chaba may be used as natural preservatives.

Optical and spectral techniques for studying high-voltage laser-triggered switch

In the present paper we have performed sets of experiments to study laser triggering high voltage switch. In this study, instead of electrical diagnostics, optical technique was utilized to characterize the discharge process. A Q-switched nanosecond Nd:YAG laser was used for triggering the switch. Dynamics of discharge, and the time delay of laser produced pre-plasma was monitored by fast photo diode signal which was connected to a fast oscilloscope. The spectrum of discharge emission was also recorded by photo spectrometer from which plasma parameters i.e. electron temperature, and density were estimated.

Organic Polymer-Based Photodiodes for Optoelectronic Reservoir Computing with Time-Based Coding.

The integration of optoelectronic devices with reservoir computing offers a novel and effective approach to in-sensor computing. This work presents a hybrid digital-physical solution that leverages the high-performance poly[(bithiophene)-alternate-(2,5-di(2-octyldodecyl)-3,6-di(thienyl)-pyrrolyl pyrrolidone)] (DPPT-TT) organic polymer-based photodiodes for the hardware implementation of reservoir computing system. The photodiodes demonstrate nonlinear photoelectric responses, fading memory, and cyclical stability, in relation to the temporal information on light stimuli. These attributes enable effective mapping, historical context sensitivity, and consistent performance, with time-encoded inputs, which are particularly essential for accurate and continuous processing of time series data. The optoelectronic reservoir computing system with pulse width modulation (PWM) coding demonstrates impressive performance in the prediction of chaotic sequences, achieving a normalized root-mean-square error as low as 0.095 with optimized parameters. The DPPT-TT-based photodiodes and time-based coding offer a hardware-efficient solution for reservoir computing, significantly advancing Internet of Things applications.

Investigation and Estimation of the Daily UVI Behavior Based on Global Radiation over Selected Cities in Iraq

The ultraviolet Index (UVI) is a measure of the level of ultraviolet (UV) radiation and the potential danger of sun exposure. It is a linear scale that measures the intensity of UV radiation concerning sunburn, ranging from 0 to 11 or more. A higher UVI indicates a greater potential for damage to the skin and eyes and a shorter time for harm to occur. Objective: The current study aims to investigate the (UVI) in several Iraqi cities and assess its relationship with global radiation to determine potential health risks for the population Radiation and Plant Health: Although the focus of the paper is on human health, you could argue that understanding the impact of UV radiation on plants is relevant to agriculture. High levels of UV radiation can damage some crops, reducing yield. The paper establishes a link between global radiation and UVI, and since global radiation affects plant growth, there's a very indirect connection. Materials and Methods: The UVI data were collected using an autonomous DAVIS weather station (Vantage Pro2) equipped with a Solar UV Radiation Sensor DS6490. Results: The maximum daily value in late spring and early autumn with very high levels during summer days ranged from 12.43 to 10.16, while minimum levels were found in fall and winter at 2.1 and 2.4 and it was uncovered throughout the months of December and January. In March, October, and November, UVI levels were primarily moderate. The high level of UVI which exceeds 7 UVI over shown 7 months per year, particularly during the three summer months with very high UVI values (12.43 to 9.47). The necessary measures must be taken to protect against exposure to UV rays on days when the values are high, as well as to preserve crops on these days. Conclusions: UVI levels tend to increase or decrease on a monthly period, the greatest rate of variation was 5.1 % in March and the lowest was 1.7 % in June and July respectively. The shows a correlation coefficient of-0.91 for daily values and-0.93 for monthly values. We note that UVC has been filtered into the atmosphere and does not reach the surface of the earth, and it is considered one of the most dangerous types.

Symmetry-Broken Electronic State of CsPbBr3 Cubic Perovskite Nanocrystals.

The development of densely packed, self-assembled perovskite nanocrystals (PeNCs) with a favorable transition dipole moment (TDM) orientation is crucial for their application in solution-processable electronic devices. In this study, we fabricated anisotropic CsPbBr3 PeNCs with a symmetry-broken electronic state on quartz substrates modified by 3-aminopropyltrimethoxysilane (APS). Densely packed and self-assembled monolayers of cubic PeNCs were formed on the substrates by using a dip coating technique. The angle-dependent absorption and photoluminescence (PL) spectra confirmed that the PeNC monolayer on the APS-treated substrate exhibited anisotropic electronic states in the in-plane and out-of-plane directions of the substrate. In contrast, when the quartz substrate was modified with the long alkyl silane coupling agent, octadecyltrimethoxysilane, the absorption and PL spectra exhibited no angular dependence, indicating the absence of anisotropy. Experimental and simulated results confirmed the presence of vertical TDMs in the densely packed PeNCs on the APS-treated substrate, which could be attributed to the effect of the amino groups of the APS on the facet of the cubic PeNCs facing the quartz substrate. Hence, surface chemical modifications of the substrate can aid in the precise control of the symmetry of the electronic states and TDM orientation in cubic PeNCs. These findings can promote the development of densely packed, high-coverage PeNC films with a controllable TDM orientation for applications in electronic devices such as solar cells, sensors, and light-emitting diodes.

Feline eye-inspired artificial vision for enhanced camouflage breaking under diverse light conditions.

Biologically inspired artificial vision research has led to innovative robotic vision systems with low optical aberration, wide field of view, and compact form factor. However, challenges persist in object detection and recognition against complex backgrounds and varied lighting. Inspired by the feline eye, which features a vertically elongated pupil and tapetum lucidum, this study introduces an artificial vision system designed for superior object detection and recognition in a monocular framework. Using a slit-like elliptical aperture and a patterned metal reflector beneath a hemispherical silicon photodiode array, the system reduces excessive light and enhances photosensitivity. This design achieves clear focus under bright light and enhanced sensitivity in dim conditions. Theoretical and experimental analyses demonstrate the system's ability to filter redundant information and detect camouflaged objects in diverse lighting, representing a substantial advancement in monocular camera technology and the potential of biomimicry in optical innovations.