Dark Noise Research Articles

Intrinsic charge manipulation for solution‐processed organic photodetectors with high sensitivity and fast response

AbstractCharge manipulation is crucial in optoelectronic devices. The unoptimized interfacial charge injection/extraction in solution‐processed bulk‐heterojunction (BHJ) organic photodetectors (OPDs) presents significant challenges in achieving high detectivity and fast response speed. Here, we first develop an approach for intrinsic charge manipulation induced by molecularly engineered donors to block electron injection and facilitate hole extraction between the indium tin oxide (ITO) transparent anode and the photoactive layer. By utilizing a polymer donor with 3,4‐ethylenedioxythiophene (EDOT) as the conjugated side chain, a polymer‐rich layer forms spontaneously on the ITO substrate due to the increased oxygen interactions between ITO and EDOT. This results in electron‐blocking‐layer (EBL)‐free devices with lower dark current and noise without a reduction in responsivity compared to control devices. As a result, the EBL‐free devices exhibit a peak specific detectivity of 2.36 × 1013 Jones at 950 nm and achieve a −3 dB bandwidth of 30 MHz under −1 V. Enhanced stability is also observed compared to the devices with poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). This work demonstrates a new method to intrinsically manipulate charge injection in BHJ photoactive layers, enabling the fabrication of solution‐processed EBL‐free OPDs with high sensitivity, rapid response, and good stability.

Rapid wavelength interval selection technology for multi-channel intensity-interrogation surface plasmon resonance imaging sensing

Intensity-interrogation surface plasmon resonance (I-SPR) provides the fastest imaging speed among various SPR techniques, including wavelength, phase, and angle-based detection. It also integrates easily with other devices and has substantial practical application potential. However, I-SPR's reliance on direct detection of reflected light intensity renders it sensitive to light source fluctuations and detector dark noise, and its dynamic range is relatively limited. To address these challenges, we have developed a multi-channel I-SPR sensing platform featuring rapid wavelength interval selection technology. This system optimizes the sensing wavelength according to the refractive indices of different samples, mitigating issues related to inconsistent SPR signals from various biomolecules. Our improved I-SPR technology enables high-throughput biomolecular detection with a refractive index range size of 2.035 × 10−2 for dynamic monitoring, reaching a leading role among the existing I-SPR technologies. This represents the widest linear dynamic range for I-SPR to date. Experimental results on protein binding kinetic constants KD are consistent with those obtained from commercially available instruments. We believe that this study is expected to accelerate the development of SPR technology toward broader biological applications.

Parametric Research on the Deep-Junction Silicon SPADs for Wide Spectral Response and Low Dark Count Noise

Parametric Research on the Deep-Junction Silicon SPADs for Wide Spectral Response and Low Dark Count Noise

Achieving Tunable Band Structure and Photocarrier Dynamics by Regulating 2D Atomic Layer Stacking Toward High‐Performance Self‐Powered Broadband and Deep‐UV Photodetection

Abstract2D materials with unique layer‐dependent electronic structure can bring precise control to their photocarrier dynamics for optimizing and expanding optoelectronic applications, while the challenge of controlling layer stacking makes the layer dependency law still underexplored in emerging 2D ternary metal chalcogenides. Herein, 2D rhombohedral‐phase ZnIn2S4 (R‐ZIS) with controllable layer thickness is achieved by confined‐growth strategy in high yield, exhibiting continuously tunable direct bandgap (2.39–2.77 eV) with evident upshift of conduction band minimum (CBM) and Fermi level (EF), demonstrated arising from the synergistic effect of reduced interlayer interaction with inevitably increasing Zn defects. Remarkably, the carrier dynamics of R‐ZIS in photoelectrochemical (PEC) device is successfully regulated by adjusted CBM and EF, resulting in continuously tunable optical absorption band, photocarrier separation efficiency, self‐powered capability, and dark current noise. Beneficial from tailored band structure and carrier dynamics, self‐powered PEC‐type photodetector with broadband photoresponse (254–765 nm), is achieved fast response speed (12.3/5.3 ms) and high responsivity (90.29 mA W−1) in multilayer R‐ZIS, while deep‐UV photodetector with ultra‐high specific detectivity (1.62 × 1012 Jones) at 254 nm in monolayer R‐ZIS, exhibiting the record performance in both fields. This work motivates the development of tailored band structure for 2D‐materials‐based optoelectronic devices in strategy and mechanism.

Optoelectronics of Lead‐Free Antimony‐ and Bismuth‐Based Metal Halides for Sensitive and Low‐Noise Photodetection

AbstractOrganic–inorganic hybrid halide perovskites have emerged as the most promising optoelectronic materials for next‐generation solution‐processed devices, primarily attributed to their distinctive properties such as cost‐effectiveness, facile fabrication process, high light absorption coefficient, tunable bandgap, and relatively high charge carrier mobility. Nevertheless, the presence of Pb elements is inevitable in most high‐performance perovskite optoelectronic devices, posing environmental pollution concerns and impeding their commercialization. In this study, two novel non‐toxic bismuth‐ and antimony‐based perovskite materials with environmentally conscious approaches are developed. Their structures and optoelectronic properties have been systematically characterized. Subsequently, photoconductive‐ and photodiode‐type photodetectors are designed and fabricated. Notably, the photodiode configuration exhibits exceptionally low dark current and noise, superior detection sensitivity, fast response speed, and good device stability. Owing to these superior performance metrics, the devices demonstrate great potential for real applications. Furthermore, this study furnishes a theoretical framework and design perspectives for the solution‐processed semiconductor materials.

Analysis of noise and its characteristics in avalanche photodiode

Avalanche photodiodes (APDs) produce noise during operation, which affects the device performance. However, the previous research on its noise is mainly theoretical analysis and is only reflected as optical noise. Therefore, according to the characteristics of APD material and the mechanism of noise generation, the main noise of the device is analyzed in this paper. First, the test method of noise in APDs is established, including testing of dark noise, optical noise, and multiplication noise in high frequency bands. The main noises in APDs are 1/f noise, thermal noise, shot noise, generation recombination noise, and multiplication shot noise, and shot noise is suppressed by Fermi–Dirac distribution and Coulomb action. Second, the reliability of APDs is evaluated by measuring and analyzing the noise parameters of the device through thermal aging experiments. It is concluded that the defects introduced by thermal aging can be reflected by the change in noise, which is consistent with the results in the literature. This method can comprehensively obtain the noise in APDs, which is helpful to improve the working efficiency, life, and reliability of the device.

A 64 × 128 3D-Stacked SPAD Image Sensor for Low-Light Imaging.

Low-light imaging capabilities are in urgent demand in many fields, such as security surveillance, night-time autonomous driving, wilderness rescue, and environmental monitoring. The excellent performance of SPAD devices gives them significant potential for applications in low-light imaging. This article presents a 64 (rows) × 128 (columns) SPAD image sensor designed for low-light imaging. The chip utilizes a three-dimensional stacking architecture and microlens technology, combined with compact gated pixel circuits designed with thick-gate MOS transistors, which further enhance the SPAD's photosensitivity. The configurable digital control circuit allows for the adjustment of exposure time, enabling the sensor to adapt to different lighting conditions. The chip exhibits very low dark noise levels, with an average DCR of 41.5 cps at 2.4 V excess bias voltage. Additionally, it employs a denoising algorithm specifically developed for the SPAD image sensor, achieving two-dimensional grayscale imaging under 6 × 10-4 lux illumination conditions, demonstrating excellent low-light imaging capabilities. The chip designed in this paper fully leverages the performance advantages of SPAD image sensors and holds promise for applications in various fields requiring low-light imaging capabilities.

High-performance InGaAs/GaAsSb extended short-wave infrared Electron-Injection photodetector

In this paper, we report a high-sensitive extended short-wave infrared (e-SWIR) Electron-Injection (EI) photodetector based on InGaAs/GaAsSb type-II superlattice (T2SL). To achieve high gain and low dark current noise, the EI photodetector involved in this letter employs a multi-layer heterogeneous band structure, composed of InAlAs, GaAsSb and InGaAs/GaAsSb T2SL, which can facilitate electron injection and effectively reduce recombination and thermal generation within the device. Thanks to the unique band alignment, this EI photodetector operates in high-gain linear-mode and requires only a small bias voltage about 0.8 V. At 200 K, the detector exhibits a 100 % cut-off wavelength of ∼ 2.7 μm, a peak responsivity of 3693.2 A/W corresponding to a gain of 7979.0 at 1.4 V, and a gain-normalized dark current density (GNDCD) of 1.4 × 10-6 A/cm2, which results in a remarkable specific detectivity of 6.0 × 1013 cm·Hz1/2/W. When operating at room temperature, this EI photodetector presents a decent responsivity of over 2000.0 A/W. Our results pave a potential way for ultra-sensitive e-SWIR infrared detection at high temperature.

High-quality lateral monolayer-multilayer graphene junction formed by selective laser thinning for self-powered photodetection

The formation of an asymmetric junction is key to graphene-based photodetectors of high-sensitive photodetectability, because such a junction can not only facilitate the diffusion or drift of photogenerated carriers but also realize a self-powered operation. Here, a monolayer-multilayer graphene junction photodetector is accomplished by selectively thinning part of a multilayer graphene to a high-quality monolayer. Benefiting from the large photoabsorption cross section of multilayer graphene and strong asymmetry caused by the significant differences in optoelectronic properties between monolayer and multilayer graphene, the monolayer-multilayer graphene junction shows a 7-fold increase in short-circuit photocurrent as compared with that at the monolayer graphene-metal contact in scanning photocurrent images. The asymmetric configuration also enables the photodetector to work at zero bias with minimized dark current noise and stand-by power consumption. Under global illumination with visible light, a photoswitching ratio of 3.4 × 103, a responsivity of 8.8 mA W−1, a specific detectivity of 1.3 × 108 Jones and a response time of 11 ns can be obtained, suggesting a promising photoresponse. Moreover, it is worth mentioning that such a performance enhancement is achieved without compromising the broadband spectral response of graphene photodetector and it is hence applicable for long wavelength spectral range including infrared and terahertz.

Ultralow-Noise MoS2/Type II Superlattice Mixed-Dimensional van der Waals Barrier Long-Wave Infrared Detector.

Low-noise, high-performance long-wave infrared detectors play a crucial role in diverse applications, including in the industrial, security, and medical fields. However, the current performance of long-wave detectors is constrained by the noise associated with narrow bandgaps. Therefore, exploring novel heterostructures for long-wavelength infrared detection is advantageous for the development of compact and high-performance infrared sensing. In this investigation, we present a MoS2/type II superlattice mixed-dimensional van der Waals barrier long-wave infrared detector (Mixed-vdWH). Through the design of the valence band barrier, substantial suppression of device dark noise is achieved, resulting in 2 orders of magnitude reduction in dark current. The device exhibits outstanding performance, with D* reaching 4 × 1010 Jones. This integration approach synergizes the distinctive properties of two-dimensional layered materials (2DLM) with the well-established processing techniques of traditional three-dimensional semiconductor materials, offering a compelling avenue for the large-scale integration of 2DLM.

Simulation of a Pulsed Metastable Helium Lidar

Measurements of atmosphere density in the upper thermosphere and exosphere are of great significance for studying space–atmosphere interactions. However, the region from 200 km to 1000 km has been a blind area for traditional ground-based active remote sensing techniques due to the limitation of facilities and the paucity of neutral atmosphere. To fulfill this gap, the University of Science and Technology of China is developing a powerful metastable helium resonance fluorescent lidar incorporating a 2 m aperture telescope, a high-energy 1083 nm pulsed laser, as well as a superconducting nanowire single-photon detector (SNSPD) with high quantum efficiency and low dark noise. The system is described in detail in this work. To evaluate the performance of the lidar system, numerical simulation is implemented. The results show that metastable helium density measurements can be achieved with a relative error of less than 20% above 370 km in winter and less than 200% in 270–460 km in summer, demonstrating the feasibility of metastable helium lidar.

Dark continuous noise from mutant G90D-rhodopsin predominantly underlies congenital stationary night blindness

Congenital stationary night blindness (CSNB) is an inherited retinal disease that causes a profound loss of rod sensitivity without severe retinal degeneration. One well-studied rhodopsin point mutant, G90D-Rho, is thought to cause CSNB because of its constitutive activity in darkness causing rod desensitization. However, the nature of this constitutive activity and its precise molecular source have not been resolved for almost 30 y. In this study, we made a knock-in (KI) mouse line with a very low expression of G90D-Rho (equal in amount to ~0.1% of normal rhodopsin, WT-Rho, in WT rods), with the remaining WT-Rho replaced by REY-Rho, a mutant with a very low efficiency of activating transducin due to a charge reversal of the highly conserved ERY motif to REY. We observed two kinds of constitutive noise: one being spontaneous isomerization (R*) of G90D-Rho at a molecular rate (R* s-1) 175-fold higher than WT-Rho and the other being G90D-Rho-generated dark continuous noise comprising low-amplitude unitary events occurring at a very high molecular rate equivalent in effect to ~40,000-fold of R* s-1 from WT-Rho. Neither noise type originated from G90D-Opsin because exogenous 11-cis-retinal had no effect. Extrapolating the above observations at low (0.1%) expression of G90D-Rho to normal disease exhibited by a KI mouse model with RhoG90D/WTand RhoG90D/G90D genotypes predicts the disease condition very well quantitatively. Overall, the continuous noise from G90D-Rho therefore predominates, constituting the major equivalent background light causing rod desensitization in CSNB.

Fine tuning of gas system and performance studies of RPC detectors in the INO's mini-ICAL detector

The India-based Neutrino Observatory's (INO) Iron CALorimeter (ICAL) experiment will be instrumented with about 28,800 large area glass Resistive Plate Chambers (RPCs) as active detector elements. The mini-ICAL, which is a 600-times scaled-down prototype version of the ICAL, is currently in operation at the Inter Institutional Centre for High Energy Physics (IICHEP), a transit campus of the INO project in Madurai, India. The 4 m×4 m detector comprises an ∼ 85 t magnet, built using 11 layers of iron plates to accommodate 10 layers of RPCs — two RPCs per layer. A closed-loop gas system (CLS) is designed to supply gas mixture of R134a (95.2%), isobutane (4.5%), and SF 6 (0.3%) to the mini-ICAL, collect the return gas from the RPCs, purify it using filters, and recirculate the mixture into the detector. Contamination of any kind into the gas mixture will severely affect the characteristics of the RPC detectors, such as the dark current and noise rates, and consequently deteriorate performance of the RPC detector. The contamination is mainly caused due to leaks within the gas system, in the gas lines and in the RPC gas gap volume. This paper deals with systematic identification and mitigation of leaks within the closed-loop gas system and performance improvement of the RPCs installed in the mini-ICAL detector.

New method for optimizing the detection of low-energy soft X-rays (200–300 eV) in a CMOS detector

Complementary metal-oxide semiconductor (CMOS) sensors have been widely used as soft X-ray detectors in several fields owing to their recent developments and unique advantages. The CMOS detector parameters have been extensively studied and evaluated. However, the methods for discriminating signals and dark noise have not been sufficiently studied, particularly for low-energy soft X-rays. Setting a threshold, which is widely used for discrimination, is not suitable for low-energy soft X-rays because of the crossing of the energy bands of dark noise and signals. In this study, we analyzed the charge correlation of the CMOS detector GSENSE2020BSI (G2020BSI) and proposed a new two-dimensional segmentation method to optimize the discrimination of signals according to the charge correlation. The effectiveness of the method used to discriminate low-energy soft X-rays on the G2020BSI detector was qualitatively evaluated. The optimal feature parameters used in the two-dimensional segmentation method were investigated for G2020BSI. However, the two-dimensional segmentation method is insensitive to feature parameters.

A Data-driven Approach for Mitigating Dark Current Noise and Bad Pixels in Complementary Metal Oxide Semiconductor Cameras for Space-based Telescopes

In recent years, there has been a gradual increase in the performance of complementary metal oxide semiconductor (CMOS) cameras. These cameras have gained popularity as a viable alternative to charge-coupled device cameras in a wide range of applications. One particular application is the CMOS camera installed in small space telescopes. However, the limited power and spatial resources available on satellites present challenges in maintaining ideal observation conditions, including temperature and radiation environment. Consequently, images captured by CMOS cameras are susceptible to issues such as dark current noise and defective pixels. In this paper, we introduce a data-driven framework for mitigating dark current noise and bad pixels for CMOS cameras. Our approach involves two key steps: pixel clustering and function fitting. During the pixel clustering step, we identify and group pixels exhibiting similar dark current noise properties. Subsequently, in the function fitting step, we formulate functions that capture the relationship between dark current and temperature, as dictated by the Arrhenius law. Our framework leverages ground-based test data to establish distinct temperature–dark current relations for pixels within different clusters. The cluster results could then be utilized to estimate the dark current noise level and detect bad pixels from real observational data. To assess the effectiveness of our approach, we have conducted tests using real observation data obtained from the Yangwang-1 satellite, equipped with a near-ultraviolet telescope and an optical telescope. The results show a considerable improvement in the detection efficiency of space-based telescopes.

Research on proton displacement damage effects in charge-domain accumulation type TDI CMOS image sensors

TDI CMOS image sensors are the most widely used photodetectors in space earth observation and multispectral imaging. The displacement damage caused by high-energy proton irradiation in the space environment leads to the continuous degradation of TDI CMOS image sensor parameters, seriously affecting its performance, reliability, and service life. This paper focuses on a space-based TDI CMOS image sensor chip and carries out 3 MeV proton irradiation tests and post-irradiation annealing tests to obtain the change rules of optical and electrical parameters. The degradation mechanism of sensitive parameters of TDI CMOS image sensors caused by proton irradiation is analyzed, and the sensitive region of proton displacement damage are discussed. The study demonstrates that after proton irradiation, the parameters especially full well capacity and temporal dark noise of the device degrade less, with small sensitivity to proton irradiation. However, the dark current, CTE, and pixel column FPN significantly degrade, and the degree of degradation is linearly related to the proton irradiation dose. In addition, the test also obtained the short-term and long-term annealing changes of sensitive parameters after proton irradiation of TDI CMOS image sensors, providing scientific advice for TDI CMOS image sensors space proton radiation effect tests and evaluations. The research results of this paper provide important references for the evaluation of radiation effects, on-orbit performance estimation, and radiation resistance reinforcement of space-based TDI CMOS image sensors.

Enhancing SDGSAT-1 night light images using a panchromatic guidance denoising algorithm

The Glimmer Imager on board the Sustainable Development Science Satellite 1 (SDGSAT-1) is capable of providing high-resolution nighttime light images. However, the presence of stripe noise and dark current noise in L4A images affects the authenticity of image information, thus limiting its scientific applications. This study proposes a panchromatic guidance denoising algorithm to enhance the quality of nighttime light images based on the spectral consistency properties between the panchromatic and RGB channels. This algorithm utilizes two low-noise panchromatic bands to obtain a denoised light area and subsequently removes a significant amount of noise from non-light areas in the RGB bands based on this light area. Our results indicate that this algorithm can effectively remove noise from SDGSAT-1 nighttime light images, achieving a noise removal rate greater than 99.8% in the selected dark ocean area. It also preserves more reasonable radiometric characteristics and spatial details of high-spatial resolution nighttime light images when compared to other popular denoising algorithms. The perturbation caused by moonlight can be effectively eliminated using this algorithm, which further improves the comparability and application of SDGSAT-1 nighttime light images under different lunar phases.

Polarization upgrade of specMACS: calibration and characterization of the 2D RGB polarization-resolving cameras

Abstract. The spectrometer of the Munich Aerosol Cloud Scanner (specMACS) is a high-spatial-resolution hyperspectral and polarized imaging system. It is operated from a nadir-looking perspective aboard the German High Altitude and LOng range (HALO) research aircraft and is mainly used for the remote sensing of clouds. In 2019, its two hyperspectral line cameras, which are sensitive to the wavelength range between 400 and 2500 nm, were complemented by two 2D RGB polarization-resolving cameras. The polarization-resolving cameras have a large field of view and allow for multi-angle polarimetric imaging with high angular and spatial resolution. This paper introduces the polarization-resolving cameras and provides a full characterization and calibration of them. We performed a geometric calibration and georeferencing of the two cameras. In addition, a radiometric calibration using laboratory calibration measurements was carried out. The radiometric calibration includes the characterization of the dark signal, linearity, and noise as well as the measurement of the spectral response functions, a polarization calibration, vignetting correction, and absolute radiometric calibration. With the calibration, georeferenced, absolute calibrated Stokes vectors rotated into the scattering plane can be computed from raw data. We validated the calibration results by comparing observations of the sunglint, which is a known target, with radiative transfer simulations of the sunglint.

Interface engineering by constructing vertical junction for reduced noise and improved sensitivity in 2D photodetector

Two-dimensional (2D) materials have been widely demonstrated as promising candidates for next generation photodetectors, while the noticeable channel current is still a limiting factor for photodetection sensitivity. In this work, the interface engineering has been developed by constructing a vertical pn and Schottky junction in the 2D WS2 channel, resulting in a reduced dark current and noise spectral density, significantly improving the sensitivity. Specifically, the WS2 bottom surface is coupled with p-type tellurium (Te) nanoribbon and gold (Au) stripes, thus a vertical pn and Schottky junction can be constructed at WS2/Te and WS2/Au interface, respectively. In both device architectures, the dark current and electric noise are much suppressed due to the formation of depletion region in WS2 channel. Meanwhile, the out-of-plane built-in electric field at junction can facilitate the separation of photo-excited electron–hole pairs, which subsequently yields a faster temporal response. For the WS2/Au device, the incident light can be reflected by the bottom Au and propagate through the WS2 layer again, further boosting the photo-absorption, thus the photodetection sensitivity. The engineered WS2 photodetectors exhibit the noise spectral density as low as 5.36 × 10−14 A Hz−1/2 and high specific detectivity (D*) up to 1.12 × 1011 Jones, which has one–two orders of magnitude improvement compared to the pristine device. This work provides an effective and universal interface engineering strategy to achieve low noise and high sensitivity in 2D photodetectors.

Optimization of pulse shape discrimination based on frequency domain for SiPM-based NaIL scintillator detector

Frequency gradient analysis (FGA) neutron-gamma pulse shape discrimination (PSD) based on Fourier transform has proved to be an effective method for discrimination between two types of pulses by simply constructing a discrimination parameter by subtracting the amplitude of the 1st frequency component from the 0th frequency component. However, the discrimination parameter constructed by the above method could not meet the requirements at some lower sample rates, and the dark noise caused using optoelectronic devices such as miniaturized SiPMs array further erodes the difference between the two frequency components. This paper proposes a new discrimination parameter construction method based on FGA for neutron-gamma discrimination, which is referred as mFGA (modified FGA). This discrimination parameter uses the 0th frequency component and other frequency components to enhance the discrimination performance. A neutron detector module consisting of a 25.4 mm× 25.4 mm× 50.8 mm NaI:Tl,6Li (NaIL) scintillator and an array of 8 × 8 SiPMs was established to verify the method of mFGA. The module measured a 252Cf neutron source under three shielding conditions: no shield, 5 cm high-density polyethylene (HDPE), and 10 cm lead brick. The proposed mFGA method was used to calculate the figure of merit (FoM) under each shielding condition and compared to the traditional frequency gradient method (FGA) and the traditional charge comparison method (CCM). The results show that the discrimination performance with the mFGA method is significantly improved. Taking the HDPE shielding group as an example, the performances of the three methods are FoM-FGA =1.14, FoM-mFGA =2.75, FoM-CCM =0.92. At the same time, with the increase of energy, due to the neutron gamma pulse becoming similar, and the discrimination performance of FGA and CCM decrease significantly. The discrimination performance of the mFGA method is relatively stable in all energy regions. Therefore, the proposed method is superior to the traditional FGA of the 0th frequency minus the 1st frequency and has a good application prospect for neutron-gamma discrimination with detectors of poor signal quality.