Increase In Dark Current Research Articles

A strategy for achieving high-performance single layer polymer photodetectors through dark current reduction using PMMA additives

Suppressing dark current density is crucial for optimizing the performance of organic photodetectors (PDs), particularly in terms of detectivity (D∗) and linear dynamic range (LDR). Organic PDs often utilize the bulk heterojunction structure of organic solar cells to significantly increase photocurrent. However, unlike solar cells, which are unaffected by dark current, photodetectors' performance is substantially limited by it. The interconnected network of bulk heterojunctions leads to a noticeable increase in dark current, thus degrading device performance. Typically, reducing dark current involves adding a modification layer or using multilayer planar heterojunctions, which effectively reduce dark current but often delay response speed and complicate manufacturing. This study presents an alternative approach by incorporating a small concentration of PMMA into single-layer polymer photodetectors, significantly reducing dark current without affecting photocurrent. For this single-layer polymer PD, an ultra-low dark current density of 1.25 × 10−8 A/cm2, a high Dsh∗ of 2.74 × 1012 Jones, an LDR of 120.5 dB, and a fast response time with 1.6 μs were achieved. The capacitance-voltage (C-V), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) measurements revealed that the PMMA additive reduces internal defects, increases bulk resistance, optimizes phase separation, and enhances carrier transport efficiency. The improved device performances are attributed to a more efficient vertical arrangement of the donor-acceptor interface and carrier channels, thus reducing carrier recombination loss. These findings offer a new direction for fabricating high-performance single-layer photodetectors.

The CRILIN calorimeter: gamma radiation resistance of crystals and SiPMs

The Crilin calorimeter is a semi-homogeneous calorimetric system based on Lead Fluoride (PbF2) crystals with UV-extended Silicon Photomultipliers (SiPMs) proposed for the Muon Collider. This study investigates the radiation resistance of crystals and SiPMs, subjected to 10 kGy gamma irradiation, equivalent to a 10-year service life in the Muon Collider. Our findings indicate that while PbF2 crystals exhibit a decrease in transmittance post-irradiation with partial recovery over time, the alternative PbWO4-Ultra Fast (PWO-UF) demonstrates exceptional radiation hardness, maintaining stable transmittance. SiPMs showed an increase in dark current and breakdown voltage post-irradiation, with less degradation observed in the SiPM biased during the exposure to radiation compared to the unbiased component. These results underscore the viability of PbF2 for radiation-tolerant calorimeters, though improvements in production homogeneity are needed. The superior performance of PWO-UF crystals suggests they are a promising alternative for high-radiation applications, but their higher cost must be carefully considered.

Characterization of SiPM performance in a small satellite in low earth orbit using LabOSat-01

In this work, the performance of SensL MicroFC-60035 SiPM devices was studied during a 1460-day mission in Low Earth Orbit (LEO) using the LabOSat-01 characterization payload. Two of these platforms, carrying two SiPMs each, were integrated into the ÑuSat-7 satellite (COSPAR-ID: 2020-003B). Analysis revealed that these SiPMs experienced an increase in dark current over time due to damage from trapped and solar proton radiation. The total ionizing dose received by the payload and the SiPMs was measured using p-MOSFET dosimeters, with a resulting value of 5 Gy, or a 1 MeV neutron equivalent fluence of ϕn=5⋅109 n/cm2. The dark current was observed to increase up to 500 times. Parameters such as Gain and Photon Detection Efficiency remained unchanged throughout the mission. These findings align with previous performance reports involving different SiPMs irradiated with various particles and energies.

Radiation damage of InGaAs avalanche photodiode under gamma ray irradiation

The γ-ray irradiation characteristics of InGaAs avalanche photodiode (APD) in a space radiation environment have been comprehensively investigated through an in-depth study. The results show that γ-ray can cause the dark current and low frequency noise of InGaAs APD to increase, while the avalanche breakdown characteristics, multiplication gain, spectral response and capacitance of the device are less affected by irradiation, and almost no obvious changes occur, which suggests that these parameters are insensitive to ionizing radiation. In addition, the activation energy of the device under different bias voltages is significantly increased by the ionization damage after irradiation. Finally, the annealing experiments at different temperatures after irradiation were carried out. It is found that the interface state induced by radiation is the main factor leading to the increase of dark current, low frequency noise and activation energy of InGaAs APD. Reducing the interface state can improve the device’s ability to inhibit ionizing radiation damage.

Defect Analysis in a Long-Wave Infrared HgCdTe Auger-Suppressed Photodiode.

Deep defects in the long-wave infrared (LWIR) HgCdTe heterostructure photodiode were measured via deep-level transient spectroscopy (DLTS) and photoluminescence (PL). The n+-P+-π-N+ photodiode structure was grown by following the metal-organic chemical vapor deposition (MOCVD) technique on a GaAs substrate. DLTS has revealed two defects: one electron trap with an activation energy value of 252 meV below the conduction band edge, located in the low n-type-doped transient layer at the π-N+ interface, and a second hole trap with an activation energy value of 89 meV above the valence band edge, located in the π absorber. The latter was interpreted as an isolated point defect, most probably associated with mercury vacancies (VHg). Numerical calculations applied to the experimental data showed that this VHg hole trap is the main cause of increased dark currents in the LWIR photodiode. The determined specific parameters of this trap were the capture cross-section for the holes of σp = 10-16-4 × 10-15 cm2 and the trap concentration of NT = 3-4 × 1014 cm-3. PL measurements confirmed that the trap lies approximately 83-89 meV above the valence band edge and its location.

Boosting photoelectrochemical performance through appling magnetic field in manganese-doped cobalt ferrite photoanodes

An efficient photoelectrochemical water-splitting process is of paramount importance as it provides a sustainable and clean method for generating hydrogen fuel, which is crucial for addressing the world’s growing energy needs while mitigating environmental concerns. Herein, the effects of applying a magnetic field on the photoelectrochemical performance of photoanodes composed of Cobalt ferrite (CoFe2O4) and Manganese (Mn)-doped CoFe2O4 are investigated. The CoMnxFe2-xO4 nanoparticles were synthesized using a sol–gel method, with varying values of x (0.0, 0.1, 0.3, and 0.5). X-ray diffraction analysis consistently reveals a singular cubic spinel structure for all four samples. Magnetic analyses demonstrate an enhancement in magnetic characteristics, including saturation magnetization, coercivity, and anisotropy field in the CoMn0.3Fe1.7O4 sample compared to the other three samples. Photoelectrochemical (PEC) measurements indicate that the photocurrent increases in all four samples when a static magnetic field is applied. However, the CoMn0.3Fe1.7O4 sample shows a more pronounced enhancement. Specifically, the dark current density increases by more than 115 % when a magnetic field of 190 ± 20 mT is applied. Additionally, it rises by 387 % under light illumination with the magnetic field. This enhancement in PEC performance is attributed to electron spin polarization adjusted through the external magnetic field.

Reliability modelling and assessment of CMOS image sensor under radiation environment

The Complementary Metal-Oxide Semiconductor (CMOS) image sensor is a critical component with the function of providing accurate positioning in many space application systems. Under long-time operation in space environments, there are radiation related degradation and various uncertainties affecting the positioning accuracy of CMOS image sensors, which further leads to a reliability reduction of CMOS image sensors. Obviously, the reliability of CMOS image sensors is related to their specified function, degradation, and uncertainties; however, current research has not fully described this relationship. In this paper, a comprehensive approach to reliability modelling of CMOS image sensors is proposed based on the reliability science principles. Firstly, the performance margin modelling of centroid positioning accuracy is conducted. Then, the degradation model of CMOS image sensors is derived considering the dark current increase induced by the total ionizing dose effects. Finally, various uncertainties are analyzed and quantified, and the measurement equation of reliability is proposed. A case study of a CMOS image sensor is conducted to apply the proposed method, and the sensitivity analysis can provide suggestions for design and use of CMOS image sensors to ensure reliability. A simulation study is conducted to present the advantages of the proposed comprehensive approach.

Evidence for ionization damage in mid-wave infrared nBn detectors

The effects of 63 MeV proton and 60Co gamma irradiation on the operation of 4.3 μm cutoff nBn photodetectors are demonstrated separately, and both are shown to yield a total ionizing dose (TID) effect. The effect is shown here in an InAsSbBi nBn detector and has been observed in other bulk alloy nBn detectors, and is unusual as it is notably absent in superlattice nBn detectors. The non-antireflection coated detectors exhibit a pre-radiation quantum efficiency of 17% at 3.3 μm wavelength and a dark current density of 50 μA/cm2, or roughly 300× the Rule 07 expectation, at their ideal operating voltage of −0.4 V bias at 150 K. Step-wise proton irradiation and in situ measurement indicate that the dark current increases to about 400× Rule 07 at the highest proton dose level of 150 krad(Si) (9.10 × 1011 p+/cm2), while the quantum efficiency is degraded at a relatively faster rate than the majority of analogous detectors characterized by our lab. Both the photocurrent and dark current are also shown to exhibit a turn-on voltage magnitude reduction of 100 mV following either gamma or proton irradiation, a trend which is attributable to negative trapped charge at the barrier interface (TID effect). This theory is further supported by an observed capacitance density magnitude reduction with dose and affirmed with Silvaco TCAD simulations. Following both proton exposure and subsequent anneal and gamma exposure and subsequent anneal; dark current, photocurrent, and CV all approach their pre-radiation baseline values.

Role of oxygen functional groups and attachment of Au nanoparticles on graphene oxide sheets for improved photodetection performance.

Integrating low-dimensional graphene oxide (GO) with conventional Si technology offers innovative strategies for developing ultrafast wideband photodetectors. In this study, we synthesized GO and explored its potential application in broadband photodetection alongside silicon heterostructures. The as-synthesized GO contains various oxygen functional groups, as evidenced by X-ray photoelectron and Fourier transform infrared spectroscopy. These functional groups contribute to increased photo absorption, enhancing photodetection performance. The systematic reduction of these functional groups from the GO surface via thermal annealing decreases photo absorption and consequently lowers the photocurrent. This reduction diminishes photo absorption and amplifies the dark current by approximately 25 times, from 20 nA to 496 nA. This dark current increase is attributed to the electron mobility following the reduction of functional groups. However, attaching plasmonic gold nanoparticles (Au NPs) to the GO surface enhances UV-Vis absorption in the visible region, enabling broadband detection. The even distribution of attached Au NPs on the GO surface is confirmed through field emission transmission electron microscopy. While thermal annealing of GO diminishes the responsivity from 4.6 A W-1 to 3.0 A W-1, the attachment of Au NPs augments the responsivity by more than two-fold, reaching 10.0 A W-1. Thus, it highlights the importance of rich oxygen functional groups in GO and the attachment of Au NPs to achieve more efficient photo-sensing properties.

Mechanisms of Dark Current Increase and Pixel Anomalies Induced by 2 GeV Ta-irradiation in 8T-CMOS Image Sensors

Mechanisms of Dark Current Increase and Pixel Anomalies Induced by 2 GeV Ta-irradiation in 8T-CMOS Image Sensors

InGaAs-Based MSM Photodetector: Researching Absorption Layer, Barrier Layer, and Digital Graded Superlattice Layer with 3D Simulation

The effects of absorption, barrier, and digital graded layer thickness on dark current and photocurrent in Metal Semiconductor Metal (MSM) photodetectors by using 3D Silvaco TCAD are reported. The photo-dark current ratio (Iphoto/Idark) is calculated using the photocurrent and dark current values obtained by simulation. In study A (absorption layer thickness variation) the photocurrent, dark current and photo-dark current ratio are increased with increased absorption layer thickness, and the dark current is 1.138x10-7 A levels. In Study B (barrier layer thickness variation), when the barrier layer is added to the absorption layer, the dark current is decreased to 1.56x10-11 A levels. It is reported that the photo-dark current ratio with increasing barrier layer thickness increases. In study C (digital graded superlattice layer thickness variation), the dark current increases, and photocurrent decreases with the increase of the digital graded superlattice layer thickness. However, the photo-dark current ratio with increasing digital graded superlattice layer thickness decreases. Furthermore, a similar trend of development is observed on photo-dark current with adding of the barrier layer and digital graded superlattice layer on the absorption layer. These findings demonstrate the importance of optimizing layer thickness in MSM photodetectors for improved device performance.

Study of displacement damage effects in InGaAs PIN photodiode under 10 MeV proton irradiation

The displacement damage effect of 10 MeV proton radiation on a high-speed InGaAs PIN photodiode has been experimentally investigated to evaluate the stability of the device in a space radiation environment. The results show that the dark current and low-frequency noise of the device increase significantly after irradiation, while the capacitance of the device decreases slightly after irradiation, where the spectral response parameters are less affected by irradiation. The increase in dark current is essentially linear with the displacement damage dose. Finally, the effect of proton irradiation on the optical communication system is simulated and the results show that the bit error rate of the system increases with the increase in irradiation fluence, which seriously affects the sensitivity of the optical communication system.

Electrophysical parameters of p-i-n photodiodes, irradiated with 60Co γ-quanta

The results of studies of changes in the electrical parameters of p-i-n photodiodes manufactured on monocrystalline silicon wafers of p-type conductivity orientation (100) with ρ = 1000 Ohm cm, when irradiated with γ-quanta from a 60Co source, are presented. It has been established that as a result of irradiation of p-i-n photodiodes with doses up to 2·1015 quanta/cm2, the reverse dark current increases by more than an order of magnitude. However, the shape of the curve of the dependence of the current on the applied reverse voltage of irradiated p-i-n photodiodes does not change qualitatively, as for the original devices there are three regions with different dependences of current on voltage: sublinear, superlinear and linear, due to different mechanisms of generation-recombination processes in the depletion region of the p-n junction. The main reason for the increase in the reverse current of p-i-n photodiodes as a result of irradiation with γ-quanta is the formation of generation-recombination centers of radiation origin due to the condensation of primary radiation defects (vacancies and/or self-interstitial atoms) on technological residual structural defects formed during the growth of silicon single crystals, and during subsequent high-temperature treatments during the formation of devices.

Preparation and Performance Study of Photoconductive Detector Based on Bi2O2Se Film

Bi2O2Se, as a novel two-dimensional semiconductor material, has been prepared and used in the field of photodetection. Herein, Bi2O2Se nanosheets were prepared using a hydrothermal method. Bi2O2Se films were also prepared using a drop-coating method. A photoconductive detector based on the Bi2O2Se film was constructed. The influence of nanosheet size was considered. Ultrasonic crashing treatments and different drying processes were used for the improvement of device performance. The obtained results demonstrate that the Bi2O2Se film based on treated nanosheets is denser and more continuous, leading to a higher photocurrent (1.4 nA). Drying in a vacuum can further increase the photocurrent of the device (3.0 nA). The photocurrent would increase with the increase in drying temperatures, while the dark current increases synchronously, leading to a decrease in the on/off ratio. The device based on Bi2O2Se film was dried in a vacuum at 180 °C and exhibited high responsivity (28 mA/W) and detectivity (~4 × 109 Jones) under 780 nm light illumination. Together, these results provide a data foundation and vision for the further development of photodetectors based on Bi2O2Se material.

Non-monotonic evolution of the responses of ZnO-nanoparticle UV-sensitive devices under ambient aging

Ultraviolet (UV) sensitive devices based on spin-coated zinc-oxide nanoparticles (ZnO) were fabricated and characterised. They were subsequently stored in the ambient and dark conditions with low humidity for 56 days, during which time they were intermittently recharacterised to determine the aging effect on their sensing properties, including responsivity, sensitivity, and response and recovery times. Over the 56-day period, both the dark and illumination currents increased, causing the non-monotonic evolution of the performances of the devices – the responsivity improved by 9–18 folds, the sensitivity remained stable, and the response and recovery times deteriorated as they were 46 and 33 times longer, respectively. These changes were associated with an increase in the number of adsorbed oxygen molecules on the ZnO surface with time. This resulted in more photodesorbed oxygen molecules and thus more remaining charge carriers under illumination, which increased the photo-generated current and consequently responsivity. However, it also caused the current to rise and decay more slowly when the illumination appeared and disappeared, respectively, leading to the prolonged response and recovery times. The longer recovery times led in an increase in dark current, which, when combined with an increase in illumination current, resulted in a stable sensitivity. The trends of these sensing parameters were similar, but to varying degrees, regardless of the change in the radiation levels and ZnO layer thicknesses.

Ionizing Radiation Effects on Hole Collection Backside-Illuminated p-Type Deep-Trench-Pinned Photo-MOS Pixels Under Image Acquisition

Dark current degradation, origins, and annealing behavior after x-ray irradiation are studied in a P-type, hole collecting, backside-illuminated image sensor currently being developed at STMicroelectronics and based on deep-trenched photo-MOS pixels. Different biasing conditions during irradiation, i.e. grounded or biased and sequenced, are compared. The dark current increase with total ionizing dose (TID) and the dark current annealing behavior seem to be driven by the backside interface between the P-epitaxy of the pixels and the ONO stack. Despite still being under development, this pixel architecture already exhibits both very good electro-optical performance and a better radiation hardness than pinned photodiode-based CMOS Image sensors that benefit from the same advanced CIS processing technologies. At high total dose range, the photogate challenges custom Radiation-Hardened-by-Design photodiodes by exhibiting a comparable radiation tolerance while bringing new features such as high-resolution or Correlated Double Sampling.

Radiation-Induced Degradation Mechanism of X-Ray SOI Pixel Sensors With Pinned Depleted Diode Structure

The X-ray Silicon-On-Insulator (SOI) pixel sensor named XRPIX has been developed for the future X-ray astronomical satellite FORCE. XRPIX is capable of a wide-band X-ray imaging spectroscopy from below 1 keV to a few tens of keV with a good timing resolution of a few tens of μs. However, it had a major issue with its radiation tolerance to the total ionizing dose (TID) effect because of its thick buried oxide layer due to the SOI structure. Although new device structures introducing pinned depleted diodes dramatically improved radiation tolerance, it remained unknown how radiation effects degrade the sensor performance. Thus, this paper reports the results of a study of the degradation mechanism of XRPIX due to radiation using device simulations. In particular, mechanisms of increases in dark current and readout noise are investigated by simulation, taking into account the positive charge accumulation in the oxide layer and the increase in the surface recombination velocity at the interface between the sensor layer and the oxide layer. As a result, it is found that the depletion of the buried p-well at the interface increases the dark current, and that the increase in the sense-node capacitance increases the readout noise.

Morphologically controlled photodetector performance of molybdenum disulfide nanostructures

The objective of this work is to control the morphology of molybdenum disulfide nanostructures using hydrothermal technique for improving the visible-light photodetector performance. The morphology comprises nanosheets with dimensions and packing density that are dependent on the synthesis temperature. As the synthesis temperature increases from 170 to 210 °C, the dimensional change of nanosheets is accompanied by increased packing density, as confirmed from scanning and transmission electron microscopy images. The dark current increases from 0.9 to 1.18 μA while the bright current increases from 78.57 to 112.59 μA as synthesis temperature increases from 170 to 210 °C. In addition, there is an improvement in all other parameters such as sensitivity, responsivity and detectivity of the photodetector with increase in synthesis temperature. The MoS2 based photodetectors revealed an ultrahigh sensitivity and responsivity of 95% and 11.25 mA/W, very high detectivity of 0.11 × 1011 Jones and fast rise-time and fall-time of around 0.5 and 0.7 ms respectively. X-ray diffraction and x-ray photoelectron spectroscopy studies reveal that there is no change either in the crystallographic texture or stoichiometry of the samples with change in morphology. It is, thus concluded that improved photodetector performance is entirely morphological in origin. The present work represents a facile method based on morphological control to improve the visible light photodetector performance of MoS2 nanostructures.

AlGaN-based metal–semiconductor–metal photodiodes fabricated with nonplanar structure geometry for ultraviolet light detection

Based upon GaN-on-Si wafers with a Al0.24Ga0.76N/AlN/GaN heterostructure, metal–semiconductor–metal photodetectors (MSM PDs) with nonplanar structure geometry are proposed for ultraviolet (UV) light detection. Although the presence of a highly conductive two-dimensional electron gas (2DEG) channel in the Al0.24Ga0.76N/AlN/GaN heterostructure is beneficial for realizing a high-electron-mobility transistor with a drain current of 600 mA/mm and a transconductance of 96 mS/mm, a high dark current is also observed in Schottky-barrier based MSM PDs. Using the nonplanar structure design for the MSM PDs (i.e., one Schottky contact formed on the top surface of the AlGaN mesa while the other is on the GaN buffer) achieves a significant decrease in PD’s dark current (<6 × 10−10 A). In addition, an anomalous increase in dark current of the proposed MSM PDs was found at forward bias, which could be attributed to the reduced potential barrier of the electrons in 2DEG and/or the lowering of the Schottky barrier height by hole trapping at the metal/semiconductor interface. Due to the improved signal to noise ratio and increased dissociation of the photogenerated carriers at the reverse junction (i.e., the reversely biased Schottky contact), the proposed MSM PDs operating at reverse bias exhibit enhanced UV photoresponsivity at λ < 360 nm. In addition to being used for UV light detection, these MSM PDs with a 3-dB bandwidth of 29.6 Hz are also useful for potential optical communications applications.

A Study on the Increase of Leakage Current in AlGaN Detectors with Increasing Al Composition.

The dark leakage current of AlxGa1-xN Schottky barrier detectors with different Al contents is investigated. It was found that the dark leakage of AlxGa1-xN detectors increased with increasing Al content. The XRD and SIMS results showed that there was no significant difference of the dislocation density and carbon impurity concentration in five AlxGa1-xN samples with different Al content. This was likely not the main reason for the difference in dark leakage current of AlxGa1-xN detectors. However, the results of positron annihilation showed that the vacancy defect concentration increased with increasing Al content. This was consistent with the result that the dark leakage current increased with increasing Al content. With the increase of vacancy concentration, the vacancy defect energy levels also increased, and the probability of electron tunneling through defect levels increased. In contrast, the Schottky barrier height decreased, which eventually led to the increase of dark leakage current. This discovery should be beneficial to an accurate control of the performance of AlxGa1-xN detectors.