Increase In Dark Current Research Articles

Shockley–Read–Hall Lifetime Study and Implication in HgCdTe Photodiodes for IR Detection

The Shockley–Read–Hall (SRH) mechanism might be a limiting factor of an infrared (IR) photodiode's dark current. This limitation is twofold. SRH generation might occur in the depletion region of the photodiode. In that case, the corresponding current is usually limiting the low-temperature dark current. Moreover, SRH generation might also occur in the diffusion volume, close to the space charge region, resulting in an increase of the diffusion dark current, usually limiting the high-temperature behavior of the photodiode. Hence, the determination of the SRH lifetime of IR materials is of first importance and has to be measured (or at least estimated) to define upcoming trends in future high-performance IR detectors. During the last few years, a lot of papers have been published about SRH lifetime in III–V materials (InSb, superlattices, InAsSb) and a few other communications have been more focused on comparing different material systems including III–V and II–VI materials. Those latter communications proposed very long SRH lifetimes (longer than ms) for HgCdTe, instead of the classical 10–100 μs usually admitted until now. This paper aims at investigating this SRH lifetime in HgCdTe based on experimental measurements carried out at the Laboratoire d’electronique des technologies de l’information (LETI) on HgCdTe grown in-house. Direct lifetime measurement (photoconductive or photoluminescence decay) as well as indirect estimations from photodiode dark currents are discussed in order to clarify this question of SRH lifetime and its consequences in upcoming advanced IR detection structures. In the end, it appeared that except for p/n extrinsic heterojunctions (for which the narrow gap depleted volume is not well known), most of the devices tested seemed limited by SRH lifetimes in the 10–100-μs range.

Silicon carbide PIN diode detectors used in harsh neutron irradiation

Silicon carbide (SiC) neutron detectors based on PIN diode with Ti/Au electrode structure have been successfully developed and considered to be a good option for neutron detection related to harsh radiation environment, but these detectors suffered inevitable irradiation damage and performance degradation, ultimately damaged the applications severely. Unfortunately, the systematic research focusing on the degradation and irradiation defects is lack, and the mechanism of degradation is not clear yet. In this paper, these issues are carefully studied: SiC detectors were irradiated by neutrons emitted from fusion neutron generator and nuclear reactor with fluence ranging from 1 × 1014 n/cm2 to 2 × 1016 n/cm2, then the performance degradation and neutron induced defects were carefully investigated. It is concluded that the SiC detectors could endure neutron irradiation as least 1016 n/cm2. Although neutron irradiation could induce breakdown of PN junction, decrease of charge collection efficiency and worsening of energy resolution, all the detectors are still alive; furthermore, they could still acquire integrated response spectra to alpha particles with neglectable increase of dark current at neutron fluence of 2 × 1016 n/cm2. The di-carbon antisite defects and vacancy-type defects induced by neutron irradiation should be responsible for the performance degradation, according to low temperature photoluminescence and positron annihilation Doppler broadening measurements. Possible degradation mechanism was discussed as well.

Radiation Effects Due to 3MeV Proton Irradiations on Back-Side Illuminated CMOS Image Sensors**Supported by the National Natural Science Foundation of China under Grant No 11675259, the National Defense Pre-research Foundation of China under Grant No 6140A2404051, and the West Light Foundation of Chinese Academy of Sciences under Grant Nos 2016-QNXZ-B-8 and 2016-QNXZ-B-2.

Benefitting from the higher quantum efficiency and sensitivity compared with the front-side illumination (FSI) CMOS image sensors (CISs), backside illumination (BSI) CMOS image sensors tend to replace CCDs and FSI CISs for space applications. However, the radiation damage effects and mechanisms of BSI CISs in the radiation environment are not well understood. We provide radiation effects due to 3 MeV proton irradiations of BSI CISs dedicated to imaging by the analyses of mean dark current increase, dark current nonuniformity and full well capacity in pixel arrays and isolated photodiodes. Additionally, the present annealing certifies the radiation-induced defects, which are responsible for the parameter degradations in BSI CISs.

Photoelectrochemical Activity of CdS/CdSe-Deposited TiO2 photoanodes Due to Electrolytes with and without Sacrificial Reagents

Literature on the photoelectrochemical (PEC) activity of TiO2 electrodes modified by CdS and or CdSe depositions are mostly performed using electrolytes with sacrificial reagents. The overall performance of a PEC system can vary significantly simply due to the use of different electrolytes, especially those with and without sacrificial reagents. In this paper, we have used a well-known TiO2 nanotube structure modified by CdS/CdSe nanoparticles deposited by successive ionic layer adsorption and reaction (SILAR) method to highlight the difference in PEC activities arising from sulfite oxidation and water oxidation. Linear Sweep Voltammograms measured under a standard AM1.5G simulated spectra, 1 sun (100 mWcm-2) exhibited a photocurrent density of 0.92 mAcm-2 at 1.23 V vs. RHE for the TiO2/CdS/CdSe photoactive electrodes using an aqueous alkaline electrolyte (1 M NaOH) for which water oxidation occurs. However, for the similar photoanode an 8-fold higher photocurrent of 7.4 mAcm-2 (at 1.23 V vs. RHE) was observed using an Na2S/Na2SO3 aqueous electrolyte where sulfite oxidation was the dominant mechanism for the enhanced photocurrent. A maximum STH efficiency of 0.71% and water splitting efficiency of 12.4% was determined for water oxidation. The STH efficiency parameter is more relevant to water splitting systems and to report such device efficiencies we propose that the ‘water splitting efficiency’ parameter is much more meaningful since it correlates the PEC activity specifically to water splitting and not to other pathways that produce an artificially enhanced photocurrent through the use of sacrificial reagents. The incident photon-to-current conversion efficiency spectrum measured at 1.23 V (vs. RHE) bias for the TiO2 photoanodes modified by CdS/CdSe nanoparticles revealed that the current conversion efficiency is lower (~17% or less) when absorption occurs solely from the external CdSe layers indicating higher recombination during charge transport. The increase of dark current observed in the linear sweep voltammetry plots for the voltage range of -0.25 V to +0.15 V vs. RHE was attributed to anodic dissolution of the photoanodes in aqueous electrolytes containing no sacrificial reagents. The photocurrents and onset potentials for the CdS/CdSe modified TiO2 photoanodes were found to improve under acidic conditions showing a slightly increased PEC activity and faster reaction kinetics.

Neutron irradiation test of Hamamatsu, SensL and AdvanSiD UV-extended SiPMs

In this paper, we report the measurement of the neutron radiation hardness of custom Silicon Photomultipliers arrays (SiPMs) manufactured by three companies: Hamamatsu (Japan), AdvanSiD (Italy) and SensL (Ireland). These custom SiPMs consist of a 2×3 array of 6×6 mm2 monolithic cells with pixel sizes of respectively 50 μm (Hamamatsu and SensL) and 30 μm (AdvanSiD). A sample from each vendor has been exposed to neutrons generated by the Elbe Positron Source facility (Dresden), up to a total fluence of ∼ 8.5 × 1011 n1 MeV/cm2. Test results show that the dark current increases almost linearly with the neutron fluence. The room temperature annealing was quantified by measuring the dark current two months after the irradiation test. The dependence of the dark current on the device temperature and on the applied bias have been also evaluated.

Damage Factor for Radiation-Induced Dark Current in InGaAs Photodiodes

In this paper, a compendium of InGaAs photodiode irradiation test results is presented. These photodiodes were irradiated either with γ-rays, protons, neutrons, electrons, pions, alpha particles, or carbon ions of various energies. The displacement damage dose formalism was found to be effective in describing the radiation-induced dark current increase of any of the studied InGaAs photodiodes. The exploitation of capacitancebias voltage and current-bias voltage measurements also allows us to deduce a damage factor that can be used to assess the radiation-induced dark current in a great number of radiation environments.

Ageing and proton irradiation damage of a low voltage EMCCD in a CMOS process

Electron Multiplying Charge Coupled Devices (EMCCDs) have revolutionised low light level imaging, providing highly sensitive detection capabilities. Implementing Electron Multiplication (EM) in Charge Coupled Devices (CCDs) can increase the Signal to Noise Ratio (SNR) and lead to further developments in low light level applications such as improvements in image contrast and single photon imaging. Demand has grown for EMCCD devices with properties traditionally restricted to Complementary Metal-Oxide-Semiconductor (CMOS) image sensors, such as lower power consumption and higher radiation tolerance. However, EMCCDs are known to experience an ageing effect, such that the gain gradually decreases with time. This paper presents results detailing EM ageing in an Electron Multiplying Complementary Metal-Oxide-Semiconductor (EMCMOS) device and its effect on several device characteristics such as Charge Transfer Inefficiency (CTI) and thermal dark signal. When operated at room temperature an average decrease in gain of over 20% after an operational period of 175 hours was detected. With many image sensors deployed in harsh radiation environments, the radiation hardness of the device following proton irradiation was also tested. This paper presents the results of a proton irradiation completed at the Paul Scherrer Institut (PSI) at a 10 MeV equivalent fluence of 4.15× 1010 protons/cm2. The pre-irradiation characterisation, irradiation methodology and post-irradiation results are detailed, demonstrating an increase in dark current and a decrease in its activation energy. Finally, this paper presents a comparison of the damage caused by EM gain ageing and proton irradiation.

Soft X-ray radiation damage in EM-CCDs used for Resonant Inelastic X-ray Scattering

Advancement in synchrotron and free electron laser facilities means that X-ray beams with higher intensity than ever before are being created. The high brilliance of the X-ray beam, as well as the ability to use a range of X-ray energies, means that they can be used in a wide range of applications. One such application is Resonant Inelastic X-ray Scattering (RIXS). RIXS uses the intense and tuneable X-ray beams in order to investigate the electronic structure of materials. The photons are focused onto a sample material and the scattered X-ray beam is diffracted off a high resolution grating to disperse the X-ray energies onto a position sensitive detector. Whilst several factors affect the total system energy resolution, the performance of RIXS experiments can be limited by the spatial resolution of the detector used. Electron-Multiplying CCDs (EM-CCDs) at high gain in combination with centroiding of the photon charge cloud across several detector pixels can lead to sub-pixel spatial resolution of 2–3 μm. X-ray radiation can cause damage to CCDs through ionisation damage resulting in increases in dark current and/or a shift in flat band voltage. Understanding the effect of radiation damage on EM-CCDs is important in order to predict lifetime as well as the change in performance over time. Two CCD-97s were taken to PTB at BESSY II and irradiated with large doses of soft X-rays in order to probe the front and back surfaces of the device. The dark current was shown to decay over time with two different exponential components to it. This paper will discuss the use of EM-CCDs for readout of RIXS spectrometers, and limitations on spatial resolution, together with any limitations on instrument use which may arise from X-ray-induced radiation damage.

Water splitting vs. sulfite oxidation: An assessment of photoelectrochemical performance of TiO2 nanotubes modified by CdS/CdSe nanoparticles

A major portion of the existing literature on TiO2 nanotubes modified by CdS and CdSe report an enhanced photoelectrochemical (PEC) performance using electrolytes with inorganic sacrificial electron donors where a dominant sulfite oxidation occurs. In this study, we distinguish the PEC performance arising entirely from water splitting to that originated by sulfite oxidation in the TiO2 nanotube system modified by CdS/CdSe nanoparticle depositions. The photocurrent density measured under the AM1.5G simulated spectra, 1 sun (100 mWcm−2) intensity for the TiO2 nanotubes modified by CdS/CdSe nanoparticles and using an aqueous alkaline electrolyte (1 M NaOH) was observed to be 0.92 mAcm−2 at 1.23 V vs. RHE which was 8-fold lower than in the case for sulfite oxidation (Jph/SO = 7.4 mAcm−2 at 1.23 V vs. RHE) using an Na2S/Na2SO3 aqueous electrolyte. A maximum STH efficiency of 0.71% and water splitting efficiency of 12.4% was determined for water oxidation using an aqueous alkaline electrolyte. To rationalize such device efficiency, we propose that the ‘water splitting efficiency’ parameter is much more meaningful since it correlates the PEC activity specifically to water splitting and not to other pathways that produce an artificially enhanced photocurrent through the use of sacrificial reagents. The incident photon-to-current conversion efficiency spectrum measured at 1.23 V (vs. RHE) bias for the TiO2 photoanodes modified by CdS/CdSe nanoparticles revealed that the current conversion efficiency is lower (∼17% or less) when absorption occurs solely from the external CdSe layers indicating higher recombination during charge transport. The increase of dark current observed in the linear sweep voltammetry plots for the voltage range of −0.25 V to +0.15 V vs. RHE was attributed to anodic dissolution of the photoanodes in aqueous electrolytes containing no sacrificial reagents. The photocurrents and onset potentials for the CdS/CdSe modified TiO2 photoanodes improved under acidic conditions showing a slightly increased PEC activity and faster reaction kinetics.

Preparation and Characterization of CdO Thin Films Obtained by Oxidation of Obliquely Evaporated Cd Thin Films

In this work, oblique angle deposition technique (OAD) was used to grow cadmium thin films onto glass substrates at different angles (1o and 01o), and then oxidized in air at (011 °C) for 0 hour by conventional furnace as the oxidation source. The effect of deposition angle on the structural, morphology, optical and electrical properties of cadmium oxide thin film were studied. XRD technique used to study the crystalline structure of these films confirm the polycrystalline nature of these films and the higher intensity accompanied that deposited with (01 ) with preferred orientation (000). Some structural parameters such as grain size was calculated. The surface morphology shows an improvement with higher incident angle. The optical properties shows that the transmition decreasing with increases deposition angle and the optical energy gap (Eg) values are (4.2 and 4.9) eV for normal and oblique deposition respectively. The dark current increases linearity with applied voltage and deceases with increasing deposition angle at the fixed applied voltage (ohmic behavior) with activation energy found to be (1.0022 1.0040) ( eV) for normal and oblique deposition respectively .

Origin of large dark current increase in InGaAs/InP avalanche photodiode

The large dark current increase near the breakdown voltage of an InGaAs/InP avalanche photodiode is observed and analyzed from the aspect of bulk defects in the device materials. The trap level information is extracted from the temperature-dependent electrical characteristics of the device and the low temperature photoluminescence spectrum of the materials. Simulation results with the extracted trap level taken into consideration show that the trap is in the InP multiplication layer and the trap assisted tunneling current induced by the trap is the main cause of the large dark current increase with the bias from the punch-through voltage to 95% breakdown voltage.

Total Ionizing Dose Effects on a Radiation-Hardened CMOS Image Sensor Demonstrator for ITER Remote Handling

Total ionizing dose effects are studied on a radiation hardened by design (RHBD) $256\times 256$ -pixel CMOS image sensor (CIS) demonstrator developed for ITER remote handling by using X- and $\gamma $ -ray irradiations. The (color) imaging capabilities of the RHBD CIS are demonstrated up to 10 MGy (SiO2), 1 Grad (SiO2), validating the radiation hardness of most of the designed integrated circuit. No significant sensitivity (i.e., responsivity and color filter transmittance) or readout noise degradation is observed. The proposed readout chain architecture allows achieving a maximum output voltage swing larger than 1 V at 10 MGy (SiO2). The influence of several pixel layout (the gate oxide thickness, the gate overlap distance, and the use of an in-pixel P+ ring) and manufacturing process parameters (photodiode doping profile and process variation) on the radiation-induced dark current increase is studied. The nature of the dark current draining mechanism used to cancel most of the radiation-induced degradation is also discussed and clarified.

Reduction of dark current and gain increase in InAs avalanche photodiode with AlGaAs blocking layer

This article presents a new method to reduce the dark current and increase the avalanche gain in InAs avalanche photodiode (APD) by adding Al0.84Ga0.16As blocking layer. This photodiode has displayed a high avalanche gain around 400 in 8V bias voltage. Furthermore, a very low dark current and low excess noise factor between 0.1 and 1.9 in a temperature of 180K to 300K is observed. Finally, in comparison with other devices, a considerable increase of the gain along with decrease in dark current is observed.

Electro-Optical Characterization of SiPMs With Green Bandpass Dichroic Filters

There is an increasing interest to use silicon photomultipliers (SiPMs) in medical applications like Photoplethysmography or Functional Near Infrared Spectroscopy, allowing the monitoring of physiological signs through non-invasive equipment. The use of large area SiPMs with embedded color filters for environmental light rejection could bring relevant advantages in these applications in terms of higher signal-to-noise ratio of the measurements. Here, we report on the first electro-optical characterization results obtained on n-on-p SiPMs with green interference bandpass filters glued on the top side of the detector SMD package. We will show how the use of the filter considerably increases, especially for large overvoltage values, the SiPM dark noise rate, due to the significant amplification of optical cross-talk effects (up to 150% of dark current increase at 50%-OV). This makes necessary a careful evaluation of the SiPMs performances in order to define the best operating conditions and layout characteristics of the detectors that will be used in the final applications.

Simulation of the effects of defects in low temperature Ge buffer layer on dark current of Si-based Ge photodiodes**Project supported by the Key Project of Natural Science Foundation of China (No. 61534005), the National Science Foundation of China (No. 61474081), the National Basic Research Program of China (No. 2013CB632103), the Natural Science Foundation of Fujian Province (No. 2015D020), and the

The influence of defects in low temperature Ge layer on electrical characteristics of p-Ge/i-Ge/n-Si and n-Ge/i-Ge/p-Ge photodiodes (PDs) was studied. Due to a two-step growth method, there are high defect densities in low-temperature buffer Ge layer. It is shown that the defects in low-temperature Ge layer change the band diagrams and the distribution of electric field, leading to the increase of the total dark current for p-Ge/i-Ge/n-Si PDs, whereas these defects have no influence on the dark current for n-Ge/i-Ge/p-Ge PDs. As a complement, a three-dimensional simulation of the total current under illumination was also performed.

Dependence of dark current and photoresponse on polarization charges for AlGaN‐based heterojunction p–i–n photodetectors

The influence of the polarization charges on the properties of AlGaN‐based heterojunction p–i–n ultraviolet photodetectors was investigated. It is found that the polarization charges at the hetero‐interface can enhance the electric field intensity and result in an increased dark current. On the contrary, the polarization charges can lower the photoresponse because the direction of polarization electric field is opposite to the applied electric field in the light absorption layer.

Dark Current Spectroscopy in Neutron, Proton and Ion Irradiated CMOS Image Sensors: From Point Defects to Clusters

Dark current spectroscopy is tested on twenty CMOS image sensors irradiated with protons, neutrons and various ions at different energies. The aim of this work is to differentiate the effect of coulomb and nuclear interactions on the radiation-induced dark current distribution and to identify the main radiation-induced defects responsible for the dark current increase for each type of interaction. For low-energy protons and low-energy light ions (which produce well-separated low energy coulomb interactions), we find that most of the pixels belong to a quantized dark current spectrum at low dark current. In these pixels, the dark current increase seems mainly dominated by specific point defects such as the divacancy and the vacancy-phosphorus complex. Thus, these simple defects seem to form when the displacement damage is rather low and sparse. On the contrary, for nuclear interactions (with neutrons or high-energy protons) producing high coulomb NIEL silicon PKAs or for low energy heavy ions (also having high coulomb NIEL), the DCS spectrum is not visible and all the pixels belong to an exponential hot pixel tail which extends to very high dark current. In these pixels, the dark current increase is mainly dominated by defects with close-to-midgap energy levels. These defects seem more complex than point defects because they can have many different generation rates (explaining the smooth hot pixel tail) and because they tend to form when the displacement damage is high and dense.

Gaas Displacement Damage Dosimeter Based on Diode Dark Currents

GaAs diode dark currents are correlated over a very large proton energy range as a function of displacement damage dose (DDD). The linearity of the dark current increase with DDD over a wide range of applied voltage bias deems this device an excellent candidate for a displacement damage dosimeter. Additional proton testing performed in situ enabled error estimate determination to within 10% for simulated space use.

Hierarchical rutile TiO2 heterostructures and plasmon impregnated TiO2/SnO2-Ag bilayer nanocomposites as proficient photoanode systems

Highly proficient Titania heterostructures were successfully developed on Fluorine-doped Tin Oxide (FTO) substrate through the facile single step hydrothermal method where 18h of autoclaving period resulted in the formation of nanorods with a scanty topping of nanoflowers. Further, plasmon impregnation (SnO2-Ag) into the Titania heterostructures by spin coating technique yielded bilayer nanocomposite (TiO2/SnO2-Ag) films. Substantial enhancement in absorption intensity was evidenced with a slight red shift in the case of bilayer nanocomposite owing to the incorporation of the noble metal. An appreciable increase in dark and photo current was observed in both the Titania heterostructure and bilayer composite films suggesting the possibility of their application in Dye Sensitized Solar Cells (DSSCs) while the plasmon impregnated bilayer composite exhibited significantly enhanced photoconductivity than the former.

Effects of finger dimension on low-frequency noise and optoelectronic properties of Ge metal-semiconductor-metal photodetectors with interdigitated Pt finger electrodes

We investigated the effect of interdigitated Pt finger electrode dimension on the low-frequency noise and optoelectrical properties of Ge metal-semiconductor-metal (MSM) infrared photodetectors (PDs). This dark current reduction led to an increase in the normalized photo current to dark current ratio (NPDR). The decrease in finger width/spacing facilitated the occurrence of the electric field crowding near contact electrode. This resulted in the image-force Schottky barrier lowering, which could be responsible for the increase in dark current. From the low frequency noise measurements performed at the frequencies in the range of 10Hz–1kHz, the Ge MSM PDs had 1/fγ frequency dependence with γ ranging from 1.07 to 1.20, regardless of finger dimension. The current crowding, in particular at the vicinity of the finger electrodes, was more pronounced in the Ge MSM PDs having smaller finger width/spacing, which could be a main cause of the increase in the low frequency noise.