Reduction Of Dark Current Research Articles

Low dark current broadband 360-1650 nm ITO/Ag/n-Si Schottky photodetectors.

This work designed an ITO/Ag/n-Si Schottky photodetector with broad wavelength detection and low dark current. The introduction of Ag interfacial layer and post rapid thermal annealing dramatically increase the barrier height of ITO/n-Si Schottky diode by 0.32 eV, leading to the 2300 × reduction of dark current. A well-behaved ITO/Ag (8 nm)/n-Si Schottky diode with a high rectification ratio ( ± 1 V) of 4 × 105 and low dark current (-1 V) of 9.2 nA was achieved. Such low dark current device spontaneously provides high sensitivity for visible/near infrared wavelength detection, in which substantial responsivity for wavelengths from 360 to 1650 nm was realized through both inter-band and internal photoemission. The design here provides an encouraging strategy for monolithically integrated pure Si photodetectors operating at long wavelength up to 1650 nm.

Analysis of the influence and mechanism of sulfur passivation on the dark current of a single GaAs nanowire photodetector

Nanowire photodetectors, which have the advantages of fast response and high photoelectric conversion efficiency, can be widely applied in various industries. However, the rich surface states result in large dark current and can hinder the development of high-performance nanowire photodetectors. In this paper, the influence and mechanism of sulfur surface passivation on the dark current of a single GaAs nanowire photodetector have been studied. The dark current is significantly reduced by about 30 times after surface passivation. We confirm that the origin of the reduction of dark current is the decrease in the surface state density. As a result, a single GaAs nanowire photodetector with low dark current of 7.18 × 10−2 pA and high detectivity of 9.04 × 1012 cmHz0.5W−1 has been achieved. A simple and convenient way to realize high-performance GaAs-based photodetectors has been proposed.

Dark Current Sharing and Cancellation Mechanisms in CMOS Image Sensors Analyzed by TCAD Simulations

Technology computer aided design (TCAD) simulations are conducted on a 4T PPD pixel, on a conventional gated photodiode (PD), and finally on a radiation hardened pixel. Simulations consist in demonstrating that it is possible to reduce the dark current due to interface states brought by the adjacent gate (AG), by means of a sharing mechanism between the PD and the drain. The sharing mechanism is activated and controlled by polarizing the AG at a positive OFF voltage, and consequently the dark current is reduced and not compensated. The drawback of the dark current reduction is a reduction of the full well capacity of the PD, which is not a problem when the pixel saturation is limited by the readout chain. Some measurements performed on pixel arrays confirm the TCAD results.

Dark current reduction in microjunction-based double electron barrier type-II InAs/InAsSb superlattice long-wavelength infrared photodetectors

Microjunction InAs/InAs1−xSbx type-II superlattice-based long-wavelength infrared photodetectors with reduced dark current density were demonstrated. A double electron barrier design was employed to reduce both bulk and surface dark currents. The photodetectors exhibited low surface leakage after passivation with SiO2, allowing the use of very small size features without degradation of the dark current. Fabricating microjunction photodetectors (25 × 25 µm2 diodes with 10 × 10 µm2 microjunctions) in combination with the double electron barrier design results in a dark current density of 6.3 × 10−6 A/cm2 at 77 K. The device has an 8 µm cut-off wavelength at 77 K and exhibits a quantum efficiency of 31% for a 2 µm-thick absorption region, which results in a specific detectivity value of 1.2 × 1012 cm·Hz1/2/W.

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.

Oxygen Plasma Surface Activation of Electron‐Depleted ZnO Nanoparticle Films for Performance‐Enhanced Ultraviolet Photodetectors

Zinc oxide (ZnO) nanoparticles (NPs) with uniform particle radius comparable to the desired Debye length provide a low‐cost and a scalable scheme to achieve optimized electron depletion effect, which is the key to high performance ultraviolet (UV) photodetection. Here, a simple and improved sol–gel method for in situ synthesis of highly crystalline constituent ZnO‐NP mesoporous thin films is reported. In combination with optimal oxygen plasma treatment to activate the ZnO‐NP surface, the UV‐detection performance is enhanced remarkably with a reduced dark current by one order of magnitude and an increased UV detectivity by over 300%. Moreover, such UV photodetectors exhibit extraordinary performance with high responsivity of up to 0.8 A W−1V−1 at 340 nm UV power of 0.003 mW cm−2, detectivity of 1.4 × 1011 Jones, and rise/decay time of 3.4 s/5.0 s. These results illustrate that the sol–gel ZnO‐NP films provide a promising template for high‐performance UV detectors to take full advantages of the electron depletion effect.

Low dark current in mid-infrared type-II superlattice heterojunction photodiodes

A mid-infrared (MWIR, 3–5μm) InAs/GaSb type-II superlattice (T2SL) photodiode device with very low dark current is presented. The novel heterojunction device is compared to a conventional pn-homojunction device. Photodetectors with reduced dark current allow an increased operating temperature and thus to lower the cooling requirements for high performance infrared imaging applications. We report on a dark current reduction by a factor of more than 100 at a typical operation voltage of −100mV at 77K, which was realized merely by device design. This measured dark current is the lowest reported to our knowledge for T2SL-detectors operating in the 3–5μm range. At the same time, the photo current signal is unaffected by the heterostructure design over the entire bias voltage range.

Studies of Dark Current Reduction in InAsSb Mid-Wave Infrared HOT Detectors through Two Step Passivation Technique

Studies of Dark Current Reduction in InAsSb Mid-Wave Infrared HOT Detectors through Two Step Passivation Technique

Progress of MCT Detector Technology at AIM Towards Smaller Pitch and Lower Dark Current

We present our latest results on cooled p-on-n planar mercury cadmium telluride (MCT) photodiode technology. Along with a reduction in dark current for raising the operating temperature (T op), AIM INFRAROT-MODULE GmbH (AIM) has devoted its development efforts to shrinking the pixel size. Both are essential requirements to meet the market demands for reduced size, weight and power and high-operating temperature applications. Detectors based on the p-on-n technology developed at AIM now span the spectrum from the mid-wavelength infrared (MWIR) to the very long wavelength infrared (VLWIR) with cut-off wavelengths from 5 μm to about 13.5 μm at 80 K. The development of the p-on-n technology for VLWIR as well as for MWIR is mainly implemented in a planar photodetector design with a 20-μm pixel pitch. For the VLWIR, dark currents significantly reduced as compared to ‘Tennant’s Rule 07’ are demonstrated for operating temperatures between 30 K and 100 K. This allows for the same dark current performance at a 20 K higher operating temperature than with previous AIM technology. For MWIR detectors with a 20-μm pitch, noise equivalent temperature differences of less than 30 mK are obtained up to 170 K. This technology has been transferred to our small pixel pitch high resolution (XGA) MWIR detector with 1024 × 768 pixels at a 10-μm pitch. Excellent performance at an operating temperature of 160 K is demonstrated.

Dark current reduction in nano-avalanche photodiodes by incorporating multiple quantum barriers

ABSTRACTMultiple quantum barriers have been used to suppress the dark current of nanoscale avalanche photodiodes (APDs). The n+–π–p+-structured Si–3C-SiC heterojunction-based multiple quantum barrier (MQB) APDs are considered and a detailed model of dark current has been developed from the self-consistent solution of the coupled Schrödinger–Poisson equations. Four major types of electron–hole pair (EHP) generation mechanisms such as (1) thermal generation, (2) band-to-band tunnelling generation, (3) trap-assisted tunnelling generation and (4) avalanche generation are considered for calculating variation of the total dark current with reverse bias voltage. It is observed that the dark current can be suppressed significantly by increasing both the number and thickness of quantum barriers. However, the authors have also admitted that both the number and thickness of quantum barriers cannot be increased indefinitely, since it will cause deterioration in spectral response of the device in near-infrared range (λ < 1100 nm).

Perovskite/Polymer Hybrid Thin Films for High External Quantum Efficiency Photodetectors with Wide Spectral Response from Visible to Near‐Infrared Wavelengths

The characteristics such as high charge carrier mobility, long diffusion length, low dark current, and sharp absorption edge of perovskites make the material ideal for realizing photodetection, that is, simultaneously fast and sensitive. However, narrow spectral (850 nm) response limits their application. Here, this study successfully demonstrates an integrated perovskite/polymer device structure based on perovskite/hybrid thin films for efficient light harvesting. The expansion of the photoresponse spectrum is achieved by selecting an appropriate low band gap polymer (poly(diketopyrrolopyrrole‐terthiophene)), which has a wider response (950 nm). It can be seen that the resulting photodetectors (PDs) yield an external quantum efficiency of ≈70% over a 500–700 nm range, and the photoresponse extends to 950 nm, which is obviously wider than the photoresponse of perovskite‐based PDs. Moreover, the dark current density of the hybrid PDs is more efficiently suppressed compared with polymer‐based PDs. The reduced dark current enhances the detectivity and linear dynamic range of the fabricated hybrid PDs, which achieve values of 1013 Jones and 110 dB, respectively.

Noise Reduction in Silicon Photomultipliers for Use in Functional Near-Infrared Spectroscopy

Silicon photomultipliers (SiPMs) have been recently proposed for different applications in medical imaging area, inclunding functional near-infrared spectroscopy (fNIRS), due to their single photon sensitivity, fast timing response, low operation bias, compactness, and low cost. Here, we report on the electro-optical performances of an SiPM technology suitably optimized for continuous wave (CW)-fNIRS application through the integration of a near-infrared (NIR) long-pass filter on the detector’s package. The use of the filter considerably decreases, especially for large overvoltage (OV) values, the SiPM’s dark noise rate, due to the significant reduction of optical cross talk effects (up to 90% of dark current reduction at 50%-OV). Moreover, the filter reduces also the absorption of environmental light of more than 85% in the SiPMs linear operation range above the breakdown, allowing at the same time a good photon detection efficiency in all the NIR range above 700 nm cut-on wavelength. These results open new perspectives for the employment of large area SiPMs operating with improved signal-to-noise ratio in advanced CW-fNIRS systems.

Dark Current Blooming in Pinned Photodiode CMOS Image Sensors

This paper demonstrates the existence of dark current blooming in pinned photodiode (PPD) CMOS image sensors (CISs) with the support of both experimental measurements and TCAD simulations. It is usually assumed that blooming can appear only under illumination, when the charge collected by a pixel exceeds the full well capacity (FWC) (i.e., when the photodiode becomes forward biased). In this paper, it is shownthat blooming can also appear in the dark by dark current leakage from hot pixels in reverse bias (i.e., belowthe FWC). The dark current blooming is observed to propagate up to nine pixels away in the experimental images and can impact hundreds of pixels around each hot pixel. Hence, it can be a major image quality issue for the state-of-the-art PPD CISs used in dark current limited applications, such as low-light optical imaging and should be considered in the dark current subtraction process. This paper also demonstrates that one of the key parameter for dark current optimization, the transfer gate bias during integration, has to be carefully chosen depending on the application because the optimum bias for dark current reduction leads to the largest dark current blooming effects.

Dark current reduction strategies using edge-on aligned donor polymers for high detectivity and responsivity organic photodetectors

The difluorobenzene-incorporated polymer showed strong ordering in edge-on mode, resulting in a significant reduction in the leakage current, and thus PFBT2OBT:PC70BM devices showed highly improved detectivity of over 1013 Jones at −2V.

Radiation Hardening of Digital Color CMOS Camera-on-a-Chip Building Blocks for Multi-MGy Total Ionizing Dose Environments

The Total Ionizing Dose (TID) hardness of digital color Camera-on-a-Chip (CoC) building blocks is explored in the Multi-MGy range using <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co gamma-ray irradiations. The performances of the following CoC subcomponents are studied: radiation hardened (RH) pixel and photodiode designs, RH readout chain, Color Filter Arrays (CFA) and column RH Analog-to-Digital Converters (ADC). Several radiation hardness improvements are reported (on the readout chain and on dark current). CFAs and ADCs degradations appear to be very weak at the maximum TID of 6 MGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), 600 Mrad. In the end, this study demonstrates the feasibility of a MGy rad-hard CMOS color digital camera-on-a-chip, illustrated by a color image captured after 6 MGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) with no obvious degradation. An original dark current reduction mechanism in irradiated CMOS Image Sensors is also reported and discussed.

Enhanced infrared detectors using resonant structures combined with thin type-II superlattice absorbers

We examined the spectral responsivity of a 1.77 μm thick type-II superlattice based long-wave infrared detector in combination with metallic nanoantennas. Coupling between the Fabry-Pérot cavity formed by the semiconductor layer and the resonant nanoantennas on its surface enables spectral selectivity, while also increasing peak quantum efficiency to over 50%. Electromagnetic simulations reveal that this high responsivity is a direct result of field-enhancement in the absorber layer, enabling significant absorption in spite of the absorber's subwavelength thickness. Notably, thinning of the absorbing material could ultimately yield lower photodetector noise through a reduction in dark current while improving photocarrier collection efficiency. The temperature- and incident-angle-independent spectral response observed in these devices allows for operation over a wide range of temperatures and optical systems. This detector paradigm demonstrates potential benefits to device performance with applications throughout the infrared.

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.

Application of nitrogen-doped TiO2 nano-tubes in dye-sensitized solar cells

Our research aimed to improve the overall energy conversion efficiency of DSCs by applying nitrogen-doped TiO2 nano-tubes (N-TNT) for the preparation of DSCs photo-anodes. The none-doped TiO2 nano-tubes (TNTs) were synthesized by alkaline hydrothermal treatment of Degussa P25 TiO2 particles in 10M NaOH. The nano-tubes were N-doped by reflux in various concentrations of NH4NO3. The effects of nitrogen doping on the structure, morphology, and crystallography of N-TNT were analyzed by transmission electron microscopy (TEM), infrared spectroscopy (IR), Raman spectroscopy, and X-ray photoelectron spectra (XPS). DSCs fabricated with doped N-TNT and TNT was characterized by J-V measurements. Results showed that nitrogen doping significantly enhanced the efficiency of N-TNT cells, reaching the optimum value (η=7.36%) with 2M nitrogen dopant, compared to η=4.75% of TNT cells. The high efficiency of the N-TNT cells was attributed to increased current density due to the reduction of dark current in the DSCs.

Spectral response, dark current, and noise analyses in resonant tunneling quantum dot infrared photodetectors.

Reduction of dark current at high-temperature operation is a great challenge in conventional quantum dot infrared photodetectors, as the rate of thermal excitations resulting in the dark current increases exponentially with temperature. A resonant tunneling barrier is the best candidate for suppression of dark current, enhancement in signal-to-noise ratio, and selective extraction of different wavelength response. In this paper, we use a physical model developed by the authors recently to design a proper resonant tunneling barrier for quantum infrared photodetectors and to study and analyze the spectral response of these devices. The calculated transmission coefficient of electrons by this model and its dependency on bias voltage are in agreement with experimental results. Furthermore, based on the calculated transmission coefficient, the dark current of a quantum dot infrared photodetector with a resonant tunneling barrier is calculated and compared with the experimental data. The validity of our model is proven through this comparison. Theoretical dark current by our model shows better agreement with the experimental data and is more accurate than the previously developed model. Moreover, noise in the device is calculated. Finally, the effect of different parameters, such as temperature, size of quantum dots, and bias voltage, on the performance of the device is simulated and studied.

Dark current reduction of small molecule organic photodetectors by controlling gap states of molybdenum oxide buffer layers

The gap states of the molybdenum-oxide (MoOx) hole-extraction layer (HEL) in an organic photodetector (OPD) device, which originate from oxygen-vacancy defects, are controlled by appropriate plasma treatments on the MoOx layer. The density of MoOx gap states, investigated using X-ray photoelectron spectroscopy (XPS), is enhanced and depressed with Ar- and O2-plasma treatments, respectively. The dark current of an OPD with a MoOx HEL is considerably reduced by controlling the MoOx gap states using the plasma-treatment method. The mechanism of dark-current reduction may be interpreted by reduced gap states and by a suitable energy level bending and alignment.