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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. [ABSTRACT FROM AUTHOR]

To improve the low responsivity of the silicon avalanche photodiode in the near-ultraviolet wavelength range, we designed a near-ultraviolet highly responsive Si-APD basic structure with a multiplication layer neighboring the photosensitive surface through the analysis of the optical absorption characteristics, junction breakdown characteristics, and avalanche multiplication characteristics. The dark current and electric field distribution of the device were investigated. Meanwhile, the structural parameters of the surface non-depleted layer, multiplication layer, and absorption layer were optimized. It was found that the breakdown voltage of the device is 21.07 V. At an applied bias voltage of 20.02 V, the device exhibits a responsivity of 6.79–14.51 A/W in the wavelength range of 300–400 nm. These results provide valuable insights for the design of silicon avalanche photodiode with high responsivity in the near-ultraviolet range. [ABSTRACT FROM AUTHOR]

A new three-dimensional (3D) electric field enhanced generation model has been developed to describe the electric field effects on the thermal electron–hole pair generation rate. The originality of this model lies in the full three-dimensional description of the synergetic mechanism between the Poole–Frenkel barrier lowering and the phonon-assisted tunneling mechanism. To do this, a classical one-dimensional (1D) model has been integrated over all possible directions of emission of the carriers. The 3D model has been implemented in a Monte Carlo tool devoted to the simulation of the dark current increase induced by radiations in image sensors. Our three-dimensional simulation has been compared to one-dimensional electric field effects’ simulations and experimental data found in the literature in the context of gold contamination. The consequence of using a three-dimensional electric field enhanced generation (EFEG) model is the reduction of the dispersive effect on the dark current distribution of the electric field; hence, each dark current peak is narrower and shows a higher peak’s amplitude. The three-dimensional model needs to slightly change the cross-sectional parameters used for a 1D EFEG case to keep a realistic description of each dark current peak of the histogram. In the rest of the paper, we extended our work on constraints relative to space applications. The histograms of the simulated dark current taking into account one- and three-dimensional electric field enhancement effects have been estimated and compared to experimental data acquired after a proton irradiation at room temperature. The use of a three-dimensional model tends to give a more realistic prediction of the dark current non-uniformity in an irradiated pixel array. [ABSTRACT FROM AUTHOR]

We report on an investigation of dark current contributions from common microscale crystallographic defects in type-II InAs/GaInSb superlattice infrared PIN type photodiode structures grown on (100) GaSb substrates and have identified three general classifications. Defects on several wafers of varying design were examined from multiple perspectives to correlate electrical activity with structural properties, to develop the identification and classification scheme. Active defects were first identified by current density vs voltage (J-V) measurements and electron beam induced current (EBIC) scans of individual diodes with micrometer resolution. The EBIC scans were then correlated with plan-view optical and atomic force microscopy images, both before and after anisotropic etch-pit analysis using a newly developed etchant. The atomic scale structure of active and inactive defects was then compared using cross-sectional transmission electron microscopy (TEM) on vertical slices of defects extracted using focused ion beam milling. Analysis of the TEM images yielded important clues as to the structure and root causes of benign and active defects, in which only significant disruptions at the epi-substrate interface appear to play a key role in producing microscale defects that efficiently promote dark current. [ABSTRACT FROM AUTHOR]

We use the leaky electronic state in the continuum concept to create a photovoltaic and photoconductive dual-mode operation superlattice infrared photodetector working at a temperature as high as room temperature. An asymmetric superlattice InGaAs/InAlAs is designed to virtually increase the material band offset and to create a localized state in the continuum with a preferential direction for electron extraction. These two characteristics are responsible for low dark current and high operating temperature of the device. At λ p = 4.1 μ m response peak, the highest specific detectivity is 5.7 × 10 10 Jones for + 5.0 V at 80 K, and at room temperature, it is 1.3 × 10 5 Jones for null bias. [ABSTRACT FROM AUTHOR]

High-temperature operation of metal–semiconductor–metal (MSM) UV photodetectors fabricated on pulsed laser deposited β-Ga2O3 thin films has been investigated. These photodetectors were operated up to 250 °C temperature under 255 nm illumination. The photo to dark current ratio of about 7100 was observed at room temperature and 2.3 at a high temperature of 250 °C with 10 V applied bias. A decline in photocurrent was observed until a temperature of 150 °C beyond which it increased with temperature up to 250 °C. The suppression of the UV and blue band was also observed in the normalized spectral response curve above 150 °C temperature. Temperature-dependent rise and decay times of temporal response were analyzed to understand the associated photocurrent mechanism at high temperatures. Electron–phonon interaction and self-trapped holes were found to influence the photoresponse in the devices. The obtained results are encouraging and significant for high-temperature applications of β-Ga2O3 MSM deep UV photodetectors. [ABSTRACT FROM AUTHOR]

The germanium-tin (Ge-Sn) alloy has been considered a candidate for applications in Short Wave Infrared optical electronics, because it has the property of transforming pure germanium (Ge), typically an indirect bandgap material, into a direct bandgap material. In this paper, the effects of volumetric and potential energy changes are utilized to calculate how the band structure of the Ge-Sn alloy changes with respect to the fraction of tin (Sn). The results indicate that a transition occurs for a Sn fraction ranging from 5.81% to 8.75% with the alloy lattice-constant bowing parameter that ranges from 0.3 Å to 0.0 Å. [ABSTRACT FROM AUTHOR]

Recently, electrolysis technology has been widely applied in nitrogen and phosphorus removal in river water due to its high efficiency, but its effects on aquatic animals, especially on their neurodevelopmental system, are still unclear. In this study, zebrafish (Danio rerio) embryos were used as model organisms and were put into an electrolytic reaction device with a Ti/IrO2/RuO2 mesh plate as the anode and a Ti mesh plate as the cathode to explore the effects of prolonged electrolysis on the nervous system. The neural development of zebrafish embryos was injured when the current density was greater than 0.89 A/m2. Compared with the control group, the movement speed of zebrafish larvae (120 h postfertilization, hpf) was significantly reduced from 65.48 ± 23.69 to 48.08 ± 22.73 mm/min in a dark environment with an electric current density of 0.89 A/m2 in the electrolysis group. In addition, the acetylcholinesterase activity of zebrafish larvae (120 hpf) gradually decreased from 7.60 ± 0.55 to 6.00 ± 0.01 U/mg prot and the dopamine concentration was reduced from 46.96 ± 0.85 to 40.86 ± 1.05 pg/mL with an electric current density from 0 to 0.89 A/m2 in the electrolysis groups. Furthermore, the expression of nerve-related genes (syn2a, mbp, nestin, and AChE) was significantly inhibited when the current density was more than 0.89 A/m2. However, there were few adverse effects on the neural development of zebrafish embryos when the current density was less than 0.86 A/m2. Thus, a current density of 0.86 A/m2 is a reference value to reduce the harm to the neural development of fish when electrolysis technology is used in river water pollutant treatment. [ABSTRACT FROM AUTHOR]

As long as high resolution or long-range observation is to be achieved using infrared detection, it will be necessary to cool down the detector in order to reach the best sensitivity and dynamics. This paper describes different cooling solutions currently used for this purpose discussing advantages and drawbacks. Some guideline is given for cooler choice and selection. The focus is on rotary Stirling coolers illustrated by description of the RMs1 cooler dedicated to high operating temperature size, weight, and power infrared detectors. A user case study is presented with cooler power consumption and cool down time of the RMs1 cooler when integrated in IRnova's Oden MW IDDCAs. [ABSTRACT FROM AUTHOR]

The viability of epitaxial regrowth of non-intentionally doped InP to passivate lateral mesa surfaces of InGaAs photodiodes lattice-matched to InP is investigated, evaluating whether the residual doping of the regrown layer can be responsible for un unexpected increase of the surface current. The effect of residual doping is evaluated via numerical calculations of dark current, considering the range of doping concentrations expected for non-intentionally doped InP. The calculations show that the increase in dark current due to the residual doping of the regrown InP layer is not enough to justify the observed increase in surface current. On the other hand, the technique is still valid as a passivation method if the photodetector pixel is isolated by etching only the top contact layer. [ABSTRACT FROM AUTHOR]

Infrared detector technologies engineered from III-V semiconductors such as strained-layer superlattice, quantum well infrared photodetectors, and quantum dot infrared photodetectors provide additional flexibility to engineer bandgap or spectral response cut-offs compared to the historical high-performance detector technology of mercury/cadmium/telluride. The choice of detector cut-off depends upon the sensing application for which the system engineer is attempting to maximize performance within an expected ensemble of operational scenarios that define objects or targets to be detected against specific environmental backgrounds and atmospheric conditions. Sensor performance is typically characterised via one or more metrics that can be modelled or measured experimentally. In this paper, the authors will explore the impact of detector cut-off wavelength with respect to different performance metrics such as noise equivalent temperature difference and expected target detection or identification ranges using analytical models developed for several representative sensing applications encompassing a variety of terrestrial atmospheric conditions in the mid-wave and long-wave infrared wavelength bands. The authors will also report on their review of recently published literature concerning the relationships between cut-off wavelength and the other detector performance characteristics such as quantum efficiency or dark current for a variety of detector technologies. [ABSTRACT FROM AUTHOR]

Dual-band infrared detector, which acquires more image information than single-band detectors, has excellent detection, recognition, and identification capabilities. The dual-band detector can have two bumps to connect with each absorber layer, but it is difficult to implement small pitch focal plane arrays and its fabrication process is complicated. Therefore, the most effective way for a dual-band detector is to acquire each band by biasselectable with one bump. To aim this, a dual-band MWIR/LWIR detector based on an InAs/GaSb type-II superlattice nBn structure was designed and its performance was evaluated in this work. Since two absorber layers were separated by the barrier layer, each band can be detected by bias-selectable with one bump. The fabricated dual-band device exhibited the dark current and spectral response characteristics of MWIR and LWIR bands under negative and positive bias, respectively. Spectral crosstalk that is a major issue in dualband detectors was also improved. Finally, a 20 μm pitch 640 x 512 dual-band detector was fabricated, and both MWIR and LWIR images exhibited an average noise equivalent temperature difference of 30 mK or less at 80 K. [ABSTRACT FROM AUTHOR]

The authors report two approaches, the first based on growth of lattice matched InGaAs/GaAsSb superlattice on InP substrate with tunable bandgap in the 2 to 3 µm range. The second approach is based on bulk random alloy InGaAsSb, which is tunable from 1.7 µm to 4.5 µm and lattice matched to the GaSb lattice constant. In each case, detector structures were fabricated and characterised. The authors have assessed the performance of these materials relative to commercially available extended short wave infrared devices through comparison to IGA-Rule 17 dark current performance level. A complementary barrier structure used in the InGaAsSb design showed improved quantum efficiency. The materials compare favourably to commercial technology and present additional options to address the challenging extended short wave infrared spectral band. [ABSTRACT FROM AUTHOR]

Current advances in type-II superlattice (T2SL) research at Fraunhofer IAF are elaborated on in this paper. First, the use of metastructures for quantum efficiency (QE) enhancement in the longwave infrared (LWIR) is presented. Finite element modelling results are reported on that suggest a potential for doubling of the QE at certain wavelengths with the investigated device structure. Next, characterisation results of midwave infrared (MIWR) InAs/InAsSb T2SL nBn detectors are shown. The low, diffusion-limited dark current above 120 K and a QE of 60% are comparable to the state-of-the-art. Finally, groundwork for InAs/GaSb T2SL MWIR/LWIR dual-band detector arrays based on a back-to-back heterojunction diode device concept is presented. The dry etching technology allows for steep etch trenches and full pixel reticulation with a fill factor of about 70% at 12 μm pitch. The detector characterisation at 77 K and ±250 mV bias demonstrates the bias-switchable operation mode with dark current densities of 6.1·10-9 A/cm² in the MWIR and 5.3·10-4 A/cm² in the LWIR. [ABSTRACT FROM AUTHOR]

The operation of narrow-gap semiconductor devices under non-equilibrium mode is used at temperatures where the materials are normally intrinsic. The phenomenon of minority carrier exclusion and extraction was particularly discussed in the case of the suppression of Auger thermal generation in heterojunction photodiodes, especially important in the long-wave infrared range. This paper shows that the reduction of the dark current in the HgCdTe photodiode operating in the mid-wave infrared range is primarily the result of suppression of the Shockley-Read-Hall generation in the non-equilibrium absorber. Under a reverse bias, the majority carrier concentration is held equal to the majority carrier doping level. This effect also leads to a decreased majority carrier population at the trap level and an effective increase in the carrier lifetime. The analysed device was with the following design: p+-Bp cap-barrier unit, p-type absorber doped at the level of 8 ·1015 cm-3, and wide-bandgap N+ bottom contact layer. At room temperature, the lowest dark current density of 3.12 ·10-1 A/cm2 was consistent with the theoretically predicted Shockley-Read-Hall suppression mechanism, about two times smaller than for the equilibrium case. [ABSTRACT FROM AUTHOR]

In this work, the authors investigated the influence of proton-irradiation on the dark current of XBp longwave infrared InAs/GaSb type-II superlattice barrier detectors, showing a cutoff wavelength from 11 µm to 13 µm at 80 K. The proton irradiations were performed with 63 MeV protons and fluences up to 8·1011 H+/cm² on a type-II superlattice detector kept at cryogenic (100 K) or room temperature (300 K). The irradiation temperature of the detector is a key parameter influencing the effects of proton irradiation. The dark current density increases due to displacement damage dose effects and this increase is more important when the detector is proton-irradiated at room temperature rather than at cryogenic temperature. [ABSTRACT FROM AUTHOR]

The Si- and InP-based APDs as the most important weak light semiconductor photodetectors to have achieved commercial success and are widely used in irradiation environments. Investigating the influencing mechanism of neutron irradiation on the above two types of APDs is of scientific and practical importance. In this paper, the dark current and gain characteristics of Si- and InP-based APDs around breakdown voltage were analyzed in detail before and after irradiation. The increase of dark current and the decrease of gain were observed for both the neutron irradiated Si- and InP-based APDs. Generation centers induced by neutrons are responsible for the increased dark current. The decrease of gain can be attributed to the increase of multiplied dark current and the change of electric field distribution in APD. The Si-based APD exhibits soft breakdown with the breakdown voltage reduced by ~8 V under the neutron fluence of 1.0 × 1012 cm−2, while the soft breakdown occurs along with a small change of breakdown voltage of ~1.5 V under the neutron fluence of 1.0 × 1013 cm−2 for InP-based APD. The difference in the change of breakdown voltage probably occurs because the Si-based APD uses p-doped Si as the multiplication layer, in which the neutron induced carrier removing effect cannot be ignored to keep the electric field distribution away from the optimal state. Therefore, using an intrinsic multiplication layer in APD is helpful to improve the neutron radiation resistance. The findings here are not only useful for the radiation hardened design of APD, but also deepen the understanding of irradiation mechanism. [ABSTRACT FROM AUTHOR]

Molecular beam epitaxy of Ge (111) thin films on epitaxial-Gd2O3/Si(111) substrates is reported, along with a systematic investigation of the evolution of Ge growth and structural defects in the grown epilayer. While Ge growth begins in the Volmer-Weber growth mode, the resultant islands coalesce within the first ∼10 nm of growth, beyond which a smooth two-dimensional surface evolves. Coalescence of the initially formed islands results in the formation of rotation and reflection microtwins, which constitute a volume fraction of less than 1%. It is also observed that while the stacking sequence of the (111) planes in the Ge epilayer is similar to that of the Si substrate, the (111) planes of the Gd2O3 epilayer are rotated by 180° about the [111] direction. In metal-semiconductor-metal Schottky photodiodes fabricated with these all-epitaxial Ge-on-insulator (GeOI) samples, significant suppression of dark current is observed due to the presence of the Gd2O3 epilayer. These results are promising for applications of these GeOI structures as virtual substrates or for realization of high-speed group-IV photonic components. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amorphous Ga 2 O 3 films avoid problems such as large lattice mismatch and strict preparation conditions. • The heterostructure broadens the photodetector response band and photoelectric performance. • The Ga 2 O 3 /CH 3 NH 3 PbI 3 hybrid heterojunction PD was constructed, and the photoelectric performance of the PD was effectively improved. In this paper, Ga 2 O 3 /CH 3 NH 3 PbI 3 photodetector (PD) with high external quantum efficiency (EQE) was successfully prepared by spin coating CH 3 NH 3 PbI 3 on the film surface of Ga 2 O 3 /Au MSM PD. Compared with Ga 2 O 3 film device, the dark current of heterojunction device decreased from 5.20 to 0.09nA, and the responsivity increased from 0.18 to 14.01 A/W at 40 V bias. It is worth noting that under the same bias voltage (40 V), the EQE of Ga 2 O 3 /CH 3 NH 3 PbI 3 PD is as high as 6686 %, which is 78 times of Ga 2 O 3 /Au PD (85.89 %). The high EQE is attributed to collision ionization doubling caused by the effect of an applied electric field. In addition, the construction of heterojunction speeds up the response speed of PD. This work has important implications for the selection of heterogeneous materials and the construction of PDs to optimize device performance. [ABSTRACT FROM AUTHOR]

Two GaAs p+-i-n+ mesa X-ray photodiodes were characterized for their electrical and photon counting X-ray spectroscopic performance over the temperature range of 100 °C to -20°C. The devices had 10 μm thick i layers with different diameters: 200 μm (D1) and 400 μm (D2). The electrical characterization included dark current and capacitance measurements at internal electric field strengths of up to 50 kV/cm. The determined properties of the two devices were compared with previously reported results that were made with a view to informing the future development of photon counting X-ray spectrometers for harsh environments, e.g., X-ray fluorescence spectroscopy of planetary surfaces in high temperature environments. The best energy resolution obtained (Full Width at Half Maximum at 5.9 keV) decreased from 2.00 keV at 100 °C to 0.66 keV at -20 °C for the spectrometer with D1, and from 2.71 keV at 100 °C to 0.71keV at -20°C for the spectrometer with D2. Dielectric noise was found to be the dominant source of noise in the spectra, apart from at high temperatures and long shaping times, where the main source of photopeak broadening was found to be the white parallel noise. [ABSTRACT FROM AUTHOR]

Process induced efficiency variation is a major concern for all thin film solar cells, including the emerging perovskite based solar cells. In this article, we address the effect of pinholes or process induced surface coverage aspects on the efficiency of such solar cells through detailed numerical simulations. Interestingly, we find that the pinhole size distribution affects the short circuit current and open circuit voltage in contrasting manners. Specifically, while the JSC is heavily dependent on the pinhole size distribution, surprisingly, the VOC seems to be only nominally affected by it. Further, our simulations also indicate that, with appropriate interface engineering, it is indeed possible to design a nanostructured device with efficiencies comparable to those of ideal planar structures. Additionally, we propose a simple technique based on terminal I–V characteristics to estimate the surface coverage in perovskite solar cells. [ABSTRACT FROM AUTHOR]

The dark current and spectral photoresponse thresholds of a semiconductor photodetector are normally determined by the minimum energy gap (Δ) of the material, or the interfacial energy gap of the heterostructure. In this manuscript, we discuss the performance of an asymmetric p-GaAs/AlxGa1-xAs heterostructure-based infrared photodetector, which shows an extended wavelength threshold beyond the limit set by Δ. The measured dark current was found to agree well with fits obtained from a 3D carrier drift model using the designed value of Δ~0.40 eV (~3.1 µm). In contrast, the spectral photoresponse showed extended wavelength thresholds of Δ68 µm, ~45 µm, and ~60 µm at positive, zero, and negative biases, respectively, at 5.3 K. For a reference (symmetric) photodetector, the dark current was fitted with the designed value of D ~0.30 eV, and excellent agreement was obtained for both the measured dark current and spectral response. This underlies the advantage of using asymmetric infrared photo-detector designs, in which an extension to the detected wavelengths can be obtained with little compromise to the dark current characteristics. [ABSTRACT FROM AUTHOR]

A theoretical analysis of the mid-wavelength infrared range detectors based on the HgCdTe materials for high operating temperatures is presented. Numerical calculations were compared with the experimental data for HgCdTe heterostructures grown by the MOCVD on the GaAs substrates. Theoretical modelling was performed by the commercial platform SimuAPSYS (Crosslight). SimuAPSYS fully supports numerical simulations and helps understand the mechanisms occurring in the detector structures. Theoretical estimates were compared with the dark current density experimental data at the selected characteristic temperatures: 230 K and 300 K. The proper agreement between theoretical and experimental data was reached by changing Auger-1 and Auger-7 recombination rates and Shockley- Read-Hall carrier lifetime. The level of the match was confirmed by a theoretical evaluation of the current responsivity and zero-bias dynamic resistance area product (R0A) of the tested detectors. [ABSTRACT FROM AUTHOR]

We fabricated amorphous selenium (a-Se) photodetectors with a lateral metal-insulator-semiconductorinsulator- metal (MISIM) device structure. Thermal aluminum oxide, plasma-enhanced chemical vapor deposited silicon nitride, and thermal atomic layer deposited (ALD) aluminum oxide and hafnium oxide (ALD-HfO2) were used as the electron and hole blocking layers of the MISIM photodetectors for dark current suppression. A reduction in the dark current by three orders of magnitude can be achieved at electric fields between 10 and 30 V/μm. The effective dark current suppression is primarily ascribed to electric field lowering in the dielectric layers as a result of charge trapping in deep levels. Photogenerated carriers in the a-Se layer can be transported across the blocking layers to the Al electrodes via Fowler-Nordheim tunneling because a high electric field develops in the ultrathin dielectric layers under illumination. Since the a-Se MISIM photodetectors have a very low dark current without significant degradation in the photoresponse, the signal contrast is greatly improved. The MISIM photodetector with the ALD-HfO2 blocking layer has an optimal signal contrast more than 500 times the contrast of the photodetector without a blocking layer at 15 V/μm. [ABSTRACT FROM AUTHOR]

In this paper, the performance of an Al0.52In0.48P 63Ni radioisotope cell is reported over the temperature range of -20 °C to 140°C. A 400 µm diameter p+-i-n+ (2 µm i-layer)Al0.52In0.48P mesa photodiode was used as a conversion device in a novel betavoltaic cell. Dark current measurements on the Al0.52In0.48P detector showed that the saturation current increased increasing the temperature, while the ideality factor decreased. The effects of the temperature on the key cell parameters were studied in detail showing that the open circuit voltage, the maximum output power, and the internal conversion efficiency decreased when the temperature was increased. At -20 °C, an open circuit voltage and a maximum output power of 0.52V and 0.28 pW, respectively, were measured. [ABSTRACT FROM AUTHOR]

We investigated the dark current components of thin planar InGaAs photodiodes grown by metalorganic vapor-phase epitaxy for optical nano-resonators. Owing to their high electric field enhancement, nano-resonators make it possible to substantially reduce the thickness of the active region to about 100?nm all the while maintaining high quantum efficiency. In the present study, to cover a broad spectral band, we combined several resonance peaks induced by guided-mode resonances in a given spectral range. This type of geometry allowed us to introduce InAlAs at the edge of a thin InGaAs active region in order to drastically reduce both the diffusion current and the generation/recombination current. We found that, in such devices, tunneling dark current components increase as the thickness of the active layer is reduced and dominate the reverse dark current. By optimizing the epitaxial stack, while keeping its total thickness constant (the optical properties of the nano-resonator remained unchanged), we showed that we are already able to achieve a specific detectivity of up to 1 × 1013?cm √Hz W-1 for λ = 1.55 μm&. [ABSTRACT FROM AUTHOR]

We present a dark current analysis in waveguide-coupled germanium vertical p-i-n photodetectors. In the analysis, a surface leakage current and a bulk leakage current were separated, and their activation energies were extracted. The surface leakage current originating from the minority carrier generation on the Ge layer sidewalls, governed by the Shockley-Read-Hall process and enhanced by the trap-assisted-tunneling process, was identified as the main contribution to the dark current of vertical p-i-n photodiodes at room temperature. The behavior of this surface leakage current as a function of temperature and reverse bias voltage is well reproduced by using the Hurckx model for trap-assisted-tunneling. [ABSTRACT FROM AUTHOR]

Pseudomorphic GeSn layers with Sn atomic percentages between 4.5% and 11.3% were grown by chemical vapor deposition using digermane and SnCl4 precursors on Ge virtual substrates grown on Si. The layers were characterized by x-ray diffraction rocking curves and reciprocal space maps. Photoconductive devices were fabricated, and the dark current was found to increase with Sn concentration. The responsivity of the photoconductors was measured at a wavelength of 1.55 µm using calibrated laser illumination at room temperature and a maximum value of 2.7mA/W was measured for a 4.5% Sn device. Moreover, the responsivity for higher Sn concentration was found to increase with decreasing temperature. Spectral photoconductivity was measured using Fourier transform infrared spectroscopy. The photoconductive absorption edge continually increased in wavelength with increasing tin percentage, out to approximately 2.4 µm for an 11.3% Sn device. The direct band gap was extracted using Tauc plots and was fit to a bandgap model accounting for layer strain and Sn concentration. This direct bandgap was attributed to absorption from the heavy-hole band to the conduction band. Higher energy absorption was also observed, which was thought to be likely from absorption in the light-hole band. The band gaps for these alloys were plotted as a function of temperature. These experiments show the promise of GeSn alloys for CMOS compatible short wave infrared detectors. [ABSTRACT FROM AUTHOR]

Suppressing recombination on silicon contact interfaces is a topic being addressed for various applications such as photo sensors and solar cells. Although salicidation of the contacts enables low contact resistance, it is usually avoided for these applications as it increases the recombination rate on the contact interfaces. This study explores the use of salicided polysilicon buffer layer in photodiodes' contacts, acting to reduce the recombination rate at the silicide contact. The contact incorporates the advantage of low contact resistance due to silicidation with polysilicon interface that reduces recombination by creating carrier selective junction. The introduction of a polysilicon interlayer was found to increase the short circuit current and the fill factor and to decrease the dark leakage current. The improvement in the light collection parameters was found to be more pronounced under high light intensity (1000W/m2) than under low light intensity (400 W/m2). The benevolent effect of the polysilicon interlayer is expected to be noticed in devices that are sensitive to contacts' performance. This includes not only image sensors but also high efficiency silicon solar cells. [ABSTRACT FROM AUTHOR]

This work investigates the effect of surface fields on the dynamic resistance of a planar HgCdTe mid-wavelength infrared photodiode from both theoretical and experimental aspects, considering a gated n-on-p diode with the surface potential of its p-region modulated. Theoretical models of the surface leakage current are developed, where the surface tunnelling current in the case of accumulation is expressed by modifying the formulation of bulk tunnelling currents, and the surface channel current for strong inversion is simulated with a transmission line method. Experimental data from the fabricated devices show a flat-band voltage of VFB = -5.7 V by capacitance-voltage measurement, and then the physical parameters for bulk properties are determined from the resistance-voltage characteristics of the diode working at a flat-band gate voltage. With proper values of the modeling parameters such as surface trap density and channel electron mobility, the theoretical R0A product and corresponding dark current calculated from the proposed model as functions of the gate voltage Vg demonstrate good consistency with the measured values. The R0A product remarkably degenerates when Vg is far below or above VFB because of the surface tunnelling current or channel current, respectively; and it attains the maximum value of 5:7 x 107 Ω ⋅ cm² around the transition between surface depletion and weak inversion when Vg ≈ -4 V, which might result from reduced generation-recombination current. [ABSTRACT FROM AUTHOR]

Direct conversion flat panel detectors are of great significance to the field of medical X-ray imaging since they offer imaging performance and diagnostic capabilities not achievable with other methods. Currently, mammographic direct conversion detectors employ a layer of amorphous selenium (a-Se) photoconductor. Although its properties ideally fit the requirements of mammography, where “soft” X-rays are used, a-Se cannot be used in high-energy X-ray procedures. To extend the diagnostic capabilities of the direct conversion detectors, amorphous lead oxide (a-PbO) is proposed as an alternative photoconductor. It is a high effective atomic number material and thus has a higher X-ray stopping power over the wide X-ray energy range. a-PbO is, therefore, a suitable candidate for applications in radiography, fluoroscopy, and digital tomosynthesis. Here, we report on the development of a blocking structure with a polyimide (PI) layer needed to maintain low dark current at high electric fields. We demonstrate that a 1-μm-thick PI blocking layer allows the operation of the detector at strong electric fields (≥10 V/ μm) while suppressing the dark current to an innocuous level (< 1 pA/mm2). It also improves temporal performance by reducing signal lag. No ghosting effect was observed at exposure rates up to 1 R/s; however, at high radiation levels, the detector’s sensitivity degraded. This degradation is not permanent as the detector restores its original sensitivity after several hours of rest in the dark without bias applied. [ABSTRACT FROM AUTHOR]

Dark current mechanisms of terahertz quantum-well photodetectors (THz QWPs) are systematically investigated experimentally and theoretically by measuring two newly designed structures combined with samples reported previously. In contrast to previous investigations, scattering-assisted tunneling dark current is found to cause significant contributions to total dark current. A criterion is also proposed to determine the major dark current mechanism at different peak response frequencies. We further determine background limited performance (BLIP) temperatures, which decrease both experimentally and theoretically as the electric field increases. This work gives good description of dark current mechanism for QWPs in the THz region and is extended to determine the transition fields and BLIP temperatures with response peaks from 3 to 12 THz. [ABSTRACT FROM AUTHOR]

Dark current characteristics of 7 Monolayers (ML) InAs/ 4 ML GaSb SL pin photodiodes are simulated using ATLAS software. Using appropriate models and material parameters, we obtain good agreement between the simulated and the experimental dark current curves of photodiodes grown by molecular beam epitaxy. The n-type non-intentionally-doped (nid) SL samples exhibit a dependence of the lifetime with temperature following the T-1/2 law, signature of Shockley-Read- Hall (SRH) Generation-Recombination current. We also studied the dependence of the dark current with the absorber doping level. It appears that the absorber doping level must not exceed a value of 2x1015cm-3, above this value the dark current is increasing with increased doping level. However for this doping value, a dark current as low as 5 x 10-9 A/cm2, at 50mV reverse bias at 77K can be obtained. [ABSTRACT FROM AUTHOR]

We report a high-performing heterojunction photodetector by enhanced surface effects. Periodically, patterned Si substrates were used to enlarge the photo-reactive regions and yield proportionally improved photo-responses. An optically transparent indium-tin-oxide (ITO) was deposited on a Si substrate and spontaneously formed an ITO/Si heterojunction. Due to an electrical conductive ITO film, ITO/Si heterojunction device can be operated at zero-bias, which effectively suppresses the dark current, resulting in better performances than those by a positive or a negative bias operation. This zero-bias operating heterojunction device exhibits a short response time (~ 22.5 ms) due to the physical reaction to the incident light. We revealed that the location of the space charge region (SCR) is crucial for a specific photon-wavelength response. The SCR space has the highest collection efficiency of the photo-generated carriers. The photo-response can be maximized when we design the photodetector by superposing the SCR space over a corresponding photon-absorption length. The surface enhanced Si pillar devices significantly improved the photo-responses ratios from that of a planar Si device. According to this design scheme, a high photo-response ratio of 5560% was achieved at a wavelength of 600 nm. This surfaced-enhanced heterojunction design scheme would be a promising approach for various photoelectric applications. [ABSTRACT FROM AUTHOR]

An HgCdTe long-wavelength infrared focal plane array photodetector is proposed by modulating light distributions based on the photonic crystal. It is shown that a promising prospect of improving performance is better light harvest and dark current limitation. To optimize the photon field distributions of the HgCdTe-based photonic crystal structure, a numerical method is built by combining the finite-element modeling and the finite-difference time-domain simulation. The optical and electrical characteristics of designed HgCdTe mid-wavelength and long-wavelength photon-trapping infrared detector focal plane arrays are obtained numerically. The results indicate that the photon crystal structure, which is entirely compatible with the large infrared focal plane arrays, can significantly reduce the dark current without degrading the quantum efficiency compared to the regular mesa or planar structure. [ABSTRACT FROM AUTHOR]

The effects of surface charge on the dark current of the separate-absorption-grading-charge-multiplication InGaAs/InP avalanche photodiodes (APDs) are discussed using drift-diffusion simulation. The dark current increases exponentially with the increasing of surface charge density, and gets multiplied, thus influencing the performance of the APDs, especially in Geiger mode. The mechanism of the surface charge leakage current is discussed, and a floating guard ring structure is proposed to suppress the influence of surface charge effectively. [ABSTRACT FROM AUTHOR]

A generalized drift-diffusion model for the calculation of both the quantum dot filling profile and the dark current of quantum dot infrared photodetectors is proposed. The confined electrons inside the quantum dots produce a space-charge potential barrier between the two contacts, which controls the quantum dot filling and limits the dark current in the device. The results of the model reasonably agree with a published experimental work. It is found that increasing either the doping level or the temperature results in an exponential increase of the dark current. The quantum dot filling turns out to be nonuniform, with a dot near the contacts containing more electrons than one in the middle of the device where the dot occupation approximately equals the number of doping atoms per dot, which means that quantum dots away from contacts will be nearly unoccupied if the active region is undoped. [ABSTRACT FROM AUTHOR]

Theoretical studies and numerical simulations on design, performance, and improvements of terahertz quantum-well photodetector (THz QWP) are presented. In the first part of this paper, we discuss the device band structure resulting from a self-consistent solution and simulation results. First, the temperature dependence of device characteristics is analyzed. Next, we deduce the condition of optimal doping concentration for maximizing dark current limited detectivity Ddet* when QWP is lightly doped. Accordingly, unlike in previously published reports, doping concentration is not fixed and is selected by the above condition. In the second part of this paper, we propose two schemes for improving operation temperature. The first is to incorporate an optical antenna which focuses incident THz wave. Numerical results show that the QWP with peak frequency higher than 5.5 THz is expected to achieve background-noise-limited performance at 77 K or above when employing a 106 times enhancement antenna. The second scheme is to use a laser as the signal source to achieve photon-noise-limited performance (PLIP) at high temperatures. Simulations show that when operating below critical temperature QWPs in the range of 1 ∼ 7 THz can reach PLIP under practical illumination intensities. [ABSTRACT FROM AUTHOR]

We have studied the conduction band electronic level structure of GaInAsN/(Al)GaAs-based quantum well (QW) infrared photodetectors using intersubband photocurrent (PC) spectroscopy and dark current analysis. Photoluminescence and intersubband absorption were carried out as complementary spectroscopic techniques. Based on the observed transition energy, we associated the photocurrent peaks with electron excitations from bound states in the quantum wells to quasi-bound states in the continuum. A good agreement with the experimental results was obtained using a 10-band k · p model that took into account the inhomogeneous distribution of nitrogen atoms along the quantum well's growth direction. [ABSTRACT FROM AUTHOR]

Ge-on-Si photodiodes were fabricated from germanium films grown using low-pressure chemical vapor deposition. The mechanisms responsible for the dark current in these devices are studied using geometric analysis, temperature-dependent current-voltage characterization, deep level transient spectroscopy, and device modeling. It is found that an important source of leakage current is associated with the surface depletion region, which is impacted by the nature of the fixed charge at the Ge/dielectric interface. This source of leakage especially affects devices with smaller area, on the order of 10 × 10 μm2. Through a post-metallization anneal (PMA), the dark current of these devices can be reduced by ∼1000X. A similar reduction can be obtained by intentionally doping the top of the germanium film p-type. After the PMA, it is found that the dark current density of large devices is ∼1 mA/cm2, due mainly to generation of minority carriers in the depletion region of the device. The effect of reducing the threading dislocation density is also discussed. [ABSTRACT FROM AUTHOR]

Replacement of commonly gold (Au) with other non-precious metals is a crucial step for low-cost perovskite solar cells (PSCs). However, severe performance degradations always occurred when we get rid of the Au electrode, mainly because of the deteriorated hole-transporting properties. Here, we reported that the efficiency of the PSCs featuring silver (Ag) back-electrode can be increased from 17.02 to 18.62% after introducing a thin molybdenum trioxide (MoO3) film in between the Spiro-OMeTAD and the Ag electrode. Characterizations from impedance spectrum and dark current density showed that the addition of MoO3 can effectively reduce the series resistance and reverse saturation current density of the devices, thereby leading to improved fill factor and open-circuit voltage. The enhancements in hole transport and extraction at the interface were further confirmed by the external quantum efficiency and photoluminescence tests. Our results suggested that silver electrode with MoO3 is a promising design strategy for efficient and cost-effective PSCs. [ABSTRACT FROM AUTHOR]

This paper reports the growth and characterization of InAlSb photodiodes grown on a InSb substrate for high operation temperature application. The studied InAlSb structures cover a cutoff wavelength range from 4.4 μm to 4.8 μm by tuning the Al composition in the absorber layers. A high Al composition barrier layer was inserted between the P-type contact layer and the absorber layer to reduce leakage current from the contact layer. To study the potential for high operation temperature device application, we here consider a 4.5 μm cutoff InAlSb p–i–n photodetector as an example. The detector exhibited a differential resistance at zero bias R0A in excess of 3.8 × 104 Ωcm2 and a quantum efficiency of 57% at 110 K, providing a specific detectivity of more than 1.5 × 1011 cmHz1/2/W and a background limited operating temperature of 130 K with a 300 K background. The dominant mechanism of dark current and its relationship with operating temperature were analyzed in detail. InAlSb detectors are potentially low-cost, have high operating temperature, low dark current and a high quantum efficiency, which can meet the demands of high performance infrared detectors for small platforms. [ABSTRACT FROM AUTHOR]

Self-powered photodetectors (PDs) are highly desirable for many applications, ranging from smart cities to optical communications. Herein, we report on a self-powered broadband [UV to near-infrared (NIR)] PD based on a single-crystalline SiC (100)/Si (100) heterojunction. In self-powered photovoltaic detection mode, the detector exhibits a high responsivity (2500 V/W at $\text {8.0} \times \text {10}^{\text {-6}}$ W/cm2, 521 nm) and specific detectivity (~1013 Jones at $8.0 \times 10^{-6}$ W/cm2, 521 nm) under UV, visible, and NIR spectral illuminations thanks to the superior rectification property of the heterojunction which results in significantly reducing the dark current. The device also shows high illumination ON/ OFF switching ratios, as high as $\text {2.2} \times \text {10}{^{\text {7}}}$ , with an excellent stability and repeatability. A detailed insight about electron–hole pairs generation, separation, and Fermi-energy level shifting at different illumination conditions has been elucidated via energy band diagrams. [ABSTRACT FROM AUTHOR]

The cooling requirement is still a great burden of sensitive infrared (IR) detectors. To overcome this challenge, a detailed investigation of InSb P-intrinsic-N diodes was conducted. Its dark current was comprehensively studied for the design and optimization of high-performance nonequilibrium IR detectors. The doping concentration, exclusion junction, and layer geometry were engineered to lower the Auger suppression trigger current density ${J}_{\text {onset}}$ , leading to a low dark saturation current ${J}_{\text {sat}}$. The result indicated that the Auger suppression can be triggered at ${J}_{\text {onset}}={15}$ A/cm2 and ${V}_{\text {onset}} = {0.8}$ V, while ${J}_{\text {sat}}$ can be kept as low as 10 A/cm2. The nature of Auger suppression has been studied by calculating the carrier concentration profile in the diode with different bias voltages. It is proven that the exclusion diode has the most significant effect on the Auger suppression. The specific detectivity of optimized nonequilibrium InSb detectors at different temperatures has been compared favorably with the results reported by other groups. Such a nonequilibrium InSb IR detector has a high potential in room temperature and above application. [ABSTRACT FROM AUTHOR]

Abstract The work function at the surface of 4,4′Cyclohexylidenebis[N,N-bis(4-methylphenyl) benzenamine (TAPC) layer could be increased by doping MoO 3 having high ionization energy. Therefore, in this work, we attempted to dope MoO 3 into electron-blocking layer material of TAPC to improve the device performance of organic photodetector (OPD), which effectively suppressed dark current density and increased external quantum efficiency (EQE). When a 5% MoO 3 dopant was used, the optimal OPD under reverse-biased of 3 V showed a dark current density of 1.11 nA/cm2, the EQE of 41.8% under a wavelength of 360 nm, and the detectivity of the specific wavelength surpassed 1012 Jones. In this study, we found that the decrease in the dark current density was responsible to the lower energy level of lowest unoccupied molecular orbital of TAPC and slower electron transporting capacity, which enabled the effective suppression of leakage current in OPD under bias. Furthermore, the device's EQE was substantially increased for an optimized concentration of MoO 3 doped into TAPC. Graphical abstract The electron blocking layer of TAPC doped with MoO 3 was proposed to reduce the dark current in organic ultraviolet photodetectors. Image 1 Highlights • We attempted to dope MoO 3 into electron-blocking layer material to improve the device performance. • The optimal organic photodetector under reverse-biased of 3 V showed a dark current density of 1.11 nA/cm2. • The dark current density was responsible to the LUMO level of TAPC. • The device's EQE was substantially increased for an optimized concentration of MoO 3 doped into TAPC. • The optimized C 60 -OPD shows an LDR of almost 90 dB. [ABSTRACT FROM AUTHOR]

Abstract Nanostructured TiO 2 /CNT (carbon nanotube) hybrids have been lately the focus of extensive research for their application in electroactive devices. A variety of structural combinations of TiO 2 and CNT has been reported, but most of them employ TiO 2 nanoparticles over the carbon nanotubes. One-dimensional nanomaterials, such as nanotubes, usually possess enhanced properties when compared to nanoparticles, like improved electron mobility. This work presents a novel synthesis process of nanoarchitectures of CNTs intimately connected to cobalt-doped TiO 2 nanotubes. The Co-TiO 2 nanotubes were obtained by anodization and employed as a substrate for CNT synthesis by chemical vapor deposition (CVD). CVD was performed in a range of temperatures between 650 °C and 850 °C. The synthesized nanostructures were characterized via X-ray diffraction, Raman spectroscopy, scanning, and transmission electron microscopy. The generated photocurrent density of the nanoarchitectures was measured by linear voltammetry. The sample synthesized at 750 °C exhibited well-formed Co-TiO 2 /CNT arrays; it further showed superior photocurrent performance. The results indicate that TiO 2 /CNT nanoarchitectures are promising candidates for application as photoactive materials. [ABSTRACT FROM AUTHOR]

Here we study and analyze the performance of a graphene-based photodetector integrated onto a silicon-on-insulator microring using optical and electrical simulations. The electrical simulation reveals the role of material interface losses and allows one to extract key behavioral parameters such as dark current, responsivity and bandwidth. [ABSTRACT FROM AUTHOR]