Low dark current photocathode guns are highly desired for high-brightness continuous-wave operations.Direct-current superconducting radio-frequency(DC-SRF)gun,a hybrid photocathode gun combining a DC gap and an SRF ca...Low dark current photocathode guns are highly desired for high-brightness continuous-wave operations.Direct-current superconducting radio-frequency(DC-SRF)gun,a hybrid photocathode gun combining a DC gap and an SRF cavity,effectively isolates the photocathode from the SRF cavity and offers significant advantages in terms of minimizing dark current levels.This paper presents an in-depth analysis of the dark current of a newly developed high-brightness DC-SRF photocathode gun(DC-SRF-Ⅱ gun).Particularly,a systematic experimental investigation of the dark current was conducted,and a comprehensive understanding of its formation was achieved through compliant simulations and measurements.Additionally,measures for attaining sub-nanoampere dark currents in the DC-SRF-Ⅱ gun are presented,including design considerations,cavity processing,assembly,and conditioning.The findings of this study establish a strong foundation for achieving high-performance operation of the DC-SRF-Ⅱ gun and provide a valuable reference for other photocathode guns.展开更多
Hybrid organic-inorganic perovskite photodetectors have gained significant attention due to their superior potential for optoelectronic applications,offering various advantages such as low-cost processing,high charge ...Hybrid organic-inorganic perovskite photodetectors have gained significant attention due to their superior potential for optoelectronic applications,offering various advantages such as low-cost processing,high charge carrier mobility,and lightweight properties.However,these perovskite photodetectors exhibit relatively low absorption in the near-infrared(NIR)range,which limits their potential applications.Here,to address this challenge,the integration of gold nanorods(Au NRs)utilizing localized surface plasmon resonance(LSPR)effects in the NIR range has been developed,leading to enhanced light absorption in the active region and higher photocurrent generation.Additionally,∼7.9 nm of thin polyethyleneimine ethoxylated(PEIE)interlayers were incorporated into the Au NR photodetectors,suppressing dark current by blocking charge injection.As a result,the synergistic effect of the Au NR/PEIE hybrid layer has led to a high-performance photodetector with a responsivity of 0.360 A/W and a detectivity of 1.81×10^(10) Jones,demonstrating a noticeable enhancement compared to the control device.Finite-difference time-domain(FDTD)simulations,morphological characterizations,and photoluminescence studies further support the mechanism for enhancing the performance of the device.We believe that our plasmon-enhanced protocol holds strong potential as a promising platform for perovskite optoelectronic devices.展开更多
The focus of this study is on investigating the vanadyl 2,9,16,23-tetraphenoxy-29H, 31H-phthalocyanine(VOPc Ph O)and its blend with o-xylenyl C60 bis-adduct(OXCBA), for use as a lateral ultraviolet organic photodetect...The focus of this study is on investigating the vanadyl 2,9,16,23-tetraphenoxy-29H, 31H-phthalocyanine(VOPc Ph O)and its blend with o-xylenyl C60 bis-adduct(OXCBA), for use as a lateral ultraviolet organic photodetector. The research focuses on improving dark current reduction, which is a challenge in lateral organic photodetector. By integrating the OXCBA, low dark current values of 4.83 nA·cm^(-2)(D_(shot)^(*)= 1.414 × 10^(11)Jones) have been achieved as compared to the stand-alone VoPcPhO device of 14.06 nA·cm^(-2). The major contributing factors to dark current reduction are due to the efficient charge transfer at the photoactive-electrode interface, the deep highest occupied molecular orbital(HOMO)level of OXCBA, which leads to favorable energy level alignments hindering hole injection, and the occurrence of bulk heterojunction vertical phase segregation between VOPcPhO and OXCBA. These findings shed light on the relationship between the organic photoconductor's material composition, morphology, and performance metrics and open new avenues for metal phthalocyanine-based lateral ultraviolet organic photodetectors with low dark current and enhanced performance.展开更多
Avalanche photodiode(APD)is a kind of photodetector with important applications in optical communication,light detection and ranging(LIDAR)and other fields.APDs fabricated using the recently developed AlGaAsSb as the ...Avalanche photodiode(APD)is a kind of photodetector with important applications in optical communication,light detection and ranging(LIDAR)and other fields.APDs fabricated using the recently developed AlGaAsSb as the multiplication material exhibit excellent noise performance.In this work,we report a low-noise separate absorption,grading,charge,and multi-plication(SAGCM)InGaAs/AlGaAsSb APD operating at 1550 nm.A double-mesa structure was fabricated to reduce the dark cur-rent.Numerical simulations were conducted to compare two different mesa-structured APDs.By analyzing the electric field distri-bution,it was found that the electric field at the edge of the multiplication region in the double-mesa APD is nearly 100 kV/cm lower than that of the single-mesa structure.Experimental results demonstrate that after device punch-through,the double-mesa APD’s dark current can be reduced by up to four times compared to the single-mesa APD.Quantitative analysis of the dark current components in the AlGaAsSb APD further confirms that the low sidewall electric field in the double-mesa struc-ture effectively suppresses the trap-assisted tunneling.Additionally,noise measurements indicate a k-value of approximately 0.014,which is significantly lower than that of traditional multiplication materials.This work provides preliminary validation for further performance improvements in low noise and low dark current AlGaAsSb APDs.展开更多
Type-Ⅱsuperlattice(T2SL)materials are the key element for infrared(IR)detectors.However,it is well known that the characteristics of the detectors with the T2SL layer are greatly affected by the strain developed duri...Type-Ⅱsuperlattice(T2SL)materials are the key element for infrared(IR)detectors.However,it is well known that the characteristics of the detectors with the T2SL layer are greatly affected by the strain developed during the growth process,which determines the performance of IR detectors.Therefore,great efforts have been made to properly control the strain effect and develop relevant analysis methods to evaluate the strain-induced dark current characteristics.In this work,we report the strain-induced dark current characteristics in InAs/GaSb T2SL MWIR photodetector.The overall strain of InAs/GaSb T2SL layer was analyzed by both high-resolution X-ray diffraction(HRXRD)and the dark current measured from the absorber layer at the elevated temperatures(≥110 K),where the major leakage current component is originated from the reduced minority carrier lifetime in the absorber layer.Our findings indicate that minority carrier lifetime increases as the tensile strain on the InAs/GaSb T2SL is more compensated by the compressive strain through‘InSb-like’interface,which reduces the dark current density of the device.Specifically,tensile strain compensated devices exhibited the dark current density of less than 2×10^-5 A/cm^2 at 120 K,which is more than one order of magnitude lower value compared to that of the device without tensile strain relaxation.展开更多
The mechanism for electrical conduction is investigated by the dark temperature-dependent current–voltage characteristics of Si PIN photodiodes with different photosensitive areas.The characteristic tunneling energy ...The mechanism for electrical conduction is investigated by the dark temperature-dependent current–voltage characteristics of Si PIN photodiodes with different photosensitive areas.The characteristic tunneling energy E（00） can be obtained to be 1.40 me V,1.53 me V,1.74 me V,1.87 me V,and 2.01 me V,respectively,for the photodiodes with L = 0.25 mm,0.5 mm,1 mm,1.5 mm,and 2 mm by fitting the ideality factor n versus temperature curves according to the tunneling-enhanced recombination mechanism.The trap-assisted tunneling-enhanced recombination in the i-layer plays an important role in our device,which is consistent with the experimental result that area-dependent leakage current is dominant with the side length larger than 1 mm of the photosensitive area.Our results reveal that the quality of the bulk material plays an important role in the electrical conduction mechanism of the devices with the side length larger than 1 mm of the photosensitive area.展开更多
The development of portable X-ray detectors is necessary for diagnosing fractures in unconscious patients in emergency situations.However,this is quite challenging because of the heavy weight of the scintillator and s...The development of portable X-ray detectors is necessary for diagnosing fractures in unconscious patients in emergency situations.However,this is quite challenging because of the heavy weight of the scintillator and silicon photodetectors.The weight and thickness of X-ray detectors can be reduced by replacing the silicon layer with an organic photodetectors.This study presents a novel bithienopyrroledione-based polymer donor that exhibits excellent photodetection properties even in a thick photoactive layer(~700 nm),owing to the symmetric backbone and highly soluble molecular structure of bithienopyrroledione.The ability of bithienopyrroledione-based polymer donor to strongly suppress the dark current density(Jd~10−10 A cm^(−2))at a negative bias(−2.0 V)while maintaining high responsivity(R=0.29 A W−1)even at a thickness of 700 nm results in a maximum shot-noise-limited specific detectivity of D_(sh)^(*)=2.18×10^(13)Jones in the organic photodetectors.Printed organic photodetectors are developed by slot-die coating for use in X-ray detectors,which exhibit D_(sh)^(*)=2.73×10^(12)Jones with clear rising(0.26 s)and falling(0.29 s)response times upon X-ray irradiation.Detection reliability is also proven by linear response of the X-ray detector,and the X-ray detection limit is 3 mA.展开更多
The TiO2 nanoporous film photoelectrode, as a crucial component of dye-sensitized solar cells, has been investigated. The photovoltaic properties and the dark current were studied by two surface modification methods. ...The TiO2 nanoporous film photoelectrode, as a crucial component of dye-sensitized solar cells, has been investigated. The photovoltaic properties and the dark current were studied by two surface modification methods. One was to apply a compact layer between the conductive glass substrate and nanoporous TiO2 film. Another was to produce TiO2 nanoparticles among the microstructure by TICl4 treatment. A suitable concentration and number of times for TICl4 treatment were found in our experiment. The dark current is suppressed by surface modifications, leading to a significant improvement in the solar cells performance. An excessive concentration of TICl4 will produce more surface states and introduce a larger dark current reversely. The dye is also regarded as a source of charge recombination in dark to some extent, due to an amount of surface protonations introduced by the interracial link in the conductive glass substrate/dye interface and dye/TiO2 interface.展开更多
A new Dark Current Suppression (DCS) CMOS readout circuits for large format Quantum-Well-Infrared Photo-detector (QWIP) Focal-Plane-Array (FPA) with novel Correlated-Double-Sampling (CDS) structure based on dynamic so...A new Dark Current Suppression (DCS) CMOS readout circuits for large format Quantum-Well-Infrared Photo-detector (QWIP) Focal-Plane-Array (FPA) with novel Correlated-Double-Sampling (CDS) structure based on dynamic source-follower are proposed, which can overcome the drawbacks of the present techniques, such as sensitive to the non-uniformity of the QWIP materials, poor readout noise features, low frame frequency, limited injection efficiency and dynamic range, etc. The dummy is adopted to realize dark current suppression, while the cascode current mirror (with current ratio of 1:10) can increase charge sensitivity and reduce integration time. Through the novel CDS structure, the output waveform is boxcar, and the frame frequency is increased. Simulation results demonstrate that, in high background sense, the proposed DCS circuit can suppress the dark current, achieve good readout performance, such as low power consumption, high charge sensitivity, high resolution, large dynamic range, and insensitive to the non-uniformity of the QWIP materials.展开更多
The dark current of In_(0.47) Ga_(0.53) As/InP heterojunction photodiodes (HPDs) was analysed. We found that there exists a new dark current component──deep level-assisted tunnelling current.DLTS was used to measure...The dark current of In_(0.47) Ga_(0.53) As/InP heterojunction photodiodes (HPDs) was analysed. We found that there exists a new dark current component──deep level-assisted tunnelling current.DLTS was used to measure the In_(0.47)Ga_(0.53)As/InP HPDs. An electronic trap which has a thermal activation energy of O.44 eV, level concentration of 3.10×10￣(13)cm￣(-3) and electronic capture cross section of 1.72×10￣(12)cm￣2 has been found.It's existence results in the new tunnelling current.展开更多
For the last several years, the linear array x-ray detector for x-ray imaging with gallium arsenide direct conversion sensitive elements has been developed and tested at the In-stitute for High Energy Physics. The arr...For the last several years, the linear array x-ray detector for x-ray imaging with gallium arsenide direct conversion sensitive elements has been developed and tested at the In-stitute for High Energy Physics. The array consists of 16 sensitive modules. Each module has 128 gallium arsenide (GaAs) sensitive elements with 200 μm pitch. Current article describes two key program procedures of initial dark current compensation of each sensitive element in the linear array, and sensitivity adjustment for alignment of strip pattern in the raw image data. As a part of evaluation process a modular transfer function (MTF) was measured with the slanted sharp-edge object under RQA5 technique as it described in the International Electrotechnical Commission 62220-1 standard (high voltage 70 kVp, additional aluminium filter 21 mm) for images with compensated dark currents and adjusted sensitivity of detector elements. The 10% level of the calculated MTF function has spatial resolution within 2 - 3 pair of lines per mm for both vertical and horizontal orientation.展开更多
Suppressing the dark current density in organic diodes is essential for developing practical consumer electronics such as in-door photovoltaics and photodetectors.While extensive research has explored dark current fro...Suppressing the dark current density in organic diodes is essential for developing practical consumer electronics such as in-door photovoltaics and photodetectors.While extensive research has explored dark current from thermodynamics and kinetics(of free and trapped charges)perspectives,a clear relationship between nanostructure and dark current remains elusive.In this contribution,the relationship between the structural/morphological order of non-fullerene acceptors(NFAs)with the dark current and shunts in their organic photodetectors(OPDs)is investigated.Starting with the state-of-the-art NFA C9-12(BTP-eC9),we systematically tune the molecular structural symmetry and alkyl chain length.We find that unsymmetrizing the end groups and/or extending the alkyl chains of NFAs leads to swollen intermolecular packing in solid state,effectively suppressing microscopic shunting paths.Additionally,increasing alkyl chain length promotes more oriented intermolecular packing in the out-of-plane direction,reducing energetic disorder and consequently suppressing the thermal generation of dark charges.These combined benefits lead to a simultaneous suppression of both thermally activated diode current and shunt current in OPDs based on unsymmetrical non-fullerene acceptors with long alkyl chains.展开更多
The influence of hydrogenation on the dark current mechanism ofHgCdTe photovoltaic detectors is studied. The hydrogenation is achieved by exposing samples to a H2/Ar plasma atmosphere that was produced during a reacti...The influence of hydrogenation on the dark current mechanism ofHgCdTe photovoltaic detectors is studied. The hydrogenation is achieved by exposing samples to a H2/Ar plasma atmosphere that was produced during a reactive ion etching process. A set of variable-area photomask was specially designed to evaluate the hydrogenation effect. It was found that the current-voltage characteristics were gradually improved when detectors were hydrogenated by different areas. The fitting results of experimental results at reverse bias conditions sustained that the improvement of current-voltage curves was due to the suppression of trap assisted tunneling current and the enhancement of minority lifetime in the depletion region. It was also found that the dominative forward current was gradually converted from a generation-recombination current to a diffusion current with the enlargement of the hydrogenation area, which was infered from the ideality factors by abstraction of forward resistance-voltage curves of different detectors.展开更多
In this paper,we demonstrate nBn InAs/InAsSb type II superlattice(T2SL)photodetectors with AlAsSb as the barrier that targets mid-wavelength infrared(MWIR)detection.To improve operating temperature and suppress dark c...In this paper,we demonstrate nBn InAs/InAsSb type II superlattice(T2SL)photodetectors with AlAsSb as the barrier that targets mid-wavelength infrared(MWIR)detection.To improve operating temperature and suppress dark current,a specific Sb soaking technique was employed to improve the interface abruptness of the superlattice with device passivation using a SiO_(2) layer.These result in ultralow dark current density of 6.28×10^(-6)A/cm^(2)and 0.31 A/cm^(2)under-600 mV at 97 K and297 K,respectively,which is lower than most reported InAs/InAsSb-based MWIR photodetectors.Corresponding resistance area product values of 3.20×10^(4)Ω·cm^(2)and 1.32Ω·cm^(2)were obtained at 97 K and 297 K.A peak responsivity of 0.39 A/W with a cutoff wavelength around 5.5μm and a peak detectivity of 2.1×10^(9)cm·Hz^(1/2)/W were obtained at a high operating temperature up to 237 K.展开更多
Semiconductive metal–organic frameworks(MOFs)have attracted great interest for the electronic applications.However,dark currents of present hybrid organic–inorganic materials are 1000–10,000 times higher than those...Semiconductive metal–organic frameworks(MOFs)have attracted great interest for the electronic applications.However,dark currents of present hybrid organic–inorganic materials are 1000–10,000 times higher than those of commercial inorganic detectors,leading to poor charge transportation.Here,we demonstrate a ZIF-8(Zn(mim)_(2),mim=2-methylimidazolate)wafer with ultra-low dark current of 1.27 pA·mm^(-2) under high electric fields of 322 V·mm^(-1).The isostatic pressing preparation process provides ZIF-8 wafers with good transmittance.Besides,the presence of redox-active metals and small spatial separation between components promotes the charge hopping.The ZIF-8-based semiconductor detector shows promising X-ray detection sensitivity of 70.82μC·Gy^(-1)·cm^(-2) with low doses exposures,contributing to superior X-ray imaging capability with a relatively high spatial resolution of 1.2 lp·mm^(-1).Simultaneously,good peak discrimination with the energy resolution of~43.78%is disclosed when the detector is illuminated by uncollimated 241Am@5.48 MeVα-particles.These results provide a broad prospect of MOFs for future radiation detection applications.展开更多
Metal halide perovskites(MHPs)have demonstrated excellent performances in detection of X-rays and gamma-rays.Most studies focus on improving the sensitivity of single-pixel MHP detectors.However,little work pays atten...Metal halide perovskites(MHPs)have demonstrated excellent performances in detection of X-rays and gamma-rays.Most studies focus on improving the sensitivity of single-pixel MHP detectors.However,little work pays attention to the dark current,which is crucial for the back-end circuit integration.Herein,the requirement of dark current is quantitatively evaluated as low as 10^(−9)A/cm^(2)for X-ray imagers integrated on pixel circuits.Moreover,through the semiconductor device analysis and simulation,we reveal that the main current compositions of thick perovskite X-ray detectors are the thermionic-emission current(J_(T))and the generation-recombination current(J_(g-r)).The typical observed failures of p-n junctions in thick detectors are caused by the high generation-recombination current due to the band mismatch and interface defects.This work provides a deep insight into the design of high sensitivity and low dark current perovskite X-ray detectors.展开更多
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...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.展开更多
We investigate the dark current mechanism for an unpassivated mid wavelength(MW) type II InAs/GaSb superlattice infrared photodetector by doing the variablearea diode tests. The bulk resistance-area product and the re...We investigate the dark current mechanism for an unpassivated mid wavelength(MW) type II InAs/GaSb superlattice infrared photodetector by doing the variablearea diode tests. The bulk resistance-area product and the resistivity due to the surface current are determined to be17.72 X cm2 and 704.23 X cm at 77 K, respectively. It is found that for all the mesa sizes used, the dark current is dominated or predominated by the surface component, and with scaling back the mesa size, the surface current increases while the bulk component decreases. The activation energy is determined to be 145 meV for the temperature range around 140–280 K, while it is 6 meV when temperature is below 100 K. It is also found that the dark current is dominated by the generation-recombination current for the MW device when temperature is between140 and 280 K.展开更多
Herein we propose a new equivalent circuit including double heterojunctions in series to simulate the current–voltage characteristic of P–I–N planar structure perovskite solar cells. This new method can theoretical...Herein we propose a new equivalent circuit including double heterojunctions in series to simulate the current–voltage characteristic of P–I–N planar structure perovskite solar cells. This new method can theoretically solve the dilemma of the parameter diode ideal factor being larger than2 from an ideal single heterojunction equivalent circuit,which usually is in the range from 1 to 2. The diode ideal factor reflects PN junction quality, which influences the recombination at electron transport layer/perovskite and perovskite/hole transport layer interface. Based on the double PN junction equivalent circuit, we can also simulate the dark current–voltage curve for analyzing recombination current(Shockley–Read–Hall recombination) and diffusion current(including direct recombination), and thus carrier recombination and transportation characteristics. This new model offers an efficacious and simple method to investigate interfaces condition, film quality of perovskite absorbing layer and performance of transport layer, helping us furtherimprove the device efficiency and analyze the working mechanism.展开更多
基金partially supported by the National Key Research and Development Program of China(Nos.2016YFA0401904 and 2017YFA0701001)the State Key Laboratory of Nuclear Physics and Technology,Peking University(Nos.NPT2022ZZ01).
文摘Low dark current photocathode guns are highly desired for high-brightness continuous-wave operations.Direct-current superconducting radio-frequency(DC-SRF)gun,a hybrid photocathode gun combining a DC gap and an SRF cavity,effectively isolates the photocathode from the SRF cavity and offers significant advantages in terms of minimizing dark current levels.This paper presents an in-depth analysis of the dark current of a newly developed high-brightness DC-SRF photocathode gun(DC-SRF-Ⅱ gun).Particularly,a systematic experimental investigation of the dark current was conducted,and a comprehensive understanding of its formation was achieved through compliant simulations and measurements.Additionally,measures for attaining sub-nanoampere dark currents in the DC-SRF-Ⅱ gun are presented,including design considerations,cavity processing,assembly,and conditioning.The findings of this study establish a strong foundation for achieving high-performance operation of the DC-SRF-Ⅱ gun and provide a valuable reference for other photocathode guns.
基金supported by the National Research Foundation of Korea(NRF)Grant funded by the Korean Government(Nos.2020R1A2C3003958 and 2021R1C1C2010169)the Basic Science Research Program(Priority Research Institute)through the NRF of Korea funded by the Ministry of Education(No.2021R1A6A1A10039823)the Korea Basic Science Institute(National Research Facilities and Equipment Center)grant funded by the Ministry of Education(No.2020R1A6C101B194).
文摘Hybrid organic-inorganic perovskite photodetectors have gained significant attention due to their superior potential for optoelectronic applications,offering various advantages such as low-cost processing,high charge carrier mobility,and lightweight properties.However,these perovskite photodetectors exhibit relatively low absorption in the near-infrared(NIR)range,which limits their potential applications.Here,to address this challenge,the integration of gold nanorods(Au NRs)utilizing localized surface plasmon resonance(LSPR)effects in the NIR range has been developed,leading to enhanced light absorption in the active region and higher photocurrent generation.Additionally,∼7.9 nm of thin polyethyleneimine ethoxylated(PEIE)interlayers were incorporated into the Au NR photodetectors,suppressing dark current by blocking charge injection.As a result,the synergistic effect of the Au NR/PEIE hybrid layer has led to a high-performance photodetector with a responsivity of 0.360 A/W and a detectivity of 1.81×10^(10) Jones,demonstrating a noticeable enhancement compared to the control device.Finite-difference time-domain(FDTD)simulations,morphological characterizations,and photoluminescence studies further support the mechanism for enhancing the performance of the device.We believe that our plasmon-enhanced protocol holds strong potential as a promising platform for perovskite optoelectronic devices.
基金financial support from the Ministry of Science,Technology and Innovation with Grant No. MOSTI004-2023SRF。
文摘The focus of this study is on investigating the vanadyl 2,9,16,23-tetraphenoxy-29H, 31H-phthalocyanine(VOPc Ph O)and its blend with o-xylenyl C60 bis-adduct(OXCBA), for use as a lateral ultraviolet organic photodetector. The research focuses on improving dark current reduction, which is a challenge in lateral organic photodetector. By integrating the OXCBA, low dark current values of 4.83 nA·cm^(-2)(D_(shot)^(*)= 1.414 × 10^(11)Jones) have been achieved as compared to the stand-alone VoPcPhO device of 14.06 nA·cm^(-2). The major contributing factors to dark current reduction are due to the efficient charge transfer at the photoactive-electrode interface, the deep highest occupied molecular orbital(HOMO)level of OXCBA, which leads to favorable energy level alignments hindering hole injection, and the occurrence of bulk heterojunction vertical phase segregation between VOPcPhO and OXCBA. These findings shed light on the relationship between the organic photoconductor's material composition, morphology, and performance metrics and open new avenues for metal phthalocyanine-based lateral ultraviolet organic photodetectors with low dark current and enhanced performance.
基金supported by the National Natural Science Foundation of China(61774152),which are gratefully acknowledged.
文摘Avalanche photodiode(APD)is a kind of photodetector with important applications in optical communication,light detection and ranging(LIDAR)and other fields.APDs fabricated using the recently developed AlGaAsSb as the multiplication material exhibit excellent noise performance.In this work,we report a low-noise separate absorption,grading,charge,and multi-plication(SAGCM)InGaAs/AlGaAsSb APD operating at 1550 nm.A double-mesa structure was fabricated to reduce the dark cur-rent.Numerical simulations were conducted to compare two different mesa-structured APDs.By analyzing the electric field distri-bution,it was found that the electric field at the edge of the multiplication region in the double-mesa APD is nearly 100 kV/cm lower than that of the single-mesa structure.Experimental results demonstrate that after device punch-through,the double-mesa APD’s dark current can be reduced by up to four times compared to the single-mesa APD.Quantitative analysis of the dark current components in the AlGaAsSb APD further confirms that the low sidewall electric field in the double-mesa struc-ture effectively suppresses the trap-assisted tunneling.Additionally,noise measurements indicate a k-value of approximately 0.014,which is significantly lower than that of traditional multiplication materials.This work provides preliminary validation for further performance improvements in low noise and low dark current AlGaAsSb APDs.
基金supported by the research fund of Chungnam National University
文摘Type-Ⅱsuperlattice(T2SL)materials are the key element for infrared(IR)detectors.However,it is well known that the characteristics of the detectors with the T2SL layer are greatly affected by the strain developed during the growth process,which determines the performance of IR detectors.Therefore,great efforts have been made to properly control the strain effect and develop relevant analysis methods to evaluate the strain-induced dark current characteristics.In this work,we report the strain-induced dark current characteristics in InAs/GaSb T2SL MWIR photodetector.The overall strain of InAs/GaSb T2SL layer was analyzed by both high-resolution X-ray diffraction(HRXRD)and the dark current measured from the absorber layer at the elevated temperatures(≥110 K),where the major leakage current component is originated from the reduced minority carrier lifetime in the absorber layer.Our findings indicate that minority carrier lifetime increases as the tensile strain on the InAs/GaSb T2SL is more compensated by the compressive strain through‘InSb-like’interface,which reduces the dark current density of the device.Specifically,tensile strain compensated devices exhibited the dark current density of less than 2×10^-5 A/cm^2 at 120 K,which is more than one order of magnitude lower value compared to that of the device without tensile strain relaxation.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFF0104801)the National Natural Science Foundation of China(Grant Nos.61335004,61675046,and 61505003)
文摘The mechanism for electrical conduction is investigated by the dark temperature-dependent current–voltage characteristics of Si PIN photodiodes with different photosensitive areas.The characteristic tunneling energy E（00） can be obtained to be 1.40 me V,1.53 me V,1.74 me V,1.87 me V,and 2.01 me V,respectively,for the photodiodes with L = 0.25 mm,0.5 mm,1 mm,1.5 mm,and 2 mm by fitting the ideality factor n versus temperature curves according to the tunneling-enhanced recombination mechanism.The trap-assisted tunneling-enhanced recombination in the i-layer plays an important role in our device,which is consistent with the experimental result that area-dependent leakage current is dominant with the side length larger than 1 mm of the photosensitive area.Our results reveal that the quality of the bulk material plays an important role in the electrical conduction mechanism of the devices with the side length larger than 1 mm of the photosensitive area.
基金granted by the Korea Research Institute of Chemical Technology(KRICT)of the Republic of Korea(No.2422-10)the National Research Foundation(NRF)(NRF-2021R1C1C2007445 and RS-2023-00280495)of Republic of Korea.
文摘The development of portable X-ray detectors is necessary for diagnosing fractures in unconscious patients in emergency situations.However,this is quite challenging because of the heavy weight of the scintillator and silicon photodetectors.The weight and thickness of X-ray detectors can be reduced by replacing the silicon layer with an organic photodetectors.This study presents a novel bithienopyrroledione-based polymer donor that exhibits excellent photodetection properties even in a thick photoactive layer(~700 nm),owing to the symmetric backbone and highly soluble molecular structure of bithienopyrroledione.The ability of bithienopyrroledione-based polymer donor to strongly suppress the dark current density(Jd~10−10 A cm^(−2))at a negative bias(−2.0 V)while maintaining high responsivity(R=0.29 A W−1)even at a thickness of 700 nm results in a maximum shot-noise-limited specific detectivity of D_(sh)^(*)=2.18×10^(13)Jones in the organic photodetectors.Printed organic photodetectors are developed by slot-die coating for use in X-ray detectors,which exhibit D_(sh)^(*)=2.73×10^(12)Jones with clear rising(0.26 s)and falling(0.29 s)response times upon X-ray irradiation.Detection reliability is also proven by linear response of the X-ray detector,and the X-ray detection limit is 3 mA.
基金supported by National Basic Research Program of China （No. 2006CB202600） the Natural Science Foundation of Nantong University （No. 06Z120）+1 种基金 the Fund for High Technology Research of Jiangsu Province （No. BG2005022） ＂The Six Top Talents Project＂ of Jiangsu
文摘The TiO2 nanoporous film photoelectrode, as a crucial component of dye-sensitized solar cells, has been investigated. The photovoltaic properties and the dark current were studied by two surface modification methods. One was to apply a compact layer between the conductive glass substrate and nanoporous TiO2 film. Another was to produce TiO2 nanoparticles among the microstructure by TICl4 treatment. A suitable concentration and number of times for TICl4 treatment were found in our experiment. The dark current is suppressed by surface modifications, leading to a significant improvement in the solar cells performance. An excessive concentration of TICl4 will produce more surface states and introduce a larger dark current reversely. The dye is also regarded as a source of charge recombination in dark to some extent, due to an amount of surface protonations introduced by the interracial link in the conductive glass substrate/dye interface and dye/TiO2 interface.
基金Supported by the National Natural Science Foundation of China(No.60077025)
文摘A new Dark Current Suppression (DCS) CMOS readout circuits for large format Quantum-Well-Infrared Photo-detector (QWIP) Focal-Plane-Array (FPA) with novel Correlated-Double-Sampling (CDS) structure based on dynamic source-follower are proposed, which can overcome the drawbacks of the present techniques, such as sensitive to the non-uniformity of the QWIP materials, poor readout noise features, low frame frequency, limited injection efficiency and dynamic range, etc. The dummy is adopted to realize dark current suppression, while the cascode current mirror (with current ratio of 1:10) can increase charge sensitivity and reduce integration time. Through the novel CDS structure, the output waveform is boxcar, and the frame frequency is increased. Simulation results demonstrate that, in high background sense, the proposed DCS circuit can suppress the dark current, achieve good readout performance, such as low power consumption, high charge sensitivity, high resolution, large dynamic range, and insensitive to the non-uniformity of the QWIP materials.
文摘The dark current of In_(0.47) Ga_(0.53) As/InP heterojunction photodiodes (HPDs) was analysed. We found that there exists a new dark current component──deep level-assisted tunnelling current.DLTS was used to measure the In_(0.47)Ga_(0.53)As/InP HPDs. An electronic trap which has a thermal activation energy of O.44 eV, level concentration of 3.10×10￣(13)cm￣(-3) and electronic capture cross section of 1.72×10￣(12)cm￣2 has been found.It's existence results in the new tunnelling current.
文摘For the last several years, the linear array x-ray detector for x-ray imaging with gallium arsenide direct conversion sensitive elements has been developed and tested at the In-stitute for High Energy Physics. The array consists of 16 sensitive modules. Each module has 128 gallium arsenide (GaAs) sensitive elements with 200 μm pitch. Current article describes two key program procedures of initial dark current compensation of each sensitive element in the linear array, and sensitivity adjustment for alignment of strip pattern in the raw image data. As a part of evaluation process a modular transfer function (MTF) was measured with the slanted sharp-edge object under RQA5 technique as it described in the International Electrotechnical Commission 62220-1 standard (high voltage 70 kVp, additional aluminium filter 21 mm) for images with compensated dark currents and adjusted sensitivity of detector elements. The 10% level of the calculated MTF function has spatial resolution within 2 - 3 pair of lines per mm for both vertical and horizontal orientation.
基金supported by the National Natural Science Foundation of China(52203238,52273196,52073221)funding from the Research Council of Finland(357196)。
文摘Suppressing the dark current density in organic diodes is essential for developing practical consumer electronics such as in-door photovoltaics and photodetectors.While extensive research has explored dark current from thermodynamics and kinetics(of free and trapped charges)perspectives,a clear relationship between nanostructure and dark current remains elusive.In this contribution,the relationship between the structural/morphological order of non-fullerene acceptors(NFAs)with the dark current and shunts in their organic photodetectors(OPDs)is investigated.Starting with the state-of-the-art NFA C9-12(BTP-eC9),we systematically tune the molecular structural symmetry and alkyl chain length.We find that unsymmetrizing the end groups and/or extending the alkyl chains of NFAs leads to swollen intermolecular packing in solid state,effectively suppressing microscopic shunting paths.Additionally,increasing alkyl chain length promotes more oriented intermolecular packing in the out-of-plane direction,reducing energetic disorder and consequently suppressing the thermal generation of dark charges.These combined benefits lead to a simultaneous suppression of both thermally activated diode current and shunt current in OPDs based on unsymmetrical non-fullerene acceptors with long alkyl chains.
文摘The influence of hydrogenation on the dark current mechanism ofHgCdTe photovoltaic detectors is studied. The hydrogenation is achieved by exposing samples to a H2/Ar plasma atmosphere that was produced during a reactive ion etching process. A set of variable-area photomask was specially designed to evaluate the hydrogenation effect. It was found that the current-voltage characteristics were gradually improved when detectors were hydrogenated by different areas. The fitting results of experimental results at reverse bias conditions sustained that the improvement of current-voltage curves was due to the suppression of trap assisted tunneling current and the enhancement of minority lifetime in the depletion region. It was also found that the dominative forward current was gradually converted from a generation-recombination current to a diffusion current with the enlargement of the hydrogenation area, which was infered from the ideality factors by abstraction of forward resistance-voltage curves of different detectors.
基金supported by the National Science and Technology Major Project(No.2018YFE0200900)。
文摘In this paper,we demonstrate nBn InAs/InAsSb type II superlattice(T2SL)photodetectors with AlAsSb as the barrier that targets mid-wavelength infrared(MWIR)detection.To improve operating temperature and suppress dark current,a specific Sb soaking technique was employed to improve the interface abruptness of the superlattice with device passivation using a SiO_(2) layer.These result in ultralow dark current density of 6.28×10^(-6)A/cm^(2)and 0.31 A/cm^(2)under-600 mV at 97 K and297 K,respectively,which is lower than most reported InAs/InAsSb-based MWIR photodetectors.Corresponding resistance area product values of 3.20×10^(4)Ω·cm^(2)and 1.32Ω·cm^(2)were obtained at 97 K and 297 K.A peak responsivity of 0.39 A/W with a cutoff wavelength around 5.5μm and a peak detectivity of 2.1×10^(9)cm·Hz^(1/2)/W were obtained at a high operating temperature up to 237 K.
基金supported by the National Natural Science Foundations of China(Nos.U2032170 and 62104194)The project was also supported by the Natural Science Basic Research Plan in Shaanxi Province of China(No.2021GXLH-01-03)+2 种基金the ND Basic Research Funds(No.G2022WD)the Research Fund of the State Key Laboratory of Solidification Processing(NPU)China(No.2022-TS-07).
文摘Semiconductive metal–organic frameworks(MOFs)have attracted great interest for the electronic applications.However,dark currents of present hybrid organic–inorganic materials are 1000–10,000 times higher than those of commercial inorganic detectors,leading to poor charge transportation.Here,we demonstrate a ZIF-8(Zn(mim)_(2),mim=2-methylimidazolate)wafer with ultra-low dark current of 1.27 pA·mm^(-2) under high electric fields of 322 V·mm^(-1).The isostatic pressing preparation process provides ZIF-8 wafers with good transmittance.Besides,the presence of redox-active metals and small spatial separation between components promotes the charge hopping.The ZIF-8-based semiconductor detector shows promising X-ray detection sensitivity of 70.82μC·Gy^(-1)·cm^(-2) with low doses exposures,contributing to superior X-ray imaging capability with a relatively high spatial resolution of 1.2 lp·mm^(-1).Simultaneously,good peak discrimination with the energy resolution of~43.78%is disclosed when the detector is illuminated by uncollimated 241Am@5.48 MeVα-particles.These results provide a broad prospect of MOFs for future radiation detection applications.
基金supported by the Major State Basic Research Development Program of China(No.2021YFB3201000)the National Natural Science Foundation of China(Grant Nos.62074066,62134003,and 12050005)+2 种基金the Fund for Innovative Research Groups of the Natural Science Foundation of Hubei Province(Nos.2021CFA036 and 2020CFA034)Shenzhen Basic Research Program(No.JCYJ20200109115212546)the Fundamental Research Funds for the Central Universities.
文摘Metal halide perovskites(MHPs)have demonstrated excellent performances in detection of X-rays and gamma-rays.Most studies focus on improving the sensitivity of single-pixel MHP detectors.However,little work pays attention to the dark current,which is crucial for the back-end circuit integration.Herein,the requirement of dark current is quantitatively evaluated as low as 10^(−9)A/cm^(2)for X-ray imagers integrated on pixel circuits.Moreover,through the semiconductor device analysis and simulation,we reveal that the main current compositions of thick perovskite X-ray detectors are the thermionic-emission current(J_(T))and the generation-recombination current(J_(g-r)).The typical observed failures of p-n junctions in thick detectors are caused by the high generation-recombination current due to the band mismatch and interface defects.This work provides a deep insight into the design of high sensitivity and low dark current perovskite X-ray detectors.
基金Project supported by the Key Project of Natural Science Foundation of China(No.61534005)the National Science Foundation of China(No.61474081)+2 种基金the National Basic Research Program of China(No.2013CB632103)the Natural Science Foundation of Fujian Province(No.2015D020)the Science and Technology Project of Xiamen City(No.3502Z20154091)
文摘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.
基金supported in part by the National Natural Science Foundation of China (61176014, 61307116, 61290303, and 61021003)the National Basic Research Program of China (2010CB327602)
文摘We investigate the dark current mechanism for an unpassivated mid wavelength(MW) type II InAs/GaSb superlattice infrared photodetector by doing the variablearea diode tests. The bulk resistance-area product and the resistivity due to the surface current are determined to be17.72 X cm2 and 704.23 X cm at 77 K, respectively. It is found that for all the mesa sizes used, the dark current is dominated or predominated by the surface component, and with scaling back the mesa size, the surface current increases while the bulk component decreases. The activation energy is determined to be 145 meV for the temperature range around 140–280 K, while it is 6 meV when temperature is below 100 K. It is also found that the dark current is dominated by the generation-recombination current for the MW device when temperature is between140 and 280 K.
基金the 973 Program of China(No.2014CB643506 and 2013CB922104)the China Scholarship Council(No.201506165038)+3 种基金the Natural Science Foundation of China(No.21673091)the Natural Science Foundation of Hubei Province(No.ZRZ2015000203)Technology Creative Project of Excellent Middle and Young Team of Hubei Province(No.T201511)the Wuhan National High Magnetic Field Center(2015KF18)is acknowledged
文摘Herein we propose a new equivalent circuit including double heterojunctions in series to simulate the current–voltage characteristic of P–I–N planar structure perovskite solar cells. This new method can theoretically solve the dilemma of the parameter diode ideal factor being larger than2 from an ideal single heterojunction equivalent circuit,which usually is in the range from 1 to 2. The diode ideal factor reflects PN junction quality, which influences the recombination at electron transport layer/perovskite and perovskite/hole transport layer interface. Based on the double PN junction equivalent circuit, we can also simulate the dark current–voltage curve for analyzing recombination current(Shockley–Read–Hall recombination) and diffusion current(including direct recombination), and thus carrier recombination and transportation characteristics. This new model offers an efficacious and simple method to investigate interfaces condition, film quality of perovskite absorbing layer and performance of transport layer, helping us furtherimprove the device efficiency and analyze the working mechanism.
