Numerical Simulation and Analysis of Bipolar Junction Photogate Transistor for CMOS Image Sensor

A new photodetector--bipolar junction photogate transistor is presented for CMOS image sensor and its analytical model is also established.With the technical parameter of the 0.6μm CMOS process,the bipolar junction photogate transistor is analyzed and simulated.The simulated results illustrate that the bipolar junction photogate transistor has the similar characteristics of the traditional photogate transistor.The photocurrent density of the bipolar junction photogate transistor increases exponentially with the incidence light power due to introducing the injection p+n junction.Its characteristic of blue response is rather improved compared to the traditional photogate transistor that benefits to increase the color photograph made up of the red,the green,and the blue.

High responsivity photodetectors based on graphene/WSe_(2) heterostructure by photogating effect

Graphene, with its zero-bandgap electronic structure, is a highly promising ultra-broadband light absorbing material.However, the performance of graphene-based photodetectors is limited by weak absorption efficiency and rapid recombination of photoexcited carriers, leading to poor photodetection performance. Here, inspired by the photogating effect, we demonstrated a highly sensitive photodetector based on graphene/WSe_(2) vertical heterostructure where the WSe_(2) layer acts as both the light absorption layer and the localized grating layer. The graphene conductive channel is induced to produce more carriers by capacitive coupling. Due to the strong light absorption and high external quantum efficiency of multilayer WSe_(2), as well as the high carrier mobility of graphene, a high photocurrent is generated in the vertical heterostructure. As a result, the photodetector exhibits ultra-high responsivity of 3.85×10~4A/W and external quantum efficiency of 1.3 × 10~7%.This finding demonstrates that photogating structures can effectively enhance the sensitivity of graphene-based photodetectors and may have great potential applications in future optoelectronic devices.

A novel wide-dynamic-range logarithmic-response bipolar junction photogate transistor for CMOS imagers

In this paper, a new photodetector, bipolar junction photogate transistor (BJPG), is proposed for CMOS imagers. Due to an injection p+n junction introduced, the photo-charges drift through the p+n junction by the applied electronic field, and on the other hand, the p+n junction injects the carriers into the channel to carry the photo-charges. Therefore this device can increase the readout rate of the pixel signal charges and the photoelectron transferring efficiency. Using this new device, a new type of logarithmic pixel circuit is obtained with a wide dynamic range which makes photo-detector more suitable for imaging the naturally illuminated scenes. The simulations show that the photo current density of BJPG increases logarithmically with the incident light power due to the introduced injection p+n junction. The noise characteristics of BJPG are analyzed in detail and a new gate-induced noise is proposed. Based on the established numerical analytical model of noise, the power spectrum density curves are simulated.

Hybrid Field-Effect Transistors and Photodetectors Based on Organic Semiconductor and CsPbI_3 Perovskite Nanorods Bilayer Structure

The outstanding performances of nanostructured allinorganic CsPbX_3(X = I, Br, Cl) perovskites in optoelectronic applications can be attributed to their unique combination of a suitable bandgap, high absorption coefficient, and long carrier lifetime, which are desirable for photodetectors. However, the photosensing performances of the CsPbI_3 nanomaterials are limited by their low charge-transport efficiency. In this study, a phototransistor with a bilayer structure of an organic semiconductor layer of 2,7-dioctyl [1] benzothieno[3,2-b] [1] benzothiophene and CsPbI_3 nanorod layer was fabricated. The high-quality CsPbI_3 nanorod layer obtained using a simple dip-coating method provided decent transistor performance of the hybrid transistor device.The perovskite layer efficiently absorbs light, while the organicsemiconductor layer acts as a transport channel for injected photogenerated carriers and provides gate modulation. The hybrid phototransistor exhibits high performance owing to the synergistic function of the photogating effect and field effect in the transistor,with a photoresponsivity as high as 4300 A W^(-1), ultra-high photosensitivity of 2.2 9 106, and excellent stability over 1 month.This study provides a strategy to combine the advantages of perovskite nanorods and organic semiconductors in fabrication of high-performance photodetectors.

Localized electric-field-enhanced low-light detection by a 2D SnS visible-light photodetector

Due to their excellent carrier mobility,high absorption coefficient and narrow bandgap,most 2D IVA metal chalcogenide semiconductors(GIVMCs,metal=Ge,Sn,Pb;chalcogen=S,Se)are regarded as promising candidates for realizing high-performance photodetectors.We synthesized high-quality two-dimensional(2D)tin sulfide(SnS)nanosheets using the physical vapor deposition(PVD)method and fabricated a 2D SnS visible-light photodetector.The photodetector exhibits a high photoresponsivity of 161 A·W-1 and possesses an external quantum efficiency of 4.45×10^(4)%,as well as a detectivity of 1.15×10^(9) Jones under 450 nm blue light illumination.Moreover,under poor illumination at optical densities down to 2 mW·cm^(-2),the responsivity of the device is higher than that at stronger optical densities.We suggest that a photogating effect in the 2D SnS photodetector is mainly responsible for its low-light responsivity.Defects and impurities in 2D SnS can trap carriers and form localized electric fields,which can delay the recombination process of electron-hole pairs,prolong carrier lifetimes,and thus improve the low-light responsivity.This work provides design strategies for detecting low levels of light using photodetectors made of 2D materials.

原位集成光浮栅的多层SnS_(2)/少层MoS_(2)异质结用于高性能光电探测器与光学成像

自单层MoS_(2)光电晶体管问世以来,二维层状材料一直被认为是实现下一代新型光电器件与系统的最引人瞩目的候选材料之一.然而,大多数报道的二维层状材料光电探测器都存在一定的缺点,如响应率低、暗电流大、比探测率低、开关比低、响应速率慢等.在本研究中,通过堆叠由大气压化学气相沉积技术所生长的MoS_(2)和SnS_(2)纳米片,制备出了多层SnS_(2)/少层MoS_(2)范德华异质结.相应的SnS_(2)/MoS_(2)异质结光电探测器展示出了具有竞争力的综合性能:大开关比(171)、高响应率(28.3 A W^(-1)),以及出色的比探测率(1.2×10^(13)Jones).此外,该器件还实现了响应/恢复时间低至1.38 ms/600μs的超快响应速率.其优异的性能与SnS_(2)/MoS_(2)异质结的Ⅱ型能带排列以及原位形成的无缝光浮栅的协同作用相关,这有助于分离光激发的电子-空穴对,并延长非平衡载流子的寿命.得益于出色的光敏性,该SnS_(2)/MoS_(2)器件实现了概念验证的光学成像应用.总体而言,本研究为实现具有优异综合性能的先进光电探测器提供了独特视角.

High-performance ultraviolet-visible photodetector with high sensitivity and fast response speed based on MoS_(2)-on-ZnO photogating heterojunction

Photogating is an effective strategy to modulate the channel conductance of the device with light-induced gate field or voltage,thereby improving the performance of optoelectronic devices.In this work,to overcome the long response time and low photoresponse of one-dimensional ZnO,a MoS_(2)-on-ZnO photogating vertical heterojunction photodetector is design and constructed.Herein,the ZnO nanowire with high carrier mobility can response ultraviolet light and supply a highspeed carrier transport channel,while the MoS_(2) flake as a photogating layer can response with visible light and transfer photogenerated electrons into the ZnO nanowire to adjust its conductivity.Thus,the irradiation of visible light is equivalent to applying a photo-induced gate voltage on the ZnO nanowire.In addition,the photogenerated electrons will not transmit through the MoS_(2) with low carrier mobility,so that not only the visible light response of the photodetector can be realized,but also its ultraviolet light response is able to be improved.Under ultraviolet light irradiation,the photoresponsivity of the photodetector can be reached to 273 A W-1and the response speed is less than 24 ms.More important,based on this unique heterojunction structure,MoS_(2)-on-ZnO photodetector also illustrates an excellent visible light response with a high photoresponsivity(74 A W-1) and fast response speed(<24 ms) due to the photogating effect.This work not only paves the way to design high-performance photodetectors with high photoresponsivity and fast response speed,but also provide a promising approach to improve the performance of optoelectronic devices using photogating effect.

Retinomorphic hardware for in-sensor computing

Rapid developments in the Internet of Things and Artificial Intelligence trigger higher requirements for image perception and learning of external environments through visual systems.However,limited by von Neumann's bottleneck,the physical separation of sense,memory,and processing units in a conventional personal computer-based vision system tend to consume a significant amount of energy,time latency,and additional hardware costs.By integrating computational tasks of multiple functionalities into the sensors themselves,the emerging bio-inspired neuromorphic visual systems provide an opportunity to overcome these limitations.With high speed,ultralow power and strong adaptability,it is highly desirable to develop a neuromorphic vision system that is based on highly precise in-sensor computing devices,namely retinomorphic devices.We here present a timely review of retinomorphic devices for visual in-sensor computing.We begin with several types of physical mechanisms of photoelectric sensors that can be constructed for artificial vision.The potential applications of retinomorphic hardware are,thereafter,thoroughly summarized.We also highlight the possible strategies to existing challenges and give a brief perspective of retinomorphic architecture for in-sensor computing.

High Responsivity and Ultra-Low Detection Limits in Nonlinear a-Si:H p-i-n Photodiodes Enabled by Photogating

Photodetectors operating at the wavelength in the visible spectrum are key components in high-performance optoelectronic systems.In this work,massive nonlinearities in amorphous silicon p-i-n photodiodes enabled by the photogating are presented,resulting in responsivities up to 744 mA/W at blue wavelengths.The detectors exhibit significant responsivity gains at optical modulation frequencies exceeding MHz and a more than 60-fold enhanced spectral response compared to the non-gated state.The detection limits down to 10.4 nW/mm^(2) and mean signal-to-noise ratio enhancements of 8.5dB are demonstrated by illuminating the sensor with an additional 6.6μW/mm^(2) red wavelength.Electro-optical simulations verify photocarrier modulation due to defect-induced field screening to be the origin of such high responsivity gains.The experimental results validate the theory and enable the development of commercially viable and complementary metal oxide semiconductor(CMOS)compatible high responsivity photodetectors operating in the visible range for low-light level imaging and detection.

Enhanced NO_2 gas sensing of a single-layer MoS_2 by photogating and piezo-phototronic effects

NO_2 sensors with ultrahigh sensitivity are demanded for future electronic sensing systems. However,traditional sensors are considerably limited by the relative low sensitivity, high cost and complicated process. Here, we report a simply and reliable flexible NO_2 sensor based on single-layer MoS_2. The flexible sensor exhibits high sensitivity to NO_2 gas due to ultra-large specific surface area and the nature of two-dimensional(2 D) semiconductor. When the NO_2 is 400 ppb(parts per billion), compared with the dark and strain-free conditions, the sensitivity of the single-layer sensor is enhanced to 671% with a625 nm red light-emitting diode(LED) illumination of 4 mW/cm^2 power under 0.67% tensile strain.More important, the response time is dramatically reduced to $16 s and it only needs $65 s to complete90% recovery. A theoretical model is proposed to discuss the microscopic mechanisms. We find that the remarkable sensing characteristics are the result of coupling among piezoelectricity, photoelectricity and adsorption-desorption induced charges transfer in the single-layer MoS_2 Schottky junction based device.Our work opens up the way to further enhancements in the sensitivity of gas sensor based on single-layer MoS_2 by introducing photogating and piezo-phototronic effects in mesoscopic systems.

Perovskite/organic-semiconductor heterojunctions for ultrasensitive photodetection

Broadband photodetectors with unprecedented responsivity were reported.It widens the application of organometal halide perovskites in highly sensitive,low-cost and flexible photodetectors.The fundamental device physics revealed will have significant impact on the design of future ultrasensitive photodetectors and other optoelectronic devices.

吃奖 Felix Streuli的烧烤赛季

猎物是狩猎者的奖状,面对烧烤赛季,拿什么来彰表那些卓尔不凡的BBQ冠军?瑞士著名摄影师FelixStreuli操刀的这个食品创意系列结合了原本风马牛不相及的两种意象。