Large Dark Current Research Articles

High-Performance Devices Based on InSe-In1-xGaxSe Van der Waals Heterojunctions.

Multilayer InSe is a promising material for high-performance optoelectronic applications because of its small direct band gap and good light absorption. However, as a photoconductive photodetector, multilayer InSe photodetectors endure large dark current and high driving power. In this work, we study the electrical properties of InGaSe alloys and demonstrate the high-performance devices based on multilayer InSe-In0.24Ga0.76Se van der Waals heterojunctions (vdWHs). The electrical properties of InGaSe alloy samples strongly depend on the ratio of In to Ga, and the In0.24Ga0.76Se alloy shows a p-type transport behavior. More importantly, a multilayer InSe-In0.24Ga0.76Se vdWH device is demonstrated as a high-performance forward diode, photodiode, and self-powered photodetector (SPPD). The multilayer InSe-In0.24Ga0.76Se diode shows a high forward rectification ratio of over 103 without gate modulation at room temperature, which is superior to most of the multilayer vdWH devices. Moreover, the vdWH photodiode has a broadband photoresponse spectrum (400-1000 nm) and a high-performance photoresponse. The light switching ratio, detectivity (D*), and responsivity (R) are 103, 1012 Jones, and 49 A W-1 for 400 nm illumination, respectively. Furthermore, the vdWH SPPD also shows a sensitive photoresponse to a broadband spectrum of 400-1000 nm. Our work offers an opportunity for multilayer vdWH device applications in high-performance electronic and optoelectronic devices.

Integration of MEMS IR detectors with MIR waveguides for sensing applications.

Waveguides have been utilized for label-free and miniaturized mid-infrared gas sensors that operate on the evanescent field absorption principle. For integrated systems, photodetectors based on the photocarrier generation principle are previously integrated with waveguides. However, due to the thermal excitation of carriers at room temperature, they suffer from large dark currents and noise in the long-wavelength region. In this paper, we introduce the integration of a MEMS-based broadband infrared thermopile sensor with mid-infrared waveguides via flip-chip bonding technology and demonstrate a proof-of-concept gas (N2O) sensor working at 3.9 µm. A photonic device with input and output grating couplers designed at 3.72 µm was fabricated on a silicon-on-insulator (SOI) platform and integrated with a bare thermopile chip on its output side via flip-chip bonding in order to realize an integrated photonic platform for a myriad range of sensing applications. A responsivity of 69 mV/W was measured at 3.72 µm for an 11 mm waveguide. A second device designed at 3.9 µm has a 1800 ppm resolution for N2O sensing.

A readout integrated circuit for sensitive infrared photodetection operating in intense backgrounds

Infrared photodetection generally presents some u.ndesirable features: low detector shunt resistance, large pixel dark current, high noise levels, and intense background signal. These impose challenges to design the readout integrated electronics to properly extract signal information from the detector, mainly due to the effect of low injection efficiency and the limited on-chip voltage supply. Signal sensitivity and saturation are, therefore, often compromised. This work presents the analysis of a readout integrated circuit, coined as the Bouncing Pixel, that prevents signal saturation and that is suitable for infrared electronics due to its high injection efficiency, high sensitivity of 51.65 mV/μA and high dynamic range of at least 105 dB. The simulation data presented in this work follows an application driven design flow for a CO2 gas detection system, considering real models for the infrared light source and the photodetector, optical modeling using the HITRAN database, and reliable readout integrated circuit simulation using device models for a standard TSMC CMOS 180 nm technology. Circuit noise analysis is included. Simulations show that the detection of a CO2 molar fraction as low as 3 ppm could be achieved, suggesting that the Bouncing Pixel is a good solution for high performance infrared readout integrated electronics, even with low chip supply voltages.

Ultraviolet Photodetectors Based on CH3NH3PbCl3 Perovskite Quantum Dots‐Doped Poly(triarylamine)

Ultraviolet (UV) photodetectors have attracted significant attention because of their wide applications in environment monitoring, flame detecting, missile tracking, and so on. However, commercial UV photodetectors based on wide bandgap inorganic semiconductors normally require high‐vacuum and high‐temperature deposition techniques. To reduce the fabrication cost, solution‐processed organic or hybrid semiconductors are introduced as promising candidates for low‐cost UV detection. Particularly, due to the low cost, flexibility, and chemical variety, organic semiconductors have shown remarkable progress in the past two decades. However, UV photodetectors based on organic active layers are suffering from relatively low responsivity due to the poor charge transport. Therefore, the devices based on organic semiconductors commonly operate at high bias voltage to facilitate the charge transport, and the devices also exhibit large dark current. Herein, the organic UV active layer is doped with perovskite quantum dots (QDs) to improve the device performance. It is found that the responsivity and detectivity can effectively be enhanced by the doping strategy. Furthermore, the influence of doping effect on the charge carrier mobility and temporal response is also investigated, which shows that the mobility can be increased ≈6 times with the effective doping.

Ultrasensitive ZnO Nanowire Photodetectors with a Polymer Electret Interlayer for Minimizing Dark Current

AbstractZinc oxide (ZnO) nanowires have attracted extensive interests in ultraviolet photodetection fields owing to their outstanding optoelectronic properties. The detectivity of ZnO nanowire photodetectors is often limited by large dark current due to a number of defect‐induced carriers. Herein, a thin layer of poly(2‐vinyl naphthalene) (PVN) is introduced between the ZnO nanowire and gate dielectric to deplete defect‐induced carriers with the help of the electrostatic field generated by trapped electrons in the PVN layer. The dark current is successfully reduced from 2.2 × 10−9 to 1.6 × 10−14 A. Particularly, ZnO nanowire photodetectors with a large Ilight/Idark ratio (>107), high photoresponsivity (>106 A W−1), and ultrahigh detectivity (>1018 Jones) are achieved, which are among the best performance in reported ZnO‐based photodetectors. The present simple scheme offers a new strategy to suppress dark current in semiconducting nanomaterials for ultrasensitive photodetection applications.

A Dual-Gate MoS2 Photodetector Based on Interface Coupling Effect.

2D transition metal dichalcogenides (TMDs) based photodetectors have shown great potential for the next generation optoelectronics. However, most of the reported MoS2 photodetectors function under the photogating effect originated from the charge-trap mechanism, which is difficult for quantitative control. Such devices generally suffer from a poor compromise between response speed and responsivity (R) and large dark current. Here, a dual-gated (DG) MoS2 phototransistor operating based on the interface coupling effect (ICE) is demonstrated. By simultaneously applying a negative top-gate voltage (VTG ) and positive back-gate voltage (VBG ) to the MoS2 channel, the photogenerated holes can be effectively trapped in the depleted region under TG. An ultrahigh R of ≈105 A W-1 and detectivity (D*) of ≈1014 Jones are achieved in several devices with different thickness under Pin of 53 µW cm-2 at VTG = -5 V. Moreover, the response time of the DG phototransistor can also be modulated based on the ICE. Based on these systematic measurements of MoS2 DG phototransistors, the results show that the ICE plays an important role in the modulation of photoelectric performances. The results also pave the way for the future optoelectrical application of 2D TMDs materials and prompt for further investigation in the DG structured phototransistors.

A Highly Responsive Organic Image Sensor Based on a Two‐Terminal Organic Photodetector with Photomultiplication

Highly responsive organic image sensors are crucial for medical imaging applications. To enhance the pixelwise photoresponse in an organic image sensor, the integration of an organic photodetector with amplifiers, or the use of a highly responsive organic photodetector without an additional amplifying component, is required. The use of vertically stacked, two-terminal organic photodetectors with photomultiplication is a promising approach for highly responsive organic image sensors owing to their simple two-terminal structure and intrinsically large responsivity. However, there are no demonstrations of an imaging sensor array using organic photomultiplication photodetectors. The main obstacle to a sensor array is the weak-light sensitivity, which is limited by a relatively large dark current. Herein, a highly responsive organic image sensor based on monolithic, vertically stacked two-terminal pixels is presented. This is achieved using pixels of a vertically stacked diode-type organic photodetector with photomultiplication. Furthermore, applying an optimized injection electrode and additionally stacked rectifying layers, this two-terminal device simultaneously demonstrates a high responsivity (>40 A W-1 ), low dark current, and high rectification under illumination. An organic image sensor based on this device with an extremely simple architecture exhibits a high pixel photoresponse, demonstrating a weak-light imaging capability even at 1 µW cm-2 .

Role of ZrO2 Passivation Layer Thickness in the Fabrication of High‐Responsivity GaN Ultraviolet Photodetectors

The importance of a ZrO2 passivation layer in the fabrication of high‐responsivity GaN‐based ultraviolet (UV) photodetectors (PDs) is discussed. It is found that an optimum thickness of the ZrO2 layer exists, which plays a critical role in controlling the photoresponse and transient response of the device. Beyond the optimal thickness, the performance of PDs deteriorates, which is limited by the restricted tunneling of photogenerated carriers across the oxide layer. At an optimum ZrO2 thickness of 3 nm, a spectral responsivity of 27 A W−1 at 361 nm is achieved at 4 V applied bias along with the fast response of the device with a rise (fall) time of 28 ms (178 ms), respectively. Such characteristics are found to be similar or better than the recently reported state‐of‐the‐art values for visible blind metal–semiconductor–metal PDs fabricated on GaN. The results confirm that the surface passivation with an optimal thickness of an oxide layer can be used to develop high‐responsivity GaN‐based UV PDs irrespective of having a large dark current, which is often inevitable due to the presence of a large density of dislocations in GaN epitaxial layers grown on foreign substrates.

Built-in electric field promotes photoexcitation separation and depletion of most carriers in TiO2:C UV detectors

TiO2 has been widely used in ultraviolet (UV) photodetectors, but due to the large number of structural defects and strong band-to-band recombination of the exciton in TiO2, the devices usually have large dark current (Id) and low light current (Il), which seriously reduces the sensitivity and responsivity (R) of the TiO2 based devices. In this work, carbon (C) quantum dots (QDs) are introduced into TiO2 film to ameliorate these issues. Due to the difference of work function between TiO2 nanoparticles and C QDs, the built-in electric field (Ebi) can be formed, which effectively facilitates the photogenerated exciton dissociation in the TiO2 film under UV illumination. Meanwhile, the constructed depletion region in dark reduces the majority carrier density, thus decreasing the Id of the photodetector. Moreover, the Ebi and depletion region will also contribute to the faster charge collection under UV illumination and recombination of the electron in dark, which is beneficial for the improved response/recovery speed of the device.

High-speed van der Waals heterostructure tunneling photodiodes integrated on silicon nitride waveguides

Graphene photodetectors can have broadband operation and a large bandwidth, but they usually suffer from a large dark current when biased. To solve this problem, we demonstrate van der Waals heterostructure tunneling photodiodes integrated on silicon nitride waveguides. The heterostructure is made up of layers of molybdenum disulfide, graphene, boron nitride, and graphene from bottom to top. The bottom graphene is n-doped by molybdenum disulfide while the top graphene layer remains p-doped. Between the two graphene layers, multilayer boron nitride was employed as a tunneling barrier. At ∼1550 nm, high on/off current ratios larger than 104 were measured in the dark. A responsivity of ∼0.24 A/W and a bandwidth of 28 GHz (56 GHz by deconvolving response of experimental system) were also obtained.

Self-powered behavior based on the light-induced self-poling effect in perovskite-based transport layer-free photodetectors

A transport layer-free CH3NH3PbI3 photodetector utilizing light-induced self-poling effect leads to a self-powered photodetector with large switch ratio and low dark current.

Performance Enhancement of Graphene Photodetectors via In Situ Preparation of TiO2 on Graphene Channels

AbstractGraphene has been considered a promising material for high‐performance photodetectors due to its broad light‐absorption bandwidth and fast photoresponse time. However, weak light absorption (2.3%) in monolayer graphene results in the relatively low photoresponsivity of graphene photodetectors (GPDs). Moreover, the operation stability of GPDs has become another commercialization bottleneck due to the environmental sensitivity of graphene materials. Hence, developing a compact GPD with high photoresponsivity and high stability is critical and significant. Here, an in situ, thermally oxidized TiO2 layer is used to enhance both the photoresponsivity and stability of a metal–graphene–metal photodetector. Moreover, the fabricated GPDs operate well under zero bias, avoiding the large dark current produced in traditional GPDs. These results address key challenges for high‐performance photodetectors and are promising for the development of complementary metal–oxide–semiconductor compatible graphene‐based optoelectronic applications, such as monolithic optoelectronic‐integrated broadband image sensor chips.

Room-Temperature Ultrabroadband Photodetection with MoS2 by Electronic-Structure Engineering Strategy.

Photodetection using semiconductors is critical for capture, identification, and processing of optical information. Nowadays, broadband photodetection is limited by the underdeveloped mid-IR photodetection at room temperature (RT), primarily as a result of the large dark currents unavoidably generated by the Fermi-Dirac distribution in narrow-bandgap semiconductors, which constrains the development of some modern technologies and systems. Here, an electronic-structure strategy is proposed for designing ultrabroadband covering mid- and even far-IR photodetection materials operating at RT and a layered MoS2 is manifested with an engineered bandgap of 0.13 eV and modulated electronic state density. The sample is designed by introducing defect energy levels into layered MoS2 and its RT photodetection is demonstrated for wavelengths from 445 nm to 9.5 µm with an electronic state density-dependent peak photoresponsivity of 21.8 mA W-1 in the mid-IR region, the highest value among all known photodetectors. This material should be a promising candidate for modern optoelectronic devices and offers inspiration for the design of other optoelectronic materials.

Visible-infrared dual-mode MoS2-graphene-MoS2 phototransistor with high ratio of the Iph/Idark

2D materials such as graphene and transition metal dichalcogenides exhibit novel electrical and optoelectrical properties, which are promising for the application in sensing and imaging. However, the photoresponse ability of pure monolayer graphene in room temperature and ratio of Iph and Idark are still unsatisfactory, due to the weak light absorption itself, short lifetime of photo-excited carriers and large dark current, especially in the infrared range. Here, we successfully constructed a broadband graphene-based phototransistor consisting of lateral MoS2-graphene-MoS2 heterostructure by chemical vapor deposition technique. It shows broadband photodetection and a low dark current less than 1 pA at applied bias of 0.5 V, resulting in excellent specific detectivity more than 1012 Jones and nearly 109 Jones in visible and infrared band, respectively. Moreover, the ratio of Iph and Idark could be modulated by the back-gate voltage when the phototransistor is under the infrared illumination. And a high ratio of 105 was exhibited. This type of graphene-based phototransistor by chemical vapor deposition demonstrates an approach for the room temperature broadband photodetection of monolayer graphene by energy engineering. All the results address key challenges for broadband detection by graphene-based phototransistor, and are promising for the large scale fabrication and integration in the future electronic and optoelectronic applications.

WSe2/Au vertical Schottky junction photodetector with low dark current and fast photoresponse

Atomically thin two-dimensional materials including graphene, transition metal dichalcogenides, black phosphorus and so forth have been considered as promising channel medias for electronic and optoelectronic devices in the past few years. However, the poor photoresponse time and the large dark current are the two major issues which greatly block their applications. Here, we report a vertical Au–WSe2–ITO (indium tin oxide) Schottky junction photodetector with a broadband photoresponse from 550–950 nm and a stable photovoltaic responsivity of ∼0.1 A W−1. The fast photoresponse of ∼50 μs and low dark current of ∼1 pA are achieved at the vertical Au–WSe2–ITO photodetector. These results indicate that metal contact to a 2D material-based vertical Schottky junction can achieve an excellent photoelectric response.

Ultrasensitive Room‐Temperature Terahertz Direct Detection Based on a Bismuth Selenide Topological Insulator

AbstractDespite their huge application capabilities, millimeter‐ and terahertz‐wave photodetectors still face challenges in the detection scheme. Topological insulators (TIs) are predicted to be promising candidates for long‐wavelength photodetection, due to the presence of Dirac fermions in their topologically protected surface states. However, photodetection based on TIs is usually hindered by the large dark current, originating from the mixing of bulk states with topological surface states (TSSs) in most realistic samples of TIs. Here millimeter and terahertz detectors based on a subwavelength metal–TI–metal (MTM) heterostructure are demonstrated. The achieved photoresponse stems from the asymmetric scattering of TSS, driven by the localized surface plasmon‐induced terahertz field, which ultimately produces direct photocarriers beyond the interband limit. The device enables high responsivity in both the self‐powered and bias modes even at room temperature. The achieved responsivity is over 75 A/W, with response time shorter than 60 ms in the self‐powered mode. Remarkably, the responsivity increases by several orders of magnitude in the biased configuration, with the noise‐equivalent power (NEP) of 3.6 × 10−13 W Hz−1/2 and a detectivity of 2.17 × 1011 cm Hz−1/2 W−1 at room temperature. The detection performances open a way toward realistic exploitation of TIs for large‐area, real‐time imaging within long‐wavelength optoelectronics.

High-Performance Photodetectors Based on Single All-Inorganic CsPbBr3 Perovskite Microwire

In recent years, hybrid organic–inorganic perovskites have emerged as promising photosensing materials for next-generation solution-processed photodetectors, achieving high responsivity, fast speed, and large linear dynamic range. In particular, perovskite photoresistors possess low-cost fabrication and easy integration with low dimensional structures. However, a relatively large dark current is still limiting the further development of perovskite photoresistors. Herein, we introduce full-inorganic perovskite polycrystalline microwires for high-performance photodetection, in order to enhance the device stability. Furthermore, dark current and noise can be effectively suppressed by tuning the contacts. All-inorganic CsPbBr3 microwires with a number of nanocrystals on the wire surface are prepared by a simple, low-cost, two-step, solution-processed method at room temperature. Photodetectors based on this CsPbBr3 polycrystalline single microwire are assembled on indium tin oxide electrodes and demonstrate a ...

Carrier Dynamics of Nanopillar Textured Ultrathin Si Film/PEDOT:PSS Heterojunction Solar Cell

Computational study of nanopillar Si/poly (3,4-ethylene dioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) heterojunction solar cell is performed by using finite element method to solve Poisson equation, drift-diffusion equations, and current continuity equations. The depletion width around the edge of the Si nanopillar is almost the same as that of planar junction, while the depletion width around the middle of the Si nanopillar is much wider than that of planar junction. As a result, besides the enhanced light absorption due to light trapping induced by nanopillar array as in previous studies, larger depletion region, which leads to higher electron-hole separation efficiency under light illumination, is another reason for short-circuit current increase of nanopillar solar cell. The reason for less open-circuit voltage of nanopillar solar cell is also clarified by explaining the reason for large dark current of the nanopillar solar cell compared to its planar structure counterpart as follows. The kink of the potential profile along the lines around the edge nanopillar leads to much sharper potential drop in the following depletion region, and results in greater hole density slope when the solar cells are forwarded biased. Since the Si/PEDOT:PSS behaves like a pn junction rather than a Schottky junction as clarified in the previous study and the PEDOT:PSS is much highly doped, nanopillar heterojunction has larger dark current than planar junction due to the larger hole diffusion current around Si nanopillar edge.

Laterally Biased Quantum-Well Infrared Photodetectors Operating at Room Temperature With Low Dark Currents

The technology of quantum-well infrared photodetectors has been used to fabricate focal plane arrays as the active element of infrared cameras. These arrays must be cooled down to 77 K due to the large dark current that they exhibit at higher operating temperatures. Among the different alternatives proposed to overcome this drawback, the lateral conduction scheme has been successfully employed in quantum-dot and dot-in-a-well detectors to increase their operating temperature. In these devices, the photocurrent is collected by means of two lateral Ohmic contacts on each side of an undoped quantum well and is swept out via a lateral bias voltage. However, this lateral-carrier-transport scheme has not yet been applied to the mature technology of the GaAs/(Al,Ga)As quantum-well infrared photodetectors. We demonstrate two mechanisms to develop laterally biased quantum-well infrared photodetectors. The resulting devices exhibit high differential resistance as well as low dark current values and clear infrared absorption peaks at 300 K, in good agreement with the results of numerical simulations. This work demonstrates the viability of the laterally biased structures for future developments of room temperature focal plane arrays.

High Performance BiOCl Nanosheets/TiO2 Nanotube Arrays Heterojunction UV Photodetector: The Influences of Self‐Induced Inner Electric Fields in the BiOCl Nanosheets

AbstractBiOCl nanosheets/TiO2 nanotube arrays heterojunction UV photodetector (PD) with high performance is fabricated by a facile anodization process and an impregnation method. The heterojunction at the interface and the internal electric fields in the BiOCl nanosheets faciliate the separation of photogenerated charge carriers and regulate the transportation of the electrons. Compared with the large dark current (≈10−5 A), low on/off ratio (8.5), and slow decay time (>60 s) of the TiO2 PD, the optimized heterojunction PD (6‐BiOCl–TiO2) yields dramatically decreased dark current (≈1 nA), ultrahigh on/off ratio (up to 2.2 × 105), and fast decay speed (0.81 s) under 350 nm light illumination at −5 V. Moreover, it exhibits an increased responsivity of 41.94 A W−1, a remarkable detectivity (D*) of 1.41 × 1014 Jones, and a high linear dynamic range of 103.59 dB. The loading amount and growth orientations of the BiOCl nanosheets alter the roles of the self‐induced internal electric field in regulating the behaviors of the charge carriers, thus affecting the photoelectric properties of the heterojunction PDs. These results demonstrate that rational construction of novel heterojunctions hold great potentials for fabricating photodetectors with high performance.