Low Dark Current Research Articles

High quality quasi-two-dimensional organic–inorganic hybrid halide perovskite film for high performance photodetector

Two-dimensional (2D) Ruddlesden–Popper perovskites have attracted extensive attention in photodetectors (PDs) due to their exceptional optoelectronic properties. The performances of PDs show extremely strong dependence on defects in 2D perovskites. Herein, high quality and less defective BA2FAPb2I7 perovskite films were obtained by a simple one-step spin coating method with rare earth doping assisted crystal growth. Furthermore, BA2FAPb2I7 perovskite films were used as photoresponsive materials to fabricate architectural simplicity photoconductor PDs. Under 405 nm laser illumination, the PDs show remarkable balance detect properties with a low dark current of 5.1 × 10−11 A, a large on/off ratio of 2.2 × 105, a high responsivity (R) of 4.51 A/W, an outstanding detectivity Dshot* of 4.31 × 1013 Jones, and a response speed of 80 μs/76 μs. The R and Dshot* of the PDs are outstanding in the reported quasi-2D perovskite PDs with the same structure. Our work not only paves an indubitably feasible way for fabrication of quasi-2D perovskite PDs via improving their natural material properties but also provides a clear direction for further enhancing the performance of other perovskites optoelectronics.

Self-Powered Photodetector Based on a Ag Nanoparticle-Decorated Gd2O3 Nanorod

A self-powered photodetector based on a silver nanoparticle (Ag NP)-decorated gadolinium oxide nanorod (Gd2O3 NR) has been deposited using the glancing angle deposition (GLAD) technique. Field emission gun scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM) analyses confirm the successful growth of a Ag NP-decorated Gd2O3 NR with polycrystalline nature. UV–vis spectroscopy reveals the presence of the Ag NP and Gd2O3 NR with photon absorption in visible and UV regions. The electrical analysis was studied for the voltage range of −5 to 5 V. The device demonstrated self-powered characteristics with a significantly low dark current of 0.73 nA. In addition, the device also displayed a stable switching response with a rise/fall time of 0.18/0.17 s at 0 V. Moreover, the device obtained good responsivity (11.8 mA/W) with a high detectivity of 7.63 × 1011 Jones and a low noise equivalent power of 3.67 × 10–12 W at 0 V.

Facile integration of an Al-rich Al1–x In x N photodetector on free-standing GaN by radio-frequency magnetron sputtering

Al1−x In x N, a III-nitride semiconductor material, is currently of great research interest due to its remarkable physical properties and chemical stability. When the Al and In compositions are tuned, its band-gap energy varies from 0.7 eV to 6.2 eV, which shows great potential for application in photodetectors. Here, we report the fabrication and performance evaluation of integrated Al1−x In x N on a free-standing GaN substrate through direct radio-frequency magnetron sputtering. The optical properties of Al1−x In x N will be enhanced by the polarization effect of a heterostructure composed of Al1−x In x N and other III-nitride materials. An Al1−x In x N/GaN visible-light photodetector was prepared by semiconductor fabrication technologies such as lithography and metal deposition. The highest photoresponsivity achieved was 1.52 A⋅W−1 under 365 nm wavelength illumination and the photodetector was determined to have the composition Al0.75In0.25N/GaN. A rise time of 0.55 s was observed after transient analysis of the device. The prepared Al1−x In x N visible-light photodetector had a low dark current, high photoresponsivity and fast response speed. By promoting a low-cost, simple fabrication method, this study expands the application of ternary alloy Al1−x In x N visible-light photodetectors in optical communication.

High-Performance Colloidal Quantum Dot Photodiodes via Suppressing Interface Defects.

PbS colloidal quantum dot (CQD) infrared photodiodes have attracted wide attention due to the prospect of developing cost-effective infrared imaging technology. Presently, ZnO films are widely used as the electron transport layer (ETL) of PbS CQDs infrared photodiodes. However, ZnO-based devices still suffer from the problems of large dark current and low repeatability, which are caused by the low crystallinity and sensitive surface of ZnO films. Here, we effectively optimized the device performance of PbS CQDs infrared photodiode via diminishing the influence of adsorbed H2O at the ZnO/PbS CQDs interface. The polar (002) ZnO crystal plane showed much higher adsorption energy of H2O molecules compared with other nonpolar planes, which could reduce the interface defects induced by detrimentally adsorbed H2O. Based on the sputtering method, we obtained the [002]-oriented and high-crystallinity ZnO ETL and effectively suppressed the adsorption of detrimental H2O molecules. The prepared PbS CQDs infrared photodiode with the sputtered ZnO ETL demonstrated lower dark current density, higher external quantum efficiency, and faster photoresponse compared with the sol-gel ZnO device. Simulation results further unveiled the relationship between interface defects and device dark current. Finally, a high-performance sputtered ZnO/PbS CQDs device was obtained with a specific detectivity of 2.15 × 1012 Jones at -3 dB bandwidth (94.6 kHz).

High-Performance Photodetector with a-IGZO/PbS Quantum Dots Heterojunction

Low cost, high absorption coefficient, tunable band gap, and compatibility with flexible devices make lead sulfide (PbS) quantum dots (QDs) based photoconductors promising candidates for next-generation near-infrared (NIR) photodetectors. However, the detection performance of PbS QDs-based photoconductors still needs to be further improved, because there is a trade-off among the responsivity/detectivity/bandwidth in the device development process, that is, it is difficult to improve the three parameters simultaneously. Inspired by the design idea of sensitized phototransistor, a kind of amorphous indium gallium zinc oxide (a-IGZO)/PbS QDs heterojunction photoconductor is reported in this paper. The most prominent feature of this work is that a-IGZO, like a photocurrent “amplifier”, increases the photocurrent by several orders of magnitude without generating additional noise, and thus improves the sensitivity and responsiveness of the device. Compared with the initial pure PbS QDs-based photoconductor, the heterojunction device is able to increase the photocurrent by 3000 times together with a low dark current, and improve the response speed of the device with the help of interface-assisted carrier separation and recombination. In the NIR band, the device exhibits an exciting performance with a detectivity of 1.53 × 1013 Jones, a responsivity of 19070 mA/W and a decay time of 0.39 ms, respectively. By applying the a-IGZO/PbS QDs heterojunction to paper-based devices, a flexible device with bending resistance can be obtained, and the detection performance of the device does not deteriorate after 1000 times of bending.

High-performance photodetector based on semi-encompassed CH3NH3PbCl3–ZnO microwire heterojunction with alterable spectral response

Recently, heterojunctions consisting of hybrid organic-inorganic lead (Pb) halide perovskites and other semiconductors have drawn increasing attention for the potential application in photodetectors due to their exceptional performance. However, their performance is usually limited by the relatively low crystalline quality of perovskites, and the response spectra of the devices are difficult to adjust according to the practical requirement. Here, high quality CH3NH3PbCl3 micro-sized crystals have been successfully fabricated on one side of individual ZnO microwire to form heterojunction photodetector by a two-step crystallization method. The heterojunction device presents a low dark current (60 nA at −6 V) along with a rapid response speed (rise time of <20 μs and fall time of ∼500 μs). More interestingly, the modulation of the response spectra and the responsivity can be realized by operating the device under front or back illumination due to the self-filtering properties. Our findings provide a promising method for combining perovskites with other inorganic materials to form high-performance heterojunction photodetectors.

Vitality surveillance at distance using thin-film tandem-like narrowband near-infrared photodiodes with light-enhanced responsivity

Remote measurement of vital sign parameters like heartbeat and respiration rate represents a compelling challenge in monitoring an individual's health in a noninvasive way. This could be achieved by large field-of-view, easy-to-integrate unobtrusive sensors, such as large-area thin-film photodiodes. At long distances, however, discriminating weak light signals from background disturbance demands superior near-infrared (NIR) sensitivity and optical noise tolerance. Here, we report an inherently narrowband solution-processed, thin-film photodiode with ultrahigh and controllable NIR responsivity based on a tandem-like perovskite-organic architecture. The device has low dark currents (<10-6 mA cm-2), linear dynamic range >150 dB, and operational stability over time (>8hours). With a narrowband quantum efficiency that can exceed 200% at 850 nm and intrinsic filtering of other wavelengths to limit optical noise, the device exhibits higher tolerance to background light than optically filtered silicon-based sensors. We demonstrate its potential in remote monitoring by measuring the heart rate and respiration rate from distances up to 130 cm in reflection.

Selective Enhancement of Photoresponse with Ferroelectric-Controlled BP/In2 Se3 vdW Heterojunction.

Owing to the large built-in field for efficient charge separation, heterostructures facilitate the simultaneous realization of a low dark current and high photocurrent. The lack of an efficient approach to engineer the depletion region formed across the interfaces of heterojunctions owing to doping differences hinders the realization of high-performance van der Waals (vdW) photodetectors. This study proposes a ferroelectric-controlling van der Waals photodetector with vertically stacked two-dimensional (2D) black phosphorus (BP)/indium selenide (In2 Se3 ) to realize high-sensitivity photodetection. The depletion region can be reconstructed by tuning the polarization states generated from the ferroelectric In2 Se3 layers. Further, the energy bands at the heterojunction interfaces can be aligned and flexibly engineered using ferroelectric field control. Fast response, self-driven photodetection, and three-orders-of-magnitude detection improvements are achieved in the switchable visible or near-infrared operation bands. The results of the study are expected to aid in improving the photodetection performance of vdW optoelectronic devices.

A Novel Low Dark Current 9T Global Shutter Pixel with Merged Active Area

There is an increasing demand for high-performance global shutter pixels for CMOS image sensor (CIS) in the high-end imaging field. The existing global pixels have disadvantages, such as low sensitivity, high dark current, and large pixel area. In the present work, we developed a novel 9T global shutter CIS pixel with a much smaller pixel pitch of 2.8 μm. To our knowledge, it is the most miniature reported 9T global shutter CIS pixel. The developed 9T global shutter CIS pixel shows an excellent low dark current by the strategy of merging active area, which is 38 e−/s. Moreover, the cross-talk, sensitivity, read noise, dynamic range and full well capacity show performance. The current strategy is expected to be helpful in further improving the performance of other kinds of CIS pixels.

Phenomenon of photo-regulation on gold/diamond Schottky barriers and its detector applications

A thickness asymmetric electrode structure on an oxygen-terminated type IIa diamond was designed and prepared (one electrode was semitransparent to ultraviolet light and the other blocked the transmission of ultraviolet light). This structure exhibited an apparent photo-induced rectification property under irradiation by a deuterium lamp. This is attributed to the mechanism by which the light penetrating the electrode reduces the metal–diamond contact barrier. Furthermore, we developed a light-modulated Schottky barrier diamond photodetector based on this mechanism. Solar-blind light can lower the Schottky barrier height in situ in the presence of light, which significantly enhances the photocurrent. However, the Schottky barrier is not reduced by light regulation when there is no light; therefore, the low dark current of the detector is still guaranteed. Compared with the non-photo-regulated Schottky barrier detector, the photo-regulated Schottky barrier detector exhibits a 128% increase in responsivity at 220 nm under a 1.6 V/μm bias. For such an obvious difference in detection performance, this mechanism has rarely been a focus of studies on diamond detectors. In addition to diamond detectors, light-modulated barrier technology can also be applied to other fields related to the diamond surface potential, such as color center control and Schottky diodes; it can also be used to control or evaluate device performance.

High-Performance Cascaded Surface-Illuminated Ge-on-Si APD Array

In this letter, we report a cascaded surface-illuminated Germanium-on-Silicon (Ge-on-Si) avalanche photodiode (APD) array with a low dark current. The photodetector array cascades seven Ge-on-Si APDs through interconnecting the charge regions to form photomultiplier tubesiPMTjC which increases the effective light absorption area compared to the single APD scheme. To the best of our knowledge, this is the first time that Ge-on-Si PMT has been reported. The optimum response of single-electrode (2 pixels) Ge-on-Si APD is 2.4 A/W with a dark current of 100 nA, and the optimum bandwidth is 52 MHz. PMT has a responsivity of approximately 3 times that of a single-electrode Ge-on-Si APD for the same dark current (100 nA). With low dark current, our PMT has a better optical amplification effect than the parallel Ge-on-Si PD. We have also further tested the current tuning properties of the Ge-on-Si APD arrays with different applied Ge voltages. The test demonstrates the feasibility of cascading three-electrode APD arrays. A cascaded Ge-on-Si APD array with good photodetection properties at low-light conditions has been demonstrated which provides guidance for the design of large-scale Ge-on-Si APD arrays for light detection and ranging application.

Orientation and mobility control of 4HCB organic film for flexible X-ray detectors with high performance

• The space-confined melt process is used to produce highly orientated organic semiconducting crystalline films with a large area. • Confined molecular packing significantly improves the hole mobility. • The 4HCB based X-ray detectors can achieve a high sensitivity with low dark current, result in outstanding direct imaging capabilities. • The device shows steady flexibility, with no degradation in detecting function after 100 cycles of bending. In comparison to inorganic counterparts, organic semiconducting (OSC) crystalline films are promising for building large-area and flexible ionizing radiation detectors for X-ray imaging or dosimetry due to their tissue equivalence, simple processing and large-scale production accessibility. Fabrication processes, however, hinder the ability to generate aligned and large-area films with high carrier mobility. In this work, the space-confined melt process is used to produce highly orientated 4HCB (4-hydroxycyanobenzene) OSC films with a large area of 15 × 18 mm 2 . The out-of-plane direction of the 4HCB film is <001>, and the benzene rings are found to be extensively overlapped inside the in-plane direction, according to the XRD patterns. The film exhibits a high resistivity up to 10 12 Ω cm, and high hole mobility of 10.62 cm 2 V −1 s −1 . Furthermore, the 4HCB (80-μm-thick film) based X-ray detectors can achieve a sensitivity of 93 μC Gyair −1 cm −2 and on/off ratio of 157. The device also shows steady flexibility, with no degradation in detecting function after 100 cycles of bending. Finally, the proposed 4HCB film detectors demonstrated a high-resolution X-ray imaging capability. The imaging of several materials with sharp edges (copper and polytetrafluoroethylene) has been obtained. This work has developed a fast but efficient approach for producing large-area, highly oriented OSC films for high-performance X-ray detectors.

Influence of oxygen vacancy and metal–semiconductor contact on the device performance of amorphous gallium oxide photodetectors

Here we investigate the influence of the oxygen vacancy content and the electrode contact on the performance of deep ultraviolet photodetectors based on amorphous Ga2O3 films. The fine-tuning of the oxygen ratio effectively reduces the oxygen vacancy content, which obtains optimized device performance with a responsivity of 5.78 A W−1 and a rise/fall time of 301/89 ms. The metal contact formation and its impact on the device performance are further studied. Compared to the Ohmic-type device using Ti electrodes, the Schottky-type devices using Au and Al electrodes exhibit a shorter rise time and a lower dark current.

Regulation of the electron concentration distribution in TiO2/BaTiO3 photodetector

TiO2 film ultraviolet photodetectors (UVPDs) always suffered from high dark current and low on-off ratio, which have been studied by many works. To improve the performance of the UVPDs based on TiO2, we fabricated a UVPD based on TiO2 with self-polarized BaTiO3 (SPBTO) through a spin-coating method. Compared with the dark current (1.12 nA) and on-off ratio (1.15 × 103) of the single TiO2 film UVPD, that of TiO2-SPBTO film UVPD are 1.27 × 10−1 nA and 1.17 × 104, respectively. The result shows that TiO2-SPBTO has better photoelectric detection capabilities, which may be due to the modulating the electronic distribution of TiO2 films by SPBTO film. To explore the mechanism of the device, we analyzed the carrier distribution within the heterojunction by finite element analysis, which demonstrated that the SPBTO film modulates the electron concentration distribution of TiO2 film, resulting in a lower dark current and a higher on-off ratio. This work provides a potential candidate for high-performance UVPDs.

Band Gap Engineering of Amorphous MgSnO Film for Deep-Ultraviolet Photodetection

Deep-ultraviolet (DUV) detectors have great application prospects in many fields. In this letter, after Sn was doped in MgO by magnetron sputtering, a band gap regulation of the MgSnO from 4.13 eV to 4.67 eV was conducted with a good absorption coefficient for deep-ultraviolet light realized. On this MgSnO film obtained, interdigital electrodes were constructed via mask evaporation technique, based on which a photoconductive deep-ultraviolet detector with metal-semiconductor-metal structure was fabricated. This detector has exhibited excellent characteristics, including low dark current (10−9 A), relatively-high switching ratios (102), ultra-high responsivity (5.87 A/W) and a superior external quantum efficiency (3937%) under 10 V bias.

Ligand-induced charge transport modulation and enhanced photoresponse in hybrid MoS2/quantum dot phototransistors

Mix-dimensional heterostructures of colloidal quantum dots (QDs) and two-dimensional (2D) layered materials have attracted growing interest in photodetection due to the combination of high optical absorption and superior charge transport characteristic. However, the QD sensitizing layer usually introduces uncontrolled doping to the 2D materials originating from the capping ligands, which deteriorates the gate modulation capability and interfacial charge transfer efficiency. In this work, we demonstrated that the photoresponse of MoS2/QD hybrid phototransistor was greatly enhanced by selecting ligand treatment strategy. The carrier concentration and mobility in MoS2 could be effectively tuned via surface doping of 3-mercaptopropionic acid ligand, resulting in high on–off current ratio and low dark current of around 10 pA. The signal-to-noise ratio was improved by three orders of magnitude compared to the pristine MoS2 devices, indicating a dramatically enhanced photoresponse sensitivity. The specific detectivity reached 3.1 × 1013 Jones at the illumination power of 2.3 mW/cm2. The photoresponse speed of the hybrid device was enhanced by about 100 times, owing to the effective interfacial charge transfer which was revealed by the photoluminescence quenching and optoelectrical characterizations. Our work may push a new path to design the interface of mix-dimensional heterostructure and develop high-performance electronic and optoelectronic devices.

An Ultrasensitive Sandwiched Heterostructure Planar Photodetector with Gradient Quasi‐2D Perovskite

Abstract2D Ruddlesden–Popper perovskites have attracted increasing attention for their outstanding optoelectronic properties and improved stability compared to the 3D counterparts. The unique nature of the crystal growth orientations and the uneven distribution in the 2D perovskites provide a great opportunity to construct a promising lateral photodetector device that has not been fully uncovered. Here, by improving the random orientation to the vertical orientation of the film in the lateral device structure, the dark current is expected to be significantly suppressed in the photodetector. Accompanied by the gradient phase distribution, a p‐type conductive channel at the bottom and another electron collection layer on the top are applied to achieve a high on/off ratio. Overall, the resultant photodetector realizes a low dark current of 10−10 A and exhibits impressive photodetection performance, including a high responsivity of 10.10 A W−1, a notable detectivity of 6.83 × 1012 Jones, and fast response speeds (14 ms/31 ms).

Low dark current and high stability X-ray detector based on FAPbI3/Ga2O3 heterojunction

X-ray detectors have drawn great attention due to their wide applications in medical imaging and industrial inspection. Lead halide perovskite exhibits excellent X-ray detection merits because of its high-Z element and outstanding photoelectric properties. However, the perovskite-based X-ray detectors exhibit poor stability, low resistivity and large dark leakage current due to the soft lattice and ion migration of perovskite materials. Herein, we used Ga2O3 compact layer to form a heterojunction structure with formamidinum lead iodide (FAPbI3) to largely ease these issues. Compared with the bare FAPbI3 detector, the dark current of the FAPbI3/Ga2O3 heterojunction detector is reduced by 3 orders of magnitude and the photo-to-dark current ratio (PDCR) increased by 31-fold. The detection limit of 0.23 mGys−1 is obtained which is 20 times lower than the FAPbI3 detector and short response time of 20 ms is obtained. More importantly, the FAPbI3/Ga2O3 device exhibits better repeatability due to the suppression of ion migration by Ga2O3. This work provides an effective strategy to obtain low dark current and stable perovskite-based photodetector.

Ultrasensitive self-powered heterojunction ultraviolet photodetector of p-GaN nanowires on Si by halide chemical vapour deposition

In this study, we report the fabrication of quasi-aligned p-GaN nanowires (NWs) on n-Si (1 1 1) substrate by halide chemical vapour deposition (HCVD) using MgCl2 precursor and followed by low-energy electron beam irradiation to activate the Mg acceptor doping in GaN NWs. We aimed to attain a comprehensive understanding of p-doping in GaN NWs growth, extensive characterizations and fabrication of UV photodetector (PDs) based on p-GaN NWs/n-Si heterojunction. To realize the efficient UV photodetectors, we measure the current–voltage (I–V) characteristics of heterojunction PDs under dark and illuminated conditions and the I–V curve demonstrates good rectifying behaviours with 0.2 V turn-on voltage. At zero bias, the heterojunction PDs show a reverse photocurrent of 1.27 × 10−6 A with a very low dark current of 2.35 × 10−9 A under 325 nm UV illumination. Besides, the significance of the self-powered operation of UV PDs and the charge transfer mechanism are discussed with the aid of the energy band diagram. The substantial photocurrent increment with varying applied potential leads to narrowing the photo potential in the interface. The excitonic bound states present in p-GaN NWs/n-Si heterojunction is further elucidated. As a result, the heterojunction PDs demonstrate the high responsivity, detectivity, and external quantum efficiency of 134 mA W−1, 3.73 × 1013 Jones, and 51% respectively, at 0.1 V low applied potential under the reverse bias condition. The proposed work provides an archetype for Mg doping in GaN NWs ensembles, which will help to facilitate the heterojunction with n-Si to unleash the potential of self-powered UV PDs.

Self-Powered and Broadband Bismuth Oxyselenide/p-Silicon Heterojunction Photodetectors with Low Dark Current and Fast Response

Inorganic nanomaterials such as graphene, black phosphorus, and transition metal dichalcogenides have attracted great interest in developing optoelectronic devices due to their efficient conversion between light and electric signals. However, the zero band gap nature, the unstable chemical properties, and the low electron mobility constrained their wide applications. Bismuth oxyselenide (Bi2O2Se) is gradually showing great research significance in the optoelectronic field. Here, we develop a bismuth oxyselenide/p-silicon (Bi2O2Se/p-Si) heterojunction and design a self-powered and broadband Bi2O2Se/p-Si heterojunction photodetector with an ultrafast response (2.6 μs) and low dark current (10-10 A without gate voltage regulation). It possesses a remarkable detectivity of 4.43 × 1012 cm Hz1/2 W-1 and a self-powered photoresponse characteristic at 365-1550 nm (ultraviolet-near-infrared). Meanwhile, the Bi2O2Se/p-Si heterojunction photodetector also shows high stability and repeatability. It is expected that the proposed Bi2O2Se/p-Si heterojunction photodetector will expand the applications of Bi2O2Se in practical integrated circuits in the field of material science, energy development, optical imaging, biomedicine, and other applications.